Construction of walnut protein/tea polyphenol/alginate complex for enhancing heat and gastrointestinal tolerance of lactic acid bacteria

The presence of live cells in the intestinal tract is crucial for the beneficial effects of probiotic products containing lactic acid bacteria. However, many bacterial cells lose viability during production, storage, and gastric passage. Protein-based hydrogels and polysaccharide-based capsules effectively enhance the viability of live probiotic cells in products, but the underlying mechanisms and in vivo effectiveness are unclear. In this study, a complex was developed by self-aggregating walnut protein, tea polyphenol, and Lactobacillus rhamnosus cells under acidic conditions, followed by alginate coating. Complex formation was facilitated by hydrogen bonding and hydrophobic interactions. The complex had a low thermal diffusion coefficient of 4.9 × 10⁻⁷ m²/s, making the bacterial cells resistant to temperature fluctuation. Cell survival rate was 75.5% after 12 h at 55 °C and 92.8% after freeze-drying. Shelf-life predictions were 14 years at 4 °C. and 2.3 months at 25 °C, with a live cell count exceeding 10⁶ CFU/g. The product demonstrated a 60% increase in live bacterial cells compared to free cells in simulated gastric fluid, and achieved complete release in simulated intestinal fluid within 120 min. This method was successfully applied to L. rhamnosus, L. casei and L. plantarum. Oral administration of the L. rhamnosus product significantly increased the abundance of Lactobacillus and L. rhamnosus in the colon and cecum of mice. These findings present a new method for producing highly active probiotic products using plant materials and provide insights into the underlying mechanisms from a thermodynamic perspective, contributing to the industrialization and advancement of probiotics.