Application of direct injection-ion mobility spectrometry-mass spectrometry (DI-IMS-MS) for the analysis of phenolics in honeybush and rooibos tea samples

Abstract

Consumer awareness of the health benefits of herbal teas such as rooibos and honeybush has led to an increase in production demand and to inevitable accidental or deliberate adulteration. In this study, direct injection-ion mobility spectrometry-mass spectrometry (DI-IMS-MS) is proposed as a rapid methodology for the differentiation of rooibos and honeybush blends (adulterations). Analytical data was obtained from 100 rooibos, 130 honeybush and 7 blend samples. Principal component analysis (PCA) showed differences between samples of rooibos and honeybush blends, and further showed the diagnostic value of marker compounds in distinguishing Cyclopia intermedia, C. genistoides and C. subternata, mainly used for honeybush production. Markers such as eriodictyol-C-hexose isomers, orientin, aspalathin, and vitexin were characteristic of blends containing more than 80 % rooibos plant material, and quinic acid, iriflophenone-3-C-glucoside-4-O-glucoside, C-glycosylxanthones isomers (mangiferin and isomangiferin), and eriodictyol were characteristic of blends containing more than 80 % C. intermedia plant material. Furthermore, the C-glycosylxanthones isomers (mangiferin and isomangiferin) were prominent in C. genistoides, quinic acid was prominent in C. subternata and piscidic acid was prominent in C. intermedia plant material. Phenolic compounds in the herbal teas were further characterised based on an array of complementary descriptors (e.g., retention time, arrival times, accurate mass information, tandem MS fragmentation data, and TWCCSN2) to strengthen compound identification.