Design of double emulsion gels loaded with Lactiplantibacillus plantarum subsp. plantarum to enhance their survival during processing and in vitro digestion

In this work, we investigated food-grade water-in-oil-in water (W1/O/W2) double emulsion gels (DEGs) that can serve as a vehicle for delivering probiotic bacteria. The objects of our study were three DEGs uploaded with Lactiplantibacillus plantarum subsp. plantarum in which (i) the W2 was gelled with whey protein by adding calcium chloride, (ii) the O was gelled with carnauba wax, (iii) both W2 and O were gelled. The structural differences between the samples were analysed using SEM, which revealed differences in a surface morphology, porosity, particle distribution, and overall gel network integrity. It was found that all DEGs loaded with probiotics significantly improved cell viability in a sufficient amount (more than 6 log CFU/g) during 56-day storage, heat treatment (60 °C and 72 °C for 1 h), and four freezing-thawing cycles compared to free cells. During in vitro digestion structural changes of DEGs occurred. The low lipolysis degree (4–7 %) of the DEGs contrasts with the relatively high protein hydrolysis degree (40–50 %) after digestion. Under simulated digestion viscosity curves revealed DEGs thinning due to enzymatic hydrolysis. Furthermore, probiotic viability was significantly influenced by the structural characteristics of DEGs. Free probiotic cells exhibited substantial cell reduction, particularly after intestinal digestion, indicating high sensitivity to digestive conditions. To sum up, DEG matrix provides a protective barrier against enzymes and acids, making DEGs favorable for delivering L. plantarum cells while maintaining their viability during storage, thermal treatment, freezing-thawing, and in vitro digestion.