Abstract: In order to study the effect of sugar type on the freeze-thaw properties of soy protein isolate (SPI)-sugar covalent complex, this experiment examined and compared the emulsifying properties, creaming index, oiling off, degree of grafting, Fourier transform infrared (FTIR) spectra and fluorescence spectra of SPI complexes with glucose (G), maltose (M) and dextran (D). The results showed that under the conditions of reaction temperature 80 ℃, reaction time 3 h, protein concentration 4%, and SPI-to-M ratio 4:1, SPI-M complex was obtained whose emulsifying activity and emulsion stability were 1.41 and 1.29 times as high as those of the control sample, respectively. After one, two and three freeze-thaw cycles, the creaming index decreased by 29.68%, 28.3%, and 29.57%, respectively, and the oiling off decreased by 4.8%, 16.8%, and 22.6%, respectively. The freeze-thaw stability of SPI-M was significantly improved relative to the control group, and its emulsifying activity and freeze-thaw stability were better than those of SPI-G and SPI-D. The grafting degree of SPI-M was significantly higher than that of SPI-G and SPI-D. FTIR spectroscopy indicated that the sugar molecules were inserted into the SPI molecule through covalent bonds. Fluorescence analysis indicated that the protein structure changed.

Key words: soy protein isolate, emulsifying properties, creaming index, freeze-thaw cycles, freeze-thaw stability