Abstract: The extraction of protein from hydraulic?expeller-pressed macadamia nut meal by alkali dissolution and acid precipitation was optimized using one-factor and orthogonal array design methods. The composition and functionality of the protein extract were evaluated. The results showed that alkaline pH, extraction time and temperature all had highly significant effects on extraction efficiency (P < 0.01), and these factors could be ranked in decreasing order of significance: alkaline pH, extraction time and temperature. The optimal extraction conditions were determined as follows: solid-to-liquid ratio, 1:50 (g/mL); pH value, 9.0; extraction time, 2 h; and extraction temperature, 40 ℃. Under these conditions, the yield and purity of protein extracted from macadamia nut meal were up to 95.40% and 65.46%, respectively. Albumin, globulin, gliadin and glutenin accounted for 7.29%, 14.58%, 14.95%, and 63.18% of the total proteins extracted from macadamia nut meal, respectively. The isoelectric point of the protein isolate was approximately 5.0. At the appropriate pH, the solubility, emulsifying capacity, emulsion stability and foam stability of macadamia nut meal protein isolate were good and the foamability was relatively poor. Its oil-binding capacity reached the maximum value of 50.10% at 70 ℃.

Key words: macadamia nut meal, protein, extraction process, composition analysis, functional properties