PURSE 2013

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Browsing PURSE 2013 by Author "Abeysinghe, I. S. B."

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    Metabolomics of Sri Lanka tea germplasm : a quantitative analysis of catechins, gallic acid and caffenine
    (The University of Peradeniya, 2013-07-13) Jeganathan, B.; Punyasiri, P. A. N.; Kottawa-Arachchi, J. D.; Ranatunga, M. A. B.; Abeysinghe, I. S. B.; Gunasekare, M. T. K.; Bandara, B. M. R.
    Tea (Camellia sinensis L.) contains a myriad of metabolites of varying chemical structures. Early efforts to correlate metabolites with the quality of tea have been focused on single metabolite variation in tea cultivars. The literature available on the analysis of a broad range of metabolites in tea accessions is minimal. We have begun a systematic study on metabolic profiling of the Sri Lankan tea germplasm through the analysis of principal metabolites of tea leaves. The results of this study will enable, the commercial exploitation of germplasm accessions for making diverse products of tea of desired quality, the definition of biochemical diversity of the Sri Lankan tea germplasm, the stratification of germplasm accessions into diverse clusters, and the identification of parent candidates for breeding programmes. We report our preliminary results on the quantitative analysis of tea flush from 40 germplasm accessions for total polyphenol content (TPP) and six metabolites. Green leaf samples of 40 germplasm accessions collected from the ex situ field genebank of the Tea Research Institute of Sri Lanka were analysed for total polyphenols using the Folin Ciocalteu’s colorimetric method (ISO 14502-1), and for six metabolites to include 4 catechins, caffeine and gallic acid, using high performance liquid chromatography (ISO/CD 14502-2). The measurements were made for two extracts prepared from each accession. The TPP was found to be 165.16 - 275.78 mg/g (w/w, dry weight). The contents of the six metabolites varied in the following ranges: epigallocatechin gallate (EGCg, 37.18±2.70 - 109.44±8.35 mg/g), epigallocatechin (EGC, 6.11±0.43 - 47.60±0.20 mg/g), epicatechin gallate (ECg, 13.73±3.66 - 43.52±4.00 mg/g), epicatechin (EC, 4.44±0.42 – 21.88±1.27 mg/g), caffeine (13.72±0.53 – 43.48±1.48 mg/g) and gallic acid (0.10±0.03 - 1.56±0.12 mg/g). The highest contents of EGCg, ECg, EGC and EC were observed for the accessions TRI62/9, TRI62/9, TRI4076 and TRI777 while the lowest amounts were shown by the accessions KEN16/3, PBGT41, PLLG2 and PLLG2, respectively. High levels of EC and ECg were observed in high-quality black tea producing cultivars whereas low-quality tea producing cultivars had low levels of EC and ECg.
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    Optimisation of sampling methodology for metabolite profiling of Sri Lanka tea
    (The University of Peradeniya, 2013-07-04) Punyasiri, P. A. N.; Jeganathan, B.; Kottawa-Arachchi, J. D.; Abeysinghe, I. S. B.; Ranatunga, M. A. B.; Gunasekare, M. T. K.; Bandara, B. M. R.
    The quality of tea (Camelia sinensis) products depends on the chemical composition of fresh tea leaves, which is determined by the inherent genetic attributes of the cultivar and geo-climatic factors. Thus, metabolite profiling of the Sri Lankan tea germplasm by chemical analysis of tea flush would contribute immensely to the success of tea breeding programmes. However, the polyphenols, particularly catechins (flavan-3-ols), which are eventually responsible for the quality of tea, are readily oxidized by enzymes (polyphenol oxidase) and such enzymes are activated by light. The collection, handling and storage of a large number of leaf samples for metabolite profiling thus require a sampling procedure that would minimize the oxidation of polyphenols and formation of artefacts. We have compared two methods of sampling, fresh leaves (as in the conventional procedures) and freeze-dried leaves (a new procedure), for quantification of some critical metabolites, namely catechins and caffeine, by employing two cultivars, one (DT1) of which is known to yield high quality black tea and the other (TRI 2025) poor quality black tea. Tea flush of cultivars DT1 and TRI 2025 in the ex situ field genebank of the Tea Research Institute, Talawakelle was separately collected, kept at 4 °C, immediately brought to the laboratory, stored at -80 °C for 6 hours, freeze-dried for 24 hours, ground to a fine powder, and sealed in triple laminated aluminium foil. In the conventional sampling procedure, tea flush was brought to the laboratory at room temperature and immediately subjected to solvent extraction. The tea samples were extracted into boiling 70% methanol in water and the extracts analysed for the total polyphenols using the Folin Ciocalteu’s colorimetric method (ISO 14502-1) and for caffeine, (-)-epicatechin, (-)-epigallocatechin, (-)-epigallocatechin gallate, (-)-epicatechin gallate, gallic acid and theobromine using a HPLC method (ISO/CD 14502-2). The amounts of metabolites recorded in the new sampling procedure were significantly higher than those recorded in the conventional sampling procedure, indicating that the new method is suitable for metabolite profiling studies of the Sri Lankan tea germplasm.