Brewing Science Laboratory, Department of Microbiology, University of Nigeria, Nsukka, Nigeria; Institute of Applied Biochemistry, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572, Japan; Department of Food Science, University of Pretoria, 0002 Pretoria, South Africa
Ezeogu, L.I., Brewing Science Laboratory, Department of Microbiology, University of Nigeria, Nsukka, Nigeria, Department of Food Science, University of Pretoria, 0002 Pretoria, South Africa; Okolo, B.N., Brewing Science Laboratory, Department of Microbiology, University of Nigeria, Nsukka, Nigeria; Ogbonna, J.C., Institute of Applied Biochemistry, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572, Japan
Tryptic digests of sprouts from two Nigerian sorghum cultivars were evaluated for their effects on very-high-gravity-fermentation using Saccharomyces cerevisiae WY1006. Yeast growth, fermentation vigor, and ethanol production were considerably (P < 0.05) enhanced by small amounts (1.25 to 6.25 g/L) of digests. CO2 emission rates after 24 hr were 48.3 to 69.2 mg/hr (Local White [TDSS-LW] digest) and 67.1 to 89.2 mg/hr (Local Red [TDSS-LR] digest) compared with 41.3 mg/hr in the unsupplemented control. Yeast growth increased 1.6- to 2.0- and 1.7- to 2.2-fold, respectively with TDSS-LW and TDSS-LR. At 83.7 to 105.0 and 102.0 to 128.8 g/L, respectively, TDSS-LW and TDSS-LR supported significantly (P < 0.05) higher ethanol production than did the control (64.0 g/L). Final ethanol values with TDSS-LR were always (P < 0.05) higher than those with TDSS-LW, but very comparable with values from yeast extract-supplemented media (105.9 to 137.5 g/L). Sprout digest concentrations supporting maximum ethanol production were 5.0 and 3.75 g/L, respectively for TDSS-LW and TDSS-LR. At 3.75 g/L or below, more ethanol was produced by yeast in media with TDSS-LR than was observed in corresponding yeast extract-containing media. Results suggest that tryptic digests of sorghum sprouts can serve as viable alternatives to expensive yeast extract in ethanologenic fermentation. © 2005 American Society of Brewing Chemists, Inc.