Abstract: The conditions for simultaneous ultrasonic-assisted extraction of alkali-soluble protein from broken indica rice mixed with Flammulina velutipes root waste were optimized using an orthogonal array design method, and the nutritional characteristics of the protein were studied by an amino acid analyzer and in vitro digestion. The results showed that the optimal extraction conditions were found to be extraction at 50 ℃ and 500 W for 25 min with a 9:2 ratio of rice to mushroom waste (m/m) and a solid-to-solvent ratio of 1:20 (g/mL), resulting in an extraction yield of (69.30 ± 1.30)% and a protein purity of (80.07 ± 0.63)%. The color difference of the protein was 50.31 ± 0.48, and the lysine content was increased compared with the protein extracted from pure rice. Moreover, the contents of 16 amino acids were complemented in the mixed protein, and the amino acid ratio coefficient was 79.70, which was higher than that of either protein source; the in vitro digestibility was (89.40 ± 0.90)%. Simultaneous ultrasonic-assisted extraction of protein from indica rice mixed with Flammulina velutipes is an effective method to improve the protein quality of either of them alone.

Key words: simultaneous extraction, ultrasonic, protein indica rice, Flammulina velutipes, protein, nutritional value