Yogurt is widely appreciated for its high nutritional value and health benefits. The recent addition of plant extracts rich in phenolic compounds and bioflavonoids has attracted considerable interest, particularly as milk and dairy products contain a low amount of these beneficial elements. Olive leaf extract (OLE) has been studied as a potential source of bioactive compounds. This study assessed the impact of incorporating OLE on the physicochemical properties, total phenol content, antioxidant activity (assessed by DPPH and ABTS methods), rheological characteristics and color of yogurts made from cow's, sheep’s, and goat's milk. The milk was enriched with OLE at concentrations of 0.5%, 1%, 1.5% and 2% (v/v) and analyzed after complete coagulation.

The results showed a decrease in pH and an increase in acidity during storage, with the buffering effect of OLE attenuating these variations. OLE-enriched yogurts had a higher total phenol content and increased antioxidant activity. In addition, the water holding capacity (WHC) of the yogurts increased with the addition of OLE, probably due to interactions between yogurt proteins and polyphenols, resulting in a reduction in syneresis. Color analysis revealed that OLE reduced brightness (L* values) and shifted in hue towards red (positive a* values) and yellow (positive b* values). The texture profile showed that higher levels of supplementation increased the firmness of cow's milk while reducing it for other types of milk. These results highlight the potential of OLE as a functional ingredient to improve the nutritional and health benefits of dairy products. Considering all the results and previous work, the addition of 1.5% OLE proved to be optimal. To confirm this conclusion, sensory analyses should be carried out.