The effect of proniosomal encapsulated hydroxytyrozole on yoghurt quality

Olive leaf polyphenols are bioactive components responsible for health-protective properties and oleuropein and its main hydrolysis product hydroxytyrosol have bioactive properties such as antioxidant and antimicrobial activity. However, these compounds may lose their beneficial properties during storage and may cause undesirable flavors in food products. In this study, nanocapsules containing the extract obtained from the aqueous part of lyophilized olive leaves were produced by the proniosome method, which is the powder form of niosomal encapsulation, and added to yogurt samples after fermentation and milk samples before fermentation in different amounts. The yogurt samples were then analyzed for their physicochemical properties, total phenolic content, antioxidant capacity, microbiological properties, textural properties, bioaccessibility of bioactive compounds by in vitro digestive system method, flavor analysis and sensory properties. In addition, yogurt samples were examined for changes in pH, acidity, syneresis (water release), color and in vitro digestion and antioxidant capacity during 14 days of storage. The application of the produced nanocapsules in yogurt increased the antioxidant activity and decreased the syneresis rate, although no significant change was observed in physicochemical and sensory properties compared to yogurt containing non-encapsulated extract. In addition, after simulated in vitro digestion, the antioxidant capacity values of yogurt determined by DPPH and ABTS methods increased compared to the storage days. In conclusion, proniosomal olive leaf liquid extract rich in hydroxytyrosol has the potential to improve the functional properties of yogurt.