Optimization of protein extraction from tree peony (Paeonia suffruticosa Andr.) seed using response surface methodology

Optimization of extraction ratio (ER) of tree peony seed protein (TPSP) was investigated using response surface methodology (RSM). The second-degree equation for ER of TPSP had high coeffi cient (0.9625) of determination. The probability (P) value of regression model signifi cance was less than 0.001 by analysis of central composite rotatable design. Relationships of ER to pH, liquid/solid ratio, squares of all factors, and cross-product factors (x2x3, x2x4, x3x4) were signifi cant (P1x2, x1x3, x1x4) were not signifi cant factors (P>0.05). Optimum extraction conditions were 3.42 h, pH 9.50, 50.80 ºC, and 9.54 ml g–1 of liquid/solid ratio with the maximum ER (43.60%) . SDS-PAGE indicated TPSP had mainly four proteins (180, 100, 60, and 35 kDa) with four subunits of 60, 48, 38, and 23 kDa. TPSP had a good amino acid composition with abundant essential amino acids (39.76%) determined by amino acid analysis