Evaluation of buckwheat and barley tea wastes as ethanol fermentation substrates

Buckwheat tea waste (BWTW) and barley tea waste (BTW), by-products of the beverage industry, are alternative carbohydrate sources for ethanol production. In this study, optimal enzyme loading for enzymatic saccharification of BWTW and BTW was determined, and simultaneous saccharification and fermentation (SSF) was performed by Saccharomyces cerevisiae and Mucor indicus to produce ethanol. Optimal enzyme loading for enzymatic saccharification of 2 % w/v BWTW and BTW was 0.5 % (weight of enzyme/weight of tea wastes) for BWTW and 0.1 % for BTW. Ethanol production from BWTW by S. cerevisiae and M. indicus after 48 h of SSF was 49.9/100 g of BWTW and 47.9/100 g of BWTW, respectively, with 0.5 % enzyme loading. Ethanol production from BTW by S. cerevisiae and M. indicus after 48 h of SSF was 20.5/100 g of BTW and 21.6/100 g of BTW, corresponding to 62 and 66 % of the theoretical yield based on starch content, respectively, with 0.1 % of enzyme loading. Furthermore, S. cerevisiae produced 76 % of the theoretical yield based on the total glucose from starch in BWTW and BTW when a mixture of BWTW and BTW was used as a substrate, with 0.2 % enzyme loading and no additional nitrogen or mineral sources.