OPTIMIZATION OF A QUANTITATIVE HPLC DETERMINATION OF POTENTIALLY ANTICARCINOGENIC FLAVONOIDS IN VEGETABLES AND FRUITS

A rapid method based on RP-HPLC with UV detection is presented for the quantitative determination of five major flavonoid aglycons, viz. quercetin, kaempferol, myricetin, luteolin, and apigenin, in freeze-dried vegetables and fruits, after acid hydrolysis of the parent glycosides. Completeness of hydrolysis and extraction have been optimized by testing systematically different conditions such as acid concentration, reaction period, and methanol concentration in the extraction solution using samples containing various types of flavonoid glycosides. Optimum hydrolysis conditions are presented for flavonol glucuronides, flavonol glucosides, and flavone glycosides. Identity of the flavonoids was confirmed with diode array. Repeatability of the method was good, with coefficients of variation of 2.5-3.1 % for quercetin, 4.6-5.6 % for kaempferol, 4.6 % for myricetin, 3.3 % for luteolin, and 2.8 % for apigenin. CV of the within-laboratory reproducibility was less than 2 times the CV of repeatability. Recoveries of the flavonols quercetin, kaempferol, and myricetin ranged from 77 to 110 %, and recoveries of the flavones apigenin and luteolin ranged from 99 to 106 %. The method presented allows a fast, quantitative, and reproducible determination of five flavonoids in freeze-dried foods.