Characterization of Flavonol Conjugates in Immature Leaves of Pak Choi [Brassica rapa L. Ssp. chinensis L. (Hanelt.)] by HPLC-DAD and LC-MS/MS

Abstract

The flavonoid composition of immature leaves of pak choi [Brassica rapa L. ssp. chinensis L. (Hanelt.)] was investigated. Flavonol aglycone content was measured in 11 pak choi varieties, indicating significant differences (P < 0.05) in content between varieties and relatively high contents of kaempferol and isorhamnetin. Levels of quercetin ranged from 3.2 to 6.1 mg/100 g of dry weight (DW), whereas levels of isorhamnetin and kaempferol were significantly higher (8.1-35.1 and 36.0-102.6 mg/100 g of DW, respectively). A large number of glycoside and hydroxycinnamic acid derivatives of quercetin, kaempferol, and isorhamnetin were identified in cv. 'Shanghai' by LC/UV-DAD/ESI-MS/MS. The UV-DAD data allowed identification of hydroxycinnamic acid derivatives, but detailed MS/MS fragmentations were required for the structure elucidation. Pak choi could be a potentially important source of dietary flavonols, in particular, kaempferol and isorhamnetin.

Application of ultra performance liquid chromatography-photodiode detector-quadrupole/time of flight-mass spectrometry (UPLC-PDA-Q/TOF-MS) method for the characterization of phenolic compounds of Lepidium sativum L. sprouts

“…Next, dihexoside moiety (2 9 162 amu = 324 amu) is lost which gives rise to a deprotonated kaempferol ion (m/z 285.0403) as a base peak. This kind of fragmentation indicates the occurrence of glycosylation in accordance with literature data which show that in Brassica species, only sugar moieties such as glucose and rhamnose are predominantly bound in positions -7 [19,32,33,35,36]. In the disaccharide moieties present in analyzed compounds [2,3,5, and 6 (Table 1)] after fragmentation, the loss of 324 amu and low abundance of 162 amu selon occur, which, according to Ferreres et al [31], corresponds to a diglucoside with a 1-6 linkage, that is, gentiobioside.…”

“…Liang et al [25] identified five malate derivatives in turnip leaves (Brassica rapa) by NMR spectroscopy with the assistance of HPLC-MS, including hydroxyferuloylmalate as a new compound. Rochfort et al [19] also detected two major compounds in pak choi with the molecular masses of [M -H] -at m/z 309 and 339 but were unable to identify them.…”

“…These compounds were described in leaves of pack choi [B. rapa L. ssp. chinensis L. (Hanelt)] [19], B. rapa L. ssp. sylvestris L., flower of B. rapa [32], and leaves, stems, and flower buds of B. rapa var.…”

“…Rochfort et al [19] determined the total contents of aglycones kaempferol, isorhamnetin, and quercetin to range between 0.7 and 1.2 mg/g of dm in B. rapa L. ssp. chinensis L. These results were obtained for aglycones after hydrolysis reactions.…”

“…Derivatives of flavonols, kaempferol and quercetin, are the main flavonoids reported in Brassica vegetables [16][17][18][19]. It is not known how flavonol composition and conditions of seed sprouting influence phenolic compounds in L. sativum.…”