Preparation of a pure inoculum of acetic acid bacteria for the selective conversion of glucose in strawberry purée into gluconic acid

Strawberry surpluses, which may account for about 20% of the whole production, could be an example of what is happening with other fruits. This surplus is largely transformed into strawberry purée which, although is especially suitable for various bioconversions, is mainly used as an additional ingredient to produce other foods. With a view to using strawberry purée to obtain a new, naturally sweet beverage containing no glucose, the conversion of glucose into gluconic acid, while maintaining the original fructose of the purée, was assessed. Additionally it is important to preserve the sensory and nutritional properties of the fruit so pasteurized rather than sterilized purée must be used.The use of Gluconobacter japonicus strain (CECT 8443) was studied by batch experiments. Different preparation stages were evaluated for ascertaining whether the inoculum required pre-cultivation in strawberry purée and whether using pasteurized rather than sterilized substrate would influence prevalence of the inoculated strain over unwanted microorganisms—yeasts, mainly.The strain converted glucose into gluconic acid preserving the original fructose content of the substrate. The optimum inoculum preparation conditions involved microbial growth in Glucose Yeast Extract Peptone synthetic medium for 24 h first and in sterilized strawberry purée for 24 h additional then.