Alginate microcapsules enriched with biofilm-like Lactiplantibacillus plantarum: characterization, stability, and application in fermented soy yoghurts

Abstract

Probiotic viability easily decreases during oral delivery, preparation, transportation, and storage processes. Here, we developed a dual encapsulation strategy based on sodium alginate (SA)/Ca²⁺ crosslinking and in situ formation of biofilm to protect Lactiplantibacillus plantarum (L. plantarum) from the adverse environments and used the encapsulated L. plantarum to prepare fermented soy yoghurt. First, L. plantarum with excellent exopolysaccharide-producing ability was encapsulated in the SA gel to form L. plantarum microcapsules (LMs). Then, LMs were cultured in MRS broth with 1 % Ca²⁺ to form the LM biofilm (LMB) with a probiotic loading of 1.5 × 10¹² CFU/g. The established LMB showed excellent resistance to the gastrointestinal tract and elevated temperatures. After 28 days of storage at 4 °C, LMB still exhibited high viable bacterial counts (8.7 log CFU/g). Moreover, LMB can be used as a starter culture to prepare fermented soy yoghurt (SY-LMB) with excellent rheological properties. The viable bacterial counts in SY-LMB reached 12.6 log CFU/mL after 21 days of storage, which was much higher than that of the commercial soy yoghurts (9.1 log CFU/mL). More importantly, after digestion with gastrointestinal fluids, the viable bacterial counts in SY-LMB and LMB were still as high as 8.1 log CFU/mL and 10.0 log CFU/g, respectively. Overall, we provided a very effective dual encapsulation strategy that can efficiently improve the survival rates of probiotics in the harsh environments and provided an effective starter culture for preparing the plant-based yoghurt.