Improving freeze-thaw stability of soy protein isolate-glucosamine emulsion by transglutaminase glycosylation

This paper studies the improvement of freeze-thaw stability of emulsions by incorporating glucosamine into soy protein isolate (SPI) by using transglutaminase. The occurrence of enzymatic glycosylated SPI reaction is confirmed by SDS-PAGE. Through the measurement of creaming index and oiling off, we find that both soy protein isolate-enzymatic without glucosamine (SPI-E) and glycosylated SPI by transglutaminase (SPI-G) can effectively improve the freeze-thaw stability of emulsions. The analysis of particle size, degree of flocculation and coalescence indicates that macromolecular aggregates were formed because transglutaminase enzyme promoted glycosylation and also promoted the cross-linking of protein and protein or the internal cross-linking of protein. Therefore, the particle size of the SPI-G emulsion before freezing and thawing is larger than that of the SPI emulsion. After freeze-thaw cycles, it can be seen that although the particle size of SPI-G is increasing, it is significantly smaller than that of SPI emulsion after freeze-thaw. According to the optical microscope, it can be seen that the SPI emulsion has obvious aggregation of oil droplets after freeze-thawing, and SPI-G effectively improves oil droplet aggregation. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.