Optimization of biomass production of Acetobacter pasteurianus KU710511 as a potential starter for fruit vinegar production

The objective of the present work was first the isolation of novel acetic acid bacteria strains from natural Moroccan habitats, and then, the evaluation of their ability to produce microbial starters for vinegar production on a large scale. The strains were isolated from figs, dates, cactus, and traditional fruit vinegars. Four strains, selected from a total of 63 isolates, were confirmed as belonging to Acetobacter species according to biochemical and molecular studies based on 16s rRNA sequence analysis. Acetous fermentation tests, performed on date and apple fermented juices using selected Acetobacter strains, showed a high capacity of acidification. The most efficient strain KU710511, isolated from Morrocan cactus (Opuntia ficus-indica), was identified as Acetobacter strain closely related to A. pasteurianus and yielded 42.5 g/L acidity in apple juice. Cell growth optimization was carried out for KU710511 using response surface methodology (RSM). The linear, quadratic, and interaction effects of four factors-ethanol, acetic acid, glucose concentrations and pH-were studied by the application of a central composite design. Thirty experiments were designed to predict the maximum concentration of cell biomass. The optimal calculated values of ethanol, acetic acid, glucose and pH allowing the prediction of the maximum biomass production (2.21 g/L) were 28.18, 10.12, 15.15 and 5.33 g/L, respectively. Subsequently, further batch fermentations were carried out in a 6-L lab-bioreactor at optimal conditions. The results were in line with the predicted values. It can be concluded that the studied strain is well suited to be used as a parental strain to prepare a starter for fruit vinegar production.   Key words: Isolation, vinegar, starter, Acetobacter, acetic fermentation, response surface methodology.