Hop acids can efficiently replace antibiotics in ethanol production.

Abstract

This study was carried out at the Fermentation Technology Institute of the University of Hohenheim. The aim of the study was to evaluate the potential of hop acids as natural antibacterials in distillery mashes for alcoholic fermentation. Lactostab™ and Isostab™ were investigated for their effect on growth and lactic acid production by two selected strains of lactobacilli. The potential of improving ethanol yields by use of Lactostab™ and Isostab™ during alcoholic fermentation of wheat mash and sugar beet molasses mash was monitored. Penicillin G and Virginiamycin were used as referential substances for comparison of antibacterial activity. Lactostab™ and Isostab™ prevented growth of lactobacilli and production of lactic acid at ppm levels. Production of lactic acid and acetic acid was blocked at inhibitory concentrations of Lactostab™ and Isostab™. Both substances acted bactericidal when inhibitory concentrations were doubled. Virginamycin and Penicillin G were tested as conventional antibacterial reference. Of all tested antibacterials, Virginiamycin was most effective and acted bactericidal at a concentration of only 0.5 ppm. However, ethanol yields obtained at inhibitory/ bactericidal concentrations of hop acids were in every respect comparable to those obtained with inhibitory/ bactericidal concentrations of antibiotics. Penicillin G, at a concentration of only 0.25 ppm, inhibited bacteria growth in most trials, but induced resistance in L. fermentum in wheat mash fermentation. Lactostab™ and Isostab™ consist of hop components contained in beer and spent hops and bear no risk for human or animal health. Thus, they provide an excellent, safe alternative to control bacteria in ethanol fermentations.