Double-crosslinked pea protein isolation-sodium alginate composite microgels embedding Lactobacillus plantarum: Effect of calcium chloride concentration

Abstract

Lactobacillus plantarum (L. plantarum) was embedded in pea protein isolation (PPI)/sodium alginate (SA) composite microgels prepared by double crosslinking with transglutaminase (TGase) concentration of 10.0 U/g PTN and calcium chloride (CaCl₂) concentrations of 0, 0.05, 0.10, 0.15, 0.20, and 0.25 g/L, respectively. The influence of the CaCl₂ concentration on the structure, physicochemical properties, and functional properties of the composite microgels was investigated to reveal the conformational relationship between the structure and the delivery effect of encapsulated probiotics. The results showed that higher concentrations of CaCl₂ favoured the unfolding and aggregation of proteins through hydrophobic interactions and Ca²⁺ bridges, thus increasing gel strength and mechanical properties, as well as enhancing thermal stability. When CaCl₂ was added up to a concentration of 0.20 g/L, the encapsulation efficiency (EE) of microgels reached a maximum of 92.62 ± 1.90 %. During in vitro digestion, the resistance of the composite microgels to simulated gastric fluid (SGF) increased with rising CaCl₂ concentration, whereas the number of viable bacteria released in simulated intestinal fluid (SIF) decreased. After 120 min of immersion in the intestinal fluid, PS-Ca²⁺_2.0 % released the least number of viable bacteria at 4.10 × 10⁸ CFU/g than other double-crosslinked microgels, which can avoid the premature release of probiotics in the small intestine, and was conducive to realize the colon-targeted delivery of probiotics. Overall, the structural and functional enhancements achieved by CaCl₂ addition highlight the potential of PPI-SA composite microgels for probiotic protection and delivery.