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ABSTRACT |
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Some of the change's occurring during storage of tea are described. |
Teas are often subject to varying periods 3-6 months of storage from
the time of production to reaching consumers. The changes which
occur during storage have been studied by several workers, who have
identified factors which affect the characteristics of tea.
Among these are the increase of moisture accompanied by growth of
microorganisms (1), increase in thearubigins and extractable
caffeine, and decline in theaflavin levels (2-4). An important
factor in the decline of theaflavin leavels in stored tea is the
residual polyphenol oxidase and peroxidase activity in processed
black tea. It was also shown that storage of tea under extreme
conditions of low temperature, low moisture, and low oxygen
availability, as well as acid treatment of tea during the
fermentation stage of manufacture, led to a maarked reduction in
residual enzyme activity and a decrease in the rate of deterioration
of the theaflavin during storage.
Studies of chemical changes occurring during
storage (5) showed that storage led to a loss of flavor and
astringency, and the development of undesirable characteristics.
These changes were accompanied by lipid hydrolysis; loss of
theallavins, amino acids, sugar, and photosynthetic pigments; and an
increase in nondialysable pigments. These changes were accelerated
by high moisture and elevated temperatures. Different tea clones
showed variations in the rate as well as extent of the theaflavin
degradation. It was observed that teas made during the hot and humid
season in Malawi deteriorated more rapidly in theaflavin content.
Dougan et al. (6) reported that the decline
in the value of tea during a storage period of 6 months was
attributable to the effect of temperature and moisture on theaflavin
content, briskness, strength, color of infused leaf, and flavor.
About half the loss of value was the result of the decrease of
theaflavin content and other udidentified compounds which were
affected equally by changes in moisture content and temperature.
Relationships were studied between chemical
composition, acceptability, time of storage, temperature, and
moisture content. Tea was stored for varying times at temperatures
of 15℃,25℃,and
35℃, under relative humidities of 33%, 57%, and 75%. In this study,
theaflavins, catechins, thearubigins, total soluble solids, and
moisture content, as well as changes in the composition of volatile
compooounds, were determined.
Studies of the changes in chemical constituents of nonprocessed tea
leaves during storage in different mixtures of nitrogen, oxygen, and
carbon dioxide showed differences in oxygen uptakeand carbon dioxide
output, and marked changes in ascorbic acid and amino acids, but
hardly any changes in tannin and caffeine (7).
Microbiological change during storage of tea (8) with free access
to air and moisture consisted of steady increase in fungal growth;
the bacterial count, how ever, remained constant. The
bacterial count stabilized at about 10 microorganisms per gram,
which suggests the bacteriostaatic property of tea.
An investigation of the polyphenolic constituents of liquors
prepared by brewing black tea in boiling water (9) showed that
exposure to high temperatures during storage led to a decrease in
theaflavin content and resulted in an off taste. In this study, it
was also found addition of antioxidants, such as ascorbic
acid, or the addition of antimicrobial reagents, such as benzoatess,
was helpful in preserving the quality of tea liquors.
Investigations of the aroma components of various teas during
storage (10) revealed the occurrence of chemical changes in
nonfermented sencha green teaa, semifermented pouchong tea, and in
black tea. Development during storage of 2,4 heptadienal, hexanoic
acids, and ionone-related compounds was common to all types of tea
although specific trends were different. Yamanishi (11) reported
that deterioration of quality of green tea was accompanied by:
1.Reduction in vitamin C content.
2.Change in color from bright green to olive green to dull
brownish-green
3.Change in color of tea liquor from bright yellow or
slightly greenish to brownish-yellow.
4.Change in aroma from leafy and refreshing to dull and
heavy.
5.Change of well-balance taste of astringency and
bitterness to "flat" taste.
As in the case of black tea, these changes during storage of
green tea are accelerated by moisture, oxygen, elevated
temperatures, and exposure to light.
The basis understanding of factors which bring about changes
during the storage of tea may be useful for devising means for
preserving tea in its freshly processed form, which would overcome
some of the difficulties in the proposed establishment of a tea
buffer stock for stabilizing market prices.
EFFECTS OF THE TIME AND INTENSITY OF ROOT PRUNING ON ROOT
REGENERATION IN TEA PLANTS.
Masataka Yamashita, Kurume Branch, National Research
Institute of Vegetables, Ornametal Plants and Tea. 14041 Beppu,
Makurazaki-shi, Kagoshima, 898 Japan
It has been pointed out that root systems play important
roles to shoot growth, yield and quality. But, there are a few
researches on roots or root systems because the influences of
roots on the yield and quality are indirect, the observation of
roots requires much labour and time and direct managements to roots
are difficult. The roots, however, support the nutrient and water
uptake, and biosynthesis of some hormons and useful chemical
components. Therefore, the development and functions of root systems
could greatly control the shoot growth, yield and quality.
On basis of this conception, the rejuvination of the tea
plants by the root pruning technique has been studied. It has
experientially known that the technique was affected by many factors
such as time, intensity and frequency of pruning, manuaring,
variaties, plant age, plant vigour and relationship between the root
regeneration, and the time and intensity of the root pruning were
discussed.
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