Effect of temperature and yeast concentration on the autolysis of Kluyverommyces fragilis grown on lactose-based media

Abstract

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 ( X 0) and reaction temperatures ( T) by carrying out a composite design experiment. By using the response surface methodology and canonical analysis, the experimental responses (viz. Kjeldhal, Y KP, and Lowry, Y LP, protein and total carbohydrates, Y TC, solubilisation yields) were fitted to the only statistically significant factors with mean percentage errors ranging from 1.7 to 7%. Whereas yeast 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 X 0 (80–110 g/ dm 3) and T (51.5–54.5 ° C) associated with Kjeldhal and Lowry protein recoveries greater than 88 and 51.5%, respectively, and with total carbohydrates solubilisation ranging from 50 to 55%. After establishing the validity of these data at the 95% confidence level, an optimal operating condition ( X 0 = 100 g/ dm 3 and T = 54 ° C) was further tested in the absence of NaCl. Since the observed 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 level of 0.05), the latter operating condition might be further employed to produce no-salt autolysates with 54% crude protein and a chemical score of 45% as referred to the FAO/WHO standard (1973).