Improvement of the Flavor and Quality of Watermelon Vinegar by High Ethanol Fermentation using Ethanol-Tolerant Acetic Acid Bacteria

Acetic acid fermentation is an essential step in the production of high-quality fruit vinegar and typically involves the use of acetic acid bacteria (AAB). The present study showed that the high cell mass and acetic acid yields of ethanol-tolerant AAB under high ethanol conditions were related to the high activities and stability of both pyrroloquinoline quinone (PQQ)-dependent alcohol dehydrogenase and PQQ-dependent aldehyde dehydrogenase. Additionally, in acetic acid fermentation with watermelon wine (8 % ethanol), the main organic acids (acetic, tartaric and malic acids) produced by ethanol-tolerant Acetobacter pasteurianus AAB4 were higher than those by conventional A. pasteurianus AS1.41 (1.42-fold, 3.53-fold and 2.12-fold, respectively). Also, the main esters (ethyl acetate and phenylethyl acetate) produced by AAB4 were higher than those by AS1.41 (1.69-fold and 1.48-fold, respectively). In addition, the total sweet and umami free amino acids produced by AAB4 increased significantly. According to sensory analysis, the flavor, taste and overall acceptance score of watermelon vinegar produced by AAB4 were significantly higher than those by AS1.41. Therefore, high ethanol fermentation with ethanol-tolerant AAB improved the flavor and quality of watermelon vinegar, indicating that this technology can be applied to fruit vinegar production.