P-38 - Determination of Beer Spoilage Lactic Acid Bacteria Focusing on the Cell Surface Structure of Bacteria

Lactic acid bacteria (LAB) are microorganisms responsible for beer spoilage. In particular, Levilactobacillus brevis is a LAB that often spoils beer; however, not all L. brevis strains spoil beer. The hops used to produce beer not only impart a bitter taste but also have antibacterial properties. Notably, L. brevis strains without hop-resistance do not spoil beer. The presence of hop-resistance genes is a criterion used for determining whether a microorganism causes beer spoilage. However, certain L. brevis strains despite possessing hop-resistance genes, do not spoil beer. This may be due to the insufficient or inhibited expression of hop-resistance genes. If these genes are expressed, through the subsequent processes, proteins related to the cell surface may be produced, and the cell surface structure of L. brevis may change. As such, we used a Bruker‘ｓ IR Biotyper to measure these changes on cell surfaces, which detects the molecular structure and state of a cell surface using Fourier-transform infrared (FT-IR) spectroscopy. We calculated the similarity between the samples and identified differences between the strains based on the obtained results. We compared our collection of 100 L. brevis strains and typed them in terms of the presence of hop-resistance genes and their ability to spoil beer. We found that the IR Biotyper was successfully evaluate the ability of L. brevis strains to spoil beer through changes in the bacterial cell surface via the expression of hop-resistance genes. This device is expected to contribute to being accurate the risk assessment and improving the management of beer production, thereby enhancing both productivity and product quality.