Enzymatic hydrolysis of food waste and ethanol fermentation

Abstract

Although food waste (FW) can serve as a valuable substrate containing large amounts of organic materials such as soluble sugar, starch, and cellulose, it is recognized as an environmental pollutant, and the hydrolysis of solids in FW still serves as a rate-limiting step in its biological processes. To evaluate a new potential application of FW as an alternative substrate for ethanol production through laboratory experiments, we investigated FW hydrolysis by using individual commercial enzymes and their mixtures; batch ethanol fermentation by Saccharomyces cerevisiae; and the effect of salt, which is inherently included in FW, on ethanol fermentation. A comparison of the glucose yields of the FW broth pretreated with amyloglucosidase, carbohydrase, and a mixture of both enzymes revealed that a higher glucose yield was obtained when the enzyme mixture was used (0.46 g g−1 of dry FW) than when amyloglucosidase (0.41) or carbohydrases (0.35) were used at 3 h from the initiation of the reaction. A high ethanol yield (0.23 g g−1 of dry FW) was obtained after 15 h of fermentation by S. cerevisiae by using the FW broth hydrolyzed by the enzyme mixture and was estimated to be nearly equivalent to the ethanol yields of lignocellulose biomasses. With regard to the effect of salt on ethanol fermentation, no alteration in the fermentation parameters was observed up to a salt content of 3% w/v. At a salt content of over 4%, however, substrate uptake and cell growth dramatically decreased, and a slight reduction in ethanol yield was observed. FW utilization for ethanol production by enzymatic hydrolysis and ethanol fermentation by S. cerevisiae suggests a promising practical approach to prevent environmental pollution and obtain a product of high value, ethanol. Copyright © 2008 John Wiley & Sons, Ltd.