Chemiese karakterisering van die aroma van die heuningbosspesie Cyclopia Genistoides
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006.
Honeybush (Cyclopia spp.) is indigenous to South Africa and consists of more than 20 species of which only a few are used to make a herbal tea with a unique aroma and sweet taste. The aroma of unfermented and fermented honeybush tea differs considerably, indicating that changes take place in the chemical composition of the aroma during the fermentation process. Using a sample enrichment probe (SEP) and gas chromatography-mass spectrometry (GC-MS), the chemical composition of the aroma of unfermented and fermented C. genistoides, was analyzed and the resulting aroma profiles were compared. A total of 74 compounds were identified in the unfermented honeybush aroma, comprising, inter alia, a large number of saturated and unsaturated alcohols, aldehydes and methyl ketones that were found to be either absent, or present in lower relative concentrations, in the aroma of fermented honeybush. Most of these compounds, including 6-methyl-5-hepten-2-one, identified as one of the major constituents of unfermented honeybush, are probably responsible for its grassy, hay-like aroma. In the aroma of fermented honeybush 70 compounds were identified, of which 36 were found to be terpenoids. These compounds are probably responsible for the pleasant sweet aroma of the fermented honeybush. For instance, the major aroma constituent in the fermented honeybush, α-terpineol, is known to have a delicately floral and sweet odour. Other terpenoids occuring in significant quantities in the fermented honeybush, are linalool, cis and trans linalool oxide, nerol, geraniol, 2,6-dimethyl-1,7-octadien-3,6-diol, hexahydrofarnecyl acetone and phytol. These terpenoids are known to have sweet, sweet-woody en floral odours that probably contribute to the overall sweet aroma of the fermented honeybush. In the aroma of the unfermented honeybush a total of 25 terpenoids was identified, of which geranyl acetone, β-ionone, and dihydroactinidiolide are the most significant, since they are present in higher relative concentrations compared to the same terpenoids in the fermented honeybush. These three terpenoids have overall woody and even slightly green odours which contribute to the typical aroma of the unfermented honeybush. The terpenoids present in the aroma of unfermented and fermented honeybush belong to the following compound classes: • Terpenes • Terpene alcohols • Terpene aldehydes • Ketoterpenes • Terpene ethers • Terpene lactones Apart from the terpenoids present in the aroma of unfermented and fermented honeybush, the following classes of compounds are also present: • Aliphatic hydrocarbons (saturated) • Aliphatic alcohols (saturated and unsaturated) • Phenols • Aliphatic aldehydes (saturated and unsaturated) • Aliphatic ketones (saturated and unsaturated) • Aliphatic carboxylic acids (saturated) • Esters (methyl esters, ethyl and higher esters and aromatic esters) • Furane compounds • Lactones The present research was done to compare the chemical composition of the aroma of unfermented and fermented honeybush of one particular species, namely C. genistoides, to obtain an understanding of the evolution and/or disappearance of volatile compounds during fermentation that ultimately could help to identify compounds or compound types and their precursors responsible for its unique sweet aroma.