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TEA QUALITY
Quality is one of the critical factors determining the price of tea for export. Although yield is important to producers, quality also has a significant role to play. It is currently measured or valued in terms of price realisation or tea taster’s scores from sensory evaluation, which is prompted to be subjective, depending upon the sensory tasting skills of the taster (Fernando & Roberts, 1984; Taylor, Baker, Owour, Orchard, Othieno & Gay, 1992). Quality has also been reported to be influenced by active chemical compounds, mainly total polyphenols, which to date have attracted more researchers to be interested in this field (Roberts & Smith, 1961; Hilton & Ellis, 1972; Mcwell, Feakes & Gay, 1990; Owour, Ng’etich & Obanda, 2000; Venkatesan, Murugesan, Ganapathy & Verma, 2004). The quality of tea is formed during the growth and development of the tea, when the
compounds responsible for quality are synthesized (Bokuchava & Skobeleva, 1969; Obanda, Owour & Taylor, 1997). The chemical constituents synthesized in tea shoots may exert positive and or negative effects on the quality of tea the made. The quality index [(EGCG + ECG)/EGC] has been found to be directly related to the sensory properties of green tea (Yuan, 1962). Thus, the index has been used as an objective parameter for assisting the evaluation of quality green teas (Shao, Powell & Clifford, 1995). The climatic conditions and agronomic practices of green tea and black tea are the same (Chiu, 1990; Sud & Baru, 2000). The main principal difference between black teas and other forms of teas like green tea and oolong tea is the presence of condensed catechins, i.e. polyphenols of higher molecular weight. This is formed through enzymatic oxidation with the help of enzyme polyphenol oxidase (PPO) and peroxidase (PO) and total polyphenol contents which are the main tea quality indicators (Sanderson & Grahamn, 1973). The other chemical components of tea quality parameters are amino acids (Wang, 1996), carbohydrates (Sanderson, Co & Gonzales, 1976), organic acids (Sanderson & Selvendran, 1965), vitamins (Hu, 2001a), volatile flavour compounds and plant pigments (Taylor et al., 1992). Hence, the sensory quality attributes are astringent taste, bitterness, sweatiness and aroma (Hu, 2001b). Factors that affect the above mentioned tea quality parameters can be classified into four major categories viz., cultivars (Owour et al., 2000), environmental conditions (Chiu, 1990), cultural practices (Taylor et al., 1992) and seasonal variation (Sud & Baru, 2000). However, for the purpose of this review quality attributes of green tea, with respect to mineral nutrition, will be covered.
Effect of nitrogen on growth and development of bush tea
Regardless of season, plant height, number of branches and leaves, leaf area, and fresh and dry shoot mass increased quadratically in response to nitrogen nutrition (Tables 4.2, 4.3, 4.4 and 4.5). Regardless of season, the optimum level of N was 300 kg·ha-1. Most of the growth responses occurred between 0 and 300 kg·ha-1 N. Wanyoko (1983) reported that biomass production of green tea increased to an optimum at 250 kg·ha-1 N. Krishnapillai & Pethiyagoda (1979) reported that when different forms of nitrogenous fertilizer such as ammonium sulphate, ammonium nitrate, urea and calcium nitrate were applied at 300 kg·ha-1 N, biomass production of young tea (Camellia sinensis L.) was increased. Regardless of season, leaf tissue N and root tissue content increased quadratically to reach an optimum at 300 kg·ha-1 N (Tables 4.2, 4.3, 4.4 and 4.5). Wanyoko (1983) reported that the normal harvestable tea leaves had leaf tissue N content of 3 to 3.4 %. Regardless of season, root tissue nitrogen content increased quadratically to reach an optimum at 300 kg·ha-1 N (Tables 4.2, 4.3, 4.4 and 4.5). Anandacoomaraswamy, De Costa, Tennakoon & Van Der Werf (2002) reported that 375 kg·ha-1 N increased assimilates of N partitioned towards the shoots at the expense of roots in young clonal tea, possibly due to a high photosynthetic rates in the leaves than in the roots. No significant differences in stem girth, fresh and dry root mass, number of flowers and flower buds as well as fresh and dry stem mass were recorded in the present study.
CHAPTER 1 LITERATURE REVIEW
1.1 BOTANY OF TEA
1.2 TYPES OF TEA
1.3 TEA QUALITY
1.4 POTENTIAL HEALTH BENEFITS OF GREEN TEA
1.5 POLYPHENOLS IN GREEN TEA
1.6 MACRO ELEMENTS
1.7 MICRO ELEMENTS
1.8 SUMMARY AND CONCLUSIONS
CHAPTER 2 A NEW FLAVONOL FROM BUSH TEA (ATHRIXIA PHYLICOIDES L.)
2.1 INTRODUCTION
2.2 MATERIALS AND METHODS
2.3 RESULTS AND DISCUSSION
2.4 SUMMARY
CHAPTER 3 RESPONSE OF TOTAL POLYPHENOLS IN WILD BUSH TEA (ATHRIXIA PHYLICOIDES L.) TO SEASONAL VARIATIONS
3.1 INTRODUCTION
3.2 MATERIALS AND METHODS
3.3 RESULTS AND DISCUSSION
3.4 SUMMARY
CHAPTER 4 GROWTH AND DEVELOPMENT OF BUSH TEA (ATHRIXIA PHYLICOIDES L.) AS AFFECTED BY NITROGEN, PHOSPHORUS AND POTASSIUM NUTRITION
4.1 INTRODUCTION
4.2 MATERIALS AND METHODS
4.3 RESULTS AND DISCUSSION
4.4 SUMMARY
CHAPTER 5 RESPONSE OF LEAF TOTAL POLYPHENOL CONCENTRATIONS TO NITROGEN, PHOSPHORUS AND POTASSIUM NUTRITION OF BUSH TEA (ATHRIXIA PHYLICOIDES L.)
5.1 INTRODUCTION
5.2 MATERIALS AND METHODS
5.3 RESULTS AND DISCUSSION
5.4 SUMMARY
CHAPTER 6 EFFECTS OF N, P AND K NUTRITION ON GROWTH AND CHEMICAL COMPOSITION OF BUSH TEA (ATHRIXIA PHYLICOIDES L.) AS INFLUENCED BY SEASON
6.1 INTRODUCTION
6.2 MATERIALS AND METHODS
6.3 RESULTS AND DISCUSSION
6.4 SUMMARY
