Determination of naringin and hesperidin in citrus fruit by high-performance liquid chromatography. The antioxidant potential of citrus fruit

Naringin and hesperidin in dimethyl sulfoxide extracts of citrus fruit (oranges, red and blond grapefruit, and sweeties - a hybrid of pummelo and blond grapefruit) have been analyzed by high-performance liquid chromatography with a mobile phase prepared from 2% aqueous acetic acid and acetonitrile. The detection wavelength was at 285 nm. Antioxidant assays based on hydrogen atom-transfer reactions (oxygen radical absorbance capacity, ORAC) and on electron transfer (total phenols by use of Folin-Ciocalteu reagent, FCR; trolox-equivalent antioxidant capacity, TEAC; ferric ion-reducing antioxidant power, FRAP; and reaction with 1,1′-diphenyl-2-picrylhydrazyl, DPPH) were used to compare the antioxidant potential of citrus fruit and their main flavonoids. The three antioxidant assays (FRAP, TEAC, and DPPH) were performed with prolonged duration of the assay time, because all fruit extracts require long reaction times to approach the end point in the scavenging reaction. Lipophilic and hydrophilic fractions from citrus fruit were investigated by the ORAC reaction. Relationships between the main flavonoids, total polyphenols, and antioxidant potential obtained by use of the FRAP, TEAC, and DPPH procedures showed that correlation coefficients are higher for polyphenols than for the main flavonoids (as markers of 100% citrus juices). HPLC is a precise method for obtaining reliable data on the bioactivity of citrus fruit grown under the same geographical and climatic conditions. The bioactivity of citrus fruit studied by use of five different antioxidant assays was in the order sweetie > red grapefruit > blond grapefruit = orange. Hesperidin and naringin are only partially responsible for the overall antioxidant activity of citrus fruit.