Influence of soybean dietary fiber with varying particle sizes and transglutaminase on soy protein isolate gel

In this study, soybean dietary fiber (DF) was used as nutritional supplement and gel enhancer in soy protein isolate (SPI) gels. The effects of DF particle sizes (100-mesh, DF100; 200-mesh, DF200), DF content and transglutaminase (TGase) addition on the gel properties of DF-enriched soy protein isolate (DSPI) gels were studied. The results showed that 10 % DF100 was beneficial for improving gel hardness (from 137.61 to 148.86 g), but caused the declined gel cohesiveness (from 0.87 to 0.80). with the use of 10 % DF200, the gel cohesiveness was improved from 0.80 to 0.83. However, the water holding capacity of DSPI gels containing DF200 was poor and the ionic and hydrogen bonds were reduced. When 20 % DF100 was added, the overall gel quality decreased. The effect of TGase depended on situations. When DF was well wrapped, the addition of TGase improved the textural property and the β-turn proportion (from 40.22 % to 42.88 %) of DSPI gels owing to the enhanced protein cross-linking. While when SPI was separated by excessive amount of DF, the addition of TGase caused the deteriorated gel properties because TGase-induced local protein aggregation destroyed the gel continuousness. This research will guide the rational application of DF in gel products.