Gel properties of SPI modified by enzymatic cross-linking during frozen storage

The functional properties (elasticity and water holding capacity) of soy protein isolate (SPI) are degraded by denaturalization during frozen storage. To solve this problem, a modified SPI was prepared by cross-linking SPI and gelatin with transglutanminase (TGase). The gel properties of the modified SPI were analyzed during frozen storage. After 20 days of frozen storage, the water holding capacity (WHC) of the SPI gels decreased from 89% to 65%, whereas that of the modified soybean protein isolate (MSPI) gels remained above 85%, which was 29.6% higher than that of the SPI gels. In addition, the hardness increment of the MSPI gels only accounted for 47.1% that of the SPI gels. The moisture distribution of the MSPI gels showed no significant change during frozen storage, and the content of unfreezing water in the MSPI gels was higher than that in the SPI gels. Confocal laser scanning microscopy revealed that the microstructure of the MSPI gels suffered minimal damage after frozen storage, whereas that of the SPI gels presented a honeycomb pattern after frozen storage. Analysis of soluble protein, total SH groups, and gel chemical interaction showed that the improvement of MSPI gel properties during frozen storage was due to the slight decrease in the amount of gel soluble proteins and total SH groups and to the chemical interaction among different gels. (C) 2016 Elsevier Ltd. All rights reserved.