Unfermented Rooibos Tea:  Quantitative Characterization of Flavonoids by HPLC−UV and Determination of the Total Antioxidant Activity

Abstract

Unfermented rooibos originates from the leaves and the stems of the indigenous South African plant, Aspalathus linearis, and it has been reported to have a higher content of flavonoids compared to that of fermented rooibos. The HPLC/UV method developed in our laboratory for the analysis of the fermented rooibos was applied to the quantitative characterization of the major flavonoids present in the unfermented rooibos. Main compounds determined were aspalathin (49.92 +/- 0.80 mg/g), isoorientin (3.57 +/- 0.18 mg/g), orientin (2.336 +/- 0. 049 mg/g), and rutin (1.69 +/- 0.14 mg/g), followed in order by isovitexin, vitexin, isoquercitrin and hyperoside, quercetin, luteolin and chrysoeryol. The identity of detected flavonoids was confirmed by comparing their retention times and UV spectra with those of corresponding standards. The total antioxidant activity (TAA) of the tea infusions was measured by the ABTS*+ radical cation decolorization assay. The TAA of unfermented rooibos (0.8 Trolox meq/g) resulted 2-fold higher than that of the fermented rooibos. When compared with different water infusions of Camellia sinensis (green and black tea), this TAA value was about 50% lower.

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>

“…Further, in a comparison of IC 50 values between GRE and Asp, the values for the three enzymes were lower in GRE than in Asp alone, when controlling for the Asp content ( Table 1). As previously reported, green rooibos is known to include various flavonoids other than Asp, such as orientin, isoorientin, rutin, vitexin, isovitexin, quercetin, isoquercitrin, hyperoside, luteolin and chrysoeryol (Bramati et al, 2003). Particularly, it has been shown that quercetin, isoquercetin, and rutin have inhibitory effects on α-amylase (Li et al, 2009), maltase, and sucrase (Kim et al, 2011).…”

“…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.…”

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

“…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.…”

Effect of rutin from tartary buckwheat sprout on serum glucose-lowering in animal model of type 2 diabetes

“…Phenolic compounds in the ethanol extracts of CBS and TBS were analyzed by reverse phase-HPLC as described previously (9). The chromatograms of CBS and TBS extracts are shown in Fig.…”