Convective Hot Air Drying of Chilli Pepper: Process Optimization and Modelling the Drying Kinetics and Quality Attributes of Dried Product

Abstract The objectives of this study were to evaluate the individual and interactive effects of air velocity, relative humidity, drying temperature, and drying time on the cabinet hot air drying and quality attributes of chilli pepper as well as to determine the optimum process conditions using the rotatable central composite design (RCCD) of response surface methodology (RSM). The drying kinetics was also modelled. Four factors with three levels of RCCD were utilized: air velocity (0.5-1.5 m/s), relative velocity (65-75%), drying temperature (50-70 o C), and drying time (180-360 min). Product moisture content (PMC), total plate count (TPC), protein content (PC), and carbohydrate content (CC) were evaluated as the quality attributes (responses). The results showed that the drying experimental data significantly ( p ≤ 0.001) and adequately fitted into second-order quadratic regression models with (>0.95) to describe and predict all the responses. Drying time and drying temperature are the most significant drying conditions that exerted more pronounced linear and interactive effects on the dried chilli pepper quality attributes. The predicted optimum process conditions for the production of dried chilli pepper with minimum PMC and TPC as well as maximum PC and CC were obtained to be: drying temperature, 69.98 o C, air velocity, 1.46 m/s, relative humidity, 66.57%, and drying time, 359.86 min. Four empirical models (Page, Newton, Logarithmic, and Henderson and Pabis) were fitted to the drying data and the Page model with (>0.95) best fitted the data to describe the drying kinetics.