Application of acetate buffer in pH adjustment of sorghum mash and its influence on fuel ethanol fermentation |
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Authors: | Renyong Zhao Scott R Bean Beth Ann Crozier-Dodson Daniel Y C Fung Donghai Wang |
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Institution: | (1) Department of Biological and Agricultural Engineering, Kansas State University, Manhattan, KS 66506, USA;(2) USDA–ARS Grain Marketing and Production Research Center, Manhattan, KS 66502, USA;(3) Department of Animal Science and Industry, Kansas State University, Manhattan, KS 66506, USA |
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Abstract: | A 2 M sodium acetate buffer at pH 4.2 was tried to simplify the step of pH adjustment in a laboratory dry-grind procedure.
Ethanol yields or conversion efficiencies of 18 sorghum hybrids improved significantly with 2.0–5.9% (3.9% on average) of
relative increases when the method of pH adjustment changed from traditional HCl to the acetate buffer. Ethanol yields obtained
using the two methods were highly correlated (R
2 = 0.96, P < 0.0001), indicating that the acetate buffer did not influence resolution of the procedure to differentiate sorghum hybrids
varying in fermentation quality. Acetate retarded the growth of Saccharomyces cerevisiae, but did not affect the overall fermentation rate. With 41–47 mM of undissociated acetic acid in mash of a sorghum hybrid
at pH 4.7, rates of glucose consumption and ethanol production were inhibited during exponential phase but promoted during
stationary phase. The maximum growth rate constants (μ
max) were 0.42 and 0.32 h−1 for cells grown in mashes with pH adjusted by HCl and the acetate buffer, respectively. Viable cell counts of yeast in mashes
with pH adjusted by the acetate buffer were 36% lower than those in mashes adjusted by HCl during stationary phase. Coupled
to a 5.3% relative increase in ethanol, a 43.6% relative decrease in glycerol was observed, when the acetate buffer was substituted
for HCl. Acetate helped to transfer glucose to ethanol more efficiently. The strain tested did not use acetic acid as carbon
source. It was suggested that decreased levels of ATP under acetate stress stimulate glycolysis to ethanol formation, increasing
its yield at the expense of biomass and glycerol production.
Names are necessary to report factually on available data; however, the U.S. Department of Agriculture neither guarantees
nor warrants the standard of the product, and use of the name by the U.S. Department of Agriculture implies no approval of
the product to the exclusion of others that may also be suitable. |
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Keywords: | Acetate Ethanol Glycerol Fermentation Sorghum |
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