Studies on Proliferation of Acetic Acid Bacteria during Soursop Juice Fermentaion

A study was conducted to investigate the proliferation of acetic acid bacteria during various stages of soursop juice fermentation. Preliminary experiment was carried out to identify the genera and species of acetic acid bacteria associated with soursop fruits. The effect of pH, temperature and momentary aeration on the growth of acetic acid bacteria and its effect on the growth of Saccharomyces cerevisiae were studied. Soursop juice undergoing spontaneous fermentation was monitored for 10 days. Results showed that acetic acid bacteria were present at all stages of fermentation. A succession of acetic acid bacteria indicated that Gluconobacter oxydan was found to be associated with unspoiled fruit and at the early stage of fermentation. Acetobacter aceti was prevalent throughout fermentation days while the presence of Acetobacter pasteurianus was noted at the later stage of fermentation. These species exhibited rapid growth on short exposure of the fermenting vessel to atmospheric oxygen which resulted in a strong correlation between the growth of acetic acid bacteria and concentration of acetic acid in the fermenting sample. Higher temperature and elevated pH favoured the growth and metabolism of acetic acid bacteria. There was a reduction in maximal cell concentration of Saccharomyces cerevisiae inoculated with Acetobacter aceti as compared to species not treated with the bacteria.