Novel seamless shell-core microbead for probiotics encapsulation: Influence of gel structure on storage stability and gastrointestinal activity

Probiotics have poor stability in storage and gastrointestinal digestion, resulting in low biological activity. Therefore, we have innovatively designed a shell-core microbead that can place probiotics in an independent lipid environment as a core, with an outer layer coated with a shell film composed of gelatin and/or pectin. Addition of 3% pectin to the shell layer and cross-linking with calcium ions significantly improved the physicochemical properties of the shell film of the microbeads, including water vapor permeability (WVP), water contact angle (WCA), and gel characteristics. The microbeads have spherical structure, uniform size and low moisture content (<5%). The water solubility of gelatin microbeads (Gel-Mb, 69.62%), gelatin-pectin microbeads (Gel-Pec-Mb, 61.06%) and shell cross-linked microbeads (Cro-Pec-Mb, 52.97%) decreased gradually. Cryo-scanning electron microscopy (Cryo-SEM) showed an evident shell core structure, and an apparent gel network was observed in the surface layer of shell of Cro-Pec-Mb. SEM analysis also showed the same porous network structure on the surface of Cro-Pec-Mb. The probiotic activities of Gel-Mb, Gel-Pec-Mb and Cro-Pec-Mb were 6.87, 6.76 and 6.74 log CFU/g after 4 months storage at 4 °C, respectively. This indicates that microbead encapsulation has a high retention of probiotic activity due to the effective insulation of the lipid environment from oxygen, moisture, etc. Cro-Pec-Mb can maintain the integrity of the structure and resist the enzymatic hydrolysis of digestive enzymes, reducing probiotic inactivation during the gastrointestinal digestion, with only a decrease 1.85 log CFU/g. This study show that microbeads were a promising platform for intestinal probiotic delivery.