Phenolic content and antioxidant activity of donkey milk kefir fortified with sulla honey and rosemary essential oil during refrigerated storage

The aim of this work was to evaluate the phenolic content and antioxidant activity of donkey kefirfortified with sulla honey and rosemary essential oil, during refrigerated storage. The type offlavouring strongly influenced the antioxidant activity of the kefir: rosemary essential oil kefirshowed the highest 2,20-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid values; sulla honey kefirshowed the highest ferric-reducing antioxidant power values but, at the same time, in both fortifiedkefirs, the thiol content decreased, probably because of the formation of polyphenol-protein com-plexes that would have influence the availability of bioactive components. The antioxidant activityincreased significantly during refrigerated storage, showing the highest values after 15 days. Sen-sory analysis highlighted the fact that the donkey kefir was well accepted by consumers. Addition ofsulla honey resulted in the highest acceptability, while addition of rosemary essential oil kefir wasless accepted by consumers. This knowledge provides a basis that could lead to the production offortified donkey kefir with specific nutraceutical characteristics.