Flavonoid determination in onion, chili and leek by hard cap espresso extraction and liquid chromatography with diode array detection

A low cost extraction procedure, based on the use of a hard cap espresso machine, has been developed for the extraction of myricetin, quercetin, luteolin and kaempferol from vegetables by using 50 mL of ethanol in water (80% v/v) in <30 s. Direct determination of extracts were carried out by liquid chromatography with diode array detection (LC-DAD), offering limit of detection values from 3 to 8 μg g−1. Intra and inter-day precision ranged from 8 to 16%, and from 10 to 23%, respectively. Quantitative recoveries were assessed from leek and Habanero, Thai, and red chili samples spiked at different flavonoid concentrations with values ranging from 100 to 110%, from 80 to 108%, from 74 to 88%, and from 70 to 115%, respectively. Efficiency of the proposed extraction procedure was compared with ultrasound-assisted extraction and free quercetin was determined directly in onion samples and after a hydrolysis of extracts and/or fungal fermentation.