Abstract: In this study, transglutaminase (TGase) was used to improve the freeze-thaw stability of oil-in-water emulsion stabilized by soybean protein isolate (SPI). We evaluated the influence of TGase reaction time, enzyme dosage and the number of freeze-thaw cycles on the freeze-thaw stability of SPI-stabilized emulsion as reflected by oiling off and creaming index. Meanwhile, the microstructure and thermal characteristics of the emulsions containing SPI and TGase-modified SPI as emulsifier were compared, and the effect of TGase modification on SPI composition was examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Furthermore, the relationship between enzymatic modification and emulsion stability was analyzed. The results show that after three freeze-thaw cycles, the emulsion containing TGasemodified SPI maintained good stability. A crosslinking time of 3 h and an enzyme dosage of 1.5% were found to be optimal conditions to obtain better freeze-thaw stability. The emulsion remained stable as indicated by its microstructure. The changes in thermal properties during freeze-thaw showed that the crystallization and melting behavior of the emulsion altered. SDS-PAGE revealed that SPI composition changed after enzymatic modification, thus affecting the freeze-thaw stability of the emulsion. This study provides a theoretical foundation for applying TGase-modified SPI in frozen food.

Key words: transglutaminase, soybean protein isolate, emulsion, freeze-thaw stability