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An evaluation of the quality characteristics of kefir fortified with olive (Olea europaea) leaf extract

Özge Duygu Okur (Food Engineering, Zonguldak Bülent Ecevit University, Zonguldak, Turkey)

British Food Journal

ISSN: 0007-070X

Article publication date: 5 October 2021

Issue publication date: 21 March 2022




This study aims to produce a new type of healthy functional kefir by adding olive (Olea europaea) leaf extract and to determine its potential effect on the quality (physicochemical, sensory, phenolic contents and antioxidant properties) of kefir samples during storage at 4°C for 21 days.


For this purpose, four kefir samples were produced by using olive leaf extract in different amounts (A: 0% (control), B: 0.1%, C: 0.15% and D: 0.35%). The physicochemical, sensory, phenolic contents and antioxidant properties of kefir samples were investigated during Days 1, 7, 14 and 21 of storage. The study was conducted to optimize the olive leaf extract addition level to obtain better-quality kefir functional food.


From the results, it was determined that the addition of olive leaf extract affected the entire chemical components of the kefir samples (p < 0.05). It was found that the pH value decreased during storage. By contrast, it was observed that titration acidity values increased. The kefir sample with 0.35% olive leaf extract (D) had the highest total phenolic and antioxidant activity content (1,292.75 mg GAE/L and 10.20 mM TE, respectively) among the samples (p < 0.05). In the sensory analyses, the kefir sample with the highest score – in terms of sensory attributes – was the kefir sample containing 0.15% olive leaf extract (C).


Thus, it was concluded that kefir with added olive leaf extract could serve as a functional kefir of benefit to human health. When we looked at the enrichment studies on kefir as a functional product, no study has been found on the use of olive (Olea europaea) leaf extract, especially with kefir. In this sense, it is thought that the study will contribute to published literature.



Funding: The author received no financial support for the research, authorship and/or publication of this article.

Conflict of interest statement: No conflicts of interest exist in this study.


Okur, Ö.D. (2022), "An evaluation of the quality characteristics of kefir fortified with olive (Olea europaea) leaf extract", British Food Journal, Vol. 124 No. 5, pp. 1727-1736.



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