Application of the central composite design and response surface methodology to enzymatic Extraction of oil from Pistacia khinjuk seeds by protease

The central composite design (CCD) technique was used to study the enzymatic extraction of oil from pistacia khinjuk seeds by protease. The Temperature (A) (i.e., 40, 50 and 60 oC), pH (B) (i.e., 4, 6.5 and 9) and reaction time (C) (i.e., 4, 12 and 20) were considered as independent variables. The influence of these three regressors on percentage of oil recovery from seed was evaluated using second-order polynomial multiple regression model. Analysis of variance (ANOVA) showed a high coefficient of determination (R2) value of 0.99, thus ensuring a satisfactory adjustment of the regression model with the experimental data. The positive sign for the coefficient of pH and time in the model indicated that the percentage of oil recovery increased with increased levels of those factors. The negative effect of temperature on the oil recovery indicated that the response levels decreased as A increased. The positive sign for the coefficient of the interaction between two factors B and C on the response indicated that a simultaneous increase in the pH and the reaction time led to an increase in that response. Quadratic models were predicted for the response variables the maximum values predicted was 56%. An Optimum condition for this process was obtained based on the enzymatic extraction of pistacia khinjuk seeds by protease in the experiment where the temperature was 59.5oC and the pH and time reaction were at high level.