Composition and Content of Flavonol Glycosides in Green Beans and Their Fate during Processing

Abstract

Four varieties of green bean (Phaseolus vulgaris) were analyzed for flavonol composition and content. Two flavonol conjugates, not previously reported in green bean, were found in three of the varieties. These are quercetin 3-O-(2G-β-d-xylopyranosylrutinoside) (1), (1.0−2.0 μg/g of fresh weight) and the corresponding kaempferol analogue (2) (0.3−0.7 μg/g). The major flavonol component in all of the varieties was quercetin 3-O-glucuronopyranoside (3) (3.5−15.1 μg/g) with lesser amounts of quercetin 3-O-rutinoside (4) (0.2−4.3 μg/g) and kaempferol 3-O-glucuronopyranoside (5) (0.5−1.3 μg/g). Kaempferol rutinoside (6) was detected in only one variety (0.8 μg/g). Commercial processing, such as canning, did not result in chemical breakdown of the conjugates, although between 8.8 and 24.4%, depending on the conjugate, was leached into the cooking water. Keywords: Phaseolus; green bean; HPLC; flavonol; glycoside