a study of the quality of a local herbal tea and volatiles of parinari ...

green tea, partly because of the oxidation processes that occur during fermentation
(Hamilton-Miller, 1995). Tea quality is greatly influenced by the tea polyphenols, amino
acid and caffeine contents in tea leaves and the colour differences of tea infusions (Liang
et al., 2005b). Theaflavins, residual catechin compositions, thearubigins, sensory
characteristics of total colour, brightness and briskness of tea are used as quality
indicators of tea (Obanda et al., 2001). The total quality score of pu-erh tea was
significantly correlated to the concentration of amino acids, volatile constituents and
colour (Liang et al., 2005b).
It has been reported that tea has various bioregulatory activities such as anticarcinogenic,
antimetastatic activities, antioxidative activity, antihypercholesterolemic activity,
antidental caries activity, antihypertensive activity, antibacterial activity, and interstinal
flora amelioration activity. Major principles for these activities were shown to be
catechins, a group of polyphenolic compounds (Maeda-Yamamoto et al., 2004). In green
tea leaves, catechins are present in relatively high amounts of up to 30 % of dry matter
(Schulz et al., 1999). Green tea has the highest catechin content, and therefore provides
more health benefits. Consequently, total polyphenols and total catechins content in green
tea are two important factors in evaluating the quality of green tea (Quan et al., 2007).
The major tea catechins are (-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin
(EGC), (-)-epicatechin gallate (ECG), and (-)-epicatechin (EC) (Zuo et al., 2002).
In producing black tea, the tea leaves are withered, crushed, and allowed to undergo an
enzyme-mediated oxidation commonly referred to as fermentation (Lambert et al., 2005).
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