EFFECT OF TEMPERATURE AND YEAST CONCENTRATION ON THE AUTOLYSIS OF KLUYVEROMYCES-FRAGILIS GROWN ON LACTOSE-BASED MEDIA

The NaCl-induced autolysis of Kluyveromyces fragilis grown on lactose- based media was studied as a function of time (t) at different initial yeast concentrations (X0) and reaction temperatures (T) by carrying o ut a composite design experiment. By using the response surface method ology and canonical analysis, the experimental responses (viz. Kjeldha l, Y(KP), and Lowry, Y(LP), protein and total carbohydrates, Y(TC), so lubilisation yields) were fitted to the only statistically significant factors with mean percentage errors ranging from 1.7 to 7%. Whereas y east protein solubilisation was essentially dependent upon temperature , hydrolysis of the total carbohydrates of cell walls was found to be controlled firstly by yeast concentration and secondly by temperature. The resulting empiric models were then used to determine the optimal values of X0 (80-120 g/dm3) and T (51.5-54.5-degrees-C) associated wit h Kjeldhal and Lowry protein recoveries greater than 88 and 51.5%, res pectively, and with total carbohydrates solubilisation ranging from 50 to 55%. After establishing the validity of these data at the 95% conf idence level, an optimal operating condition (X0 = 100 g/dm3 and T = 5 4-degrees-C) was further tested in the absence of NaCl. Since the obse rved values of Y(KP) and Y(LP) after an 8 h treatment were found to be insensitive to the presence of such a catalyst (at a probability leve l of 0.05), the latter operating condition might be further employed t o produce no-salt autolysates with 54% crude protein and a chemical sc ore of 45% as referred to the FAO/WHO standard (1973).