Influence of Freeze-Drying and Oven-Drying on the Gelling Ability of Bovine Blood Protein Fractions and the Physical Properties of the Consequent Gels

This study aimed to elucidate the influence of freeze-drying and conventional oven-drying on the structure of bovine plasma and cell fraction proteins, as well as the impact of these alterations on the properties of the derived gels. Conformational changes were evaluated by FTIR spectroscopy, X-ray diffraction, exposure of sulfhydryl (SH) groups, and disulfide bond (S-S) formation. Solubility and minimal gel concentration of protein-based powders and hardness and spontaneous syneresis of the consequent hydrogels were also determined. Results showed that pre-existing alterations in protein structure strongly influence the dynamics of heat-induced gelation and, consequently, the physical characteristics of the resulting gels. These changes include initial challenges in rehydrating cell fraction powders during gelation, which can be overcome to obtain highly functional gels, as well as a lack of correlation between covalent reticulation and physical gel properties. Notably, the crystallization of endogenous NaCl in freeze-dried plasma powders, as opposed to the generally expected amorphous state, correlates with superior rehydration and functional properties in the subsequent gels. These contributions provide additional information on the intricate relationship between the processing history of the protein precursors and the resulting gel properties, which is essential for tailoring their gelation performance to various food applications.