Tea Chemistry

Article (PDF Available)inCritical Reviews in Plant Sciences 16(5):415-480 · January 1997with10832 Reads
Impact Factor: 5.44 · DOI: 10.1080/07352689709701956
The chemistry of tea as a beverage is reviewed in depth, covering both historical and current chemical perspectives. Special attention is given to the polyphenols in tea, although the general composition and properties are also treated. Current trends in tea science, particularly in the area of polyphenol complexation and antioxidant properties, are also covered. The need for a chemically based understanding, rather than one hypothesized from generalized and indirect observation, is stressed.
    • "Activation of plant polyphenol oxidase induces the browning of food, decreasing its qualities (Aquino-Bolaños and Mercado-Silva, 2004). However, polyphenol oxidase can also affect the production of tea volatiles (Harbowy and Balentine, 1997). Arthropod hemocyanin mainly transfers oxygen in the hemolymph (van Holde and Miller, 1995), while tyrosinase in microbes is positively related to pathogenicity (Mayer, 2006; Shang et al., 2012) and, in insects and other arthropods, PPO is an important innate immunity protein (Ashida and Brey, 1997; Cerenius et al., 2008; Kanost and Gorman, 2008). "
    [Show abstract] [Hide abstract] ABSTRACT: Insect prophenoloxidase (PPO) is an important innate immunity protein due to its involvement in cellular and humoral defense. It belongs to a group of type-3 copper-containing proteins that occurs in almost all organisms. Insect PPO has been studied for over a century, and the PPO activation cascade is becoming clearer. The insect PPO activation pathway incorporates several important proteins, including pattern-recognition receptors (PGRP, β GRP, and C-type lectins), serine proteases, and serine protease inhibitors (serpins). Due to their complexity, PPO activation mechanisms vary among insect species. Activated phenoloxidase (PO) oxidizes phenolic molecules to produce melanin around invading pathogens and wounds. The crystal structure of Manduca sexta PPO shows that a conserved amino acid, phenylalanine (F), can block the active site pocket. During activation, this blocker must be dislodged or even cleaved at the N-terminal sequence to expose the active site pockets and allow substrates to enter. Thanks to the crystal structure of M. sexta PPO, some domains and specific amino acids that affect PPO activities have been identified. Further studies of the relationship between PPO structure and enzyme activities will provide an opportunity to examine other type-3 copper proteins, and trace when and why their various physiological functions evolved. Recent researches show that insect PPO has a relationship with neuron activity, longevity, feces melanization (phytophagous insects) and development, which suggests that it is time for us to look back on insect PPO beyond the view of immunity in this review.
    Full-text · Article · Jul 2014 · Frontiers in Physiology
    • ". Gallic, chlorogenic and p-coumaric acid were detected in ''true " teas, whilst vanillic and caffeic acid were determined in linden infusion and chlorogenic , p-coumaric, ferulic and caffeic acid in chamomile infusion. The highest content of phenolic acids was determined in black tea, and it may have been released during the fermentation process (Harbowy & Balentine, 1997). In chamomile infusion, the highest content of caffeic (14 mg/l) and chlorogenic (2 mg/l) acids was "
    [Show abstract] [Hide abstract] ABSTRACT: The popularity of tea is increasing on the global aspect because of its role as a significant source of phenolic compounds in human diet. The purpose of this study was to determine and compare the phenolic and methylxanthine composition as well as the antioxidant capacity of white, green, Oolong and black teas, and chamomile and linden infusions depending on the extraction conditions (water temperature and multiple extractions). The content of total phenols and total flavonoids in teas and herbal infusions was determined by using UV/vis spectrophotometric methods, whilst individual polyphenols (phenolic acids and flavan-3-ols) and methylxanthines were identified and quantified by using high performance liquid chromatography coupled with photodiode array detection. In order to determine the antioxidant capacity of teas the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical scavenging assays were applied. The highest content of phenolic compounds was determined in green tea, which also demonstrated the highest antioxidant capacity, whilst herbal infusions were characterised with the lowest content of phenolic compounds, as well as the lowest antioxidant capacity. The highest content of caffeine, as the most abundant methylxanthine, was determined in black tea. Extraction at 100 °C is the most effective to extract the highest content of polyphenols and methylxanthines in all studied teas.
    Full-text · Article · Jan 2013
    • "Although wines, fruit juices and coffee are well-known for their content of bioactive compounds, especially flavonoids, the most extensively studied beverages in this respect are green, white, oolong and black teas (Graham, 1992; Harbowy & Balentine, 1997; Kilmartin & Hsu, 2003). The positive health effects of tea derive from its high content of phytochemicals with antioxidant activity, including polyphenols, vitamins (C, E), carotenoids and other compounds capable of scavenging free radicals (Wiseman, Balentine, & Frei, 1997). "
    [Show abstract] [Hide abstract] ABSTRACT: Cyclic voltammograms (CV) taken to 800 mV at a scan rate 100 mV s−1 were used to quantify electrochemical properties of antioxidants present in 10 fruit tea infusions as well as to deduce antioxidant capacity from the Q600 parameter (charge passed to 600 mV). A pronounced anodic current peak observed at 440 mV in all analysed fruit teas indicated that ortho-dihydroxy-phenol and gallate groups are the major contributors to the antioxidant capacity of investigated teas. Antioxidant composite index (ACI) was determined for each tea employing antioxidant capacity values from previous spectrophotometric determinations as well as the Q600 parameter derived from CV. A ranking of the most potent teas was obtained: the fruit tea containing a large portion of rose hip fruit exhibited the highest ACI and a CV with the most pronounced anodic current peak at 440 mV pointing to the presence of ortho-dihydroxy-phenol and gallate group containing compounds. Strong positive correlation was established between antioxidant capacities deduced from CVs with those previously determined using established spectrophotometric techniques (FRAP, ABTS and DPPH assays).
    Full-text · Article · Aug 2010 · Food Chemistry
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