Research On The Quality Improvement Of Anxi TieGuanYin Oolong Tea By Exogenous Enzymatix Treatment

TieGuanYin as a famous and representative was chosen as a research objects. Its flavour substances and aroma compounds related to sensory qualitybetween seasonal products were analyzed and summarized. Afterawards, food grades Laccase and Alpha-galactosidase were choosento improve the quality of Anxi TieGuanYin tea produced in summer season and their action mechanism were explored. Basically, the following are the major findings.1. The amount of total polyphenols including catechins, flavonoids, phenolic acid, depside, and anthocyanins was 14.14%～19.13%(w/w). Catechins accounted for 61%～75%, are the highest polyphenols while flavonols are 3.0%～5.9%. Chlorogenic acid and gallic acid as the two major acids are 0.32%～0.42%. Moreover, there are 1.6%～2.3% of caffeine,2.4%～3.2% of free amino acids and 6.4%～8.4% of soluble sugar. All of them contribute to the sensory quality of AnXi TieGuanYin oolong tea.2. The main flavor substances in AnXi TieGuanYin oolong tea have significant difference between the teas produced at the different tea season. Especially, the summer teas have a lowest sensory quality with a bitter taste, untransparent and yellowish liquor. It has found that the total polyphenols, catechin esters, gallic acid is the highest while free amino acids, flavonols, and the soluble sugar are the lowest compared with those in spring and autumn teas.3. GC-MS was applied to analysis the aroma in different seasons of AnXi TieGuanYin tea and found a total of 74 kinds of aromatic components which belonged to alcohols, aldehydes, ketones, esters, acids, alkenes, alkanes and others. Generally, alcohols compounds is the highest aromatic types, accounted for more than half of the total essential oil. The major characteristic components extracted by principal component analysis are as the order from the highest to lowest as: nerolidol, farnesene, indole, benzene acetaldehyde, phenylethyl alcohol, and 5-n-butyl-delta-elactone. The total essential oils and the characteristic components as benzene acetaldehyde aldehyde and nerolidol alcohols in spring teas have a relative lower content than those in autumn and spring teas.4. The general properties of laccase and Alpha-galactosidase in oolong teas were investigated. It the maximum absorption wavelength of laccase and alpha-galactosidase are at 270 nm and 320 nm when tea polyphenols and 4-nitrophenyl beta-D-glucopyranoside as the substrates respectively. Their optimum substrate concentrations are at 4.0 g/L and 0.40 g/L repectively. The HPLC-PDA was applied and the data showed the four types of oxidation products of tea polyphenols as theaflavins (TF), theaflavins-3,3’-galloyl ester (TF-D-G), theaflavins-3-gallate (TF-3-G) and theaflavins-3’-gallate (TF-3’-G) were produced.5. Laccase applied to the summer oolong tea can partially catalyze the oxidation of phenolic substances and increase water extract and soluble sugars, which can improve tea taste and liqor appearance. At the same time, the total essential oil, floral aroma components as nerolidol, phenylethyl alcohol, benzene acetaldehyde, and farnesene increased significantly. The tea has a higher and persistent arom ta compared to the untreated teas. It has shown that laccase can degrade the cellulose and lignin to soluble sugars and improve the softness of tea leaf. However, the excessive laccase treatment results in negative effects.6. Alpha-galactosidase treatment can increase the soluble sugar content and has a positive effects on sensory taste which can ameliorate the bitterness taste and tea liquor transparency. Total essential oil, floral aroma components as nerolidol, phenylethyl alcohol and benzene acetaldehyde increase obviously. But the ester compounds related to pleasant fragrance are lower compared to the untreated summer teas.7. It concluded that appropriate application of laccase and Alpha-galactosidase treatment can obviously improve the quality of AnXi TieGuanYin tea produced in summer season. The optimal treatment is 8.25 U of laccase and 22 U Alpha-galactosidase sprayed to the leaves before primary baking process.