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

Abstract

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.

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

“…The analysis of the number of live bacterial cells before digestion indicated that ovine fermented milk showed more viable cells by 0.2–1.9 log cfu g −1 than caprine milk, considering similar fermentation conditions. Numerous studies confirmed that ovine milk contains higher dry matter, total protein, crude fat, casein, minerals, and vitamins compared to caprine milk [ 39 , 40 , 48 , 49 ].…”

“…Raw ovine and caprine milk were heated at 85 °C for 30 min [ 47 , 48 , 49 ]. The cooled milk was divided into a total of 40 batches (20 batches for sheep’s milk and 20 batches for goat’s milk) based on the added probiotic strains ( L. casei , L. acidophilus , L. paracasei , and L. rhamnosus ) and different forms of collagen (bovine and protein hydrolysate) and doses (1.5% and 3.0%).…”

“…The milk was divided into batches ( Table 1 and Table 2 ). For each probiotic strain, ten batches of mixtures with additives were prepared [ 48 , 49 ]: Sheep’s milk. Sheep’s milk + 1.5% bovine collagen.…”

“…The bacterial inoculum contained about 9 log cfu g −1 of bacteria. A total of 40 batches of collagen–milk mixtures were obtained [ 48 , 49 ]. Each sample was stirred, transferred to 100 mL plastic cups, and fermented at 37 ± 1 °C until reaching a pH = 4.6 ± 0.2 (12–15 h).…”