Abstract: Acetic acid bacteria (AAB) play an important role in the acetic acid fermentation in order to manufacture many useful products. The aim of this study was to isolate and select the thermotolerant acetic acid bacteria from fermented cocoa beans with high acid production. Acid acetic bacterial isolates were evaluated the acid production capacity and thermotolerant ability up to 43°C. The selected isolates were identified at species level using molecular techniques. As the result, 16 strains of AAB were isolated from 7 samples of fermented cocoa beans collected from Ben Tre and Tien Giang provinces. Ten isolates had high acid-producing yeild with the diameter of yellow zone (19-23 mm) after 48 hours at 37°C on the bromocresol green ethanol agar medium. These 10 isolates could also grow at 43°C on the YPGD agar medium (added with 4.0% (v/v) of ethanol). Three thermotolerant isolates including BT1H, BT2B1, and TG1D1 were selected due to their good performances during fermentation with the concentrations of total acid produced at 4.45, 3.95, and 3.85% (w/v) respectively after 5 days of fermentation at 37°C. The isolate BT2B1 was identified as Acetobacter pasteurianus while BT1H and TG1D1 were Acetobacter tropicalis.

Keywords: Acetobacter pasteurianus, Acetobacter tropicalis, isolation, selection of thermotolerant acetic acid bacteria.