Comparison of yeast extract prepared by autolysis or steam explosion as a cheap nutrient supplement for very high gravity ethanol fermentation of cassava starch

Abstract

Very high gravity fermentation of saccharified cassava starch containing 280 g/l reducing sugar to ethanol by the osmotolerant Saccharomyces cerevisiae G2-3-2 strain required supplementation with inorganic nutrients (KH2PO4, (NH4)2HPO4, and MgSO4 · 7 H2O and yeast extract (YE) to maximize the ethanol production level and rate. Comparison of the YE prepared by the autolysis of spent brewer’s yeast at either 50 °C for 24 h (A-YE) or steam explosion at 200 °C for 20 min (SE-YE), as a replacement for commercial yeast extract (C-YE) at 7.5 g/l, revealed that A-YE gave a slightly higher ethanol concentration (113.85 g/l) than the SE-YE (107.81 g/l), and was comparable to that obtained with the C-YE (113.14 g/l). At the optimal concentration of A-YE supplementation (5.23 g/l), the ethanol concentration in the ferment reached 115.77 g/l at 24 h, an ethanol productivity of 4.82 g/l/h.