Ken-ichi Okumura,* Hitomi Fujimoto, Shizuka Asano, Susumu Masuda, and Tetsuya Watanabe
*Asahi Breweries, Ltd., 1-21, MIDORI, 1-CHOME, MORIYA-SHI, IBARAKI, Japan (kenichi.okumura@asahibeer.co.jp)

Owing to an increasing consumer preference for additive-free food, the sulfite-free wine industry has been expanding in Japan. Sulfite-free wine generally exhibits decreased resistance to spoilage microbes such as yeast, lactic acid bacteria, and acetic acid bacteria. Therefore, it is necessary to conduct a more rigorous microbial quality control of sulfite-free wine than of wine containing sulfite. In this study, we specifically examined the thermal resistance of lactic acid bacteria and acetic acid bacteria in phosphate-buffered saline containing ethanol. Lactic acid bacteria showed an approximately three-log reduction after heating at 55°C for 3 min, while acetic acid bacteria showed more than a five-log reduction after heating at 50°C for 3 min. Next, we developed a detection medium for wine spoilage acetic acid bacteria such as Acetobacter pasteurianus. The optimal growth conditions for A. pasteurianus strains in yeast peptone dextrose (YPD)-based medium supplemented with various components were investigated. Most of the tested strains showed better growth at pH 4.5 than at pH 6.8, and only strain ABBC635 required alcohol or acetic acid for growth. Based on these results, we developed an acidic, Wallerstein Laboratory (WL)-based nutrient medium supplemented with 20% wine to detect wine spoilage acetic acid bacteria. The WL-based medium is easy to prepare and has high selectivity.

Funding Support: Asahi Breweries, Ltd.