Oxygen management during kombucha production: Roles of the matrix, microbial activity, and process parameters.

Oxygen plays a key role in kombucha production, since the production of main organic acids, acetic and gluconic acids, is performed through acetic acid bacteria's oxidative metabolism. Oxygen consumption during traditional kombucha production was investigated by comparing kombucha to mono and cocultures in sugared tea of microorganisms isolated from kombucha. Two yeasts, Brettanomyces bruxellensis and Hanseniaspora valbyensis and one acetic acid bacterium Acetobacter indonesiensis were used. Results showed that tea compounds alone were mainly responsible for oxygen depletion during the first 24 h following inoculation. During the first 7 days phase of production in open vessel, the liquid surface was therefore the only access to oxygen for microorganisms, as anaerobic conditions were sustained below this area. During the 5 days second phase of production after bottling, comparison of cultures with different microbial compositions showed that oxygen was efficiently depleted in the head space of the bottles in 3-6 h if the acetic acid bacterium was present. Lower access to oxygen after bottling stimulated ethanol production in B. bruxellensis and H. valbyensis cocultures with or without A. indonesiensis. This study provides insights into the management of oxygen and the roles of the tea and the biofilm during kombucha production.