Microencapsulation of Limosilactobacillus reuteri and its Cell-Free Supernatant: Effects of Alginate-Enriched Wall Materials on Stability, Metabolite Profile, and Antimicrobial Activity.

This study evaluated the impact of spray-drying microencapsulation on the stability, metabolite profile, and antimicrobial activity of Limosilactobacillus reuteri ATCC 55,730 and its cell-free supernatant (CFS), using whey protein isolate (WPI) and maltodextrin (MD) with or without alginate (ALG) enrichment. The influence of selected prebiotics (alginate, inulin, and trehalose) on bacterial growth was also assessed. Alginate supplementation significantly enhanced bacterial growth, improved microcapsule structural integrity, and increased probiotic viability following spray drying and during storage. Organic acid analysis revealed lactic and acetic acids as the dominant metabolites, while GC-MS profiling demonstrated acetic acid as the principal volatile compound (up to 83%), accompanied by aldehydes, alcohols, hydrocarbons, and organic acid/amine derivatives. Following spray drying, the encapsulation efficiency of Lmb. reuteri was 70.85% for R1 (WPI-MD) and 73.02% for R2 (WPI-MD-ALG). Under simulated gastric conditions (pH 2.0, 120 min), the alginate-enriched formulation (R2) retained significantly higher viability (5.28 log CFU/mL) than the WPI-MD formulation without alginate (R1), which decreased to 4.46 log CFU/mL (p < 0.05). After simulated intestinal exposure, viable cell counts decreased to 4.92 and 3.96 log CFU/mL for R2 and R1, respectively, indicating greater viability retention in the alginate-enriched formulation. Additionally, Lmb. reuteri and its CFS exhibited antimicrobial activity against Lactococcus garvieae and Yersinia ruckeri, with the highest inhibition zone observed for the RS2 formulation against L. garvieae (28.67 mm). These findings indicate that alginate-assisted microencapsulation can improve probiotic viability and influence antimicrobial activity depending on the target pathogen and formulation, highlighting its potential as a natural bioactive system for food preservation and aquaculture applications.