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

Abstract

Strawberry surpluses, which may account for about 20% of the whole production, could bean example of what is happening with other fruits. This surplus is largely transformed intostrawberry purée which, although is especially suitable for various bioconversions, is mainlyused as an additional ingredient to produce other foods. With a view to using strawberrypurée to obtain a new, naturally sweet beverage containing no glucose, the conversion of glu-cose 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 fruitso pasteurized rather than sterilized purée must be used.The use of Gluconobacter japonicus strain (CECT 8443) was studied by batch experi-ments. Different preparation stages were evaluated for ascertaining whether the inoculumrequired pre-cultivation in strawberry purée and whether using pasteurized rather thansterilized substrate would influence prevalence of the inoculated strain over unwantedmicroorganisms—yeasts, mainly.The strain converted glucose into gluconic acid preserving the original fructose contentof the substrate. The optimum inoculum preparation conditions involved microbial growthin Glucose Yeast Extract Peptone synthetic medium for 24 h first and in sterilized strawberrypurée for 24 h additional then.