Lactobacilli and yeasts for phytate degradation in soy milk fermented products

Due to the increasing prevalence of dairy intolerance and the adoption of vegan/vegetarian diets, there is a growing demand for non-dairy alternatives. One commonly used substitute in vegetarian and vegan food products is soybean, which provides minerals and proteins. However, soybean also contains the antinutrient phytate (inositol hexaphosphate, IP6), which hinders nutrient absorption. To address this, microbial phytases, which are enzymes hydrolyzing phosphate groups from IP6, have gained significant attention. Degradation of IP6 releases chelated minerals, such as Fe and Zn, and solubilize IP6, resulting in increased mineral availability for intestinal absorption. The aim of the present study was to investigate 10 Lactic Acid Bacteria belonging to Lacticaseibacillus casei, Lactobacillus delbruecki, L. helveticus, and Lactiplantibacillus plantarum, and 22 yeasts, previously isolated from Tajikistan yogurt and togwa (Tanzanian traditional fermented cereal- and cassava-based product) for i) fermentation capacity (singularly or in mixed cultures) of soy milk and ii) phytase activity. All strains belonging to Lacticaseibacillus casei showed the ability to ferment soy milk and thicken the product. With respect to the yeasts, Kluvieromyces marxianus and Pichia kudriavzevii were selected. The previously observed strong phytate degrading ability of strain P. kudriavzevii TY1322 in vitro trials was confirmed in this study during soymilk fermentation. The phytate degradation was further improved when strain P. kudriavzevii TY1322 was used in co-culture with Lactobacillus casei AB3 and K. marxianus AL3 or BL8 suggesting these strains as promising candidates for phytate degradation in soy-based food fermentation.