Fed-batch culture of Sacchoromyces cerevisiae in sugar-cane blackstrap molasses:: invertase activity of intact cells in ethanol fermentation

Fed-batch cultures of Sacchoromyces cerevisiae were carried out in a 14 I fermenter (NBS, Microferm), containing sugar-cane blackstrap molasses supplemented with urea (0.5 g 1(-1)) and penicillin V (500 ui/l), under the following conditions: 32(+/-1)degrees C; pH 4.5-5.0; N = 200 min(-1); inoculum and mash volume equal to 3.0 1 and 7.0 1, respectively. The parameters varied were: filling time (T: 1, 2 or 3 h), time constant (K: 0, 0.8 or 1.6 h(-1)), total reducing sugar concentration in the feeding mash (S-m) (170, 220 or 270 g 1(-1)) and total amount of wet-pressed yeast in the inoculum (M-x0') (800, 1300 or 1800 g). By applying the quadratic regression analysis the following equations were established: Y = 78.2+2.5X(x) +/- 2.5(X-3)(2)-3.3X(4)-0.89X(1),X-2-0.79X(3),X-4 and P-v= 71.3 + 6.5X(4)-4.9X(2),X-4 for the ethanol yield (Y) and residual invertase activity (P-v), respectively. The optimised ethanol and invertase formation was observed for high S-m values under low M-x0'- and high K. (C) 2000 Elsevier Science Ltd. All rights reserved.