Quality Characteristics of Yogurt Fortified with Citrus sinensis L. Osbeck Powder

In this study, functional yogurt enriched with Citrus sinensis L. Osbeck (CS) powder was prepared, and its fermentation characteristics, antioxidant activity, and inhibition properties against enzymes related to diabetes and obesity treatments, namely α-amylase, α-glucosidase, and lipase, were investigated. The yogurt was prepared by adding 1%, 3%, and 5% CS powder to skim milk, followed by sterilization and fermentation with a mixed starter culture for 6 h at 39°C. After fermentation, the yogurt had viable cell counts between 8.05 and 8.21 log colony-forming units/mL and a pH reduction to 4.54－4.63. The total anthocyanin content increased with increasing concentrations of CS powder. 1,1-Diphenyl-2-picrylhydrazyl radical scavenging activity and ferric reducing antioxidant power values also improved, with the highest antioxidant activity observed in the yogurt prepared with 5% CS powder. With regard to enzyme activity inhibition, CS addition significantly increased the α-glucosidase inhibitory activity, whereas the α-amylase inhibitory activity remained unchanged. These findings suggest that yogurt fortified with CS powder exhibits improved antioxidant activity and selective α-glucosidase inhibition, making it a promising candidate for the preparation of functional fermented beverages.