SELECTION AND IMMOBILIZATION OF ISOLATED ACETIC ACID BACTERIA ON THE EFFICIENCY OF PRODUCING ACID IN INDONESIA

Abstrak

Screening of AAB(Acetic acid bacteria) isolates from cane sugar juice in Indonesia for acid and alcohol tolerance was performed. Among the isolates tested, strain INT-7 was observed to grow to as high as 9% acetic acid and 15% alcohol. Based on the screening study, INT-7 is belong to Acetobacter pasteurianus were chosen for vinegar fermentation. The pure culture of strain INT-7 on unpasteurized coconut sap was found to have high acidity (5.42%) compared to pasteurized sap (3.42%). Strain INT-7 exhibited higher acid production of 62.7g/L in 5% ethanol under static condition compared to reference strains JCM 7640 Acetobacter aceti and JCM 7641 A. pasteurianus with 52.3g/L and 30.8g/L acid, respectively. On other study, results revealed the efficiency (2X) of using fermentor for acid formation compared to samples fermented with shaking. In addition, the crude metabolites of INT-7 suggest inhibitory effect against the growth of E.coli and Salmonella sp. but not against S. aureus, while strain of INT-17 metabolites inhibited the growth of all pathogenic bacteria tested. The immobilization of A.pasteurianus strain INT-7 for improving the ethanol resistance was done in the alginate gel. The result showed that optimum condition of A. pasteurianus INT-7 cell entrapped (10⁷CFU/mL) on 3% alginate and the ratio of cell number and alginate solution was 1:3 v/v. The optimum condition of acetic acid fermentation by immobilized cells were initial pH 6.0, ethanol concentration 7.5% (v/v), temperature at 30^o C for 7 days produced acetic acid (35.81 g/L) is higher than free cells (16.29 g/L). The efficiency of fermentation by immobilized cells and free cells were 36.73% and 16.71%, respectively.

Keywords: Acetic acid bacteria, selection, immobilization, producing higher acid.