Effects of freeze-thaw cycles on the structure and emulsifying properties of peanut protein isolates.

This study investigated changes of the structure and emulsifying properties of peanut protein isolate (PPI) during multiple freeze-thaw (F-T) cycles. According to the Fourier transform infrared spectrum, the F-T treatment to PPI reduced the content of protein ordered structure significantly. The result of fluorescence spectrum revealed that the polarity of PPI surroundings first increased and then decreased. Similarly, the free sulfhydryl content and surface hydrophobicity of PPI increased firstly and decreased. However, the carbonyl content and particle size of PPI increased continuously after F-T treatment. The emulsification performance of PPI after F-T treatment was significantly improved. The emulsion prepared by PPI after 3 F-T cycles had the smallest mean particle size, the highest absolute value of zeta-potential and the most uniform microstructure distribution, showed the best performance of emulsifying ability. Therefore, it can be known that F-T cycles treatment could effectively change protein structure and improve protein emulsifying properties.