Major production areas of rooibos (Aspalathus linearis) deliver herbal tea of similar phenolic and phenylpropenoic acid glucoside content

Abstract

A large sample set (n=209) of fermented, unpasteurised rooibos, spanning the production years 2011–2013, was collected from the two major production areas (Western Cape and Northern Cape, South Africa). Hot water infusions, as prepared for grading, were analysed to quantify the content of ten flavonoid glycosides, the enolic phenylpropenoic acid glucoside, phenylpyruvic acid-2-O-glucoside (PPAG) and the phenolic acid, ferulic acid (FA), using a previously validated reversed phase high performance liquid chromatography with diode array detection (RP-HPLC-DAD) method. Principal component analysis showed no clear grouping of samples according to production area and/or production year, based on the content of individual compounds or sub-classes, i.e. dihydrochalcone, flavonol, flavone and PPAG+FA. Discriminant analysis indicated grouping according to year, but not according to production area. ANOVA showed significant production area×year interactions (P<0.05) for the flavonol and PPAG+FA sub-classes. The dihydrochalcone sub-class was only significantly (P<0.05) affected by production area with samples from the Western Cape having significantly higher aspalathin and nothofagin contents than those from the Northern Cape. The flavone sub-class was not affected by production area or year. The major flavones, orientin and isoorientin, were the predominant constituents of the rooibos tea infusions, followed by quercetin-3-O-robinobioside, PPAG and aspalathin. These compounds were present at levels >9mg/L, while the other compounds were present at <5mg/L.