The effect of subzero temperatures on the properties and structure of soy protein isolate emulsions

Different freezing temperatures (-5, -20, -40 and -80 ℃) could change soy protein isolate (SPI) structure and emulsion properties. After freezing at -5 ℃ and -20 ℃, the structure of the SPI loosened, the fluorescence intensity was red shifted, and the proportion of Phe, Tyr and Trp exposed increased. With decreasing temperature, the surface hydrophobicity (H₀ × 100), the number of sulfhydryl groups and the number of disulfide bonds all rose, then fell (-40 ℃), and rose again (-80 ℃). The β-sheet content in the protein secondary structure increased from 32.71% (control) to 50.66% (-40 ℃) and then decreased to 37.05% (-80 ℃), while the β-turn and random coil contents showed the opposite pattern, which also confirmed aggregation. The emulsification performance of SPI after freezing treatment was decreased. The results of this study provide theoretical support for future production of frozen foods with added SPI.