School of Agriculture and Biotechnology

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Subject: search.filters.subject.Catechins

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    Optimization of manufacturing conditions of the new purple leafed Kenyan teas (TRFK 306) – maceration style and withering duration
    (2018) Kilel, E.C.; Wanyoko, J.K.; Faraj, A.K.; Ngoda, P.
    Purple tea in Kenya, TRFK 306, has received great attention due to its perceived health benefits though how it should be optimally manufactured has not been researched on exhaustively. The current study investigated on the two possible methods of manufacture – Cut Tear and Curl (CTC) and orthodox manufacture - with varying withering time of 0, 5, 10, 15 and 20 hours. Catechins, gallic acid, caffeine, total polyphenols and antioxidant activity were assayed as quality indicators. If gallic acid and caffeine are the main chemicals targeted, then orthodox type with longer withering, 15 – 20 hours, is usually recommended. When targeting catechins especially epigallocatechin gallate and high total polyphenols, orthodox type of manufacture whichever the withering time is proposed. CTC with withering hours of 15-20 produces teas with high antioxidant activity. It was concluded that TRFK 306 is best processed by orthodox or CTC but with longer withering time.
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    Antioxidant, antimicrobial and synergistic activities of tea polyphenols
    (2015) Koech, K.R.; Wachira, F.N.; Ngure, R.M.; Wanyoko, J.K.; Bii, C.C.; Karori, S.M.; Kerio, L.C.
    Microbial resistance to conventional antibiotics has become an increasing global problem and there is a need to find out novel, potent antimicrobial agents with alternative modes of action as accessories to antibiotic therapy. This study investigated the antioxidant, antimicrobial and synergistic properties of tea polyphenols. The tea germplasm from Kenya, China and Japan that are grown in Kenya were characterised for their biochemical profiles. The total phenolic content, theaflavins and thearubigins content of different tea products used in this study were determined spectrophotometrically according to Folin-Ciocalteus and flavognost methods respectively. The individual catechin contents were characterised by high performance liquid chromatography (HPLC) and identified according to their HPLC retention times, elution order and comparison with authentic standards. The antioxidant activity of tea polyphenols was determined using UV-Vis spectrophotometer on its ability to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical. The Agar Disc Diffusion method was used to screen for antimicrobial and synergistic activities of the tea liquors. Black, green, purple coloured leaf and white (silvery tips) tea products characterised for their biochemical profiles differed significantly in the levels of total polyphenols, total catechins, catechins fractions, theaflavins and thearubigins (P ≤ 0.05). Green, purple coloured leaf (aerated) and black tea from terminal buds and white tea products analysed in this study exhibited slightly higher antioxidant activity compared to black tea. The different types of tea products assayed in this study exhibited significant influence on the inhibition zone diameters against bacteria and fungi exposed to the tea extracts. Methicillin and penicillinase resistant S. aureus ATCC 25923, C. albicans ATCC 90028 and a clinical isolate of C. neoformans were more susceptible to all tea extracts than E. coli and S. typhi. There was synergism between most tea extracts and penicillin G against methicillin and penicillinase resistant S. aureus ATTC 25923.
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    The polyphenolic composition and radical scavenging properties of Kenyan tea cultivars
    (2015) Karori, S.M; Wachira, F.N; Ngure, R.M; Mireji, P.O.; Koech, R.K
    Interest in medicinal and health enhancing properties of functional components in foods continues to arouse a lot of interest. Polyphenolic fractions in tea are potent bioactive molecules. In this study, the polyphenolic composition of 25 different types of Kenyan tea cultivars was determined using the HPLC and the Folins Ciocalteus spectrophotometric methods. Total polyphenols, total catechins, individual catechins and antioxidant activity were significantly (P < 0.05) different among tea varieties, with green tea having the highest levels of total polyphenols ranging from 19.70% to 26.12%, TC (8.51% to 17.60%), individual catechins, and AA (86.65% to 94.50%). In vitro bioassay carried out using 2, 2'-diphenyl picryl hydrazyl radical showed epigallocatechin gallate was the most potent catechin and the most potent in antioxidant activity (r = 0.968***). Epigallocatechin (r = 0.659***, P < 0.001), epicatechigallate (r = 0.454*, P < 0.001), and epicatechin (EC) (r = 0.780***, P < 0.001), showed significant (P < 0.05) antioxidant activity. Black tea contained high levels of theaflavins and thearubigins (2.072% to 17.12%), respectively which accounted for its antioxidant activity (r = 0.803*** and r = 0.859***, respectively). Gallic acid also showed significant (r = 0.530*) contribution to the antioxidant activity in black tea. Data obtained from this study reveals that different Kenyan tea cultivars have different polyphenolic composition which imparts on their unique biochemical qualities. Cultivar type is therefore a critical factor in determining the antioxidant potency of tea product and that black tea processed from suitable cultivars could be potent in antioxidant activity when compared to green tea. Green and white tea products are rich in catechins, black tea products are rich in TFs and TRs while purple tea is rich in anthocyanins.
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