Characterization of functional, biochemical and textural properties of synbiotic low-fat yogurts during refrigerated storage

This study examined the influence of exopolysaccharides (EPS) produced in situ on the viability of Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus and probiotics, the proteolytic and ACE-inhibitory activities, and textural and rheological properties of inulin-containing probiotic yogurt during refrigerated storage. Two types of yogurt were prepared using strains of S. thermophilus not producing EPS (NEPY) and producing EPS (EPY). The yield of crude EPS increased (by 2.4 times) until day 21 of storage. Presence of EPS showed a protective effect on the survival of L. delbrueckii ssp. bulgaricus and Lactobacillus acidophilus but not on S. thermophilus, Lactobacillus casei and Bifidobacterium longum. No changes in post-acidification, lactic acid content or the ACE-inhibition activity of the two types of yogurt were observed. Overall, EPS containing yogurts exhibited higher proteolysis in the presence of inulin and probiotics (0.698 units) than the corresponding control (0.563 units). The storage and loss moduli (Pa), yield stress (Pa), consistency index (Pa s) and thixotrophic behaviour (Pa s⁻¹) of both samples were similar at day 1 and the influence of EPS was observable only after day 7. Such a variation of the effect of EPS on the textural and rheological properties of low-fat yogurt appears to be partially due to the presence of probiotics.