Accelerated natural lactic fermentation of cereal-based formulas at reduced water activity

Energy required to dehydrate fermented cereal-based food formulas plays a significant part in the production cost. Therefore the effect of reduced moisture content on the fermentation was investigated. Generally, lactic fermentation at reduced moisture content resulted in increased final pH. Significant acidification still occurred at 0.33 kg water/kg dry matter corresponding to either aW = 0.925 in a sorghum-maize-soya (SMS) mixture, or aW = 0.950 in a sorghum-maize-milk powder (SMM) mixture. Acidification adequate for microbiological safety (pH < or = 4.5) was achieved at 0.54 kg water/kg dm in SMS (aW = 0.950) and 0.43 kg/kg dm in SMM (aW = 0.965). In stable accelerated natural lactic fermentations obtained by inoculum recycling ('back-slopping') at 30 degrees C, dominant lactic acid bacteria included Lactobacillus plantarum, L. brevis, L. acidophilus and Lactococcus lactis. Dominating yeasts were Saccharomyces cerevisiae and Candida krusei. L. plantarum isolated from high-moisture (1.5 kg/kg dry matter) SMS fermentations had higher specific growth rates than L. plantarum isolated from reduced moisture (0.54 kg/kg dm) SMS fermentations, when tested under similar aW conditions. This effect was not caused by previous culturing conditions; probably different strains of L. plantarum having different aW-optima dominate at high or reduced moisture conditions.