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Abstract
Thermotolerant acetic acid bacteria that can grow at 37 to 40°C were collected from places all over Thailand. They were divided into several groups according to their taxonomic and physiological properties, such as rapid ethanol oxidation, rapid acetate oxidation, cellulosic biopolymer formation, growth at 40°C, growth in 3% acetic acid, growth in 8% ethanol, formation of thermotolerant alcohol, and aldehyde dehydrogenases, etc. Though the complete taxonomic analysis has not been completed with all the strains, the majority of the acetic acid bacteria isolated have been confirmed to be classified as Acetobacter rancens subsp. pasteurianus, A. lovaniensis subsp. lovaniensis, A. aceti subsp. liquefaciens, and A. xylinum subsp. xylinum. They produced acetic acid at high temperatures such as 38 to 40°C. Even when acetic acid was initially added to 4%, they still oxidized ethanol to accumulate acetic acid, while 2% of the initial acetic acid was the upper limit for mesophilic strains*1 at higher temperatures. They oxidized higher concentrations of ethanol up to 9% without any appreciable lag time, while alcohol oxidation with mesophilic strains was delayed or became almost impossible under such conditions. Fermentation efficiency in vinegar production with the thermotolerant strains at 38 to 40°C was almost the same as that of mesophilic strains at 30°C. However, the thermotolerant strains worked rapidly with a higher fermentation rate at higher temperatures, which the mesophilic strains were unable to do. Vinegar fermentation at higher temperatures was successful in submerged culture as well as static culture. The fermentation rate as well as fermentation efficiency in continuous vinegar fermentation at higher temperatures by the thermotolerant strains in a jar fermentor was also more than 2 to 3 times that with mesophilic strains at 30°C. Thus, thermotolerant acetic acid bacteria are useful for vinegar fermentation at higher temperatures, which may reduce cooling water expenses.