Control of lactic acid bacteria during biofuel ethanol fermentation

Commercial biofuel ethanol fermentation plants utilize antibiotics to control contaminating bacteria during fermentation.  Problematic bacteria are primarily lactic acid bacteria that generate organic acids, which inhibit the yeast and reduce ethanol yields. There is a general consensus within the industry to find alternatives to antibiotics. Here, natural antimicrobials based on bacteriolytic agents, were evaluated for their activity in controlling lactic acid bacteria during ethanol fermentation.  A comprehensive survey of commercial ethanol plants was conducted and revealed the identities of predominant contaminating lactic acid bacteria.  Corn mash samples containing indigenous, mixed, and undefined bacterial populations from the plants were treated directly with the bacteriolytic agents.  Significant reductions in bacterial levels of between 17 fold to 800,000 fold were consistently observed.  Laboratory scale fermentation trials using corn mash containing mixed, undefined bacterial populations native to the commercial plants were established.  Tested in these trials, the bacteriolytic agents showed significant effect in decreasing lactic acid and acetic acid levels during fermentation.  The controlling effect on acid levels was more pronounced than what was achieved using the industry standard antibiotic, virginiamycin.