University of Birjand Journal of Horticulture and Postharvest Research 2588-4883 9 Issue 3 2026 09 01 Phytochemical composition and antioxidant activities of king orange (Citrus reticulata × sinensis) cultivated in the Mekong Delta, Vietnam 415 426 4095 10.22077/jhpr.2026.9449.1522 EN Xuan Phong Huynh Institute of Food and Biotechnology, Can Tho University, Vietnam Ngoc Thanh Nguyen Institute of Food and Biotechnology, Can Tho University, Vietnam 0000-0002-3079-1259 Minh Chau Luu Institute of Food and Biotechnology, Can Tho University, Vietnam 0009-0002-8411-2562 Thi Ngoc Bich Bui Institute of Food and Biotechnology, Can Tho University, Vietnam Hoang Dang Long Bui Institute of Food and Biotechnology, Can Tho University, Vietnam 0000-0003-0926-9033 Bach Long Tran Institute of Food and Biotechnology, Can Tho University, Vietnam Thi Kim Ngan Tran Institute of Applied Technology and Sustainable Development, Nguyen Tat Thanh University, Ho Chi Minh City, Vietnam Nguyen Tat Thanh University Center for Hi-Tech Development, Saigon Hi-Tech Park, Ho Chi Minh City, Vietnam Journal Article 2025 05 26 <strong>Purpose:</strong> King orange (<em>Citrus reticulata</em> × sinensis) is a fruit spices native to tropical and subtropical regions that holds significant economic and nutritional value and is widely consumed in daily life. The primary chemical constituents of king orange include flavonoids (such as hesperidin and naringin), organic acids, vitamin C, and phenolic compounds. Due to its unique biological properties, nutritional benefits, and divers pharmacological effects, king orange is not only a widely consumed fruit but also a promising ingredient for developing natural functional foods, pharmaceuticals, and cosmetics. This study investigated the distribution of bioactive compounds and the antioxidant capacity in different tissues of king orange cultivated in four provinces of the Mekong Delta, Vietnam. <strong>Research Method:</strong> Physical characteristics of the fruit were analyzed, and phytochemical screening was performed identify  secondary metabolites. Flavonoid and phenolic contents were quantified, and antioxidant activity was assessed using the DPPH assay. <strong>Findings:</strong> The fruits had thick, juicy flesh (42.4-51.2% w/w) and thin peel (27.2-35.2% w/w). Alkaloids, flavonoids, phenolics, and saponins were detected in both juice and peel extracts, while terpenoids were found only in the peel. The juice had the highest flavonoid and phenolic content, followed by flavedo and albedo extracts. Antioxidant activity was highest in the juice from "Can Tho" and in the peel extracts from "Vinh Long". <strong>Research limitations:</strong> No limitations were encountered. <strong>Originality/Value:</strong> Orange juice and peel are rich in bioactive compounds with antioxidant properties, highlighting their potential for health-promoting applications. <em>Citrus reticulata</em> is not only a widely consumed  fruit but also a promising raw material for the development  of natural functional food, pharmaceutical, and cosmetic products. https://jhpr.birjand.ac.ir/article_4095_d84556802efc661d20ac23e60a0f8330.pdf