Physicochemical and in vitro digestion properties of gelatin/low-methoxyl pectin synbiotic microgels co-encapsulating Lacticaseibacillus casei and pectic oligosaccharides via double-crosslinking with transglutaminase and calcium ions

In this study, we investigated the physicochemical and in vitro digestion properties of gelatin (GEL)/low-methoxyl pectin (LMP) synbiotic microgels co-encapsulating Lacticaseibacillus casei (L. casei) and pectic oligosaccharides. A single-crosslinked microgel containing L. casei was fabricated via enzymatic crosslinking with transglutaminase. The single-crosslinked microgel was incubated in calcium chloride solution at different concentrations (1%, 2%, and 3%) to produce double-crosslinked microgels. In field emission scanning electron microscopy (FE-SEM) analysis, the double-crosslinked microgels exhibited a more spherical shape with a smoother surface than the single-crosslinked microgel. The crosslinks and possible interactions in the microgels were described using X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy analyses. The encapsulation efficiency of both single- and double-crosslinked microgels was relatively high (95.64%–95.99%). After exposure to simulated gastrointestinal conditions (salivary, gastric, and intestinal phases), the survival rate of L. casei in double-crosslinked microgels (GEL/LMP3) prepared with 3% calcium ions was the highest among all the samples studied. After heat treatment (72 °C for 15 s and 63 °C for 30 min) and 20 days of storage (4 °C and 37 °C), L. casei encapsulated in all microgels, especially double-crosslinked microgels, maintained greater viability than free cells. These results suggest that double-crosslinked GEL/LMP synbiotic microgels, particularly GEL/LMP3, can be used to improve the viability of probiotic cells under gastrointestinal, heating, and storage conditions.