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Timo Kramer

University of Aberdeen, The Rowett Institute, Aberdeen, United Kingdom

Effect of growth-inhibiting factors on beer spoilage by bacteria belonging to the genus Pectinatus

Beer is a product with good microbial stability due to the presence of factors limiting the growth of common spoilage organisms, such as alcohol and hops content, low pH and anaerobic conditions. Pectinatus spp. are known to cause secondary contamination of beer, resulting in spoilage of the product due to increased turbidity of the product and the formation of off-flavours. This study explores the effectiveness of multiple approaches in inhibiting growth of Pectinatus.

Methods: Growth of several strains representing different Pectinatus species was assessed in the presence or absence of growth inhibitors by measuring the increase in optical density at 650 nm over time. Linear regression was performed on the log-transformed densities over time to calculate the growth rate of the bacteria. Differences in growth rate (h-1) were deemed statistically significant at a p-value of ≤ 0.05 when analysed with an ANOVA.

Results: Reduction of growth was obtained upon increasing the concentration of alcohol over 5% or introduction of the bacteriocin nisin. No growth-inhibiting effect was observed when testing susceptibility to hops extract. Complete inhibition of growth was observed with alcohol over 7.5% alcohol by volume (ABV) and for P. cerevisiiphilus MB134 and P. haikarae MB233 at nisin concentrations of 100 IU/ml.

Conclusion: Quantitative determination of growth of Pectinatus showed that reduction of growth rate and total inhibition of growth can be achieved through an increase in alcohol concentration and addition of nisin, an antimicrobial peptide derived from lactic acid bacteria with a Generally Recognised As Safe (GRAS) status

Timo Kramer

University of Aberdeen, The Rowett Institute, Aberdeen, United Kingdom

Timo Kramer

University of Aberdeen, The Rowett Institute, Aberdeen, United Kingdom

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