Microbial tolerance of digestive stresses depends not only on the bacterial strain but also on the structure and physicochemical properties of the supply chain and the foods that contain it. In the present study, we aimed to evaluate the effects of the type of milk (ovine, caprine) and the type and dose of collagen on the viability of four probiotic strains, Lacticaseibacillus paracasei L-26, Lacticaseibacillus casei 431, Lactobacillus acidophilus LA-5, and Lacticaseibacillus rhamnosus Lr-32, during in vitro gastrointestinal digestion. The highest survival rate under simulated in vitro digestion conditions compared to the number of cells before digestion was found in two strains, L. casei and L. paracasei, where survival rates were greater than 50% in each batch. The survival rate of the L. rhamnosus strain ranged from 41.05% to 64.23%. In caprine milk fermented by L. acidophilus, a higher survival rate was found in milk with 1.5% hydrolysate than the control, by about 6%. Survival of the L. rhamnosus strain was favorably affected by the 3% addition of bovine collagen in caprine milk, which increased survival by about 14% compared to the control sample. Adding 3% of hydrolysate to sheep's and goat's milk enhanced the survival of the L. rhamnosus strain by 3% and 19%, respectively. This study reports that fermented caprine and ovine milk may be suitable matrices for the probiotic supply of commercial dairy starter cultures and promote gut homeostasis.
Keywords: bacterial survival rate; bovine collagen; caprine milk; collagen hydrolysate; fermented goat’s milk; fermented sheep’s milk; in vitro; ovine milk; probiotic.