Effects of ultrasound-assisted α-amylase degradation treatment with multiple modes on the extraction of rice protein

The effects of ultrasound-assisted alpha-amylase degradation (UAD) treatment with multiple modes on the extraction of rice protein (RP) from rice dreg powder were studied. The results showed that UAD treatment increased protein extraction rate significantly (p < 0.05) compared to that of alpha-amylase degradation treatment and control. Among all the ultrasound mode treatments researched in this paper, sequential frequency ultrasound treatment presented higher protein extraction rate compared to that of simultaneous or single frequency ultrasound treatment. The highest protein extraction rate was obtained under 20/35 kHz of sequential frequency UAD treatment with the protein extraction rate of 89.58% and protein purity of 92.99%. The test and analysis of fourier transform infrared spectroscopy, ultraviolet visible spectroscopy, starch content, non-protein nitrogen content, SH and SS content, surface hydrophobicity, amino acids content and proteins characteristics were studied to reveal the mechanism of UAD on the protein extraction effect. After treated with UAD, the starch protein agglomerates disintegrated completely, moreover, protein advanced structure was changed to some extent and the disulfide bond was partially broken, but the Main chain structure (peptide chain), specificity of protein and amino acid composition were not obviously changed. Consequently, the structure modified RP extracted by UAD treatment presented higher solubility, emulsifying activity and foaming capacity, which was beneficial for the application of RP. In conclusion, UAD treatment is an effective method for maximizing extraction rate, purity and modifying properties of extracted protein.