Encapsulation of probiotic Lactiplantibacillus plantarum S18 in sodium alginate: process optimization using Box-Behnken design for poultry feed application.

This study aimed to develop an effective method for encapsulating lactic acid bacteria (LAB) to improve their low survival rate under harsh environmental conditions. The strains were submitted to a battery of standard tests and criteria commonly used for determining their probiotic properties and attributes. A total of 22 LAB strains were isolated; the isolates were mostly resistant to ciprofloxacin, vancomycin and sulphamethoxazole/trimethoprim (clear zones = 0 mm), whereas S18 and S21 were sensitive and S19, S20 and S22 showed intermediate susceptibility (clear zones between 16 and 20 mm). They also demonstrated high tolerance to simulated gastro-intestinal tract conditions, maintaining viability in Man, Rogosa, and Sharpe (MRS) broth at gastric pH 2.5 and in the presence of 0.3% bile salts. In biofilm formation essays, 12 isolates showed strong adhesion to polystyrene microplates, and all selected strains exhibited significant inhibitory activity against tested pathogens. The strain displaying the best promising probiotic characteristics was identified through 16 S rRNA sequencing as Lactiplantibacillus plantarum S18. Encapsulation of this strain in sodium alginate was optimized using a box-benken design. The highest encapsulation efficiency (99.99%) was achieved using a bacterial cell concentration of 10⁸ CFU/ml, calcium chloride concentration of 1.540 M, a solidification time of 12 min, and a sodium alginate concentration of 2.15%. Overall, the findings demonstrate that sodium alginate-based encapsulation effectively preserves the stability and viability of Lactiplantibacillus plantarum S18, supporting its potential use as a probiotic additive in poultry feed.