Influence of Fermentation Time and Storage Conditions on the Physicochemical Properties of Different Yogurt Varieties Using Starter Cultures and Probiotic Lactobacillus rhamnosus GG

Fermented milk products, such as yogurt, undergo significant changes in their physicochemical, sensory, textural, and rheological properties based on fermentation time and storage. This study investigated how different fermentation times (4, 5, 6, 7, and 8 h) and storage durations (1, 7, 14, and 21 days) influenced the characteristics of probiotic yogurt made from sheep milk, cow milk, and a blend of both. Using 2% of each of Lactobacillus rhamnosus GG, Lactobacillus bulgaricus, and Streptococcus thermophilus, fermentation was conducted at 40 °C. The results demonstrated that fermentation time and storage had a significant impact on pH, acidity, total bacterial count (TBC), water-holding capacity (WHC), syneresis, and sensory attributes. Probiotic yogurt made from sheep milk, when fermented for 6 h and stored for 1 day, exhibited the highest acidity (109.42 °T), total bacterial count (TBC) (592.41 × 106 cfu/g), water-holding capacity (WHC) (658.42 g/kg), and sensory score (8.62), with a final pH of 4.25. In contrast, cow milk yogurt, fermented for 5 h and stored for 14 days, had the lowest acidity (81.76 °T), TBC (305.75 × 106 cfu/g), and sensory score (6.24), with a pH of 4.44. The blended yogurt, fermented for 6–7 h and stored for 1 day, showed intermediate values, with an acidity of 89.55 °T, TBC of 284.33 × 106 cfu/g, and a sensory score of 7.24. Syneresis varied from 18.06 to 19.67, with cow milk yogurt, fermented for 6 h and stored for 1 day, exhibiting the highest level. These findings highlight the impact of fermentation time and storage on yogurt quality, with optimized conditions enhancing texture, stability, and sensory appeal. These variations in yogurt properties highlight the critical role of fermentation time and storage conditions in defining texture and stability. Notably, the optimal fermentation times for achieving desirable physicochemical and sensory properties were found to be 6 h for sheep milk yogurt, 5 h for cow milk yogurt, and 6–7 h for the blend. The findings emphasize the importance of milk composition and fermentation conditions in optimizing probiotic yogurt quality. Furthermore, the study underscores the potential of sheep milk in producing yogurt with superior sensory and textural characteristics, offering promising opportunities for the development of high-quality functional dairy products.