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 l fermenter (NBS, Microferm), containing sugar-cane blackstrap molasses supplemented with urea (0.5 g l−1) and penicillin V (500 ui/l), under the following conditions: 32(±1)°C; pH 4.5–5.0; N=200 min−1; inoculum and mash volume equal to 3.0 l and 7.0 l, 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 (Sm) (170, 220 or 270 g l−1) and total amount of wet-pressed yeast in the inoculum (MX0′) (800, 1300 or 1800 g). By applying the quadratic regression analysis the following equations were established: Y=78.2+2.5X3+2.5(X3)2−3.3X4−0.89X1,X2−0.79X3,X4 and Pv=71.3+6.5X4−4.9X2,X4 for the ethanol yield (Y) and residual invertase activity (Pv), respectively. The optimised ethanol and invertase formation was observed for high Sm values under low MX0′- and high K.