A novel high ethanol-thermo-tolerant Acetobacter pasteurianus KBMNS-IAUF-2 strain and the optimization of acetic acid production using the Taguchi statistical method

Abstract

Because of the high energy consumption for fermentor cooling, the isolation of thermo-tolerant <em>Acetobacter</em> strains for vinegar production has a high priority. The aims of this study were the isolation and identification of a high ethanol-thermo-tolerant <em>Acetobacter</em> spp. from grapes as well as the optimization of conditions for increasing the acetic acid production. The grape extract was cultured on Frateur and Carr media. The isolates were characterized against macroscopic, microscopic, and molecular traits. The resistance of the isolates against different concentrations of ethanol as well as high temperatures were measured. The best ethanol- thermo-tolerant isolate using ribotyping was identified as <em>Acetobacter pasteurianus</em> KBMNS-IAUF-2 and its 16s-rDNA sequence was deposited in GenBank, NCBI under the accession number MG547344. This strain was able to grow in Carr medium with 9% (v/v) ethanol after 48h incubation at 40°C. A Taguchi design with L9 analysis revealed that the highest yield of acetic acid production occurred at 34°C in the medium containing of 2% (v/v) ethanol and 2% (w/v) yeast extract. The temperature and yeast extract concentration with 76.70% and 6.29% were the most and least effective factors in acetic acid production, respectively. The acetic acid production yield after 24h under the optimized condition was measured as 97%. This thermo-ethanol-tolerant strain could be applied as an industrial starter for producing vinegar with grapevine flavor.