Enteric rice protein-shellac composite coating to enhance the viability of probiotic Lactobacillus salivarius NRRL B-30514

This study reports novel modified rice protein (MRP)-ammonium shellac (NH4SL) enteric composite coatings on millimeter-sized probiotics pellets to protect the survival of probiotics during storage, thermal treatments, and simulated gastrointestinal (GI) digestions. An aqueous MRP solution at pH 7.0–13.0 was dropwise added into an aqueous ethanol NH4SL solution at pH 8.2, and the mixture pH significantly affected the homogeneity of MRP-NH4SL suspensions and formed films. The MRPpH13-NH4SL suspension with pH of 9.4 had smaller MRP particles and thus better stability than other suspensions with pH of ~8.4, predominantly due to the better solubility and stability of MRP at a higher pH. Atomic force microscopy, fluorescence spectroscopy, and dynamic light scattering results indicated the complexation between MRP and NH4SL in all treatments, which increased the intermolecular repulsions to further facilitate the stability of MRPpH13-NH4SL suspension. The homogenous MRPpH13-NH4SL suspension resulted in smooth films with improved mechanical and enteric properties at a higher content of MRP having a pH-dependent solubility. Probiotics pellets coated with MRP-NH4SL had significantly more viable Lactobacillus salivarius NRRL B-30514 than uncoated pellets after 30-day ambient storage, heating at 80 °C for 20 min, and during simulated GI digestions. The composite coating also preserved the probiotics viability better than the NH4SL-only coating after 2-h gastric digestion. Therefore, MRPs can be used to modify the enteric properties of shellac-based edible coatings to deliver powdered probiotics, which is significant to manufacturing solid probiotics-containing products.