Effect of alkaline pH shifting combined with ultrasound on the structural and functional properties of peanut protein

To improve the functional properties of peanut protein, alkaline pH shift (pH 12 and pH 13) was used to treat peanut protein alone or combined with ultrasound (500 W/5 min and 30 min). The changes of in the structure, function, and lysalanine content of peanut protein before and after treatment were studied. The results showed that all treatment methods could increase the surface hydrophobicity of peanut protein and cause a red shift in the maximum emission wavelength of endogenous fluorescence. Among them, pH 12 shifting combined with long-term ultrasound treatment, pH 13 shifting alone, or combined with ultrasound treatment could also significantly increase the content of soluble aggregates in peanut protein, decrease α-helix and increase β-turn in the secondary structure. pH 12 or pH 13 shifting alone significantly increased the content of lysalanine in peanut protein, while the combination with ultrasonic treatment could reduce the content of lysalanine by 60%-66%. The solubility and emulsification of peanut protein were improved by pH 13 shifting combined with low-intensity ultrasound treatment, the solubility of peanut protein was increased by 23.23%, and the emulsifying activity and emulsifying stability index increased by 56% and 271%, respectively, and the freeze-thaw stability of the emulsion was significantly enhanced. pH 13 shifting combined with ultrasound treatment can not only significantly improve the functional properties of peanut protein, but also effectively inhibit the production of lysalanine. Therefore, it is a protein complex modification technology with high application potential.