Abstract: Irradiation technology was used to assist the grafting reaction between soybean protein isolate (SPI) and maltose (M) to improve the freeze-thaw stability of SPI emulsion. The effects of SPI concentration, m(SPI)/m(M) ratio, and irradiation dose on the grafting degree, browning degree and creaming index of modified products were studied. It was found that under the conditions: SPI concentration of 4%, m(SPI)/m(M) ratio of 4:1 and radiation dose of 7.5 kGy, the creaming index of modified SPI was decreased by 23.58%, 29.9% and 31.2%, respectively, after 1, 2 and 3 freeze-thaw cycles when compared with intact SPI. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed the grafting reaction between SPI and maltose. The oil release rate of the modified SPI emulsion after freezing and thawing was significantly improved when compared with SPI emulsion. Optical microscopy observation also confirmed that the optimized SPI microstructure was more stable. This study suggested that irradiation could enhance the grafting reaction to improve the freeze-thaw stability of SPI emulsion, which will provide a new integrative protein modification approach.

Key words: soy protein isolate, radiation, grafting reaction, emulsion, freeze-thaw stability