| As one of the six basic Chinese tea category, yellow tea is "lightly fermented" tea. Yellow tea processing is still the traditional "boring yellow" skill-based, currently. But this "boring yellow" technology has problems, such as difficult to master, yellowing process being slow, operation repeated, low productivity, and product quality is not stable enough. For these key technical issues, according to the present invention patents in this research paper declared, innovatively proposed the use of tea leaves preparation of crude enzyme preparation, yellow tea processing in "fixing leaf" or "rolled leaf" being added to the right amount of crude enzyme preparation, in order to promote "boring yellow leaves" a certain degree of control occurs (the amount of enzyme, temperature and time) "enzymatic yellowing", which effectively solves the key technical issues of traditional "boring yellow" process.This paper firstly evaluated the effect of enzymes of fresh tea leaves used in yellow tea enzymatic yellowing processing; the enzymatic yellowing conditions (enzyme amount, temperature and time) were optimized. On this basis, the trial-produced the particles form yellow tea products, and studied the yellow tea processing "enzymatic yellowing" and yellow tea quality components form the relationship. Second, the method of enzyme of fresh tea leaves extract and save was optimized; Studied the enzymatic properties of enzyme of fresh tea leaves; And detected the contain material such as tea polyphenol content of the enzyme in fresh tea leaves. This thesis mainly got the following results:(1) Analyzed on the existed yellow tea processing and technology, the enzyme in fresh tea leaves will be used in the yellow tea processing for "enzymatic yellowing" in order to achieve yellowing conditions controlled (enzyme concentration, temperature and time), the idea which has academic value.(2) Studied the adding enzyme in fresh tea leaves to the enzyme processing yellow tea "enzymatic yellowing" effect. The results showed that:"enzymatic yellowing" yellow tea had the quality features of traditional yellow tea "yellow soup, yellow leaves," and its color green-yellow, soup bright yellow, mellow taste with sweet fragrance,which quality was better than the traditional "boring yellow" yellow tea. Its polyphenol content and total chlorophyll were lower than the traditional "boring yellow" yellow tea by 0.77%, and 0,19mg/g, and soluble sugar, tea flavin and thearubigins were higher than the traditional "boring yellow" yellow tea by 0.05%,0.03% and 0.08%. This shows that the enzyme in tea leaves being used in yellow tea processing "enzymatic yellowing" had effects. This study has reference to the current method of yellow tea processing technology to improve the technology.(3) Used quadratic general rotary unitized design to optimize yellow tea processing "enzymatic yellowing" conditions (the amount of enzyme, temperature and time). The results showed that, the amount of enzyme was from 65g/500g to75.2g/500g, the leaf temperature of was from 32.0℃ to 36.5℃, the time was from 3.5h to 4,3h can obtained the best quality yellow tea. Under this condition, yellow tea sample polyphenol oxidase activity was from 1.06U/mL to 2.02U/mL, sensory evaluation score of yellow tea finished sample was from 92.4 to 95.3, polyphenols content was from 23.64% to 25.13%, heaflavin content was 0.11%, thearubigins content was from 3.08% to 3.34%. It showed that by regulating the amount of enzyme, temperature and time, you can control the degree of yellowing, control the quality of yellow tea. The optimization results to guide the yellow tea production and processing has practical significance.(4) Trial particle-shaped yellow tea products, studied the relationship between "enzymatic yellowing" and the main quality ingredients to form yellow tea.The results showed that, the tea leaves crude enzyme solution to promote the bitter taste of tea polyphenols and catechin content in yellowing processing reduced by 3.32%and 3.37%, the content of the fresh sweet substances such as amino acids and soluble sugar increased by 0.22% and 0.30%, made the tea taste of alcohol; chlorophyll content decreased by 0.05% but theaflavins and thearubigins content increased 0.07% and 0.90% respectely. It shows that "enzymatic yellowing" on the formation of yellow tea has a role in promoting the quality of ingredients. This can provide theoretical guidance for the yellow tea processing.(5) Detected the main contain ingredients of the tea leaves enzymes, optimized the method to distill and preservation of fresh tea leaves enzymes. The results showed that, tea leaves with pH5.6 citric acid-sodium phosphate buffer, lemon extracted 12h crude enzyme solution, the unit of polyphenol oxidase activity was the highest (3.80±0.21) U/g.Varieties of tea leaves to the highest polyphenol oxidase activity of Hainan large-leafed was (2.81±0.28)U/g. Enzyme tea leaves be stored at-20℃ after 2 days, its activity decreased 22.22%, so the best tea leaves crude enzyme solution with the current system. Tea leaves containing the crude enzyme solution and the amount of catechin polyphenols, respectively (8.76±0.14) mg/mL and (4.68±0.27) mg/mL, total free amino acid is (2.77±0.05) mg/mL, the amount of soluble sugars (3.29±0.30)mg/mL. This can provide methodological guidance in"enzymatic yellowing" practical application.(6) Studied the tea leaves enzymes (mainly polyphenol oxidase) enzymatic properties. The results showed that:in pH 5.6, temperature 37℃ conditions, substrate concentration in the 2.5 to 62.5mmol/L range, the tea leaves of polyphenol oxidase Km= 7.24mmol/L, Vmax is 20.92U/min, enzyme pro-kinetic equation is:1/V=0.3463X +0.0478, R2= 0.9657; when catechol as substrate, the buffer pH in the range of 5.0 to 6.0, polyphenol oxidase activity in tea leaves was highest 12.39U/mL; reaction temperature was 37℃, enzyme activity was the highest 13.53U/mL; NaCl and ascorbic acid solution on the tea leaves PPO enzyme activity showed a significant inhibitory effect, when ascorbic acid concentration 0.4mol/L, oxidase polyphenols complete inactivated. It provides the theoretical basis of control for the tea leaves enzyme activity on yellow tea processing. |
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