Microwave-assisted extraction and liquid chromatography/mass spectrometry analysis of flavonoids from grapefruit peel

The flavonoids of grapefruit peel were obtained by microwave-assisted extraction. Five constituents have been identified by liquid chromatography/mass spectrometry analysis such as hesperitin-7-O-glucoside, isonaringin, naringin, 2′,5′-dihydroxy-3,4′,5,6,7-pentamethoxyflavone and neoeriocitrin. The last two compounds are reported first in grapefruit peel. The effects of solvent, time, ratio of solvent to material (liquid/solid) and output power on the extraction were investigated. The results show that the better extraction conditions are: 80% (v/v) ethanol as extraction solvent; 3 min of extraction time, 25:1 (mL/g) as the ratio of liquid to solid; and 560 W of microwave output power. Microwave-assisted extraction is more efficient for getting flavonoids from grapefruit peel than reflux and ultrasonic extraction methods. The yield of optimized microwave-assisted extraction reached 5.81%. PRACTICAL APPLICATIONS: Grapefruit is one of the delicious fruits with abundant nutrition, such as vitamin C, carbohydrate and a small quantity of some special compounds. It may have some beneficial effects on human health, with anti-oxidant, anti-inflammatory and anti-cancer properties, or may act as agents of other mechanisms contributing to cardio-protective action. The main use of grapefruit in food industries is to make fresh juice or citrus-based drinks. The peels are often used to feed animals or are thrown away directly. Very large amounts of wastes are formed every year, because almost half of the grapefruit is composed of peels. It is reported that grapefruit peels contain a high concentrationof phenolic compounds. It is significant to find a feasible way to obtain these useful compounds from peel wastes to increase their value. In our work, microwave-assisted extraction of flavonoids from grapefruit peel is established and discussed. The extraction yield is higher than that of using traditional extraction methods. So, the results of this paper are very helpful in utilizing and making great use of natural resources.