Quantification of quality parameters for reliable evaluation of green rooibos (Aspalathus linearis)

An LC-MS/UV-Vis method was developed for the reliable identification of the most relevant flavonoids occurring in rooibos. The amounts of the dihydrochalcones aspalathin, (2',3,4,4',6'-pentahydroxy-3-C-beta-D glucopyranosyldihydrochalcone), nothofagin (2',3,4',6'-tetrahydroxy-3-C-beta-D-glucopyranosyldihydrochalcone) and other flavonoids were determined in unfermented and fermented samples, collected at different locations in South Africa. Generally, a substantial loss of both dihydrochalcones was observed after the fermentation process. An NIR spectroscopic method was developed to discriminate between unfermented and fermented rooibos and to predict the aspalathin content in unfermented rooibos. The total antioxidative activity, determined according to the ABTS(+) scavenging method, was found to correlate very good with the aspalathin content in the unfermented plant material (R-2=0.812).