Eun-Hye Kim，Yue-Rong Liang，Jian-Liang Lu，Guang-Wei Wang，Zhen-Chun Chen，Yuan-Yuan Wu，You-Ying Tu*

Department of Tea Sciences，College of Agriculture and Biotechnology，Zhejiang University，Hangzhou 310058.Philips Research Asia Shanghai，Shanghai，200233，China.

1.Introduction

As a beverage，Tea has to infuse by water before for drinking.How to get best tea taste and nutrient is depend on brewing condition and correct way.Some papers wrote the method including temperature and the ratio of tea to water for brewing tea.

However，little information was explained why people choose special brewing way.

This experiment designed three different temperatures and eight extract times to study the effects on the tea infusion quality.Main compounds of tea infusion were measured and the taste sensory was applied to evaluate the aroma，color and taste of tea infusion.The index t0.5min(50%concentration of compounds in tea infusion)could compare with soluble speed of compound and explain the reason of taste change.

2.Materials and methods

2.1.Tea samples

Pu'erh san tea was purchased from market in 2006，produced in Yunnan province，China.

2.2.Chemicals

Catechin(C)， epicatechin(EC)， gallocatechin， epigallocatechin(EGC)， gallocatechingallate，epigallocatechin gallate(EGCG)，catechin gallate，and epicatechin gallate(ECG)，were HPLC grade and purchased from Sigma Chemical Co.All the other reagents used were of analytical grade and bought from local chemical suppliers.

2.3.Preparation of tea infusion

Eight brewing time experiments were designed.Each experiment weight two grams of Pu'erh tea and added 100 ml of boiling water together into glass bottle for brewing different minutes，took out tea solution for 1 min，2 min，3 min，4 min，5 min，15 min，30 min and 60 min，respectively，then filtered and the infusion was used to detect the chemical components.

2.4.Determination of chemical components

The contents of tea polyphenol(TP)，amino acid(AA)，theaflavins(TF)，thearubigins(TR)，theabrownine(TB)and total tea sugar(TS)were determined by a spectrophotometer using the following methods:polyphenol by ferrum tartrate dying method，amino acid by ninhydrin dying method，theaflavins，thearubigins，theabrownine by Roberts'method，and total sugar by anthrone reagent dying method［1，2］.

The contents of catechins and caffeine were analyzed using a high-performance liquid chromatography(HPLC)system(SHIMADZU LC-2010A，Kyoto，Japan).Ten microlitres of the tea infusion was injected for HPLC analysis under the following conditions:The column used was Agilent TC-C18(250 mm ×4.6 mm).The mobile phase A was acetic acid/acetonitrile/water(0.5∶3∶96.5，v)，and B acetic acid/methanol/water(0.5∶30∶69.5，v).At a flow rate of 1.0 ml/min at 15℃ column temperature using the Shimadzu SPD ultraviolet detector，peaks were observed at a wavelength of 280 nm.Catechins standard sample was from Sigma Company.All organic solvents used for sample preparation and analysis were of HPLC grade.

2.5.Sensory evaluation

The sensory characteristics of tea infusions were evaluated by five panelists from the Tea Department of Zhejiang University based on the color，taste and flavor of tea infusions.According to Chinese tasting standard total score is 100%，tea aroma and infusion color was of which 20%respectively，other 60%was the taste.

2.6.Data analysis

The results were given in the form of mean standard deviation.A data summary and calculations were performed using Microsoft Excel.Differences between means were evaluated using analysis of variance student's ttest using SPSS 10.0 for Windows(SPSS，Inc.，Chicago，IL，USA).Probability value of p ＜ 0.05 was considered as the criteria for statistically significant differences.

3.Results and discussion

3.1.Effect of temperature and brewing time on main compounds of Pu'erh tea(%)

To compare the concentrations of all compounds(showed in table 1)at 80℃for brewing 3min we found that the highest concentration was caffeine，the second was AA，and other compounds TF，TS，TB and TP almost had similar concentration.When the brewing time arrived 15 min，except TF other five compounds concentrations were over 50%，caffeine also showed the biggest concentration.However，when the tea brewed for one hour TF appeared the best solubility，the concentration arrived 90%，the second was caffeine.To brew tea at 100℃ boiling water for 5 min，except TB and TS other four compound concentrations were much higher than that of for 15min，which suggested the 100℃ temperature was easily to extract most of active compounds in Pu'erh tea.Three different temperature treatments showed the significant different concentrations of six compounds in Pu'erh tea infusion.

3.2.The effects of different temperatures on extraction rate of Pu'erh tea(min)

It is obviously that whether the time index t0.5of TP，AA，Caf，TS，TF，or TB decreased with extract temperature increasing(Table2).For example，the t0.5of tea polyphenol was from 15.1min to 4.4min when extracting temperature from 80℃ changed to 100℃，which meaning higher temperature enhanced the solubility speed of tea polyphenols.

Table1.Effect of temperature and brewing duration on extraction rate of Pu'erh tea(%).

Table2.The effect of different temperatures on extraction rate of Pu'erh tea(min).

The results also showed that the solubility speed of caffeine was the highest to compare with tea polyphenols，amino acid，caffeine，soluble sugar，theaflavins and theabrownine at 80℃，the t0.5min of caffeine was 1.7min，amino acid 10.3min followed bytea polyphenols，soluble sugar was the lowest.It suggested that in the same time the concentration of amino acid in infusion was higher than that of TP，AA concentration arrived 60.5%，TP only 40.4%，which explained why the first tea infusion normally is more sweet and fresh than second or third infusion.

3.3.The effects of temperature and brewing time on taste of Pu'erh tea

The brewing temperature was mainly affected the TQS score of infusion(Table3).The results suggested that 100℃ boiling water could brew best taste tea infusion and get the highest score.The scores of aroma and taste except color appeared the similar change regulation among different temperature treatments.The reason might be concerned with the different TF concentration and its threshold according to the multiple regression analysis between sensory assessments and chemical components of Pu'erh tea.

Y=69.838+1.45X1+0.22X2+5.009X3-0.163X4，R2=0.999(in 100℃)

Here Y is TQS，X1:amino acid，X2:soluble sugar，X3:theaflavins，X4:theabrowine，X5:caffeine，X6:tea polyphenols

Table3.The sensory assessments of Pu'erh tea.

This experiment results might be useful for some people who likes tea but afraid of tea caffeine，there is very sample way to remove caffeine and keep most of health compounds in tea，just to give up the first infusion and drink from second infusion.From this study also remind us how to get best taste and keep tea active compounds.

This study was supported by a research grant of Philips"Brain-Bridge Plan".

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