Preparation And Properties Of Soy Protein-Stabilized Emulsion Gels Induced By Microbial Transglutaminase

Cross-linking induced with transglutaminase can evidently improve the properties ofprotein gels on their rheologies and textures. The protein-stabilized emulsion gels haveattracted increasing interests by academic world and industry due to their potential to beapplied as a kind of release-controlled carriers, especially for labile lipid-soluble bioactivecompounds. Therefore, the study of formations and properties of protein-stabilized emulsiongels have important significance for the development of new functional foods. This work usedthe soy protein isolate (SPI) as materials, aimed to elucidate the rheologies andmicrosturctures of SPI-stabilized emulsion gels induced by microbial transglutaminase(MTGase) by changing oil volume fraction (φ=0.2-0.6), stirring mode and the adding modeof MTGase, further to find the gelling mechanism about all kinds of emulsion gels. The mainresults are as follows：1. The properties and microstructures of MTGase induced SPI emulsion gels changedwith different oil volume fractions (φ=0.2-0.6), the water-holding capacity (WHC) and G’progressively increased with oil fractions increasing. The gelling mechanism was probablydifferent to some extent. The gelling at high φ values could be largely related to aggregationor coagulation of protein-coated oil droplets, while at low φ values, the gels were more likeenzyme-set protein gels.2. Two kinds of stirring (with intermittent or continuous mode) could be introduced inpreparation of stirred-type emulsion gels induced with transglutaminase. Properties andmicrostructures indicated that stirring during the gelation greatly facilitated the gel networkformation and increased gel stiffness of the formed emulsion gels. The WHC and G’progressively increased with oil fractions increasing. The improvement of gel stiffness and theWHC for the stirred-type emulsion gels were more noticeable with the intermittent mode thanthe continuous one. Comparison discovered that the major interaction forces involved in thegel network formation and/or maintenance were different between the two stirring modes. Thedisulfide bonds, hydrophobic interactions and electrostatic interactions were the main forcesof the gels in the intermittent mode. While the disulfide bonds and covalent cross-linking were the main forces of the gels in the continuous mode.3. Cross-linking by small amounts of microtransglutaminase prior to emulsificationcould obviously modify the formation of the emulsion gels and improve the rheologicalproperties. Properties and micstructures implied that the G’ greatly increased with the additionof the microtransglutaminase and incubation time with changes of oil fraction (φ=0.2~0.6).The gel stiffness was closely related to oil fraction. At high φ values the improvement ofemulsion gels could be attributed to covalence cross-linking and hydrophobic interactions,while that at low φ values, oil droplets played an important part in the network with thecross-linking.