Acetic acid production at high temperature by newly isolated thermotolerant Acetobacter sicerae A18

Abstract

Acetic acid is an important organic acid used in many industries such as rubber processing and food processing. Thermotolerant microorganisms including acetic acid bacteria have been increasingly considered and developed in recent years, since they are able to be potentially and popularly utilized in many different issues of fermentation technology at high temperature, leading efficient production and reducing cooling cost. The objective of this study was to select the thermotolerant acetic acid bacteria for their application in acetic acid fermentation at high temperature. In this study, 9 isolates (A1, A3, A8, A18, A23, A47, A49, A50 and A52) were selected from 20 isolates with the acetic acid production ranged from 1.72% to 2.04% (w/v) at 37°C. The amplified 16S-rDNA sequences were employed for the identification of 9 selected strains of acetic acid bacteria. These strains were dominated by representatives from the Acetobacter genus with 4 species such as A. pasteurianus, A. tropicalis, A. orientalis and A. sicerae. Acetobacter sicerae A18 was identified as the most effective fermentative acetic acid bacterial strain at 39°C with acetic acid production was 2.56% (w/v) and productivity was 62.19%. Furthermore, the favorable conditions for acetic acid fermentation by the selected target strain A. sicerae A18 were found as follow: pH at 4.0, ethanol concentration at 5.0% (v/v) and the starter density at 10⁵ cells/mL; acid concentration and productivity were 2.82% (w/v) and 66.02%, respectively.