applied sciences Article Thai Rice Vinegars: Production and Biological Properties Samuch Taweekasemsombut 1,2, Jidapha Tinoi 1,3,4, Pitchaya Mungkornasawakul 3 and Nopakarn Chandet 1,3,4,* 1 Interdisciplinary Program in of Biotechnology, Faculty of Graduate School, Chiang Mai University, Chiang Mai 50200, Thailand;
[email protected] (S.T.);
[email protected] (J.T.) 2 Department of Chemistry, Faculty of Science and Agricultural Technology, Rajamangala University of Technology Lanna, Chiang Mai 50300, Thailand 3 Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand;
[email protected] 4 Center of Excellence in Materials Science and Technology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand * Correspondence:
[email protected]; Tel.: +66-812-358-883 Abstract: Four types of traditional Thai rice—polished, black fragrant, glutinous and black glutinous rice—were separately used as raw material for vinegar production. During alcohol fermentation, using enriched baker’s dried yeast (S. cerevisiae) as a starter culture gave the highest ethanol content over 7 days of fermentation. The conversion of ethanol to acetic acid for vinegar production by Acetobacter pasteurianus TISTR 102 was performed for 25 days. The highest amount of acetic acid was detected with glutinous rice fermentation (6.68% w/v). The biological properties of Thai rice vinegars were determined, including the total phenolic content, antioxidant activity, antibacterial activity and cytotoxicity. Black glutinous rice vinegar exhibited the maximum total phenolic content of 133.68 mg GAE/100 mL. This result was related to the antioxidative activity findings, for which black glutinous rice vinegar exhibited the strongest activity against both ABTS•+ and DPPH• radicals.