Phenolic variation in wild populations of Aspalathus linearis (rooibos tea)

Rooibos tea, a herbal tea derived from Aspalathus linearis(Fabaceae-tribe Crotalarieae) has become increasingly popular as a health drink. The beneficial properties are partly ascribed to the phenolic constituents in the plant, which are enzymatically modified during processing. Within the species, distinct geographical forms can be recognised, differing in habit, fire-survival strategy, vegetative and reproductive morphology, enzyme patterns and flavonoids. Several phenolic compounds are known to occur in A. linearis. The main constituent of the commercial tea type (also known as the Rocklands type or the red tea type) is the dihydrochalcone aspalathin, but the presence of other flavonoids such as nothofagin, orientin, isoorientin, vitexin, rutin and isoquercetrin has been reported. These compounds are found in the processed product, as well as the dried leaves. The relative quantities of phenolic compounds show large qualitative and quantitative differences between populations and provenances of the wild tea types. Within populations, however, the patterns are remarkably uniform. Aspalathin was found to be the main compound in processed ("fermented") tea and also in dried leaves of several tea types. The compound is absent in some wild tea populations, where other flavonoids occur as the main phenolics, notably orientin, isoorientin and rutin. Rutin is invariably the main compound in Aspalathus pendula, a close relative of A. linearis that is rarely used to make tea. An overview of natural variation in phenolic compounds of the main wild tea types is presented. (C) 2003 Elsevier Science Ltd. All rights reserved.