Isolation of hop-sensitive variants from beer-spoilage Lactobacillus brevis strains

To elucidate the mechanisms underlying the hop-resistance ability of beer-spoilage lactic acid bacteria, we attempted to isolate hop-sensitive variants from beer-spoilage Lactobacillus brevis. As a result, the repeated subcultures at 37degreesC were found to cause the hop resistance of six beer-spoilage L. brevis strains to be lost. In contrast to the wild-type strains, the hop-resistance ability of these variants was no longer inducible, as indicated by the inability to grow in DeMan-Rogosa-Sharpe (MRS) media supplemented with progressively higher concentrations of hop compounds. The diminished adaptability to hop compounds was comparable with that of the originally non-spoilage L. brevis strain, JCM1059(T). When the variants were inoculated in beer and incubated anaerobically at 25degreesC, the viability of the strains was lost within one week, whereas the wild-type strains were able to grow during the same period of incubation. From these observations, it has been concluded that the variants obtained in this study lost the beer-spoilage ability. The biochemical characterization of the variants revealed narrower carbohydrate utilization profiles in some of the strains, notably with regard to the ability to ferment maltose.