Response surface methodology for optimisation of protein concentratepreparation from cowpea [Vigna unguiculata (L.) Walp]

The optimum conditions for the preparation of protein concentrate from cowpea were determined using response surface methodology. A central composite rotatable design, consisting of eight experimental points and five replications at the centre point, was used to investigate the effects of two independent variables, namely pH and NaCl concentration on four responses: protein content (%,), protein yield (%), reactive lysine (g/16 g N) and zinc content (mg/100 g). A second-order polynomial model was used for predicting the responses. Regression analysis indicated that more than 80% of the variation was explained by the fitted models. Experimental results showed that under optimum conditions (pH and NaCl concentration of 9.91 and 0.15 M, respectively) the protein content was ⩾84%, protein yield ⩾87%, reactive lysine ⩾1.175 g/16 g N and zinc content ⩾7.75 mg/100 g. These results were in agreement with those predicted, hence indicating the suitability of the model used.