Researchers investigated the effects of antimicrobial variables, including storage temperatures, pH, and ethanol concentrations, on common bacterial populations in low- and non-alcoholic beer. They inoculated variable-controlled replicates of non-alcoholic beer with five bacterial strains and monitored bacterial populations over 63 days. Their findings suggest that low-alcoholic beers prevent pathogen growth, while non-alcoholic beers allow it.
Study
The present study aims to investigate the impacts of ethanol concentration, storage temperature, and pH on the growth of five strains of Escherichia coli (E. coli), Salmonella enterica, and Listeria monocytigenes in low- to no alcohol-containing beers.
Non-alcoholic canned beer with baseline ethanol and pH concentrations of <0.5% and 3.65 were adjusted using O.1M sodium hydroxide (NaOH) and 99% ethanol. Final concentrations of pH 4.20, 4.50, and 4.80 and ethanol = <0.50% and 3.20% ABV in triplicate were prepared in sterile, parafilm-sealed vials. E. coli O157:H7, S. enterica, and L. monocytogenes were added to the vials, which were subsequently stored at four and 14°C for 63 days.
Periodic sampling to test for pathogen growth or die-off involved streaking beer samples on Violet Red Bile Agar (VRBA), Modified Oxford Media (OX), and Bismuth Sulfite Agar (BSA) to test for E. coli, L. monocytogenes, and S. enterica, respectively.
Statistical analyses comprised one-way analysis of variance (ANOVA) to evaluate the effects of storage temperature, ethanol content, and pH on pathogen populations.
Results
E. coli and S. enterica were found to survive in low- and non-alcoholic beer at all temperatures, pH, and % ABV under study. L. monocytogenes was observed to be less resilient, with population size declining below the detection limit after a few days.
In non-alcoholic beer, pH was associated with declines in microbial population sizes across tested strains – at 4°C, pH 4.20 resulted in a 1.23 log-transformed decrease in E. coli population size, while pH 4.50 resulted in a 2.37 log reduction in S. enterica. L. monocytogenes was below the detection limit at all pH values, though lower pH was associated with more rapid population reduction. At 14°C storage conditions, E. coli and S. enterica populations were observed to grow regardless of pH. In contrast, for L. monocytogenes, higher storage temperature was found to result in more profound population declines compared to 4°C.
In low (3.20% ABV) alcohol-content beers, all microbes presented population declines at 4°C. At 14°C, E. coli and S. enterica depicted population declines but persisted at low population sizes throughout the study period. In contrast, L. monocytogenes population sizes rapidly reduced below the minimum detection limits by day 6 for pH 4.20 and 4.50 and day 10 for pH 4.80.
These findings suggest that % ABV and storage temperature are the most critical determinants of foodborne pathogen persistence and growth, trends confirmed by ANOVA analyses.
Conclusion
In the present study, researchers investigated the effects of % ABV, storage temperature, and pH on the growth and persistence of foodborne pathogens in low- and non-alcoholic beers. They inoculated pH (4.20, 4.50, and 4.80), temperature (4 and 14°C), and % ABV (<0.50 and 3.20) standardized beer with a five-strain cocktail of E. coli, S. enterica, and L. monocytogenes and monitored bacterial growth over 63 days.
Alcohol content and storage temperature were revealed to be the most significant determinants of bacterial growth, with non-alcoholic beer being far more susceptible to microbial growth than low-alcoholic beer.
Source:
https://www.news-medical.net/news/20231026/Non-alcoholic-beers-may-be-a-happy-hour-for-bacteria-study-warns.aspx