Effects of blending and maleylation on functional property changes of whey protein concentrate and soy protein isolation

Typescript (photocopy).Changes in functional properties of unmodified and maleylated whey protein concentrate and soy protein isolate blends were studied. Both blending and maleylation affected functional characteristics; however, effects of maleylation were more pronounced than those of blending. Each blend was maleylated with 30% maleic anhydride based on the total protein content of the blend. All modified blends were purified, desalted and concentrated using an ultrafiltration membrane. About 88% of soy proteins and 97% of whey proteins were maleylated. Oil absorption capacities of all protein blends increased markedly by maleylation, about four-fold over unmodified blends. Oil absorption capacities were positively correlated to specific volumes of proteins. Only 5.4% of unmodified whey proteins and 65% of unmodified soy proteins were precipitated by calcium ions. Maleylation significantly decreased calcium sensitivity of all protein blends. Nitrogen solubilities of all protein blends were enhanced by maleylation for a pH range of 4-6. But, unlike unmodified blends, maleylated protein blends did not resolubilize in the pH range of 3-4. Heat coagulation of whey proteins decreased substantially by blending with soy protein isolate. Maleylation further decreased heat coagulability of all protein blends appreciably. Reduction in emulsion capacity was proportional to the amount of soy protein isolate in the blend. But improvements in emulsion capacity were evident upon maleylation. Emulsion viscosity of unmodified blends was inversely proportional to the amount of soy protein. However, emulsion viscosity increased significantly upon maleylation as the amount of soy protein isolate in the blend was increased. Emulsion stabilities of maleylated blends were higher than those of unmodified blends. However, maleylated soy proteins showed remarkable improvements in emulsion stabilities compared to maleylated whey proteins. Foaming capacity of unmodified blends decreased as the amount of soy protein isolate increased; however, maleylation reversed this trend. Foam stability of soy protein isolate markedly improved after maleylation, but foam stability of whey protein concentrate decreased after maleylation..