Factorial Analysis of Variance of the Inhibiting Effects of Iso-Alpha Acids, Alpha Acids, and Sulfur Dioxide on the Growth of Beer-Spoilage Bacteria in Beer

Abstract

Growth tests in beers supplemented with specific chemical substances were conducted to investigate the growth control method of beer-spoilage bacteria. Lactobacillus brevis and Pectinatus frisingensis were inoculated into beers in which the pH was set and chemical substances had been added to form a matrix. Supplementation of the beer with hop bitter compounds (iso-α-acids, α-acids, or SO₂), had an inhibitory effect on the growth of the tested strains in beer. Furthermore, the growth inhibiting compounds had a synergistic effect when used simultaneously. Two-way repeated measures analysis of variance showed that the interaction effects of combinations of iso-α-acids and α-acids in addition to α-acids and SO₂ on the growth of L. brevis and P. frisingensis in beer were highly significant. To verify the contribution degree of pH, iso-α-acids, α-acids, and SO₂ on the growth of L. brevis and P. frisingensis, growth test results using a combination of these factors set at different levels were subject to stepwise regression. The contributions of undissociated α-acids, undissociated SO₂, and multiplications of undissociated α-acids and undissociated SO₂ were especially high in the control of L. brevis growth. The contributions of pH, undissociated SO₂, and multiplications of pH and undissociated iso-α-acids were especially high in the control of P. frisingensis growth. The difference in the contributions of antibacterial compounds between L. brevis and P. frisingensis may be due to the difference in the cell wall/membrane structure. Such factorial analysis may be useful for parameter setting in future product designs and process adjustments.

Keywords:

• Alpha acids
• beer-spoilage bacteria
• iso-alpha acids
• sulfur dioxide (SO₂)
• synergistic effect

Acknowledgements

We thank Atsushi Murakami, Tetsu Sugimura, and Yumiko Kawasaki for the use of hop extracts and HPLC analysis of hop bitter compounds; and Hideharu Odai, Hiroyuki Shinohara, Toshihiko Hori, Riichiro Shibata, Hideyuki Minami, and Kei Sudo for helpful advice.