Functional and molecular properties of calcium precipitated soy glycinin and the effect of glycation with κ-carrageenan

This study describes an extraction process for the preparation of highly purified calcium precipitated glycinin (11S). Initial extraction of soy proteins using isoelectric precipitation at pH 6.8 followed by cryo-precipitation yielded 4.2% product (11S) recovery with 98% protein purity for the control extracted with NaOH. Addition of calcium chloride (CaCl2) doubled the extraction yield (9%) compared to the control and when two other salts were used (i.e., sodium (Na2SO4) and ammonium (NH4)2SO4 sulfate, average yields of 4.4% and 5.17%, respectively). Thermal and molecular stability under varying conditions (pH, salts, SDS as a protein structure perturbing agent), and effect of glycation on functional and structural properties were investigated. Size exclusion chromatography and electrophoresis confirmed the predominance of a major band with MW of ∼342 kDa with 98.4% purity. Differential scanning calorimetry (DSC) yielded one endothermic transition peak at 95.5 °C. Denaturation temperatures were >100 °C for all salt concentrations studied. The pH had a dominant influence on the structural properties of glycinin. In the presence of NaCl and CaCl2 (0.2–1 M), the protein structure showed very little denaturation and no aggregation bands were observed even on heating to 95 °C. Lower SDS concentrations (0.5–1%) resulted in denaturation and aggregation, while at 2% SDS only denaturation was observed. Glycation did not alter the conformational structure of protein. Improvements in surface properties were observed with moderate degree of glycation (6–24 h).