Enhancement of Hydrophilicity of Soybean Globulins by Deamidation and Change in Their Gelation Properties

Abstract

Deamidation of food proteins by cation-exchange resins is a promising method for modifying their functional properties without causing any peptide-bond hydrolysis. The gelation property and the water affinity of phytate-removed deamidated soybean globulin (PrDS) were evaluated in this study. Soybean globulin (US) was prepared by isoelectric precipitation, and phytate was removed by use of anion-exchange resins. Then, the phytate-removed soybean globulin (PrS) was deamidated by using cation-exchange resins of carboxylate type. The heat-induced gel property of PrDS was compared with that of PrS and US. The affinity of the soybean globulins for water was evaluated by the parameters obtained from pulsed NMR measurements. In addition, the denaturation temperature of the soybean globulins was determined with DSC. The water-retaining property of the heat-induced gel was better in the order of PrDS > PrS > US. From the pulsed NMR measurements, the amount of bound water in the untreated soybean globulin was almost constant irrespective of the water content. According to the correlation time of bound water τ_b obtained from pulsed NMR measurements, the affinity of soybean globulin for water was enhanced by deamidation, which was assumed to be the reason for the better water-retaining property of PrDS. However, the amount of bound water was decreased by phytate-removal and deamidation. DSC measurements showed that removal of phytate and deamidation made the denaturation temperature of soybean globulin slightly increase.