A novel enzyme cross-linked gelation method for preparing food globular protein-based transparent hydrogel

In this work, a novel two-step method for preparing food globular protein-based hydrogel with transparent appearance and stable network was described. First, soy glycinin dispersion (6% w/v) was heated at 95 °C for 30 min in order to obtain partial unfolding conformation and expose more residues for the following enzymatic cross-linking. An anionic polysaccharide, dextran sulfate (DS), was added before glycinin was heated, forming highly charged complexes with glycinin and maintaining the transparency of the dispersion. Microbial transglutaminase (MTGase) was introduced for gelation, creating a covalent network. Transparent cold-set hydrogels could be obtained when the weight ratio of DS to glycinin was over 1/200. It was found that larger amounts of DS and lower ionic strength were favorable for increasing the transparency of the gels. At pH 7.0, effects of DS amounts and ionic strength on the rheological and mechanical properties of the hydrogels were investigated. Hydrogels with distinctive textural properties could be obtained by different combinations of DS amount and ionic strength. Scanning electron microscopy observation indicated that the addition of DS could promote the formation of regular and stable gel network.