Physicochemical quality attributes and antioxidant properties of set-type yogurt fortified with argel (Solenostemma argel Hayne) leaf extract

The fortification of yogurt with natural bioactive compounds could improve its nutritional and health potentials. In this study, physicochemical, antioxidant, and sensory qualities of set-type yogurt were fortified with different concentrations (0.0, 0.1, and 0.2 g/100 mL) of argel leaf extract (ALE) during cold storage was assessed. Both ALE and storage time affected the quality of yogurt at different magnitudes (p < 0.05). ALE increased the acidity, lactic acid bacteria (LAB) count, water-holding capacity (WHC), viscosity, a* and b* values, springiness, total phenolic contents (TPC), antioxidant activity, and sensory attributes of yogurt. However, it reduced the yogurt's pH, syneresis, L* value, hardness, gumminess, adhesiveness, and thiobarbituric acid (TBARS) value. All yogurt types displayed the behavior of weak viscoelastic gels (G' ' G '', tan delta < 1) that had a predominantly solid-like behavior and better stability during storage. During storage, pH, LAB counts, syneresis, viscosity, a* and b*, TPC, antioxidant activity, and sensory attributes were reduced, whereas acidity, WHC, L*, a* and b*, gumminess, cohesiveness, and TBARS values were increased (p < 0.05). It was concluded that ALE (0.1 and 0.2 mg/100 mL) can be used as a natural ingredient to develop a functional yogurt with improved physical, nutritional, antioxidant, and sensorial qualities.