CHANGES OF QUALITY CHARACTERISTICS OF FUNCTIONAL FRUIT YOGURTS FORTIFIED WITH HUSK EXTRACTS OF VARIOUS NUTS DURING COLD STORAGE

Walnut, almond, and pistachio husk extracts were used to enrich the peach yogurt. The effects of the extracts on the physicochemical, biochemical, microbiological, and sensory properties of yogurt were investigated during 21 days of cold storage. Husk extracts slowed down the increase in acidity of yogurt and, correlatedly, the syneresis values of extract fortified yogurts were lower than the control yogurt. Inevitably, husk extracts caused a difference in ΔE of yogurts. However, this difference did not affect the sensory appearance scores of yogurts negatively. All extracts, especially those of walnut husk, significantly increased the antioxidant and antidiabetic activities of yogurt, but this effect was partially reduced with prolonged storage. Also, the extracts reduced the lipid oxidation of yogurt by almost half. Although some sensory values of almond and walnut samples were relatively lower than control yogurt, the panelists liked pistachio yogurts at least as much as control yogurt. The findings of this study revealed that husk extracts of various nuts can be used as both a natural preservative and a functional ingredient in fruit yoghurt.