Physicochemical properties of soybean protein isolate-based gel produced through probiotic fermentation

Soy protein isolate (SPI) was used to prepare gels through probiotic fermentation. The effects of fermentation time (0–20 h) on the physicochemical properties of resulting gel were evaluated. The effect of probiotic fermentation on physicochemical properties of gel was found to highly depend on the fermentation time. The probiotic fermentation decreased the pH value below pH 4.75 and this process also induced SPI to form a gel upon 10 h. The formation of gel was indicated by the increase of particle size, viscosity and storage modulus, and appearance of a new peak in molecular weight distribution. The formation of porous and gel-like microstructure, due to the aggregation of SPI molecules, also occurred after 10 h of fermentation. Water holding capacity of SPI-based gel reached the highest value at 15 h fermentation and decreased with further fermentation. The probiotic fermentation caused an increase of band intensity of amide-A in FTIR spectra. It also caused a decrease of surface hydrophobicity and fluorescence intensity in intrinsic tryptophan fluorescence spectra. The subunits of SPI remained intact and were not affected by probiotic fermentation.