Effect of Environmental Conditions on Fermentation Pattern of Lactobacillus fermentum G7 Showing Acetic acid-Ethanol Production Switch by Aerobic-anaerobic Conversion

Abstract

Lactobacillus fermentum G7 is a bacterium extracted from the feces of a healthy human that produces carbon dioxide. In this study, the physiological characteristics of this bacterium were examined when cultured under various temperature, sugar, and gas conditions through analysis of the concentrations of its typical fermentation products, including carbon dioxide, acetic acid, ethanol, and lactic acid. The strain showed the greatest growth when maltose was added to the culture medium, regardless of temperature and gas conditions. Neither aerobic nor anaerobic conditions greatly influenced the amount of acetic acid and ethanol production when more than 4% glucose was added to the medium. The optimum growth temperature for both the growth and the fermentation product profiles of the strain was found to be 37 °C. L. fermentum G7 produced ethanol in anaerobic conditions but not in aerobic conditions. However, the bacterium produced a greater amount of acetic acid in aerobic conditions than in anaerobic conditions, instead of producing ethanol. Moreover, in anaerobic conditions, the highest concentration of ethanol was produced when lactose was added to the medium compared with other sugars. By contrast, no ethanol was produced when fructose was added to the culture medium, even in anaerobic conditions. When the bacterium was cultured in a milk medium supplemented with the sugars glucose, fructose, maltose, and sucrose, significantly reduced amounts of fermentation products were produced in comparison to those detected in MRS broth culture. The production of lactic acid by L. fermentum G7 was lower than that of homofermentative bacteria, but high levels of acetic acid were produced, with an approximately 3-times higher level than that of other acetic acid-producing strains. Moreover, L. fermentum G7 produced approximately 1,000 times the amount of carbon dioxide produced by the homofermentative bacteria, and also produced more carbon dioxide than another heterofermentative bacterium, L. reuteri. Therefore, this bacterium shows great potential for applications as an acetic acid-producing strain in the production of dairy products, and is also expected to play a significant role as a carbon dioxide-producing strain in the production of soft drinks.