(S)- and (R)-Eriodictyol-6-C-ß-D-glucopyranoside, novel keys to the fermentation of rooibos (Aspalathus linearis)

Phytoestrogens from Aspalathus linearis

“…Table 3 shows that compound 24 has high activity approximately equal to that of genistein. Although both dihydrochalcones, 24 (nothofagin) and 23 (aspalathin), are the major constituents of Aspalathus linearis, 14,25) the estrogenic activity of 23 was less than half that of 24. This indicates that the hydroxyl group at C-3Ј reduces its estrogenic activity.…”

Commercially Important Medicinal Plants of South Africa: A Review

“…Very little information is available on the structure of the tannins from rooibos tea, but the dimer, procyanidin B3, the trimer, bis�setinidol bis�setinidol-(4 ,6:4 ,8)-catechin, and a pentamer have been identi�ed [57]. Other major phenolic compounds present in rooibos include �avones (orientin, isoorientin, vitexin, isovitexin, luteolin, and chrysoeriol), �avanones (dihydro-orientin, dihydro-isoorientin, and hemiphlorin), and �avonols (quercetin, hyperoside, isoquercitrin, and rutin) [52,[57][58][59][60]. Phenolic acids, lignans, �avone diglycosides, (�)-catechin, a phenylpyruvic acid glycoside, the �avonol quercetin-3-O-robinobioside, and the coumarins, esculetin and esculin have also been identi�ed [52,[61][62][63][64].…”

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

“…This comprises a heating and / or sun-drying step (usually between 35 -45°C) that catalyses the oxidation of phenolic compounds in the dried leaf and stem material (Joubert, 1996). This process is responsible for the distinct red-colour of both the tea material and resulting aqueous extract, and is best understood in the case of oxidative ring-cyclisation of aspalathin in the presence of heat or UV radiation and oxygen, a reaction that forms two additional closed-ring Cglycosylated eriodictyol products that, whilst not native to the rooibos plant, can be considered to be part of the fermented rooibos tisane (Marais et al, 2000). A-ring cyclisation prior to closure and formation of a third C-ring dictates the formation of two isomeric C-glycosylated forms, eriodictyol-6-C--D-glucoside and eriodictyol-8-C--D-glucoside, from the 8 C-glycosylated precursor aspalathin.…”

“…This is an important factor in considering the dietary burden of the rooibos C-glycosyl dihydrochalcones, as both unfermented ('green') and fermented (often known as 'redbush') rooibos tea is consumed. Rooibos also contains the flavones orientin and isoorientin, both native to the plant and derived from the pathway of aspalathin oxidation during fermentation via the two aforementioned eriodictyol-C-glucoside isomers (Marais et al, 2000;Rabe et al, 1994). 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).…”