Tryptic digests of sorghum malt sprouts: Evaluation of their stimulatory roles during very-high-gravity ethanol fermentation
Journal of the American Society of Brewing Chemists
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
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.