Identification and Characterization of Thermotolerant Acetobacter Strains Isolated from Brewing Coconut Vinegar in Sri Lanka

Abstract

Coconut vinegar made from coconut water or coconut sap is extensively used in many Sri Lankan dishes. As its production is done by natural fermentation, the responsible acetic acid bacteria for Sri Lankan vinegar fermentation is not known. From pellicle formed on the top of the brewing vinegar, three Acetobacter strains (SL13E-2, SL13E-3, and SL13E-4) which could grow at temperatures up to 42°C were isolated. All three strains could tolerate up to 8% and 3% ethanol concentration at 41°C and 42°C, respectively. These strains were identified as Acetobacter pasteurianus by phenotypic characterization and 16S rDNA sequence analysis. The 16S-23S internal transcribed spacer (ITS) sequence data of two strains (SL13E-2 and SL13E-3) were identical, while the other (SL13E-4) was 6 bp different from them. Acetic acid fermentation of three strains gave their highest production of 4% acetic acid at 37°C with 6% initial ethanol. They gave 2.5% acetic acid production even at 40°C with 4% initial ethanol. Compared with the other strains, SL13E-4 shows slower growth and acetic acid production rate. These strains were successfully used in simultaneous vinegar production with coconut water at higher temperatures.