The effect of proniosomal hydroxytyrosol enriched extract added during pre- and post-fermentation of yoghurt...

Olive leaf polyphenols are bioactive components that known for their health-protective properties. It is well established that oleuropein and its main hydrolysis product, hydroxytyrosol, possess some biologically active properties, including antioxidant and antimicrobial activities. However, these compounds may lose their beneficial properties in unprotected form, resulting in undesirable flavors in food products. In the present study, nanocapsules containing the lyophilised olive leaf brine extract (OLBE) in the form of proniosomes, were added to yoghurt (post-fermentation) and milk (pre-fermentation) samples at varying concentrations. The yoghurt samples were then analyzed for physicochemical properties, antioxidant capacity, microbiological properties, textural properties, bioaccessibility of bioactive compounds by the in vitro digestive system method, volatile compound analysis, and sensory properties. The effect of fermentation was similar in both methods and the best results were obtained with the addition of 0.5 g proniosome. The incorporation of nanocapsules into yoghurt resulted in an enhancement of antioxidant activity during both fermentation processes. No significant change was observed in physicochemical and sensory properties, but the syneresis rate decreased compared to yoghurt containing unencapsulated extract. At the end of simulated in vitro digestion, the antioxidant activities determined by DPPH and ABTS methods of yoghurt with post-fermentation additions were significantly higher than those with pre-fermentation additions. The present findings emphasize the potential of fermented olive leaf extract-loaded proniosomes as a functionally enhanced yoghurt additive. This additive has the capacity to fortify yoghurt while concurrently enhancing its nutritional value and quality.