Reduction of Phytate in Soy Drink by Fermentation with Lactobacillus casei Expressing Phytases From Bifidobacteria

Plant-based food products can be modified by fermentation to improve flavour and the concentration of some biologically active compounds, but also to increase the mineral availability by eliminating anti-nutrient substances such as phytates. The objective of this study was to develop a fermented soybean drink with improved nutritional quality and source of probiotic bacteria by including as starter for fermentation Lactobacillus casei strains modified to produce phytase enzymes from bifidobacteria. The L. casei strains showed a good adaptation to develop in the soy drink but they needed the addition of external carbohydrates to give rise to an efficient acidification. The strain expressing the Bifidobacterium pseudocatenulatum phytase was able to degrade more than 90 % phytate during product fermentation, whereas expression of Bifidobacterium longum spp. infantis phytase only led to 65 % hydrolysis. In both cases, accumulation of myo-inositol triphosphates was observed. In addition, the hydrolysis of phytate in soy drink fermented with the L. casei strain expressing the B. pseudocatenulatum phytase resulted in phytate/mineral ratios for Fe (0.35) and Zn (2.4), which were below the critical values for reduced mineral bioavailability in humans. This investigation showed the ability of modified L. casei to produce enzymes with technological relevance in the design of new functional foods.