Tea Chemistry

Critical Reviews in Plant Sciences (Impact Factor: 5.29). 01/1997; 16(5):415-480. DOI: 10.1080/07352689709701956

ABSTRACT 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.

Download full-text


Available from: Matthew E Harbowy, Jun 25, 2015
  • Source
    [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.
  • Source
    [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).
    Food Chemistry 08/2010; 121(3-121):820-825. DOI:10.1016/j.foodchem.2009.12.090 · 3.26 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A study was conducted to determine the effect of fermentation temperature and time on chemical composition of bush tea (Athrixia phylicoides DC.). Bush tea was fermented in incubators at different temperatures and for different times for quality improvement. Treatments for fermentation temperature consisted of control (24°C) room temperature, 30, 34, 38 and 42°C where the tea leaves were fermented for 30 min. Treatments for fermentation time consisted of control (0), 60, 90 and 120 min at an incubator temperature of 22 -26°C. A completely randomized design (CRD) was used with three replicates for both evaluations. The chemical analysis (polyphenols, tannins and antioxidants) were done using Waterman and Mole's (1994) method. The results of this study demonstrated that fermentation temperature significantly increases polyphenols at 30, 34 and 38°C whereas tannin content showed a great reduction at 38 and 42°C. Increasing fermentation time achieved a significant increase in both polyphenols (60 and 90 min) and tannin contents (90 and 120 min). However, changes in either fermentation temperature or time did not give any significant influence on antioxidant content of bush tea.