Extraction optimization of watermelon seed protein using response surface methodology

Extraction conditions for maximum protein recovery from watermelon (Citrullus vulgaris Cv Sugar baby) seed meal were investigated using response surface methodology. A central composite design with four independent variables: temperature (40, 45, 50, 55 and 60 °C); NaOH concentration (0.03, 0.06, 0.09, 0.12 and 0.15 g/L); extraction time (5, 10, 15, 20 and 25 min) and solvent/meal ratio (30:1, 40:1, 50:1, 60:1 and 70:1, v/w) was used to study the response variable (protein yield). The experimental values of protein yield ranged between 72.03 and 81.52 g/100 g seed meal. A second-degree equation for independent and response variables was computed and used to create the contour plots graphs. The predicted values obtained for protein yield revealed that coefficient of determination and standard error was 0.80 and 0.906, respectively. Optimum protein extraction was obtained with 0.12 g/L alkali concentration, 15 min extraction time and 70:1 (v/w) solvent/meal ratio at 50 °C. Confirmatory studies revealed that the protein yield under optimum conditions was 80.71 g/100 g seed meal.