Transglutaminase-induced crosslinking of soy protein isolate in crowded environments: effects of dextran...

Dextran (DE) with different molecule weights was used as a crowding reagent, and effects of varying degrees of crowding on the TGase-induced crosslinking and gelation behavior of soy protein isolate (SPI) were investigated. Results show that the conformations of SPI and TGase tend to become more compact as the crowdedness increases. Low concentrations (5%) of DE did not significantly affect the TGase crosslinking of SPI, whereas a highly crowded environment made TGase unable to effectively crosslink SPI subunits, leading to decreased formation of ε-(γ-glutamyl)-lysine isopeptide bonds (up to 65.6% decrease compared to the control). Rheological characteristics and microstructural observations reveal that increasing the concentration and molecular weight of added DE significantly decreases the elastic modulus (G') of SPI gels and promotes the formation of inhomogeneous and loose networks, indicating weakened gelling ability caused by macromolecular crowding. Compared with continuous stirring, intermittent stirring was more conducive to SPI crosslinking and gel formation in a crowded environment, reaching a maximum G' of 603 Pa with a 143.5% increase compared to the unstirred sample. These findings provide important information for the enzymatic modification of plant proteins in food processing.