This study was performed to investigate the effects of three preparation factors on the activities of milk-coagulant from Solanum aethiopicum L. Shum (SAS) fruits. These independent variables were SAS fruits powder, soaking temperature and NaCl concentration. Box-Behnken design was used to establish the relationship between variables and experimental responses. The models obtained showed satisfactory agreements between the observed and predicted values (P<0.001) with regard to milk-clotting activity (R2 = 0.98), proteolytic activity (R2 = 0.91) and ratio of clotting to proteolytic activities (R2 = 0.95). The optimum milk-coagulant prepared from SAS fruits was obtained by macerating 14.5% (w/v) of SAS fruit powder in the NaCl solution (6%, w/v) at temperature of 21°C. Under these conditions, SAS coagulant showed a milk-clotting activity of 202.21 ± 4.50 U/ml, proteolytic activity of 0.23 ± 0.03 U/ml and ratio of clotting to proteolytic activities of 879.26 ± 7.41. No statistical difference (P>0.01) was observed between the experimental and predicted responses. Based on the response surface analysis, a quadratic polynomial model could be used to optimize the preparation of the milk-coagulant from SAS fruits suitable for cheesemaking.
