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Research progress on quality formation of white tea Zhou Caibi Chen Wenpinmu (Department of Tea Science, College of Horticulture, South China Agricultural University 5 1 0 6 4 2) Abstract: From the appearance, color, soup color, flavor and aroma of white tea and the formation of polyphenols and alkaloids And aromatics
The changes of the ingredients are reviewed in order to provide a certain reference value for the improvement of the quality of white tea. Keywords: white tea; quality formation; more biochemical components, the leaf color is bright green. If the withering temperature is too high, chlorophyll is converted to pheophytin, forming a small amount of pheophytin a, the proportion of chlorophyll b, a gradually increases, and finally chlorophyll a, b tends to be stable, making the white tea color appear gray olive to dark olive [ 6 '".
1 Foreword White tea belongs to micro-fermented tea. After withering and drying,
It has formed the unique quality characteristics of white tea, such as tender leaves and tender leaves, branch and branch branches, gray-green leaves, and pale yellow and bright soup colors.
2.3 Soup color and taste Traditional white tea has no twisting process, enzymes and polyphenols cannot be fully contacted, the supply of oxygen is very small, and the secondary oxidation progresses slowly, so the soup color and taste of white tea are not as good as other teas Strong, light soup color, taste mellow and J. In the middle and late stages of withering, the tea polyphenols slowly and slightly oxidized and condensed, which increased the amount of the o-quinone of the oxidation product, and the tea polyphenols in the tea were greatly reduced, making the tea soup mellow and the soup color apricot yellow J. In the drying process, catechins changed the most. Among them, epigallocatechin gallate and gallocatechin reduced the most, making the astringent taste of the tea soup disappear and the taste was clearer L 9].
2 White tea quality formation Traditional white tea is processed through two processes of withering and drying. Its unique shape, color and flavor are mainly formed during the withering process. Due to long-term withering, white tea causes complex physical and chemical changes in the leaves, loss of water, increased leaf cell concentration, and cell membrane permeability.
Changes, hydrolytic enzymes and polyphenol oxidases are activated, causing a series of reactions in the contents to form the unique quality characteristics of white tea.
2.4 In the early stage of aroma withering, the moisture of fresh leaves evaporates, increasing the concentration of leaf cell tissues, increasing the activity of enzymes, organic matter tends to hydrolyze, and polyphenols are oxidatively condensed], low-boiling aromatic substances are significantly reduced; In the middle of withering, the low-boiling aromatic substances increased; in the late withering period, the enzyme activity gradually decreased, and the interaction between soluble polyphenols and amino acids, amino acids and sugars formed aromatic substances, which caused the white tea grass to fade, and the aroma appeared ¨; withering To 48 hours, the higher boiling point aroma components are nerolidol and phenylacetaldehyde. According to reports from Wang Li and others,
The main aroma components are: aldehyde, benzaldehyde,
2. The shape of white tea leaves is curled and the buds and branches are branched. One is that it depends on the fresh leaf picking standard and the quality of the young shoots. The other is that during the withering process, the leaf back loses water faster than the leaf surface cells, causing the leaf back and leaf surface tension. The imbalance of leaves makes the leaf margins roll from the leaf surface to the leaf back. Merging and sieving in the later stage of withering is also an important measure to promote leaf edge vertical curl, which can prevent the flat leaf state caused by sieving ... Moreover, the leaf tip, leaf margin and tender stalk, the back of the leaf with stomata loses water faster than the leaf surface, which causes the leaf surface and leaf back tension to be unbalanced, forming a special shape of white tea J. 2. 2 color
The formation of white tea color is the result of the action of pigments and polyphenols in fresh leaves. During the withering process, chlorophyll and carotene are easily destroyed, while the properties of lutein are relatively stable, which changes the ratio of chlorophyll and lutein in leaves. J. If the withering time is short during processing, and
Geraniol, phenethyl alcohol, linalool and its oxides are mainly alcohol compounds, among which the hexanal content is the highest.
3 Changes in quality components The unique shape, color, aroma and taste of white tea are mainly formed during the withering process, which is closely related to the changes in the effective components of tea.
Dry climate, less conversion and decomposition of chlorophyll, chlorophyll retention compared with mother Corresponding author