Microencapsulation with hydrocolloids as a modern technique has been used to prolong the survival of probiotics during exposure to harsh conditions. In this study, alginate-Hylon starch microcapsules with genipin cross-linked chitosan and poly-L-lysine coatings were developed to encapsulate four strains of probiotic bacteria, including Lactobacillus casei (ATCC 39392), Bifidobacterium bifidum (ATCC 29521), Lactobacillus rhamnosus (ATCC 7469), and Bifidobacterium adolescentis (ATCC 15703). The viability of probiotics was investigated under heat treatment (72, 85, and 90 °C, 0.5 min), simulated gastric juice (along with pepsin, pH = 2, 2 h at 37 °C), and simulated intestinal juice (along with pancreatin and bile salts, pH = 8, 2 h at 37 °C). The morphology and size of microcapsules were measured by scanning electron and optical microscopy. Results of this research demonstrated that, compared with the free form, microencapsulated probiotics had significantly (P < 0.05) higher viability under simulated gastro-intestinal conditions and heat treatment. Microcapsules with genipin cross-linking significantly increased the viability of probiotics compared with non-cross-linked microcapsules. Moreover, genipin did not influence the size of the microcapsules produced using the emulsion technique. In general, this research indicated that the presence of genipin as a cross-linking agent in the structure of hydrocolloids such as chitosan and poly-L-lysine, and also the presence of Hylon (high-amylose starch) as a material resistant to heat and digestive enzymes, not only increased the viability of probiotics in simulated human gastro-intestinal condition but also considerably improved the thermal resistance of microcapsules.
Keywords: Chitosan; Genipin cross-linking; Heat treatment; Hylon; Poly-L-lysine; Simulated gastro-intestinal condition.