Improving the viability of Lactobacillus plantarum LP90 by carboxymethylated dextran-whey protein conjugates: The relationship with glass transition temperature

Microcapsules can provide better protection for probiotics during freeze-drying and gastrointestinal digestion. This study aims to investigate the effect of microencapsulation using the product of the Maillard reaction of whey protein and carboxymethylated dextran (CM. dex) on the viability of Lactobacillus plantarum LP90 (Lp) as related to freeze-drying, gastrointestinal tolerability and storage stability. The results demonstrate that the glycosylation product was successfully obtained by the dry heating method, and the product was verified by SDS–PAGE, infrared spectroscopy (FTIR), and intrinsic fluorescence spectroscopy. The grafting degree of whey protein and CM. dex, as measured by the OPA method, was 53.87%, 57.60%, and 61.21% at 1, 3, and 5 days of the Maillard reaction, respectively. With increasing Maillard reaction time, the glass transition temperature (Tg) of conjugates increased, and WP–CD5d had the highest Tg, which was 156.31 °C. At the same time, WP–CD5d had the best protection effect under freeze-drying, and the survival rate was 87.37%. Microencapsulated Lp had better tolerance over 5 h of simulated gastrointestinal juice treatment fluid. Lp had the best storage stability protected by WP-CD5d, for which k was 0.102.