Abstract
Flavonol glycosides are important components of tea leaves, contributing to the bioactivities as well as bitterness and astringency of tea. However, the standards of many flavonol triglycosides are still not available, which restricts both sensory and bioactivity studies on flavonol glycosides. In the present study, we established a simultaneous preparation method of seven flavonol triglycoside individuals from tea leaves, which consisted of two steps: polyamide column enrichment and preparative HPLC isolation. The structures of seven flavonol triglycoside isolates were identified by mass and UV absorption spectra, four of which were further characterized by nuclear magnetic resonance spectra, namely, quercetin-3-O-glucosyl-rhamnosyl-glucoside, quercetin-3-O-rhamnosyl-rhamnosyl-glucoside, kaempferol-3-O-glucosyl-rhamnosyl-glucoside and kaempferol-O-rhamnosyl-rhamnosyl-glucoside. The purities of all isolated flavonol triglycosides were above 95% based on HPLC, and the production yield of total flavonol glycosides from dry tea was 0.487%. Our study provides a preparation method of flavonol triglycosides from tea leaves, with relatively low cost of time and solvent but high production yield.
Highlights
Green tea is a widely consumed beverage over the world, which has unique flavor due to the rich presence of secondary metabolites in tea leaves, for example, catechins, flavonol glycosides, caffeine and amino acids [1,2]
There is increasing interest in the pharmacological functions of flavonol glycosides on account of their higher stabilities under basic condition compared with catechins and multiple bioactive hydroxyl groups
It was reported that flavonoid glycosides inhibited the activity of α-glucosidase and α-amylase [10], and inhibited the proliferation of human oral squamous carcinoma
Summary
Green tea is a widely consumed beverage over the world, which has unique flavor due to the rich presence of secondary metabolites in tea leaves, for example, catechins, flavonol glycosides, caffeine and amino acids [1,2]. Catechin compounds and flavonol glycosides are the major phenolic compounds in tea leaves accounting for 70~80% and ~13% of tea polyphenols, which are associated with many health benefits, such as antioxidant, anti-inflammatory and anti-tumor effects, as well as the bitterness and astringency of tea infusion [3,4,5,6]. Despite the much lower concentration compared with catechins, flavonol glycosides with mellow and astringent taste are considered as essential constituents to the bitterness and astringency of tea infusion, due to its extremely low threshold and enhancing effect on the bitterness of caffeine [7,8]. The threshold of flavonol glycosides ranged from 0.001 μmol/L to 19.80 μmol/L, which were much lower than 190–930 μmol/L of catechins and 13–26 μmol/L of theaflavins [9]. It was reported that flavonoid glycosides inhibited the activity of α-glucosidase and α-amylase [10], and inhibited the proliferation of human oral squamous carcinoma
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