Quality Characteristics of Yogurt Fortified with <i>Citrus sinensis</i> L. Osbeck Powder

In this study, functional yogurt enriched with <i>Citrus sinensis</i> 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.