Determination and investigation of phenolic compounds in Citrus pulps and zests by Ultra-high performance liquid chromatography

This study aimed to evaluate in vitro the influence of extraction methods (maceration and soxhlet) and solvents (hexane, dichloromethane, ethyl acetate and methanol) on the phenolic composition and antioxidant activity of tree citrus species: C. limon, C. limetta and C. aurantifolia. The results showed that the soxhlet remains the best extraction method for quantifying polyphenols, flavonoids and condensed tannins. Polar solvents (ethyl acetate and methanol) make it possible to obtain the best extraction yields and high polyphenols and flavonoids. Citrus aurantifolia shows the highest contents for epicarps and pulps, respectively in polyphenols (326.73mg and 443.57mg EAG g-1 of FW) and in flavonoids (133.00 mg and 138.62 mg EQ g-1 of FW). The evaluation of the antioxidant activity using the 2.2-diphenyl-1-picrylhydrazyl (DPPH) for the different extracts showed that methanol and ethyl acetate extracts by soxhlet possess the best antioxidant activities. A strong antiradical power was noted for the epicarps and the pulps of C. aurantifolia fruit, respectively of 5.13 and 4.89 µg/ml. 15 phenolic compounds were tentatively identified by ultra-high-performance-liquid-chromatographic-diode array (UHPLC-DAD) in the polar Citrus pulp and epicarp extracts. In fact, the identification of three flavonols (rutin, kaempherol and quercetin), two flavanones (hesperidin and naringin), a flavone (3',4',5,7-tetrahydroxyflavone) and a phenolic acid (pyrogallic acid) were the major compounds identified in polar citrus pulp and epicarp extracts.