Abstract: The subcritical water extraction of walnut meal protein was optimized by response surface methodology. The variables optimized were extraction time, solid-to-solvent ratio, extraction temperature and pH. The response was the extraction yield of protein. One-factor-at-a-time method was used to determine the appropriate levels of independent variables for further optimization by response surface methodology. The results showed that the optimal conditions were as follows: pH, 9.0; solid-to-solvent ratio, 1:25 (g/mL); and temperature, 133 ℃. Under these conditions, the extraction yield was up to 75.01%. The results of amino acid analysis indicated that the walnut protein contained almost all kinds of amino acids with glutamic acid, arginine, and aspartate being the predominant amino acids, accounting for 59.7% of the total amino acids. Essential amino acids accounted for 20.03%. Sub critical water extraction could be considered as convenient and efficient method for the extraction of walnut protein.

Key words: walnut meal, subcritical water, protein extraction, response surface methodology, amino acid analysis