Bacterial Inhibition Without Antibiotics
by Sami Faour (Ethanol Producer Magazine/BetaTec Hop Products) A method for controlling infection and maximizing ethanol yields
…Growth of contaminating lactic acid bacteria is a major problem in industrial alcohol fermentations. These bacteria can grow under the conditions of yeast fermentation and reduce alcohol yields by consuming glucose that could have been used by yeast for ethanol production. The end products of metabolism of lactobacilli, lactic acid and acetic acid are detrimental to yeast growth and metabolism and, therefore, occur when propagations and/or fermentations are allowed to continue under less-than-sufficient microbial control. As bacterial numbers increase so do the acids formed. The metabolism of these organisms varies from that of Saccharomyces yeast with substantial production of lactic acid and lesser amounts of acetic acid made. In addition to operating the plant under as sanitary conditions as possible, the most common strategy to control Lactobacillus contamination is by the addition of antibiotics. Concerns are rising, however, about the overuse of antibiotics for industrial applications that may contribute to the emergence of resistant pathogenic bacteria strains harmful to animals and humans. Additionally, the presence of antibiotics in saleable coproducts (distillers grains) can negatively impact their marketability.
The preservative properties of hop acids that have been used in the brewing industry for more than a millennium constitute a legitimate naturally derived alternative. BetaTec’s trademarked IsoStab, an aqueous solution of isomerized alpha acids, has been successfully used in dry mill and wet mill ethanol plants since 2004. By adding the minimum inhibitory concentration of IsoStab to the yeast propagation tank and/or to the fermentation vessel, one can inhibit the growth of lactic acid bacteria during the production of ethanol and entirely avoid the need for antibiotics.