Probiotic Fermented Goat's and Sheep's Milk: Effect of Type and Dose of Collagen on Survival of Four Strains of Probiotic Bacteria during Simulated In Vitro Digestion Conditions.

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.

Effect of Storage Time and Bacterial Strain on the Quality of Probiotic Goat's Milk Using Different Types and Doses of Collagens.

Recently, increasing attention has been focused on developing new products based on goat's milk. Consumers positively perceive fermented goat's milk products as health-promoting due to their nutritional value, digestibility, and potential source of probiotics. This study aimed to evaluate the possibility of using different doses of collagen and collagen hydrolysate in the production of probiotic goat's milk fermented by four monocultures: Lacticaseibacillus casei 431® Lactobacillus acidophilus LA- 5®, Lacticaseibacillus paracasei LP26, and Lacticaseibicillus rhamnosus Lr- 32®. A total of 20 experimental groups were prepared, including control groups (without additives), and due to the added probiotic (Lacticaseibacillus casei, Lactobacillus acidophilus, Lacticaseibacillus paracasei, and Lacticaseibacillus rhamnosus), various collagen doses (1.5% and 3.0%) and collagen types (hydrolysate and bovine collagen). Physicochemical, organoleptic, and microbiological characteristics were evaluated after 1 and 21 days of cold storage. The applied additives increased the acidity of the milk even before fermentation. However, milk with bovine collagen and hydrolysate had a higher pH value after fermentation than control milk. The study showed higher than 8 log cfu g−1 viability of probiotic bacteria in goat's milk products during storage due to the proper pH, high buffering capacity, and rich nutrient content of goat's milk. The best survival rate was shown for the L. casei strain after 21 days in milk with collagen protein hydrolysate. Moreover, collagen in milk fermented by L. rhamnosus decreased syneresis compared to its control counterpart. The addition of collagen, especially the hydrolysate, increased the gel hardness of the fermented milk. The collagen additives used in the milk, both in the form of hydrolysate and bovine collagen, caused a darkening of the color of the milk and increased the intensity of the milky-creamy and sweet taste.

Effect of Collagen Types, Bacterial Strains and Storage Duration on the Quality of Probiotic Fermented Sheep's Milk.

Collagen has become popular in dietary supplements, beverages and sports nutrition products. Therefore, the aim of this study was to evaluate the possibility of using various doses of collagen and collagen hydrolysate to produce probiotic sheep's milk fermented with Lactobacillus acidophilus, Lacticaseibacillus casei, Lacticaseibacillus paracasei and Lacticaseibacillus rhamnosus. The effects of storage time, type and dose of collagen, and different probiotic bacteria on the physicochemical, organoleptic and microbiological properties of fermented sheep's milk at 1 and 21 days of refrigerated storage were investigated. The addition of collagen to sheep's milk increased the pH value after fermentation and reduced the lactic acid contents of fermented milk compared to control samples. After fermentation, the number of probiotic bacteria cells was higher than 8 log cfu g-1. In sheep's milk fermented by L. acidophilus and L. casei, good survival of bacteria during storage was observed, and there was no effect of collagen dose on the growth and survival of both strains. The addition of collagen, both in the form of hydrolysate and bovine collagen, resulted in darkening of the color of the milk and increased the sweet taste intensity of the fermented sheep's milk. However, the addition of hydrolysate was effective in reducing syneresis in each milk sample compared to its control counterpart.