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Research on the Change of Tea Polyphenols Content in Different Growing Period of Tea Leaves

Author: MoYanXia
Tutor: HuWei；HuBaoXiang；MoWeiMin
School: Zhejiang University of Technology
Course: Applied Chemistry
Keywords: polyphenols High performance liquid Chromatography (HPLC) extraction technique tea leaves
CLC: TS272.7
Type: Master's thesis
Year: 2008
Downloads: 64
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Abstract


Tea polyphenols are substantial ingredients of tea leaves. These compounds may be contained in up to 15-30% of the dry weight of the leaf. The major tea polyphenols known to display biological activity are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), epicatechin (EC). These natural products have numerous beneficial medicinal properties and strong antioxidant activity. Developing a relatively simple and quick high performance liquid chromatography (HPLC) analysis method with high accuracy, selectivity and low detection limit which will have profound significance to the polyphenols research. Recently, many successful simultaneously analyses of polyphenols have been reported. However, there is no report that determinate polyphenols in tea leaves in different growing time.This paper studies the extraction techniques for the determination of the contents of tea polyphenols. Determine by HPLC after three extraction methods and use liquid nitrogen to crush samples. The results show that the extraction amount of tea polyphenols is the largest by ultrasonic extraction. According to the experiment, the optimum experimental conditions are as follows: ingredients: one portion of tea leaves, fourteen portions of alcohol with a 50% density; immersing time: 50 minutes.On the basis of the optimum extract conditions, a method to analyze tea polyphenols from tea leaves by HPLC is developed. The basic operation paraments are in the following: C18 column (250 mm×4.6 mm, 5μm) is used as the stationary phase with UV detector 280 nm, a solution containing methanol, water and formic acid is used as the mobile phase. Column temperature is 40℃. The results show that the standard curve is linear in the range of 0.004～4.0mg/mL (r=0.996～0.999). the relative standard deviation of precision is.0.5～2.4%. the detection limit is 0.6～2.6μg/mL. The recovery of all compounds is 90.5%～98.2%. Some tea leaves in different growing time are analyzed using this method. As results, the total tea polyphenols content gradually increase as the tea leaves growing. The total tea polyphenols extractions of tea leaves in summer have the highest content of polyphenols, the tea polyphenols extractions of tea leaves in spring are the lowest. The results reveal a tendency that the content of total tea polyphenols in tea leaves changed along with seasons, which provided an evidence for confirming the optimal time point of collecting tea leaves and extracting tea polyphenols.

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