Investigation of the quality properties and functionality improvement of set-type yogurt fortified with different ratios of borage (Echium amoenum) and nettle (Urtica dioica) extracts

The purpose of this study was to evaluate the quality and functional characteristics of set-type yogurt manufactured using different concentrations of Echium amoenum extract (EE, 0.25% and 0.50%, wt/wt), Urtica dioica extract (UE, 0.25% and 0.50%, wt/wt) and mixture of them (0.25% of EE + 0.25% of UE, wt/wt). Physicochemical, rheological, antioxidant, microstructure, color, and sensory properties of manufactured yogurts were analyzed during refrigerated storage at 4°C for 21 d. According to the results, utilization of different concentrations of EE, UE, or their mixture in the formulation of set-type yogurt showed significant increase in titratable acidity, viability of lactic acid bacteria, antioxidant activity, and total phenolic content, and significant decrease in pH value. In addition to having more compact structure, the yogurt fortified with 0.25% of EE had the lowest value of syneresis and the highest values of water holding capacity along with storage and loss modulus among the experimental samples. In terms of sensory properties, whereas the yogurt containing 0.25% of EE showed similar overall acceptability to the control sample, the yogurts fortified with 0.50% of EE and 0.25% of EE + 0.25% of UE had more overall acceptance points compared with yogurts manufactured using different concentrations of UE. The results revealed the possibility for manufacture of functional set-type yogurt with potential health-promoting properties by monitoring the type and ratio of selected herbal extracts containing functional properties.