ABSTRACT
The volatile composition of honeybush (Cyclopia) species was studied by comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOF-MS). Headspace-solid phase micro-extraction (HS-SPME) was used to extract the volatile compounds from tea infusions prepared from the three species C. genistoides, C. maculata and C. subternata. A total of 287 compounds were identified, 101 of which were confirmed using reference standards, while the remainder were tentatively identified using mass spectral and retention index (RI) data. The identification power of TOF-MS enabled the tentative identification of 147 compounds for the first time in honeybush tea. The majority of the compounds identified were common to all three Cyclopia species, although there were differences in their relative abundances, and some compounds were unique to each of the species. In C. genistoides, C. maculata and C. subternata 265, 257 and 238 compounds were identified, respectively. Noteworthy was the tentative identification of cinnamaldehyde in particular C. maculata samples, which points to the likely contribution of this compound to their distinct sensory profiles. This study emphasises the complexity of honeybush tea volatile composition and confirms the power of GC×GC combined with TOF-MS for the analysis of such complex samples.
Subject(s)
Food Analysis/methods , Gas Chromatography-Mass Spectrometry , Holoprosencephaly/complications , Tea/chemistry , Volatile Organic Compounds/chemistry , Solid Phase MicroextractionABSTRACT
The applicability of comprehensive two-dimensional gas chromatography (GC×GC) using a single-stage thermal modulator was explored for the analysis of honeybush tea (Cyclopia spp.) volatile compounds. Headspace solid phase micro-extraction (HS-SPME) was used in combination with GC×GC separation on a non-polar × polar column set with flame ionisation (FID) detection for the analysis of fermented Cyclopia maculata, Cyclopia subternata and Cyclopia genistoides tea infusions of a single harvest season. Method optimisation entailed evaluation of the effects of several experimental parameters on the performance of the modulator, the choice of columns in both dimensions, as well as the HS-SPME extraction fibre. Eighty-four volatile compounds were identified by co-injection of reference standards. Principal component analysis (PCA) showed clear differentiation between the species based on their volatile profiles. Due to the highly reproducible separations obtained using the single-stage thermal modulator, multivariate data analysis was simplified. The results demonstrate both the complexity of honeybush volatile profiles and the potential of GC×GC separation in combination with suitable data analysis techniques for the investigation of the relationship between sensory properties and volatile composition of these products. The developed method therefore offers a fast and inexpensive methodology for the profiling of honeybush tea volatiles. Graphical abstract Surface plot obtained for the GC×GC-FID analysis of honeybush tea volatiles.
Subject(s)
Fabaceae/chemistry , Gas Chromatography-Mass Spectrometry/methods , Teas, Herbal/analysis , Volatile Organic Compounds/analysis , Gas Chromatography-Mass Spectrometry/instrumentation , Multivariate Analysis , Principal Component Analysis , Solid Phase Microextraction/methods , TemperatureABSTRACT
Rooibos and honeybush are popular herbal teas produced from the shrubs of Aspalathus linearis and Cyclopia spp., respectively, which are indigenous to South Africa. Both herbal teas are rich in polyphenols and their consumption is associated with several health benefits, partly ascribed to their phenolic constituents. Quantification of phenolics in extracts and teas for quality control and research purposes is generally performed using HPLC, although dedicated and often species-specific methods are required. CE offers an attractive alternative to HPLC for the analysis of phenolics, with potential benefits in terms of efficiency, speed and operating costs. In this contribution, we report quantitative CZE methods for the analysis of the principal honeybush and rooibos phenolics. Optimal separation for honeybush and rooibos phenolics was achieved in 21 and 32 min, respectively, with good linearity and repeatability. Quantitative data for extracts of "unfermented" and "fermented" rooibos and two honeybush species were statistically comparable with those obtained by HPLC for the majority of compounds. The developed methods demonstrated their utility for the comparison of phenolic contents between different species and as a function of manufacturing processes, thus offering cost effective, although less sensitive and robust, alternatives to HPLC analysis.
Subject(s)
Aspalathus/chemistry , Electrophoresis, Capillary/methods , Fabaceae/chemistry , Phenols/analysis , Teas, Herbal/analysis , Chromatography, High Pressure Liquid/methods , Fermentation , Food Quality , Humans , Plant Extracts/analysis , South AfricaABSTRACT
Anthocyanins are naturally occurring plant pigments whose accurate analysis is hampered by their complexity and unique chromatographic behaviour associated with on-column conversion reactions. This paper reports the evaluation of off-line comprehensive two-dimensional liquid chromatography (LC×LC) for the analysis of anthocyanins. Hydrophilic interaction chromatography (HILIC) was used in the first dimension in combination with reversed phase liquid chromatography (RP-LC) in the second dimension. For the selective detection of anthocyanins, diode array detection was used, while high resolution quadrupole-time-of-flight mass spectrometry (Q-TOF) was used for compound identification. As application, the HILIC×RP-LC separation of diverse anthocyanins in blueberries, red radish, black beans, red grape skins and red cabbage is demonstrated. Off-line HILIC×RP-LC revealed information which could not be obtained by one-dimensional HPLC methods, while the structured elution order for the anthocyanins simplifies compound identification and facilitates the comparison of anthocyanin content of natural products by means of contour plots.