Quantitative Characterization of Flavonoid Compounds in Rooibos Tea (Aspalathus linearis) by LC−UV/DAD

Abstract

Rooibos tea originates from the leaves and stems of the indigenous South African plant Aspalathus linearis. It has gained much attention for clinical purposes in the case of nervous tension, allergies (dermatitis), and various indigestive problems. Recently, antioxidative activity was also attributed to the tea on the basis of its flavonoid content. Therefore, an HPLC method using a C(18) reversed phase column was developed for the assay of 10 flavonoids in aqueous and methanolic infusions. Main compounds determined were the dihydrochalcone aspalthin, rutin, and orientin, and their content was in the range of 1.0 to 1.3 mg/g. The identity of detected flavonoids was confirmed by comparing their retention times and UV and MS spectra with those of corresponding standards. In addition, the MS analysis showed evidence of the presence of other compounds such as nothofagin, dihydroisoorientin, and dihydroorientin.

The Occurrence, Fate and Biological Activities ofC-glycosyl Flavonoids in the Human Diet

“…These isomeric compounds are reported to be interconvertable via a Wessely-Moser rearrangement of the flavone structure under heating in an aqueous solution: conditions similar to those that occur during tisane extraction (Koeppen and Roux, 1965). They are extractable in hot aqueous media from commercial fermented rooibos tea at 1.00 and 0.83 g kg -1 respectively; comparable to the aspalathin extracted in the same manner (1.23 g kg -1 ) (Bramati et al, 2002). The flavones vitexin and isovitexin are also present in rooibos tea, however are significantly less abundant than the aforementioned compounds (0.33 and 0.27 g kg -1 respectively).…”

“…These unusual compounds have received a significant deal of attention, not least because of their abundance in this tisane and the importance of this principal South African export to its home economy. Indeed, the routine quantification of both aspalathin (2 ,3,4,4 ,6 -pentahydroxy-3-C--Dglucopyranosyldihydrochalcone) and the 2 ,4,4 ,6 tetrahydroxylated analogue, nothofagin, has become an accepted measure of rooibos quality, with several publications detailing methodologies for analysis and abundance in material from various processing yards and following several processing protocols (Bramati et al, 2003;Bramati et al, 2002;Joubert, 1996;Joubert and deVilliers, 1997;Joubert et al, 2008;Manley et al, 2006;Pengilly et al, 2008;Rabe et al, 1994;Schulz et al, 2003;Standley et al, 2001;vonGadow et al, 1997). The predominant factor determining the concentration of these two C-glycosyl dihydrochalcones in rooibos tea is the 'fermentation' process.…”

“…The C-glycosidic bond between a saccharide moiety and flavonoid carbon skeleton largely protects the flavonoid glycoside from the hydrolytic effect of both acidic and enzymic treatments known to readily cleave O-glycosidic linkages, leading to fundamental differences in the analysis, degradation, pharmacokinetics and bioactivity of those flavonoids possessing a C-glycosyl group (Harborne, 1965). Whilst C-glycosylation of flavonoid compounds in planta is not widespread, especially in those plants traditionally used as food crops, plants capable of C-glycosylation may produce C-glycosyl flavonoids in greater amounts than O-glycosyl flavonoids by weight, such as in the examples of the Cglycosyl flavones in wheat (Triticum aestivum) and C-glycosyl dihydrochalcones in rooibos tea leaves and stems (Aspalathus linearis) (Bramati et al, 2002;Brazier-Hicks et al, 2009). …”

Green Rooibos Extract from <i>Aspalathus linearis</i>, and its Component, Aspalathin, Suppress Elevation of Blood Glucose Levels in Mice and Inhibit α-amylase and α-glucosidase Activities <i>in vitro</i>

“…In particular, aspalathin (Asp), a major flavonoid in rooibos, is present at twice the level in unfermented compared to fermented tea (Bramati et al, 2002, Bramati et al, 2003. Asp is a dihydrochalcone-C-glucoside and has been reported to ameliorate hyperglycemia (Kawano et al, 2009, Muller et al, 2012, Son et al, 2013.…”

Hepatic, renal and endogenous antioxidant status modulatory effects of chronic co-supplementation of rooibos (<i>Aspalathus linearis</i>) and red palm oil (<i>Elaeis guineensis</i>) in male Wistar rats

“…It is naturally caffeine-free and has low tannin content when compared to Camellia sinensis teas, but high in unique antioxidant polyphenols (Joubert et al, 2008). Rooibos has a flavonoid profile that is distinctly different from those found in Camellia sinensis, including the β-dihydroxy-dihydrochalcone glucoside aspalathin, and its cyclic counterpart aspalalinin, both of which are unique to rooibos (Rabe et al, 1994;Shimamura et al, 2006), the dihydrochalcone nothofagin, as well as flavonols including orietin, iso-orientin, vitexin, isovitexin, luteolin, quercetin and chrysoeriol among others (Rabe et al, 1994;Bramati et al, 2002;Joubert et al, 2008). Studies has shown that rooibos exert hepatoprotective effect in acute and chronic liver damage in rats (Ulicna et al, 2003;, and modulate oxidative stress by preventing lipid peroxidation and improving glutathione redox status in rat tissues and in humans (Nikolova et Red palm oil (RPO) is the edible oil obtained from crude palm oil extracted from the oil palm plant, (Elaeis guineesis), after a modified refining process, involving degumming and bleaching, followed by de-acidification and deodorisation by molecular distillation (Nagendran et al,200).…”