Chemical characterisation of the aroma of honeybush (Cyclopia) species

[摘要] ENGLISH ABSTRACT:Honeybush tea, also known as 'South Africa's sweetest tea, is a herbal tea made from theleaves and twigs of Cyclopia spp., indigenous to the fynbos biome in the Western and Eastern Capeprovinces of South Africa. The pleasant sweet aroma and taste of fermented honeybush, its lowtannin content and the absence of caffeine have led to widespread interest in the commercialcultivation and processing of honeybush tea since the mid-1990s. Although more than 20 species ofhoneybush grow in the wild, only a few species are commercially exploited for the manufacture oftea. Currently the more prominent species are C. intermedia, C. subternata, C. genistoides, and C.sessiliflora. The present research contributes to a comprehensive honeybush research programmebeing conducted at the Agricultural Research Council (ARC) Infruitec-Nietvoorbij in South Africa.The first phase of the present study, using C. genistoides as representative species, was aimedat developing the necessary methodology for the analysis of extremely low concentrations ofhoneybush volatiles. A high-capacity headspace sample enrichment probe was applied successfullyin conjunction with gas chromatography-mass spectrometry (GC-MS) to analyse the volatile organiccompounds present in dry or infused unfermented and fermented honeybush.A total number of 255 volatile compounds were identified in unfermented and fermentedhoneybush, the majority of which are terpenoids (138; 54%) comprising mostly terpenes, terpeneketones, terpene alcohols and terpene ethers. Of the other compound classes, the aldehydes are thelargest group, followed by esters, hydrocarbons and ketones. The stereochemistry of the identifiedcompounds was determined whenever possible. This is the most comprehensive chemicalcharacterisation of the volatile compounds in a South African herbal plant reported to date.A comparative study of green and fermented honeybush showed that the same compoundsare, to a large extent, present in both, albeit in different relative concentrations.Not all of the identified honeybush volatiles are necessarily odour-active compoundscontributing to the overall typical honeybush aroma. An important aspect of this research was thusthe identification of the 46 odour-active compounds in fermented honeybush by means of gaschromatography-olfactometry (GC-O), using detection frequency and aroma extract dilution analysismethods. Fifteen of these compounds, mainly terpenoids, were singled out as the most intenseindividual contributors to the honeybush aroma based on consideration of all the relevant GC-O data.The odours of certain compounds, i.e. (6E,8Z)-megastigma-4,6,8-trien-3-one, (6E,8E)-megastigma-4,6,8-trien-3-one, (7E)-megastigma-5,7,9-trien-4-one, 10-epi- -eudesmol, epi- -muurolol and epi- -cadinol, were perceived by GC-O assessors as typically honeybush-like.The quantitative GC-MS data of seven different Cyclopia samples (including four differentspecies and variants thereof) were compared with respect to all the volatile components andparticularly with respect to the odour-active compounds. Interesting variations were found in theconcentrations of certain odour-active compounds in the various samples.The quantitative data obtained for the odour-active honeybush volatiles and data obtained fromthe sensory analysis of eight Cyclopia samples (including four different species and variants thereof) were subjected to statistical analysis and interesting associations between compounds with certainsensory aroma attributes were established.The present study has made a major contribution to the scientific knowledge regarding one ofSouth Africa's most popular indigenous herbal teas.

[发布机构] Stellenbosch University