The effect of citric acid concentration, reaction temperature and time on the esterification of some varieties of yam flour in Nigeria

The effect of citric acid concentration, reaction temperature and time on the esterification of some varieties of yam flour in Nigeria | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The effect of citric acid concentration, reaction temperature and time on the esterification of some varieties of yam flour in Nigeria Modupe Olatide, Ebun Oladele, Labunmi Lajide, Olugbenga Oluwasina This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4590511/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Citric acid esterification of two accessions of white yam (Dioscorea rotundata ), ‘Aro’ and ‘Efuru’, Yellow yam ( D. cayanensis ) flours were carried out with four different concentrations of citric acid (10%, 20%, 30%, 40%w/v /100g sample) under varying reaction temperature and time (110 o C for 2 hours, 110 o C for 3 hours, 120 o C for 2hours and120 o C for 3hours). The Degree of substitution (DS), Reaction Efficiency, and alpha – amylase digestibility of the products were determined. The DS obtained was 0.011 – 0.178. The reaction efficiency at 110 o C for 2 hours, 110 o C for 3 hours, 120 o C for 2 hours and 120 o C for 3hours across all samples were (11.33% - 34.05%), (12.96% - 52.14%), (26.67% - 39.94%) and (32.01% - 65.11%) respectively. For esterification at 120 o C for 3hours, the reaction efficiency were higher than 50% for almost all samples at citric acid concentration of 10% - 30%w/v. However, at 40%w/v, the reaction efficiency decreased to less than 50%. Alpha amylase digestibility reduced as the concentration of citric acid, temperature and reaction time of the esterification process increased. The least reduction in digestibility (1.15%) was obtained at 110 o C for 2hours at 10% citric acid concentration, while the highest reduction in digestibility (93.42%) was obtained at 120 o C for 3hours at 30% citric acid concentration. From the results obtained, it can be concluded that concentration of citric acid, reaction temperature and time correlate positively with the degree of substitution and alpha amylase resistivity, however steric effect reduced the reaction efficiency as the concentration of citric acid dosages increased. Yam flour α- amylase Citric acid Esterification Digestibility Degree of substitution Reaction efficiency Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1 Introduction Esterification is a chemical method of producing modified starch. A green chemical method for the synthesis of resistant starch (RS) and slowly digested starch (SDS) is esterification of starch with citric acid [ 1 ]. Citric acid (2-hydroxypropane-1,2, 3 tricarboxylic) acid is a non-toxic, antioxidant food additive that is legally used in the manufacturing of edible products such jams, juices, soft drinks and biscuits [ 2 , 3 ]. Citric acid is considered safe for human health [ 4 ]. There are no specific restrictions on the use of starch citrate according to the JECFA (Joint FAO/WHO Expert Committee on Food Additives) monograph [ 5 ]. Through hydrolysis and esterification, citric acid (CA) can alter the structure, composition, and functionality of starch. These changes are mostly dependent on temperature, concentration, processing time, and the ratio of amylose to amylopectin in the starch. The hydrolysis reaction is prominent at low temperatures (below the starch gelatinization temperature). Esterification occurs when the reaction temperature is high (> 100°C) [ 6 , 7 ]. CA has one hydroxyl group and three carboxyl groups. During heating, these groups get dehydrated, forming citric anhydride, which is then esterified with the alcoholic hydroxyl group in the starch molecules [ 8 ]. Citric acid esterification can slow down the rate of starch digestion through resistance to alpha amylase hydrolysis [ 9 ]. In Nigeria, yams ( Dioscorea spp. ) are common staple food with high starch content [ 10 ]. The source, particle size, amylose to amylopectin ratio, amylose-lipid complex, amylose content, amylopectin chain length distribution, crystallinity, crystal type influence starch digestibility[ 11 ]. Yam belongs to tropical root tubers high in amylopectin and low in amylose (15.1% − 27.0%) [ 12 ]. Low amylose starches are easily hydrolyzed by alpha amylase; thereby post prandial hyperglycaemia in regions where yams are major staples is expected [ 13 , 14 ]. Based on the extent of digestion, starch is nutritionally classified into three categories: rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS). Consumption of foods high in RDS for an extended period of time has been associated with an increased risk of obesity, type II diabetes, and cardiovascular diseases. A therapeutic approach in the management of type 2 diabetes, obesity and cardiovascular diseases is reduction in postprandial hyperglycemia by inhibiting alpha amylase in the digestive tract [ 15 , 16 ]. One of such methods is the modification of starch to resistant state (RS). RS is not easily digested in the small intestine and ends up in the colon; where, it ferments to form short-chain fatty acids (SCFAs), which have been shown to be effective in preventing colon cancer [ 17 , 18 ]. Additionally, RS interacts with the immune system to trigger a variety of immunological responses [ 19 , 20 ]. As a result, RSs are regarded as functional starches [ 21 ]. RS are classified into five: physically inaccessible starch (RS-1), native starch granules (RS-2), retrograded starch (RS-3), chemically modified starch (RS-4) and amylose-lipid complexes (RS-5) [ 22 – 24 ]. Most endogenous RS are destroyed during conventional food processing [ 25 ]. However, RS-4 has been reported to retain its RS characteristics even after traditional food processing [ 26 ]. Degree of substitution (DS), a measure of the average number of hydroxyl groups replaced by other derivatives per glucose unit serves as an indicator of the citrate properties and applications [ 27 ]. The DS determination of DS by titration and back-titration based on color change of the indicator is commonly accepted and employed in both laboratory and industrial settings [ 28 , 29 ]. The majority of research to date on esterification of starch for digestion resistivity is based on isolated starch from different botanical sources. Nutritious materials like minerals, proteins, fiber, and lipids are removed during the starch extraction process. Moreover, the vast majority of starch consumption is based on flour. Also, information on citric acid esterification of Nigeria yam varieties is scarce. This work was aimed at reducing the alpha amylase digestibility of yam flours with citric acid esterification while checking the optimum reaction conditions. 2 Materials and methods 2.1 Materials Two accessions of white guinea yam (Dioscorea rotundata ) ‘Aro’ and ‘Efuru’ and Yellow yam ( D. cayanensis ) were purchased from a local market in Osun state, Nigeria. Citric acid was obtained from Tianjin Kermel Chemical, Pancreatic a-amylase type VI-B from porcine pancreas (EC 3.2.1.1, A3176) was obtained from Sigma Canada. All other chemicals and solvents were of analytical grade. 2.2 Yam flour Preparation The yam tubers were processed into flours using the method of Flores-Silva et al. , [ 30 ]. Briefly, yam tuber was peeled, cut into 1 cm slices and immediately rinsed. Slices were dried at 45°C in a convection oven and ground using commercial grinder to pass a US 50 sieve (300 µm) and stored at 25°C in sealed plastic containers until further analyses. 2.3 Citric acid esterification of yam flours Citric acid esterification of yam flours was carried out according to the method of Wepner et al. , [ 31 ] with some modifications [ 32 , 33 ]. Citric acid (10%, 20%, 30%, 40%) was prepared by dissolving (10g, 20g, 30g, 40g) in 50 mL of distilled water with constant stirring. The pH was adjusted to 3.5 with 10 M sodium hydroxide solution, and the resulting solution was brought to a final volume of 100 mL by adding water. The citric acid solution was mixed with 100 g of yam flour in stainless steel trays and conditioned for 16 h at room temperature. The mixture was dried at 40°C for 24 h until a moisture level of 5.0–10.0% w/w was reached. The samples were placed in a forced-air oven at varying times and temperatures (110 o C for 2 hours, 110 o C for 3 hours, 120 o C for 2hours and120 o C for 3hours). The dry products were cooled at room temperature for 30 min, and the unreacted citric acid was removed by washing the products repeatedly with distilled water. The washed product was dried at 40°C and ground and stored for further analysis. 2.4 Determination of the degree of substitution (DS) and reaction efficiency (RE). Determination of the degree of substitution (DS) and reaction efficiency (RE). The amount of citric acid esterified to the starch was analyzed by the method of Volkert, et al. , [ 34 ] and Zuo, et al ., [ 35 ] with minor modifications. Briefly, flour sample (2 g) was placed in a 250 mL conical flask. 20 mL of deionized water was added with gentle shaking (to avoid adherence of the samples to the wall), two drops of phenolphthalein were added and then quickly titrated with 0.1 M of aqueous sodium hydroxide solution until the endpoint was reached, i.e., the solution turned from colorless to pink. This change indicated that all the free citric acid had been neutralized. After that, 25 ml of 0.5 M aqueous sodium hydroxide solution was added. The stoppered conical flask was agitated and stirred for 60 min at room temperature. The excess alkali was back-titrated with a standard 0.5 M aqueous hydrochloric acid solution until the endpoint (the solution turn from pink to colorless). Blank titration was carried out using native flour. The degree of substitution (DS) was calculated as follows: A= (V 0 – V 1 ) × c × Μ / m ×100% (1) DS = 162A /100M − (M − 1)A (2) Here, A is the content of esterified carboxyl groups (%); M is the molar mass of the substituent (citrate: 175 g/mol); m is the mass of the samples (mg); c is the concentration of aqueous hydrochloric acid solution (mol/L); V 0 is the volume of aqueous hydrochloric acid solution consumed by the blank (mL); and, V 1 is the volume of aqueous hydrochloric acid solution consumed by the esterified starch sample (mL). The reaction efficiency (RE) was calculated as follows: Theoretical DS = C × 162 / 175 (3) RE = (DS / Theoretical DS) × 100% (4) Here, C is the mass of citric acid (g) divided by the mass of dry starch (g), and 175 is the relative molecular mass of citrate anhydride. 2.5 Determination of alpha amylase starch digestibility About 1% flour solutions of native and modified samples were prepared with 0.02 mol/L (PBS) sodium phosphate buffer saline (pH 6.9 with 0.006 mol/L sodium chloride) in appropriate beaker, covered with aluminum foil and then heated to boiling on heating mantle. 1ml of the 1% sample preparation was pipetted into test tube with the addition of 0.5mg/ml porcine pancreas α-amylase in PBS solution. The reaction mixture was then incubated for 30 minutes at 37°C for the digestion of the starch. The reducing sugar in the digested sample was determined using the dinitrosalycylic acid (DNSA) assay. 1.0 mL of DNSA color reagent (1 g of 3, 5 dinitrosalycylic acid with 20 ml of 2M NaOH and 30 g sodium potassium tartrate made up to 100 mL with distilled water) was added to the test tube. The test tube was placed in a boiling water bath for 5 minutes to develop the colour and then cooled in an ice bath. After addition of 40 ml water, the absorbance was measured at 540 nm using uv/visible spectrophotometer. A standard curve was prepared using maltose (0.0 to 10.0 mg/ml) and a linear regression analysis was used to determine the total reducing sugar present as mg maltose equivalents. 2.6 Statistical analysis The data reported were the means of triplicate measurements. Statistical analysis were carried out with Duncan’s multiple test (P ≤ 0.05) using IBM SPSS statistics version 23 software and graphpad prism version 8.0.2(263). 3 Results and discussion 3.1 Degree of Substitution (DS) of esterified yam flours The degree of substitution (DS) indicates the amount of substituent introduced in the chemically modified starch during the reaction. During citric acid (CA) modification, citrate functional groups were substituted against the free hydroxyl group in the starch chain. The DS of a starch ester has a role in the extent to which a starch is able to recrystallize or retrograde [ 36 ]. The results of the degree of substitution (DS) for the three yam varieties are as shown in Fig. 1 a - 1 c. It is observed that, the DS of the esterified samples increased with increasing CA concentration, reaction temperature and time. The lowest value of DS (0.011 ± 0.003) was obtained at 110 o C, 2 hours for EF at CA concentration of 10%, while the highest value (0.178 ± 0.006) was obtained at 120 o C, 3 hours for YF at 40% CA concentration. A decline in DS values at 40% CA concentration were prominent in AF, this trend was also observed for EF at 110 o C and YF at 110 o C for 2 hours. Variations observed for most of the DS values between 110 o C for 3 hours and 120 o C for 2 hours suggested higher DS at longer reaction time. The DS of 0.011–0.178 obtained in this work is within the range of 0.01–0.42 previously reported for starch citrates from many botanical sources [ 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 45 ]. Highest DS values in all samples were obtained at 120 o C for 3 hours, therefore making it, the optimum reaction condition for citric acid esterification of the yam flours. 3.2 Reaction Efficiency (RE) for the esterification of the yam flours The results of the reaction efficiency (RE) are as depicted in Fig. 2 a- 2 c. The reaction efficiency (RE) is directly related to the degree of substitution and mass to mass ratio of sample and the esterifying agent (Citric acid). The highest RE (65.11 ± 1.10) for AF was attained at 120 o C for 3 hours with 20% CA concentration, while the lowest (20.74 ± 0.72) was at 110 o C for 2 hours with 40% CA concentration. Longer reaction time improved the reaction efficiency. There was a general decrease in reaction efficiency at 40% CA concentration. In case of EF, highest RE (61.79 ± 1.93) was obtained at 10% citric acid concentration, 120 o C and 3 hours while the lowest (11.33 ± 2.83) was at 10% citric acid concentration, 110 o C and 2 hours which did not differ significantly from 12.37 ± 0.92 obtained at 40% CA at the same temperature and time. Similar reaction efficiency trend as obtained in EF was also obtained for YF. The reaction efficiency are generally below 50% at 110 o C for 2 hours, 110 o C for 3 hours and 120 o C for 2 hour, except 51.39% and 52.14% obtained at 110 o C for 3 hours for AF at 20% and 30% CA respectively. At 120 o C for 3hours, the reaction efficiency are higher than 50% for almost all samples at citric acid concentration of 10%- 30% except for EF at 30% CA that had 48.51 ± 0.75%. .Decline in reaction efficiency at higher concentrations of CA could be attributed to steric effect in the reaction medium. As more crosslink among the starch formed, the less space left for the citrate to enter the matrix steric space, the harder the citric acid reacts [ 46 ]. Jiangping et al . [ 33 ] reported RE of 35.1–43.2% for citric acid esterified rice starch by reactive extrusion. 3. 3 Alpha - Amylase digestibility of the yam flour (g/100g DWB ) Table 1 Alpha- Amylase digestibility of the native yam flours (g/100g DWB) Samples α- Amylase digestibility ( g/100g) AF 48.52 a ±0.56 EF 49.98 a ±0.74 YF 54.23 b ±0.56 AF= ‘Aro’ Flour, EF= ‘Efuru Flour, YF= Yellow yam Flour. DWB = Dry weight basis *Same superscript within column is not significantly different at p ≤ 0.05 Table 2a Alpha- Amylase digestibility of esterified white yam ‘Aro’ flour (AF) (g/100g DWB) Samples α- Amylase Digestibility ( g/100g)/reaction conditions 110 o C for 2 hours 110 o C for 3 hours 120 o C for 2 hours 120 o C for 3 hours AF 10 47.75 h ±0.49 47.12 h ±0.63 47.96 h ±0.39 17.64 e ±0.42 AF 20 46.71 gh ±0.80 45.80 g ±0.46 35.48 f ±0.50 4.33 a ±0.43 AF 30 17.37 e ±0.48 12.56 d ±0.68 17.16 e ±0.37 3.71 a ±0.46 AF 40 17.50 e ±0.62 11.44 d ±0.55 8.45 c ±0.42 6.70 b ±0.52 AF 10 = ‘Aro’ Flour esterified with 10%w/v citric acid, AF 20 = ‘Aro’ Flour esterified with 20%w/v citric acid, AF 30 = ‘Aro’ Flour esterified with 30%w/v citric acid, AF 40 = ‘Aro’ Flour esterified with 40%w/v citric acid. DWB = Dry weight basis *Same superscript within columns and along rows is not significantly different at p ≤ 0.05 Table 2b Alpha- Amylase digestibility of esterified white yam ‘Efuru’ flour (EF) (g/100g DWB) Samples α- Amylase Digestibility ( g/100g)/reaction conditions 110 o C for 2 hours 110 o C for 3 hours 120 o C for 2 hours 120 o C for 3 hours EF 10 49.21 j ±0.28 49.00 j ±0.70 46.77 i ±0.43 12.07 d ±0.43 EF 20 38.06 g ±0.42 28.65 f ±0.62 44.96 h ±0.94 4.96 b ±0.36 EF 30 18.06 e ±0.56 8.17 c ±1.03 12.1 d ±0.39 3.29 a ±0.39 EF 40 12.14 d ±0.61 5.38 b ±0.46 7.82 c ±0.42 5.80 b ±0.46 EF 10 = ‘Efuru’ Flour esterified with 10%w/v citric acid , EF 20 = ‘Efuru’ Flour esterified with 20%w/v citric acid, EF 30 = ‘Efure’ Flour esterified with 30%w/v citric acid, EF 40 = ‘Efuru’ Flour esterified with 40%w/v citric acid. DWB = Dry weight basis *Same superscript within columns and along rows is not significantly different at p ≤ 0.05 Table 2c Alpha-Amylase digestibility of esterified Yellow yam flour (YF) (g/100g DWB) Samples α- Amylase Digestibility ( g/100g)/reaction conditions 110 o C for 2 hours 110 o C for 3 hours 120 o C for 2 hours 120 o C for 3 hours YF 10 53.11 j ±0.96 52.77 j ±0.57 52.70 j ±0.73 13.60 d ±0.67 YF 20 46.22 i ±0.55 32.28 g ±0.86 36.95 h ±0.37 6.01 b ±0.37 YF 30 20.50 e ±0.66 21.55 ef ±0.86 20.92 e ±0.50 5.17 a ±0.39 YF 40 22.17 f ±0.57 7.89 c ±0.62 4.75 a ±0.42 6.91 b ±0.35 Index: YF 10 = Yellow yam Flour esterified with 10%w/v citric acid , YF 20 = Yellow yam Flour esterified with 20%w/v citric acid, YF 30 = Yelow yam Flour esterified with 30%w/v citric acid, YF 40 = Yellow yam Flour esterified with 40%w/v citric acid. DWB = Dry weight basis *Same superscript within columns and along rows is not significantly different at p≤0.05 The results of the native yam flour as depicted in table 1, showed that native YF has the highest alpha amylase digestibility (54.23 b ±0.56 g/100g). The digestibility of native EF and AF are not significantly different at 49.98 a ±0.74g/100g and 48.52 a ±0.56g/100g respectively. The results of the digestibility of the native yam flours showed that the yellow yam is more rapidly digested than the two varieties of the white yam. The results of alpha amylase digestibility of the esterified yam flours are as shown in table 2a – 2c, comparing the results in these tables to those in table 1, it is evidenced that esterification attenuated the alpha amylase digestibility of the samples. The degree of attenuation was greatly influenced by the concentration of citric acid used per reaction temperature and time. The results on table 2a, 2b and 2c showed varietal differences in the esterified yam samples. However, common trends in the results were noticeable. At 10% CA, 110 o C for 2 hours, 110 o C for 3 hours and 120 o C for 2 hours, the results of digestibility of esterified samples were not significantly different. Also, the least digested esterified samples (3.71±0.46g/100g, 3.29 a ±0.39g/100g and 5.17 a ±0.39 g/100g for AF 30, EF 30 and YF 30 respectively) were recorded at 30% CA, 120 o C and 3 hours. Similar result of least digestibility at 30% CA concentration was reported by Utomo et al. [46] for esterified tapioca flour. For all the CA concentrations across all samples, alpha amylase digestibility of the esterified yam flours were most resisted when esterification was performed 120 o C for 3 hours. Studies on isolated starch, have found that CA modification leads to a decrease in the content of rapidly digestible starch (RDS) and an increase in the content of slowly digestible starch (SDS) and resistant (RS) in starch [18,38, 41, 42, 44, 47, 48]. Following CA treatment of natural corn starch, RDS content decreased from 22.77% to 7.63%, SDS content decreased from 12.74% to 4.41%, and RS content increased from 64.66% to 87.96%, Shaikh et al. [48]. Additionally, Muhammed et al. [47] discovered that the in-vitro digestibility of talipot palm starch was reduced by citric acid treatment, while that of resistant starches (RSs) and slowly digestible starch (SDS) increased significantly (p ≤ 0.05) from 37.55% to 53.38% and 31.71% to 39.43%, respectively. Starch becomes resistant to enzymatic hydrolysis via the esterification reaction, which enhances the cross-linking of starch chains [48]. The formation of resistant starch (RS4), which resulted from the starch and citric acid crosslink reaction that modified the starch structure and inhibited alpha amylase's hydrolysis, is responsible for the decrease in digestibility of the esterified yam flours. 4 Conclusion Anhydride was formed by the dehydration of citric acid induced by heating. The starch-citrate adduct was produced when the anhydride and the starch's hydroxyl groups formed covalent bonds. Additional heating caused the citric acid to become more dehydrated, which in turn caused the starch's hydroxyl groups to cross-link with more hydroxyl groups to form bulky derivatized groups. The large derivatized groups inhibited the complex between the enzyme and substrate from forming. As a result, esterification with citric acid promoted the formation of resistant starch, which reduced the starch's alpha amylase digestibility and slowed down the rate of digestion. The esterified yam flours' degree of substitution (DS) and alpha amylase resistivity showed a positive correlation with higher temperatures, longer reaction times, and higher concentrations of citric acid. When developing functional foods for conditions like diabetes or obesity where a decrease in glucose intake is necessary, citric acid esterified yam flour can be incorporated. Declarations Acknowledgements Not applicable Author contributions M.O. handled Laboratory experiments, data analysis and drafting of manuscript, E.O. handled planning of research, data analysis and interpretation as well as manuscript preparation, L.L. was involved in planning of research and manuscript editing while O.O. was involved in data interpretation. Data availability Data is provided within the manuscript. Any additional data will be provided on request. Competing interests The authors declare that no competing interests exists. References Maior LdO, de Almeida VS, Barretti BRV, Ito VC, Beninca C, Demiate IM, Schnitzler E, Filho MADSC, Lacerda LG. Combination of Organic Acid and Heat–Moisture Treatment: Impact on the Thermal, Structural, Pasting Properties and Digestibility of Maize Starch. J. Therm. Anal.2021; 143:265–273. https://doi:10.1007/s10973-019-0924-1. Olsson E, Hedenqvist MS, Johansson C, Järnström L. Influence of citric acid and curing on moisture sorption, diffusion and permeability of starch films. Carbohyd Polym.2013;94:765–772. https://doi:10.1016/j.carbpol.2013.02.006. Xie XS, Liu Q. Development and physicochemical characterization of new resistant citrate starch from different corn starches. Starch Stärke. 2004;56:364–370. . https://doi:10.1002/star.200300261. Ciriminna R, Meneguzzo F, Delisi R, Pagliaro M. Citric acid: Emerging applications of key biotechnology industrial product. Chem. Cent. J. 2017;11–22. https://doi.org/10.1186/s13065-017-0251. Zehra N, Ali TM, Hasnain A. Comparative study on citric acid modified instant starches (alcoholic alkaline treated) isolated from white sorghum and corn grains. Int. J. Biol. Macromol. 2020; 155:1331–1341. https://doi.org/10.1016/j.ijbiomac.2019.10.143. Kim JY, Huber KC. Corn starch granules with enhanced load-carrying capacity via citric acid treatment. Carbohyd Polym.2013;91:39–47. . https://doi.org/10.1016/j.carbpol.2012.07.049. Shaikh F, Ali TM, Mustafa G, Hasnain, A. Comparative study on effects of citric and lactic acid treatment on morphological functional, resistant starch fraction and glycemic index of corn and sorghum starches. Int. J. Biol. Macromol.2019; 135:314–327. https://doi.org/10.1016/j.ijbiomac.2019.05.115. Hong JS, Chung HJ, Lee BH, Kim HS. Impact of static and dynamic modes of semi-dry heat reaction on the characteristics of starch citrates. Carbohyd Polym. 2020; 233: 115853. https://doi:10.1016/j.carbpol.2020.115853. Xie X, Liu Q, Cui SW. Studies on the granular structure of resistant starches (type 4) from normal, high amylose and waxy corn starch citrates. Food Res Int. 2006; 39(3):332-341. https://doi.org/10.1016/j.foodres.2005.08.004. Alabi TR, Adebola PO, Asrat A, De Koeyer D, Lopez-Montes A, Asiedu R. (2019). Spatial multivariate cluster analysis for defining target population of environments in West Africa for yam breeding. Int J Appl Geospat Res.2019;10:1–30. https://doi.org/10.4018/ijagr.2019070104 Singh J, Dartois A, Kaur L. Starch digestibility in food matrix: A review. Trends Food Sci. Technol. 2010;21:168–180. https://doi.org/10.1016/j.tifs.2009.12.001. Otegbayo B, oguniyan D, Akinwumi O. Physicochemical and functional characterization of yam starch for potential industrial applications. Starch-Starke. 2014;66(3-4): 235-250. https://doi.org/10.1002/star.201300056. Eyinla TE, Sanusi RA, Maziya-Dixon B. Evaluation of in vitro and in vivo Glycemic Index of common staples made from varieties of White Yam (Dioscorea rotundata). Front Nutr.2022; 9: 98321. https://doi.org/10.3389/fnut.2022.983212. Ampofo D, Agbenorhevi JK, Firempong CK, Adu-Kwarteng V. Glycemic index of different varieties of yam as influenced by boiling, frying and roasting. Food Sci nutr.2020; 9(2):1106 -1111. https://doi.org/10.1002/fsn3.2087 Oladele E-O, Williamson G. (2016). Impact of resistant starch in three plantain (Musa AAB) products on glycaemic response of healthy volunteers. Eur J Nutr.2016;55(1):75-81. https://doi:10.1007/s00394-014-0825-6. Oyedemi SO, Oyedemi BO, Ijeh I, Ohanyeren PE, Coopoosamy RM, Aiyegoro A O. Alpha-Amylase inhibition and antioxidative capacity of some antidiabetic plants used by the traditional healers in Southwest Nigeria. Scientific World J.2017;3592491 . https://doi.org/10.1155/2017/3592491. Li X. Resistant starch and its applications, in Functional Starch and Applications in Food, Z. Jin, Ed. Singapore: Springer Nat Singap Pte Ltd.2018; 63–90. https://doi:10.1007/978-981-13-1077-5_3. Ye J, Luo S, Huang A, Chen J, Liu C, McClements DJ. Synthesis and characterization of citric acid esterified rice starch by reactive extrusion: A new method of producing resistant starch, Food Hydrocoll. 2019;92(1):135–14. https://doi:10.1016/j.foodhyd.2019.01.064. Bermudez-Brito M, Rosch C, Schols HA, Faas MM, de Vos P. Resistant starches differentially stimulate Toll-like receptors and attenuate pro-inflammatory cytokines in dendritic cells by modulation of intestinal epithelial cells. Mol Nutr and Food Res. 2015;59(9):1814–1826. https://doi:10.1002/mnfr.201500148. L´epine AFP, de Hilster RHJ, Leemhuis H, Oudhuis L, Buwalda PL, de Vos P. Higher chain length distribution in debranched type-3 resistant starches (RS3) increases TLR signaling and supports dendritic cell cytokine production. Mol Nutr and Food Res. 2018; 63(2):1801007. https://doi:10.1002/mnfr.201801007. Gutiérrez TJ. Characterization and in vitro digestibility of non-conventional starches from guinea arrowroot and La Armuña lentils as potential Food sources for special diet regimens. Starch‐Stärke. 2018; 70 (1–2). . https://doi.org/10.1002/star.201700124 Fuentes-Zaragoza E, Sanchez-Zapata E, Sendra E, Sayas E, Navarro C, FernandezLopez J. Resistant starch as prebiotic: A review. Starch-Starke.2011;63(7):406–415. https://doi.org/10.1002/star.201000099 Birt DF, Boylston T, Hendrich S, Jane JL., Hollis J, Li L. Resistant starch: Promise for improving human health. Advances in Nutr. 2013; 4(6):587–601. . https://doi:10.3945/an.113.004325. Oladele, E-O. P. and Mbaye, A. The potential of resistant starch type 1 for nutritional food security. Food Security and Safety. 2023;2: 3-17. https://doi:10.1007/978-3-031-09614-3_1 Agama-Acevedo E, Pacheco-Vargas G, Gutierrez-Meraz F, Tovar G, Belo-Perez LA. Dietary fiber content, texture and in vitro starch digestibility of different white bread crusts. J Cereal Sci. 2019; 102824. https://doi.org/10.1016.2019.102824 Roman, L.; Campanella, O.; Martinez, M.M. Shear-induced molecular fragmentation decreases the bioaccessibility of fully gelatinized starch and its gelling capacity. Carbohydr Polym. 2019;215:198–206. . https://doi.org/10.1016.2019.03.076. Halal SLME, Colussi R, Pinto VZ, Bartz J, Radunz M, Carreno NLV, Dias, ARG, Zavareze EDR. Structure, morphology and functionality of acetylated and oxidised barley starches. Food Chem. 2015;168:247–256. https://doi.org/10.1016/j.foodchem.2014.07.046. Lu X, Luo Z, Fu X, Xiao Z. Two-step method of enzymatic synthesis of starch laurate in ionic liquids. J Agric Food Chem. 2013;61:9882–9891. https://doi:10.1021/jf401467. Miao M, Xiong, S, Jiang, B., Jiang, H., Cui, S.W. and Zhang, T. Dual-enzymatic modification of maize starch for increasing slow digestion property. Food Hydrocoll.2014; 38:180–185. https://doi:10.1016/j.foodhyd.2013.12.006. Flores-Silva PC, Berrios JDJ, Osorio-Diaz P, Bello-Perez LA. Gluten-free spaghetti made with chickpea, unripe plantain and maize flours: functional and chemical properties and starch digestibility. International J Food Sci Techno.2014;l49(9):1985-1991. https://doi.org/10.1111/ijfs.12529. Wepner B, Berghofer E, Miesenberger E. Citrate starch—Application as resistant starch in different foodsystems. Starch Stärke. 1999; 51: 354–361. https://doi.org/10.1002/(SICI)1521-379X(199910)51:103.0.CO;2-W. Sánchez‐Rivera MM, Núñez‐Santiago MdC, Bello‐Pérez LA, Agama‐ Acevedo E, Alvarez‐525 Ramirez J. (2017). Citric acid esterification of unripe plantain flour: Physicochemical properties and starch digestibility. Starch‐Stärke. 2017; 52:69(9-10). https://doi.org/10.1002/star.201700019. Jiangping YSL, Ao H, Jun C, Chengmei L, David JM. Synthesis and characterization of citric acid esterified rice starch by reactive extrusion: A new method of producing resistant starch. Food Hydrocoll. 2019; 92(2). https://doi.org/10.1016/j.foodhyd.2019.01.064. Volkert B, Lehmann A, Greco T, Nejad MH. A comparison of different synthesis routes for starch acetates and the resulting mechanical properties. Carbohydr Polym, 2010; 79 (3):571-577. . https://doi.org/10.1016/j.carbpol.2009.09.005. Zuo Y, Gu J, Yang L, Qiao Z, Tan H, Zhang Y. Preparation and characterization of dry method esterified starch/polylactic acid composite materials. International J biol macromol. 2014; 64:174-180. https://doi.org/10.1016/j.ijbiomac.2013.11.026. Morikawa K, Nishinari K. Effects of concentration dependence of retrogradation behaviour of dispersions for native and chemically modified potato starch. Food Hydrocoll.2000; 14:395–401. https://doi.org/10.1016/s0268-005x(00)00021_7. Kim SH, Kim HS. Influence of semi-dry heating reaction conditions on resistant starch citrates. Food Eng Prog.2015;4:313–319. https://doi:10.13050/foodengprog.2015.19.4.313. Mei JQ, Zhou DN, Jin ZY, Xu, XM, Chen HQ. Effects of citric acid esterification on digestibility, structural and physicochemical properties of cassava starch. Food Chem.2015; 187:378–384. https://doi:10.1016/j.foodchem2015.04.076. Kapelko-Z˙ eberska M, Zie˛ba T, Pietrzak W, Gryszkin A. Effect of citric acid esterification conditions on the properties of the obtained resistant starch. International J Food Sci Technol. 2016; 51, 1647–1654. https://doi.org/10.1111/ijfs.13136. Xia H, Li Y, Gao Q. Preparation and properties of RS4 citrate sweet potato starch by heat-moisture treatment. Food Hydrocoll. 2016; 53:172–178. https://doi.org/10.1016/j.foodhyd.2015.11.008. Lee SY, Lee KY, Lee HG. (2018). Effect of different pH conditions on the in vitro digestibility and physicochemical properties of citric acid-treated potato starch. International J Biol Macromol. 2018; 107, 1235–1241. https://doi:10.1016/j.ijbiomac.2017.09.106. Remya R, Jyothi AN, Sreekumar J. Effect of chemical modification with citric acid on the physicochemical properties and resistant starch formation in different starches. Carbohydr Polym. 2018; 202: 29–38. . https://doi:10.1016/j.carbpol.2018.08.128. Butt NA, Ali TM, Hasnain A. (2019). A. Rice starch citrates and lactates: A comperative study on hot water and cold water swelling starches. International J Biol Macromol.2019; 127:107–117. https://doi.org/10.1016/j.ijbiomac.2019.01.019 Li MN, Xie Y, Chen HQ, Zhang B. Effects of heat-moisture treatment after citric acid esterification on structural properties and digestibility of wheat starch, A- and B- type starch granules. Food Chem. 2019; 272. https://doi:10.1016/j.foodchem2018.08.079. Srikaeo K, Hao PT, Lerdluksamee C. (2019). Effects of heating temperatures and acid concentrations on physicochemical properties and starch digestibility of citric acid esterified tapioca starches. Starch Stärke. 2019;71. https://doi.org/10.1002/star.201800065. Utomo P, Nizardo NM, Saepudin, E. Crosslink modification of tapioca starch with citric acid as a functional food. AIP Conf. Proc. 2020; 2242:040055. https://doi.org/10.1063/5.0010364 Muhammed N, Kappat Valiyapeediyekkal, S, Basheer A, Cherakkathodi S, Plachikkattu Parambil A, Sarasan S, Abhilash S, Johnsy G, Benguo L. Talipot palm (Corypha umbraculifera L.) a nonconventional source of starch: Effect of citric acid on structural, rheological, thermal properties and in vitro digestibility. International J Biol Macromol. 2021; 182, 554–563. https://doi.org/10.1016/j.ijbiomac.2021.04.035 Shaikh F, Ali TM, Mustafa G, Hasnain A. Comparative study on effects of citric and lactic acid treatment on morphological functional, resistant starch fraction and glycemic index of corn and sorghum starches. International Journal of Biol Macromol. 2019; 135, 314–327. https://doi.org/10.1016/j.ijbiomac.2019.05.115. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 05 Sep, 2024 Reviews received at journal 04 Sep, 2024 Reviewers agreed at journal 28 Aug, 2024 Reviews received at journal 23 Aug, 2024 Reviewers agreed at journal 23 Aug, 2024 Reviewers invited by journal 04 Jul, 2024 Editor assigned by journal 25 Jun, 2024 Submission checks completed at journal 25 Jun, 2024 First submitted to journal 16 Jun, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Olatide","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA80lEQVRIiWNgGAWjYFAC5gYGBgNmBn4g8wCQB6QSCGlhbGA4ANQi2UCaFqBKgwMQOwlr0W1vbPz8ocBazvhG7sFDNyqsGfjZcwyYC37h1mJ25mCzxAGDdGOzG3kJh3POpDNI9rwxYJ7Zh0fLjcQGoJbDidtu5Bgczm07zGAAZDDz9uDV0vwDqKV+8wyQln+HGeyJ0NIGsiXBQAKkpQFoC5DBzPMDr1/aLM4YpBvOOPPG4HDOsXQeiTPPCg7zNuDRcrz58I2KP9by/O05xp9zaqzl+NuTNz7m+YNbCwbgAREHGNtI0AIFpNgyCkbBKBgFwx0AAMSJWShRcp6SAAAAAElFTkSuQmCC","orcid":"","institution":"Federal University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Modupe","middleName":"","lastName":"Olatide","suffix":""},{"id":325669444,"identity":"629d7d23-a498-490d-b312-505566d015f3","order_by":1,"name":"Ebun Oladele","email":"","orcid":"","institution":"Federal University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Ebun","middleName":"","lastName":"Oladele","suffix":""},{"id":325669445,"identity":"eb3027ed-31c0-482f-af98-211858a34f8c","order_by":2,"name":"Labunmi Lajide","email":"","orcid":"","institution":"Federal University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Labunmi","middleName":"","lastName":"Lajide","suffix":""},{"id":325669446,"identity":"d713ccca-d708-461c-bc96-6bd81fe768b1","order_by":3,"name":"Olugbenga Oluwasina","email":"","orcid":"","institution":"Federal University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Olugbenga","middleName":"","lastName":"Oluwasina","suffix":""}],"badges":[],"createdAt":"2024-06-16 16:53:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4590511/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4590511/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":60514993,"identity":"4da3cca0-2201-4252-9273-33dc8ea71fb8","added_by":"auto","created_at":"2024-07-17 15:18:06","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":29089,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig.1a\u003c/strong\u003e Degree of substitution for esterified “Aro” flour (AF)\u003c/p\u003e\n\u003cp\u003e*Same superscript on the reaction conditions is not significantly different at p ≤ 0.05\u003c/p\u003e","description":"","filename":"1a.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4590511/v1/79da9e4ba26e04ad5ba4f525.jpg"},{"id":60514992,"identity":"9ef65630-e291-4ac9-962a-f75c538e9007","added_by":"auto","created_at":"2024-07-17 15:18:06","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":27862,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 1b\u003c/strong\u003e Degree of substitution for esterified “Efuru” flour (EF)\u003c/p\u003e\n\u003cp\u003e*Same superscript on the reaction conditions is not significantly different at p ≤ 0.05\u003c/p\u003e","description":"","filename":"1b.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4590511/v1/17627ebffb8752e694a3b617.jpg"},{"id":60514994,"identity":"2cce99ea-67d0-437c-a580-c7be4cc69209","added_by":"auto","created_at":"2024-07-17 15:18:06","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":30245,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 1c\u003c/strong\u003e Degree of substitution for esterified Yellow yam flour (YF)\u003c/p\u003e\n\u003cp\u003e*Same superscript on the reaction conditions is not significantly different at p ≤ 0.05\u003c/p\u003e","description":"","filename":"1c.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4590511/v1/c17fbd537d93a33831691143.jpg"},{"id":60514991,"identity":"8f5f52e0-10c0-462e-94dd-6a3a5ed4c2bd","added_by":"auto","created_at":"2024-07-17 15:18:06","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":30011,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 2a\u003c/strong\u003e Reaction Efficiency for the esterification of “Aro” flour (AF)\u003c/p\u003e\n\u003cp\u003e*Same superscript on the reaction conditions is not significantly different at p ≤ 0.05\u003c/p\u003e","description":"","filename":"2a.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4590511/v1/0a6eed62d8a2f3de2760d0c4.jpg"},{"id":60515756,"identity":"940eb288-0487-4759-a3a2-41f074d25a67","added_by":"auto","created_at":"2024-07-17 15:26:06","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":28414,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig 2b\u003c/strong\u003e Reaction Efficiency for the esterification of “Efuru” flour (EF)\u003c/p\u003e\n\u003cp\u003e*Same superscript on the reaction conditions is not significantly different at p ≤ 0.05\u003c/p\u003e","description":"","filename":"2b.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4590511/v1/bf87f60aeb831bd430cf8806.jpg"},{"id":60515758,"identity":"95bce670-9c43-4858-9a48-ca2bbedc555d","added_by":"auto","created_at":"2024-07-17 15:26:06","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":30333,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 2c\u003c/strong\u003eReaction Efficiency for the esterification of Yellow yam flour (YF)\u003c/p\u003e\n\u003cp\u003e*Same superscript on the reaction conditions is not significantly different at p≤0.05\u003c/p\u003e","description":"","filename":"2c.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4590511/v1/9eb1a4d1194b551f9297ac0e.jpg"},{"id":60516553,"identity":"a67f16c8-e9bd-49b3-8391-6927ccd3b929","added_by":"auto","created_at":"2024-07-17 15:34:06","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":744605,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4590511/v1/4c6b8d26-e77c-4eef-acd1-6a24b2c5c94a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The effect of citric acid concentration, reaction temperature and time on the esterification of some varieties of yam flour in Nigeria","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eEsterification is a chemical method of producing modified starch. A green chemical method for the synthesis of resistant starch (RS) and slowly digested starch (SDS) is esterification of starch with citric acid [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Citric acid (2-hydroxypropane-1,2, 3 tricarboxylic) acid is a non-toxic, antioxidant food additive that is legally used in the manufacturing of edible products such jams, juices, soft drinks and biscuits [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Citric acid is considered safe for human health [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. There are no specific restrictions on the use of starch citrate according to the JECFA (Joint FAO/WHO Expert Committee on Food Additives) monograph [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Through hydrolysis and esterification, citric acid (CA) can alter the structure, composition, and functionality of starch. These changes are mostly dependent on temperature, concentration, processing time, and the ratio of amylose to amylopectin in the starch. The hydrolysis reaction is prominent at low temperatures (below the starch gelatinization temperature). Esterification occurs when the reaction temperature is high (\u0026gt;\u0026thinsp;100\u0026deg;C) [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. CA has one hydroxyl group and three carboxyl groups. During heating, these groups get dehydrated, forming citric anhydride, which is then esterified with the alcoholic hydroxyl group in the starch molecules [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Citric acid esterification can slow down the rate of starch digestion through resistance to alpha amylase hydrolysis [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn Nigeria, yams (\u003cem\u003eDioscorea spp.\u003c/em\u003e) are common staple food with high starch content [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The source, particle size, amylose to amylopectin ratio, amylose-lipid complex, amylose content, amylopectin chain length distribution, crystallinity, crystal type influence starch digestibility[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Yam belongs to tropical root tubers high in amylopectin and low in amylose (15.1% \u0026minus;\u0026thinsp;27.0%) [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Low amylose starches are easily hydrolyzed by alpha amylase; thereby post prandial hyperglycaemia in regions where yams are major staples is expected [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Based on the extent of digestion, starch is nutritionally classified into three categories: rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS).\u003c/p\u003e \u003cp\u003eConsumption of foods high in RDS for an extended period of time has been associated with an increased risk of obesity, type II diabetes, and cardiovascular diseases. A therapeutic approach in the management of type 2 diabetes, obesity and cardiovascular diseases is reduction in postprandial hyperglycemia by inhibiting alpha amylase in the digestive tract [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. One of such methods is the modification of starch to resistant state (RS). RS is not easily digested in the small intestine and ends up in the colon; where, it ferments to form short-chain fatty acids (SCFAs), which have been shown to be effective in preventing colon cancer [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Additionally, RS interacts with the immune system to trigger a variety of immunological responses [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. As a result, RSs are regarded as functional starches [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eRS are classified into five: physically inaccessible starch (RS-1), native starch granules (RS-2), retrograded starch (RS-3), chemically modified starch (RS-4) and amylose-lipid complexes (RS-5) [\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Most endogenous RS are destroyed during conventional food processing [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. However, RS-4 has been reported to retain its RS characteristics even after traditional food processing [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDegree of substitution (DS), a measure of the average number of hydroxyl groups replaced by other derivatives per glucose unit serves as an indicator of the citrate properties and applications [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The DS determination of DS by titration and back-titration based on color change of the indicator is commonly accepted and employed in both laboratory and industrial settings [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe majority of research to date on esterification of starch for digestion resistivity is based on isolated starch from different botanical sources. Nutritious materials like minerals, proteins, fiber, and lipids are removed during the starch extraction process. Moreover, the vast majority of starch consumption is based on flour. Also, information on citric acid esterification of Nigeria yam varieties is scarce. This work was aimed at reducing the alpha amylase digestibility of yam flours with citric acid esterification while checking the optimum reaction conditions.\u003c/p\u003e"},{"header":"2 Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eTwo accessions of white guinea yam (Dioscorea \u003cem\u003erotundata\u003c/em\u003e) \u0026lsquo;Aro\u0026rsquo; and \u0026lsquo;Efuru\u0026rsquo; and Yellow yam (\u003cem\u003eD. cayanensis\u003c/em\u003e) were purchased from a local market in Osun state, Nigeria. Citric acid was obtained from Tianjin Kermel Chemical, Pancreatic a-amylase type VI-B from porcine pancreas (EC 3.2.1.1, A3176) was obtained from Sigma Canada. All other chemicals and solvents were of analytical grade.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Yam flour Preparation\u003c/h2\u003e \u003cp\u003eThe yam tubers were processed into flours using the method of Flores-Silva \u003cem\u003eet al.\u003c/em\u003e, [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Briefly, yam tuber was peeled, cut into 1 cm slices and immediately rinsed. Slices were dried at 45\u0026deg;C in a convection oven and ground using commercial grinder to pass a US 50 sieve (300 \u0026micro;m) and stored at 25\u0026deg;C in sealed plastic containers until further analyses.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Citric acid esterification of yam flours\u003c/h2\u003e \u003cp\u003eCitric acid esterification of yam flours was carried out according to the method of Wepner \u003cem\u003eet al.\u003c/em\u003e, [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] with some modifications [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Citric acid (10%, 20%, 30%, 40%) was prepared by dissolving (10g, 20g, 30g, 40g) in 50 mL of distilled water with constant stirring. The pH was adjusted to 3.5 with 10 M sodium hydroxide solution, and the resulting solution was brought to a final volume of 100 mL by adding water. The citric acid solution was mixed with 100 g of yam flour in stainless steel trays and conditioned for 16 h at room temperature. The mixture was dried at 40\u0026deg;C for 24 h until a moisture level of 5.0\u0026ndash;10.0% w/w was reached. The samples were placed in a forced-air oven at varying times and temperatures (110\u003csup\u003eo\u003c/sup\u003eC for 2 hours, 110\u003csup\u003eo\u003c/sup\u003eC for 3 hours, 120\u003csup\u003eo\u003c/sup\u003eC for 2hours and120\u003csup\u003eo\u003c/sup\u003eC for 3hours). The dry products were cooled at room temperature for 30 min, and the unreacted citric acid was removed by washing the products repeatedly with distilled water. The washed product was dried at 40\u0026deg;C and ground and stored for further analysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Determination of the degree of substitution (DS) and reaction efficiency (RE).\u003c/h2\u003e \u003cp\u003eDetermination of the degree of substitution (DS) and reaction efficiency (RE). The amount of citric acid esterified to the starch was analyzed by the method of Volkert, \u003cem\u003eet al.\u003c/em\u003e, [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] and Zuo, \u003cem\u003eet al\u003c/em\u003e., [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e] with minor modifications. Briefly, flour sample (2 g) was placed in a 250 mL conical flask. 20 mL of deionized water was added with gentle shaking (to avoid adherence of the samples to the wall), two drops of phenolphthalein were added and then quickly titrated with 0.1 M of aqueous sodium hydroxide solution until the endpoint was reached, i.e., the solution turned from colorless to pink. This change indicated that all the free citric acid had been neutralized. After that, 25 ml of 0.5 M aqueous sodium hydroxide solution was added. The stoppered conical flask was agitated and stirred for 60 min at room temperature. The excess alkali was back-titrated with a standard 0.5 M aqueous hydrochloric acid solution until the endpoint (the solution turn from pink to colorless). Blank titration was carried out using native flour. The degree of substitution (DS) was calculated as follows:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eA= (V\u003csub\u003e0\u003c/sub\u003e \u0026ndash; V\u003csub\u003e1\u003c/sub\u003e ) \u0026times; c\u0026thinsp;\u0026times;\u0026thinsp;Μ / m \u0026times;100% (1)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eDS\u0026thinsp;=\u0026thinsp;162A /100M \u0026minus; (M\u0026thinsp;\u0026minus;\u0026thinsp;1)A (2)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eHere, A is the content of esterified carboxyl groups (%);\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eM is the molar mass of the substituent (citrate: 175 g/mol);\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003em is the mass of the samples (mg);\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003ec is the concentration of aqueous hydrochloric acid solution (mol/L);\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eV\u003csub\u003e0\u003c/sub\u003e is the volume of aqueous hydrochloric acid solution consumed by the blank (mL); and,\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eV\u003csub\u003e1\u003c/sub\u003e is the volume of aqueous hydrochloric acid solution consumed by the esterified starch sample (mL). The reaction efficiency (RE) was calculated as follows:\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eTheoretical DS\u0026thinsp;=\u0026thinsp;C \u0026times; 162 / 175 (3)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eRE = (DS / Theoretical DS) \u0026times; 100% (4)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eHere, C is the mass of citric acid (g) divided by the mass of dry starch (g), and 175 is the relative molecular mass of citrate anhydride.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Determination of alpha amylase starch digestibility\u003c/h2\u003e \u003cp\u003eAbout 1% flour solutions of native and modified samples were prepared with 0.02 mol/L (PBS) sodium phosphate buffer saline (pH 6.9 with 0.006 mol/L sodium chloride) in appropriate beaker, covered with aluminum foil and then heated to boiling on heating mantle. 1ml of the 1% sample preparation was pipetted into test tube with the addition of 0.5mg/ml porcine pancreas α-amylase in PBS solution. The reaction mixture was then incubated for 30 minutes at 37\u0026deg;C for the digestion of the starch. The reducing sugar in the digested sample was determined using the dinitrosalycylic acid (DNSA) assay. 1.0 mL of DNSA color reagent (1 g of 3, 5 dinitrosalycylic acid with 20 ml of 2M NaOH and 30 g sodium potassium tartrate made up to 100 mL with distilled water) was added to the test tube. The test tube was placed in a boiling water bath for 5 minutes to develop the colour and then cooled in an ice bath. After addition of 40 ml water, the absorbance was measured at 540 nm using uv/visible spectrophotometer. A standard curve was prepared using maltose (0.0 to 10.0 mg/ml) and a linear regression analysis was used to determine the total reducing sugar present as mg maltose equivalents.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Statistical analysis\u003c/h2\u003e \u003cp\u003eThe data reported were the means of triplicate measurements. Statistical analysis were carried out with Duncan\u0026rsquo;s multiple test (P\u0026thinsp;\u0026le;\u0026thinsp;0.05) using IBM SPSS statistics version 23 software and graphpad prism version 8.0.2(263).\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Degree of Substitution (DS) of esterified yam flours\u003c/h2\u003e\n \u003cp\u003eThe degree of substitution (DS) indicates the amount of substituent introduced in the chemically modified starch during the reaction. During citric acid (CA) modification, citrate functional groups were substituted against the free hydroxyl group in the starch chain. The DS of a starch ester has a role in the extent to which a starch is able to recrystallize or retrograde [\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e]. The results of the degree of substitution (DS) for the three yam varieties are as shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea -\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec. It is observed that, the DS of the esterified samples increased with increasing CA concentration, reaction temperature and time. The lowest value of DS (0.011\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003) was obtained at 110\u003csup\u003eo\u003c/sup\u003eC, 2 hours for EF at CA concentration of 10%, while the highest value (0.178\u0026thinsp;\u0026plusmn;\u0026thinsp;0.006) was obtained at 120\u003csup\u003eo\u003c/sup\u003eC, 3 hours for YF at 40% CA concentration. A decline in DS values at 40% CA concentration were prominent in AF, this trend was also observed for EF at 110\u003csup\u003eo\u003c/sup\u003eC and YF at 110\u003csup\u003eo\u003c/sup\u003eC for 2 hours. Variations observed for most of the DS values between 110\u003csup\u003eo\u003c/sup\u003eC for 3 hours and 120\u003csup\u003eo\u003c/sup\u003eC for 2 hours suggested higher DS at longer reaction time. The DS of 0.011\u0026ndash;0.178 obtained in this work is within the range of 0.01\u0026ndash;0.42 previously reported for starch citrates from many botanical sources [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e \u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e]. Highest DS values in all samples were obtained at 120\u003csup\u003eo\u003c/sup\u003eC for 3 hours, therefore making it, the optimum reaction condition for citric acid esterification of the yam flours.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Reaction Efficiency (RE) for the esterification of the yam flours\u003c/h2\u003e\n \u003cp\u003eThe results of the reaction efficiency (RE) are as depicted in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea- \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec. The reaction efficiency (RE) is directly related to the degree of substitution and mass to mass ratio of sample and the esterifying agent (Citric acid). The highest RE (65.11\u0026thinsp;\u0026plusmn;\u0026thinsp;1.10) for AF was attained at 120\u003csup\u003eo\u003c/sup\u003eC for 3 hours with 20% CA concentration, while the lowest (20.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.72) was at 110\u003csup\u003eo\u003c/sup\u003eC for 2 hours with 40% CA concentration. Longer reaction time improved the reaction efficiency. There was a general decrease in reaction efficiency at 40% CA concentration. In case of EF, highest RE (61.79\u0026thinsp;\u0026plusmn;\u0026thinsp;1.93) was obtained at 10% citric acid concentration, 120\u003csup\u003eo\u003c/sup\u003eC and 3 hours while the lowest (11.33\u0026thinsp;\u0026plusmn;\u0026thinsp;2.83) was at 10% citric acid concentration, 110\u003csup\u003eo\u003c/sup\u003eC and 2 hours which did not differ significantly from 12.37\u0026thinsp;\u0026plusmn;\u0026thinsp;0.92 obtained at 40% CA at the same temperature and time. Similar reaction efficiency trend as obtained in EF was also obtained for YF. The reaction efficiency are generally below 50% at 110\u003csup\u003eo\u003c/sup\u003eC for 2 hours, 110\u003csup\u003eo\u003c/sup\u003eC for 3 hours and 120\u003csup\u003eo\u003c/sup\u003eC for 2 hour, except 51.39% and 52.14% obtained at 110\u003csup\u003eo\u003c/sup\u003eC for 3 hours for AF at 20% and 30% CA respectively. At 120\u003csup\u003eo\u003c/sup\u003eC for 3hours, the reaction efficiency are higher than 50% for almost all samples at citric acid concentration of 10%- 30% except for EF at 30% CA that had 48.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.75%. .Decline in reaction efficiency at higher concentrations of CA could be attributed to steric effect in the reaction medium. As more crosslink among the starch formed, the less space left for the citrate to enter the matrix steric space, the harder the citric acid reacts [\u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e]. Jiangping \u003cem\u003eet al\u003c/em\u003e. [\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e] reported RE of 35.1\u0026ndash;43.2% for citric acid esterified rice starch by reactive extrusion.\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003e3. 3 Alpha - Amylase digestibility of the yam flour (g/100g DWB\u003c/strong\u003e) \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e Alpha- Amylase digestibility of the native yam flours (g/100g DWB)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"40%\" valign=\"top\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"60%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026alpha;- Amylase digestibility ( g/100g)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"40%\" valign=\"top\"\u003e\n \u003cp\u003eAF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"60%\" valign=\"top\"\u003e\n \u003cp\u003e48.52\u003csup\u003ea\u003c/sup\u003e\u0026plusmn;0.56\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"40%\" valign=\"top\"\u003e\n \u003cp\u003eEF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"60%\" valign=\"top\"\u003e\n \u003cp\u003e49.98\u003csup\u003ea\u003c/sup\u003e\u0026plusmn;0.74\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"40%\" valign=\"top\"\u003e\n \u003cp\u003eYF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"60%\" valign=\"top\"\u003e\n \u003cp\u003e54.23\u003csup\u003eb\u003c/sup\u003e\u0026plusmn;0.56\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eAF= \u0026lsquo;Aro\u0026rsquo; Flour, EF= \u0026lsquo;Efuru Flour, YF= Yellow yam Flour. \u0026nbsp;DWB = Dry weight basis\u003c/p\u003e\n\u003cp\u003e*Same superscript within column is not significantly different at p \u0026le;\u0026nbsp;0.05\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2a\u003c/strong\u003e Alpha- Amylase digestibility of esterified white yam \u0026lsquo;Aro\u0026rsquo; flour (AF) (g/100g DWB)\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" rowspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"80.68833652007648%\" colspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003e\u0026alpha;- Amylase Digestibility ( g/100g)/reaction conditions \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.644549763033176%\" valign=\"top\"\u003e\n \u003cp\u003e110\u003csup\u003eo\u003c/sup\u003eC for 2 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.644549763033176%\" valign=\"top\"\u003e\n \u003cp\u003e110\u003csup\u003eo\u003c/sup\u003eC for 3 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.829383886255926%\" valign=\"top\"\u003e\n \u003cp\u003e120\u003csup\u003eo\u003c/sup\u003eC for 2 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.881516587677726%\" valign=\"top\"\u003e\n \u003cp\u003e120\u003csup\u003eo\u003c/sup\u003eC for 3 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eAF\u003csub\u003e10\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e47.75\u003csup\u003eh\u003c/sup\u003e\u0026plusmn;0.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e47.12\u003csup\u003eh\u003c/sup\u003e\u0026plusmn;0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e47.96\u003csup\u003eh\u003c/sup\u003e\u0026plusmn;0.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e17.64\u003csup\u003ee\u003c/sup\u003e\u0026plusmn;0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eAF\u003csub\u003e20\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e46.71\u003csup\u003egh\u003c/sup\u003e\u0026plusmn;0.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e45.80\u003csup\u003eg\u003c/sup\u003e\u0026plusmn;0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e35.48\u003csup\u003ef\u003c/sup\u003e\u0026plusmn;0.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e4.33\u003csup\u003ea\u003c/sup\u003e\u0026plusmn;0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eAF\u003csub\u003e30\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e17.37\u003csup\u003ee\u003c/sup\u003e\u0026plusmn;0.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e12.56\u003csup\u003ed\u003c/sup\u003e\u0026plusmn;0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e17.16\u003csup\u003ee\u003c/sup\u003e\u0026plusmn;0.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e3.71\u003csup\u003ea\u003c/sup\u003e\u0026plusmn;0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eAF\u003csub\u003e40\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e17.50\u003csup\u003ee\u003c/sup\u003e\u0026plusmn;0.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e11.44\u003csup\u003ed\u003c/sup\u003e\u0026plusmn;0.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e8.45\u003csup\u003ec\u003c/sup\u003e\u0026plusmn;0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e6.70\u003csup\u003eb\u003c/sup\u003e\u0026plusmn;0.52\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAF\u003csub\u003e10\u0026nbsp;\u003c/sub\u003e= \u0026lsquo;Aro\u0026rsquo; Flour esterified with 10%w/v citric acid, AF\u003csub\u003e20\u0026nbsp;\u003c/sub\u003e= \u0026lsquo;Aro\u0026rsquo; Flour esterified with 20%w/v citric acid, AF\u003csub\u003e30\u0026nbsp;\u003c/sub\u003e= \u0026lsquo;Aro\u0026rsquo; Flour esterified with 30%w/v citric acid, AF\u003csub\u003e40\u0026nbsp;\u003c/sub\u003e= \u0026lsquo;Aro\u0026rsquo; Flour esterified with 40%w/v citric acid. DWB = Dry weight basis\u003c/p\u003e\n\u003cp\u003e*Same superscript within columns and along rows is not significantly different at p \u0026le;\u0026nbsp;0.05\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2b\u003c/strong\u003e Alpha- Amylase digestibility of esterified white yam \u0026lsquo;Efuru\u0026rsquo; flour (EF) (g/100g DWB)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" rowspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"80.68833652007648%\" colspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003e\u0026alpha;- Amylase Digestibility ( g/100g)/reaction conditions \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.644549763033176%\" valign=\"top\"\u003e\n \u003cp\u003e110\u003csup\u003eo\u003c/sup\u003eC for 2 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.644549763033176%\" valign=\"top\"\u003e\n \u003cp\u003e110\u003csup\u003eo\u003c/sup\u003eC for 3 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.829383886255926%\" valign=\"top\"\u003e\n \u003cp\u003e120\u003csup\u003eo\u003c/sup\u003eC for 2 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.881516587677726%\" valign=\"top\"\u003e\n \u003cp\u003e120\u003csup\u003eo\u003c/sup\u003eC for 3 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eEF\u003csub\u003e10\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e49.21\u003csup\u003ej\u003c/sup\u003e\u0026plusmn;0.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e49.00\u003csup\u003ej\u003c/sup\u003e\u0026plusmn;0.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e46.77\u003csup\u003ei\u003c/sup\u003e\u0026plusmn;0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e12.07\u003csup\u003ed\u003c/sup\u003e\u0026plusmn;0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eEF\u003csub\u003e20\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e38.06\u003csup\u003eg\u003c/sup\u003e\u0026plusmn;0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e28.65\u003csup\u003ef\u003c/sup\u003e\u0026plusmn;0.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e44.96\u003csup\u003eh\u003c/sup\u003e\u0026plusmn;0.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e4.96\u003csup\u003eb\u003c/sup\u003e\u0026plusmn;0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eEF\u003csub\u003e30\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e18.06\u003csup\u003ee\u003c/sup\u003e\u0026plusmn;0.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e8.17\u003csup\u003ec\u003c/sup\u003e\u0026plusmn;1.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e12.1\u003csup\u003ed\u003c/sup\u003e\u0026plusmn;0.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e3.29\u003csup\u003ea\u003c/sup\u003e\u0026plusmn;0.39\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eEF\u003csub\u003e40\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e12.14\u003csup\u003ed\u003c/sup\u003e\u0026plusmn;0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e5.38\u003csup\u003eb\u003c/sup\u003e\u0026plusmn;0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e7.82\u003csup\u003ec\u003c/sup\u003e\u0026plusmn;0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e5.80\u003csup\u003eb\u003c/sup\u003e\u0026plusmn;0.46\u003csup\u003e\u0026nbsp;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;EF\u003csub\u003e10\u0026nbsp;\u003c/sub\u003e= \u0026lsquo;Efuru\u0026rsquo; Flour esterified with 10%w/v citric acid , EF\u003csub\u003e20\u0026nbsp;\u003c/sub\u003e= \u0026lsquo;Efuru\u0026rsquo; Flour esterified with 20%w/v citric acid, EF\u003csub\u003e30\u0026nbsp;\u003c/sub\u003e= \u0026lsquo;Efure\u0026rsquo; Flour esterified with 30%w/v citric acid, EF\u003csub\u003e40\u0026nbsp;\u003c/sub\u003e= \u0026lsquo;Efuru\u0026rsquo; Flour esterified with 40%w/v citric acid. DWB = Dry weight basis\u003c/p\u003e\n\u003cp\u003e*Same superscript within columns and along rows is not significantly different at p \u0026le;\u0026nbsp;0.05\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2c\u003c/strong\u003e Alpha-Amylase digestibility of esterified Yellow yam flour (YF) (g/100g DWB)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" rowspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"80.68833652007648%\" colspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003e\u0026alpha;- Amylase Digestibility ( g/100g)/reaction conditions \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.644549763033176%\" valign=\"top\"\u003e\n \u003cp\u003e110\u003csup\u003eo\u003c/sup\u003eC for 2 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.644549763033176%\" valign=\"top\"\u003e\n \u003cp\u003e110\u003csup\u003eo\u003c/sup\u003eC for 3 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.829383886255926%\" valign=\"top\"\u003e\n \u003cp\u003e120\u003csup\u003eo\u003c/sup\u003eC for 2 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.881516587677726%\" valign=\"top\"\u003e\n \u003cp\u003e120\u003csup\u003eo\u003c/sup\u003eC for 3 hours\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eYF\u003csub\u003e10\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e53.11\u003csup\u003ej\u003c/sup\u003e\u0026plusmn;0.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e52.77\u003csup\u003ej\u003c/sup\u003e\u0026plusmn;0.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e52.70\u003csup\u003ej\u003c/sup\u003e\u0026plusmn;0.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e13.60\u003csup\u003ed\u003c/sup\u003e\u0026plusmn;0.67\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eYF\u003csub\u003e20\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e46.22\u003csup\u003ei\u003c/sup\u003e\u0026plusmn;0.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e32.28\u003csup\u003eg\u003c/sup\u003e\u0026plusmn;0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e36.95\u003csup\u003eh\u003c/sup\u003e\u0026plusmn;0.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e6.01\u003csup\u003eb\u003c/sup\u003e\u0026plusmn;0.37\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eYF\u003csub\u003e30\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e20.50\u003csup\u003ee\u003c/sup\u003e\u0026plusmn;0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e21.55\u003csup\u003eef\u003c/sup\u003e\u0026plusmn;0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e20.92\u003csup\u003ee\u003c/sup\u003e\u0026plusmn;0.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e5.17\u003csup\u003ea\u003c/sup\u003e\u0026plusmn;0.39\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.311663479923517%\" valign=\"top\"\u003e\n \u003cp\u003eYF\u003csub\u003e40\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e22.17\u003csup\u003ef\u003c/sup\u003e\u0026plusmn;0.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.88527724665392%\"\u003e\n \u003cp\u003e7.89\u003csup\u003ec\u003c/sup\u003e\u0026plusmn;0.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.84130019120459%\"\u003e\n \u003cp\u003e4.75\u003csup\u003ea\u003c/sup\u003e\u0026plusmn;0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.076481835564053%\"\u003e\n \u003cp\u003e6.91\u003csup\u003eb\u003c/sup\u003e\u0026plusmn;0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIndex: YF\u003csub\u003e10\u0026nbsp;\u003c/sub\u003e= Yellow yam Flour esterified with 10%w/v citric acid , YF\u003csub\u003e20\u0026nbsp;\u003c/sub\u003e= Yellow yam Flour esterified with 20%w/v citric acid, YF\u003csub\u003e30\u0026nbsp;\u003c/sub\u003e= Yelow yam Flour esterified with 30%w/v citric acid, YF\u003csub\u003e40\u0026nbsp;\u003c/sub\u003e= Yellow yam Flour esterified with 40%w/v citric acid. DWB = Dry weight basis\u003c/p\u003e\n\u003cp\u003e*Same superscript within columns and along rows is not significantly different at p\u0026le;0.05\u003c/p\u003e\n\u003cp\u003eThe results of the native yam flour as depicted in table 1, showed that native YF has the highest alpha amylase digestibility (54.23\u003csup\u003eb\u003c/sup\u003e\u0026plusmn;0.56 g/100g). The digestibility of native EF and AF are not significantly different at\u0026nbsp;49.98\u003csup\u003ea\u003c/sup\u003e\u0026plusmn;0.74g/100g\u0026nbsp;and\u0026nbsp;48.52\u003csup\u003ea\u003c/sup\u003e\u0026plusmn;0.56g/100g respectively. The results of the digestibility of the native yam flours showed that the yellow yam is more rapidly digested than the two varieties of the white yam. The results of \u0026nbsp;alpha amylase digestibility of the \u0026nbsp;esterified yam flours are as shown in table 2a \u0026ndash; 2c, \u0026nbsp;comparing the results in these tables to those in table 1, it is evidenced that esterification attenuated the alpha amylase digestibility of the samples. The degree of attenuation was greatly influenced by the concentration of citric acid used per reaction temperature and time. The results on table 2a, 2b and 2c showed varietal differences in the esterified yam samples. However, common trends in the results were noticeable. \u0026nbsp;At 10% CA, 110\u003csup\u003eo\u003c/sup\u003eC for 2 hours, 110\u003csup\u003eo\u003c/sup\u003eC for 3 hours and 120\u003csup\u003eo\u003c/sup\u003eC for 2 hours, the results of\u0026nbsp;digestibility of esterified samples were not significantly different.\u0026nbsp;Also, the least digested esterified samples (3.71\u0026plusmn;0.46g/100g, 3.29\u003csup\u003ea\u003c/sup\u003e\u0026plusmn;0.39g/100g and 5.17\u003csup\u003ea\u003c/sup\u003e\u0026plusmn;0.39 g/100g for\u0026nbsp;AF\u003csub\u003e30,\u0026nbsp;\u003c/sub\u003eEF\u003csub\u003e30\u0026nbsp;\u003c/sub\u003eand\u003csub\u003e\u0026nbsp;\u003c/sub\u003eYF\u003csub\u003e30\u0026nbsp;\u003c/sub\u003erespectively)\u0026nbsp;were recorded at 30% CA, 120\u003csup\u003eo\u003c/sup\u003eC and 3 hours. \u0026nbsp; Similar result of least digestibility at 30% CA concentration was reported by Utomo \u003cem\u003eet al.\u003c/em\u003e [46] for esterified tapioca flour. For all the CA concentrations across all samples, alpha amylase digestibility of the esterified yam flours were most resisted when esterification was performed 120\u003csup\u003eo\u003c/sup\u003eC for 3 hours.\u003c/p\u003e\n\u003cp\u003eStudies on isolated starch, have found that CA modification leads to a decrease in the content of rapidly digestible starch (RDS) and an increase in the content of slowly digestible starch (SDS) and resistant (RS) in starch [18,38, 41, 42, 44, 47, 48]. \u0026nbsp;Following CA treatment of natural corn starch, RDS content decreased from 22.77% to 7.63%, SDS content decreased from 12.74% to 4.41%, and RS content increased from 64.66% to 87.96%, Shaikh et al. [48]. Additionally, Muhammed et al. [47] discovered that the in-vitro digestibility of talipot palm starch was reduced by citric acid treatment, while that of resistant starches (RSs) and slowly digestible starch (SDS) increased significantly (p \u0026le; 0.05) from 37.55% to 53.38% and 31.71% to 39.43%, respectively. Starch becomes resistant to enzymatic hydrolysis via the esterification reaction, which enhances the cross-linking of starch chains [48]. The formation of resistant starch (RS4), which resulted from the starch and citric acid crosslink reaction that modified the starch structure and inhibited alpha amylase\u0026apos;s hydrolysis, is responsible for the decrease in digestibility of the esterified yam flours.\u0026nbsp;\u003c/p\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eAnhydride was formed by the dehydration of citric acid induced by heating. The starch-citrate adduct was produced when the anhydride and the starch's hydroxyl groups formed covalent bonds. Additional heating caused the citric acid to become more dehydrated, which in turn caused the starch's hydroxyl groups to cross-link with more hydroxyl groups to form bulky derivatized groups. The large derivatized groups inhibited the complex between the enzyme and substrate from forming. As a result, esterification with citric acid promoted the formation of resistant starch, which reduced the starch's alpha amylase digestibility and slowed down the rate of digestion. The esterified yam flours' degree of substitution (DS) and alpha amylase resistivity showed a positive correlation with higher temperatures, longer reaction times, and higher concentrations of citric acid. When developing functional foods for conditions like diabetes or obesity where a decrease in glucose intake is necessary, citric acid esterified yam flour can be incorporated.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u0026nbsp;\u003c/strong\u003eM.O. handled Laboratory experiments, data analysis and drafting of manuscript, E.O. handled planning of research, data analysis and interpretation as well as manuscript preparation, L.L. was involved in planning of research and manuscript editing while O.O. was involved in data interpretation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e Data is provided within the manuscript. Any additional data will be provided on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003eThe authors declare that no competing interests exists.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eMaior LdO, de Almeida VS, Barretti BRV, Ito VC, Beninca C, Demiate IM, Schnitzler E, Filho MADSC, Lacerda LG. Combination of Organic Acid and Heat\u0026ndash;Moisture Treatment: Impact on the Thermal, Structural, Pasting Properties and Digestibility of Maize Starch. J. Therm. Anal.2021; 143:265\u0026ndash;273. https://doi:10.1007/s10973-019-0924-1.\u003c/li\u003e\n\u003cli\u003eOlsson E, Hedenqvist MS, Johansson C, J\u0026auml;rnstr\u0026ouml;m L. Influence of citric acid and curing on moisture sorption, diffusion and permeability of starch films. Carbohyd Polym.2013;94:765\u0026ndash;772. https://doi:10.1016/j.carbpol.2013.02.006.\u003c/li\u003e\n\u003cli\u003eXie XS, Liu Q. Development and physicochemical characterization of new resistant citrate starch from different corn starches. Starch St\u0026auml;rke. 2004;56:364\u0026ndash;370. . https://doi:10.1002/star.200300261.\u003c/li\u003e\n\u003cli\u003eCiriminna R, Meneguzzo F, Delisi R, Pagliaro M. Citric acid: Emerging applications of key biotechnology industrial product. Chem. Cent. J. 2017;11\u0026ndash;22. https://doi.org/10.1186/s13065-017-0251.\u003c/li\u003e\n\u003cli\u003eZehra N, Ali TM, Hasnain A. Comparative study on citric acid modified instant starches (alcoholic alkaline treated) isolated from white sorghum and corn grains. Int. J. Biol. Macromol. 2020; 155:1331\u0026ndash;1341. https://doi.org/10.1016/j.ijbiomac.2019.10.143.\u003c/li\u003e\n\u003cli\u003eKim JY, Huber KC. Corn starch granules with enhanced load-carrying capacity via citric acid treatment. Carbohyd Polym.2013;91:39\u0026ndash;47. . https://doi.org/10.1016/j.carbpol.2012.07.049.\u003c/li\u003e\n\u003cli\u003eShaikh F, Ali TM, Mustafa G, Hasnain, A. Comparative study on effects of citric and lactic acid treatment on morphological functional, resistant starch fraction and glycemic index of corn and sorghum starches. Int. J. Biol. Macromol.2019;\u003cem\u003e \u003c/em\u003e135:314\u0026ndash;327. https://doi.org/10.1016/j.ijbiomac.2019.05.115.\u003c/li\u003e\n\u003cli\u003eHong JS, Chung HJ, Lee BH, Kim HS. Impact of static and dynamic modes of semi-dry heat reaction on the characteristics of starch citrates. Carbohyd Polym. 2020; 233: 115853. https://doi:10.1016/j.carbpol.2020.115853.\u003c/li\u003e\n\u003cli\u003eXie X, Liu Q, Cui SW. Studies on the granular structure of resistant starches (type 4) from normal, high amylose and waxy corn starch citrates. Food Res Int. 2006; 39(3):332-341. https://doi.org/10.1016/j.foodres.2005.08.004.\u003c/li\u003e\n\u003cli\u003eAlabi TR, Adebola PO, Asrat A, De Koeyer D, Lopez-Montes A, Asiedu R. (2019). Spatial multivariate cluster analysis for defining target population of environments in West Africa for yam breeding. Int\u003cem\u003e \u003c/em\u003eJ Appl Geospat Res.2019;10:1\u0026ndash;30. https://doi.org/10.4018/ijagr.2019070104\u003c/li\u003e\n\u003cli\u003eSingh J, Dartois A, Kaur L. Starch digestibility in food matrix: A review. Trends Food Sci. Technol. 2010;21:168\u0026ndash;180. https://doi.org/10.1016/j.tifs.2009.12.001.\u003c/li\u003e\n\u003cli\u003eOtegbayo B, oguniyan D, Akinwumi O. Physicochemical and functional characterization of yam starch for potential industrial applications. Starch-Starke. 2014;66(3-4): 235-250. https://doi.org/10.1002/star.201300056.\u003c/li\u003e\n\u003cli\u003eEyinla TE, Sanusi RA, Maziya-Dixon B. Evaluation of in vitro and in vivo Glycemic Index of common staples made from varieties of White Yam (Dioscorea rotundata). Front Nutr.2022; 9: 98321. https://doi.org/10.3389/fnut.2022.983212.\u003c/li\u003e\n\u003cli\u003eAmpofo D, Agbenorhevi JK, Firempong CK, Adu-Kwarteng V. Glycemic index of different varieties of yam as influenced by boiling, frying and roasting. Food Sci nutr.2020; 9(2):1106 -1111. https://doi.org/10.1002/fsn3.2087\u003c/li\u003e\n\u003cli\u003eOladele E-O, Williamson G. (2016). Impact of resistant starch in three plantain (Musa AAB) products on glycaemic response of healthy volunteers. Eur J Nutr.2016;55(1):75-81. https://doi:10.1007/s00394-014-0825-6.\u003c/li\u003e\n\u003cli\u003eOyedemi SO, Oyedemi BO, Ijeh I, Ohanyeren PE, Coopoosamy RM, Aiyegoro A O. Alpha-Amylase inhibition and antioxidative capacity of some antidiabetic plants used by the traditional healers in Southwest Nigeria. Scientific World J.2017;3592491 . https://doi.org/10.1155/2017/3592491.\u003c/li\u003e\n\u003cli\u003eLi X. Resistant starch and its applications, in Functional Starch and Applications in Food, Z. Jin, Ed. Singapore: Springer Nat Singap Pte Ltd.2018; 63\u0026ndash;90. https://doi:10.1007/978-981-13-1077-5_3.\u003c/li\u003e\n\u003cli\u003eYe J, Luo S, Huang A, Chen J, Liu C, McClements DJ. Synthesis and characterization of citric acid esterified rice starch by reactive extrusion: A new method of producing resistant starch, Food Hydrocoll. 2019;92(1):135\u0026ndash;14. https://doi:10.1016/j.foodhyd.2019.01.064.\u003c/li\u003e\n\u003cli\u003eBermudez-Brito M, Rosch C, Schols HA, Faas MM, de Vos P. Resistant starches differentially stimulate Toll-like receptors and attenuate pro-inflammatory cytokines in dendritic cells by modulation of intestinal epithelial cells. Mol Nutr and Food Res. 2015;59(9):1814\u0026ndash;1826. https://doi:10.1002/mnfr.201500148.\u003c/li\u003e\n\u003cli\u003eL\u0026acute;epine AFP, de Hilster RHJ, Leemhuis H, Oudhuis L, Buwalda PL, de Vos P. Higher chain length distribution in debranched type-3 resistant starches (RS3) increases TLR signaling and supports dendritic cell cytokine production. Mol Nutr and Food Res. 2018; 63(2):1801007. https://doi:10.1002/mnfr.201801007.\u003c/li\u003e\n\u003cli\u003eGuti\u0026eacute;rrez TJ. Characterization and in vitro digestibility of non-conventional starches from guinea arrowroot and La Armu\u0026ntilde;a lentils as potential Food sources for special diet regimens. Starch‐St\u0026auml;rke. 2018; 70 (1\u0026ndash;2). . https://doi.org/10.1002/star.201700124\u003c/li\u003e\n\u003cli\u003eFuentes-Zaragoza E, Sanchez-Zapata E, Sendra E, Sayas E, Navarro C, FernandezLopez J. Resistant starch as prebiotic: A review. Starch-Starke.2011;63(7):406\u0026ndash;415. https://doi.org/10.1002/star.201000099\u003c/li\u003e\n\u003cli\u003eBirt DF, Boylston T, Hendrich S, Jane JL., Hollis J, Li L. Resistant starch: Promise for improving human health. Advances in Nutr. 2013; 4(6):587\u0026ndash;601. . https://doi:10.3945/an.113.004325.\u003c/li\u003e\n\u003cli\u003eOladele, E-O. P. and Mbaye, A. The potential of resistant starch type 1 for nutritional food security. Food Security and Safety. 2023;2: 3-17. https://doi:10.1007/978-3-031-09614-3_1\u003c/li\u003e\n\u003cli\u003eAgama-Acevedo E, Pacheco-Vargas G, Gutierrez-Meraz F, Tovar G, Belo-Perez LA. Dietary fiber content, texture and in vitro starch digestibility of different white bread crusts. J Cereal Sci. 2019; 102824. https://doi.org/10.1016.2019.102824\u003c/li\u003e\n\u003cli\u003eRoman, L.; Campanella, O.; Martinez, M.M. Shear-induced molecular fragmentation decreases the bioaccessibility of fully gelatinized starch and its gelling capacity. Carbohydr Polym. 2019;215:198\u0026ndash;206. . https://doi.org/10.1016.2019.03.076.\u003c/li\u003e\n\u003cli\u003eHalal SLME, Colussi R, Pinto VZ, Bartz J, Radunz M, Carreno NLV, Dias, ARG, Zavareze EDR. Structure, morphology and functionality of acetylated and oxidised barley starches. Food Chem. 2015;168:247\u0026ndash;256. https://doi.org/10.1016/j.foodchem.2014.07.046. \u003c/li\u003e\n\u003cli\u003eLu X, Luo Z, Fu X, Xiao Z. Two-step method of enzymatic synthesis of starch laurate in ionic liquids. J Agric Food Chem. 2013;61:9882\u0026ndash;9891. https://doi:10.1021/jf401467.\u003c/li\u003e\n\u003cli\u003eMiao M, Xiong, S, Jiang, B., Jiang, H., Cui, S.W. and Zhang, T. Dual-enzymatic modification of maize starch for increasing slow digestion property. Food Hydrocoll.2014; 38:180\u0026ndash;185. https://doi:10.1016/j.foodhyd.2013.12.006.\u003c/li\u003e\n\u003cli\u003eFlores-Silva PC, Berrios JDJ, Osorio-Diaz P, Bello-Perez LA. Gluten-free spaghetti made with chickpea, unripe plantain and maize flours: functional and chemical properties and starch digestibility. International J Food Sci Techno.2014;l49(9):1985-1991. https://doi.org/10.1111/ijfs.12529.\u003c/li\u003e\n\u003cli\u003eWepner B, Berghofer E, Miesenberger E. Citrate starch\u0026mdash;Application as resistant starch in different foodsystems. Starch St\u0026auml;rke. 1999; 51: 354\u0026ndash;361. https://doi.org/10.1002/(SICI)1521-379X(199910)51:10\u0026lt;354::AID-STAR354\u0026gt;3.0.CO;2-W.\u003c/li\u003e\n\u003cli\u003eS\u0026aacute;nchez‐Rivera MM, N\u0026uacute;\u0026ntilde;ez‐Santiago MdC, Bello‐P\u0026eacute;rez LA, Agama‐ Acevedo E, Alvarez‐525 Ramirez J. (2017). Citric acid esterification of unripe plantain flour: Physicochemical properties and starch digestibility. Starch‐St\u0026auml;rke. 2017; 52:69(9-10). https://doi.org/10.1002/star.201700019.\u003c/li\u003e\n\u003cli\u003eJiangping YSL, Ao H, Jun C, Chengmei L, David JM. Synthesis and characterization of citric acid esterified rice starch by reactive extrusion: A new method of producing resistant starch. Food Hydrocoll. 2019; 92(2). https://doi.org/10.1016/j.foodhyd.2019.01.064.\u003c/li\u003e\n\u003cli\u003eVolkert B, Lehmann A, Greco T, Nejad MH. A comparison of different synthesis routes for starch acetates and the resulting mechanical properties. Carbohydr Polym, 2010;\u003cem\u003e 79\u003c/em\u003e(3):571-577. . https://doi.org/10.1016/j.carbpol.2009.09.005. \u003c/li\u003e\n\u003cli\u003eZuo Y, Gu J, Yang L, Qiao Z, Tan H, Zhang Y. Preparation and characterization of dry method esterified starch/polylactic acid composite materials. International J biol macromol. 2014; \u003cem\u003e \u003c/em\u003e64:174-180. https://doi.org/10.1016/j.ijbiomac.2013.11.026.\u003c/li\u003e\n\u003cli\u003eMorikawa K, Nishinari K. Effects of concentration dependence of retrogradation behaviour of dispersions for native and chemically modified potato starch. Food Hydrocoll.2000; 14:395\u0026ndash;401. https://doi.org/10.1016/s0268-005x(00)00021_7.\u003c/li\u003e\n\u003cli\u003eKim SH, Kim HS. Influence of semi-dry heating reaction conditions on resistant starch citrates. Food Eng Prog.2015;4:313\u0026ndash;319. https://doi:10.13050/foodengprog.2015.19.4.313.\u003c/li\u003e\n\u003cli\u003eMei JQ, Zhou DN, Jin ZY, Xu, XM, Chen HQ. Effects of citric acid esterification on digestibility, structural and physicochemical properties of cassava starch. Food Chem.2015; 187:378\u0026ndash;384. https://doi:10.1016/j.foodchem2015.04.076.\u003c/li\u003e\n\u003cli\u003eKapelko-Z˙ eberska M, Zie˛ba T, Pietrzak W, Gryszkin A. Effect of citric acid esterification conditions on the properties of the obtained resistant starch. International J Food Sci Technol. 2016; 51, 1647\u0026ndash;1654. https://doi.org/10.1111/ijfs.13136.\u003c/li\u003e\n\u003cli\u003eXia H, Li Y, Gao Q. Preparation and properties of RS4 citrate sweet potato starch by heat-moisture treatment. Food Hydrocoll. 2016; 53:172\u0026ndash;178. https://doi.org/10.1016/j.foodhyd.2015.11.008.\u003c/li\u003e\n\u003cli\u003eLee SY, Lee KY, Lee HG. (2018). Effect of different pH conditions on the in vitro digestibility and physicochemical properties of citric acid-treated potato starch. International J Biol Macromol. 2018; 107, 1235\u0026ndash;1241. https://doi:10.1016/j.ijbiomac.2017.09.106. \u003c/li\u003e\n\u003cli\u003eRemya R, Jyothi AN, Sreekumar J. Effect of chemical modification with citric acid on the physicochemical properties and resistant starch formation in different starches. Carbohydr Polym. 2018; 202: 29\u0026ndash;38. . https://doi:10.1016/j.carbpol.2018.08.128.\u003c/li\u003e\n\u003cli\u003eButt NA, Ali TM, Hasnain A. (2019). A. Rice starch citrates and lactates: A comperative study on hot water and cold water swelling starches. International J Biol Macromol.2019;\u003cem\u003e \u003c/em\u003e127:107\u0026ndash;117. https://doi.org/10.1016/j.ijbiomac.2019.01.019\u003c/li\u003e\n\u003cli\u003eLi MN, Xie Y, Chen HQ, Zhang B. Effects of heat-moisture treatment after citric acid esterification on structural properties and digestibility of wheat starch, A- and B- type starch granules. Food Chem. 2019; 272. https://doi:10.1016/j.foodchem2018.08.079.\u003c/li\u003e\n\u003cli\u003eSrikaeo K, Hao PT, Lerdluksamee C. (2019). Effects of heating temperatures and acid concentrations on physicochemical properties and starch digestibility of citric acid esterified tapioca starches. Starch St\u0026auml;rke. 2019;71. https://doi.org/10.1002/star.201800065.\u003c/li\u003e\n\u003cli\u003eUtomo P, Nizardo NM, Saepudin, E. Crosslink modification of tapioca starch with citric acid as a functional food. AIP Conf. Proc. 2020; 2242:040055. https://doi.org/10.1063/5.0010364\u003c/li\u003e\n\u003cli\u003eMuhammed N, Kappat Valiyapeediyekkal, S, Basheer A, Cherakkathodi S, Plachikkattu Parambil A, Sarasan S, Abhilash S, Johnsy G, Benguo L. Talipot palm (Corypha umbraculifera L.) a nonconventional source of starch: Effect of citric acid on structural, rheological, thermal properties and in vitro digestibility. International J Biol Macromol. 2021; 182, 554\u0026ndash;563. https://doi.org/10.1016/j.ijbiomac.2021.04.035\u003c/li\u003e\n\u003cli\u003eShaikh F, Ali TM, Mustafa G, Hasnain A. Comparative study on effects of citric and lactic acid treatment on morphological functional, resistant starch fraction and glycemic index of corn and sorghum starches. International Journal of Biol Macromol. 2019; 135, 314\u0026ndash;327. https://doi.org/10.1016/j.ijbiomac.2019.05.115.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Chemistry](https://link.springer.com/journal/44371)","snPcode":"44371","submissionUrl":"https://submission.nature.com/new-submission/44371/3","title":"Discover Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Yam flour, α- amylase, Citric acid, Esterification, Digestibility, Degree of substitution, Reaction efficiency","lastPublishedDoi":"10.21203/rs.3.rs-4590511/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4590511/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCitric acid esterification of two accessions of white yam (Dioscorea \u003cem\u003erotundata\u003c/em\u003e), ‘Aro’ and ‘Efuru’, Yellow yam (\u003cem\u003eD. cayanensis\u003c/em\u003e) flours were carried out with four different concentrations of citric acid\u0026nbsp; (10%, 20%, 30%, 40%w/v /100g sample) under varying reaction temperature and time\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e(110\u003csup\u003eo\u003c/sup\u003eC for 2 hours, 110\u003csup\u003eo\u003c/sup\u003eC for 3 hours, 120\u003csup\u003eo\u003c/sup\u003eC for 2hours and120\u003csup\u003eo\u003c/sup\u003eC for 3hours). The Degree of substitution (DS), Reaction Efficiency, and alpha – amylase digestibility of the products were determined. The DS obtained was 0.011 – 0.178. The reaction efficiency at 110\u003csup\u003eo\u003c/sup\u003eC for 2 hours, 110\u003csup\u003eo\u003c/sup\u003eC for 3 hours, 120\u003csup\u003eo\u003c/sup\u003eC for 2 hours and 120\u003csup\u003eo\u003c/sup\u003eC for 3hours across all samples were (11.33% - 34.05%), (12.96% - 52.14%), (26.67% - 39.94%) and (32.01% - 65.11%) respectively. For esterification at 120\u003csup\u003eo\u003c/sup\u003eC for 3hours, the reaction efficiency were higher than 50% for almost all samples at citric acid concentration of 10% - 30%w/v. However, at 40%w/v, the reaction efficiency decreased to less than 50%. Alpha amylase digestibility reduced as the concentration of citric acid, temperature and reaction time of the esterification process increased. The least reduction in digestibility (1.15%) was obtained at 110\u003csup\u003eo\u003c/sup\u003eC for 2hours at 10% citric acid concentration, while the highest reduction in digestibility (93.42%) was obtained at 120\u003csup\u003eo\u003c/sup\u003eC for 3hours at 30% citric acid concentration.\u0026nbsp; From the results obtained, it can be concluded that concentration of citric acid, reaction temperature and time correlate positively with the degree of substitution and alpha amylase resistivity, however steric effect reduced the reaction efficiency as the concentration of citric acid dosages increased.\u003c/p\u003e","manuscriptTitle":"The effect of citric acid concentration, reaction temperature and time on the esterification of some varieties of yam flour in Nigeria","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-17 15:18:01","doi":"10.21203/rs.3.rs-4590511/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-09-05T16:30:28+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-04T14:39:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"335861511010072834354354504934485288475","date":"2024-08-28T13:27:27+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-23T11:28:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"186508676625414709140085143592474528289","date":"2024-08-23T09:18:40+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-07-04T06:49:39+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-06-25T17:39:10+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-06-25T17:34:51+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Chemistry","date":"2024-06-16T16:51:31+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Chemistry](https://link.springer.com/journal/44371)","snPcode":"44371","submissionUrl":"https://submission.nature.com/new-submission/44371/3","title":"Discover Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"65755b0a-c21e-4329-a143-99bc45d7e8ad","owner":[],"postedDate":"July 17th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-12-04T19:39:03+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-17 15:18:01","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4590511","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4590511","identity":"rs-4590511","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}