Evaluation of Physicochemical and Textural Properties of Synbiotic Yogurt Using Propionibacterium freudenreichii and Inulin during Fermentation and Cold Storage Time

Background: Propionic acid bacteria (PAB) are probiotics that, when combined with conventional yogurt starters, can significantly influence the fermentation process and structural properties of yogurt. This study aimed to produce and evaluate a synbiotic yogurt using Propionibacterium freudenreichii (P. freudenreichii) and inulin in combination with traditional starters, focusing on their combined effect on the quality characteristics of the product during fermentation and storage at 4 °C. Methods: In this study, three yogurt formulations were developed. The first was a control sample (YC) containing exclusively the conventional starter culture, consisting of Streptococcus thermophilus (ST) and Lactobacillus delbrueckii subsp. Bulgaricus (LB). The second formulation (YC + PS4) included both the traditional starter and P. freudenreichii subsp. shermanii. The third formulation (YC + PS4 + Inulin) was enriched with the same cultures as the second group, along with 2% (w/v) inulin as a prebiotic component. These formulations were evaluated and compared based on their physicochemical attributes, including pH, titratable acidity, water holding capacity (WHC), and textural properties during fermentation and subsequent refrigerated storage at 4 °C. All measurements were performed in triplicate, and the data were statistically analyzed using two-way ANOVA, followed by Tukey's test at a significance level of p < 0.05. Results: The findings demonstrated that incorporating P. freudenreichii subsp. shermanii in combination with traditional yogurt starter cultures had a notable impact on the physicochemical and textural characteristics during refrigerated storage. The synbiotic yogurt (YC + PS4 + Inulin) exhibited the smallest decline in pH (a reduction of 0.18 units) and the lowest acidity level (111 ± 7 °D) on day 21. Additionally, viscosity reached its maximum value (25.1 g.s) in the synbiotic yogurt, whereas the lowest value (14.05 g.s) was observed in the control group. Conclusion: The produced synbiotic yogurt exhibited a significantly different profile compared with the control yogurt, with the lowest pH drop, the smallest increase in acidity, the best textural properties, and the highest water-holding capacity. Propionibacterium and inulin can be effectively utilized as a probiotic and a prebiotic, respectively, to optimize the production of beneficial metabolites in synbiotic yogurt.