| Tea (Camellia sinensis) is one of the most widely consumed beverages in the world. Being favored for its healthy benefits and pleasant flavor, the tea originated in China. In China, tea can be classified into four different types based on different processing methods employed, such as unfermented green tea, semi-fermented oolong tea, fully fermented black tea, and post fermented Pu-erh tea. As a scientific and healthy lifestyle, drinking tea has been accepted by the public. In recent years, with the strengthening of people’s concept of health, tea is getting more favour of people. The chemical constituents of tea mainly include water-soluble compositions (polyphenols and polysaccharides) and volatile compounds. The differences in chemical composition are influenced by the geographical characteristics and processing techniques. To date, there are few studies concentrated on the differences of water-soluble and volatile compounds of teas made by different processing techniques or in different regions. Therefore, this research will comprehensively study the various chemical components in different types of tea, and explore their relationship among different tea quality characteristics (taste and aroma), chemical components and tea processing technologies. The author hopes this study can provide some useful advice and reference for the great development of the tea market in our country in the future. The main research and conclusions are as follows:1. In the case of Biluochun green tea, aroma components of tea influenced by different processing steps were studied. Using fully automatic HS-SPME coupled with GC-MS, aroma compounds of Biluochun samples in six processing steps were identified, and studied the formation and transformation of volatile components in processes. Through the measurement methodology, we summarized the changes of aroma in every processing steps. The results show that a total of 67 aroma components were identified, some volatile compounds, such as linalool oxides, β-ionone and phenylacetaldehyde, increased through the processes. In the meantime, the contents of aldehydes, ketones and nitrogen compounds also increased. In contrast, the proportion of alcohols and hydrocarbons decreased in the production process. These major changes in the aroma composition can be used as quality control index of Biluchun green tea in the production process. In addition, the aroma compounds decreased most obviously in the drying process, so we suggested that the drying process in the formation of green tea aroma is an important part of quality control.2. Using HPLC, Folin-phenol method, phenol sulfuric acid method and fylly automatic HS-SPME coupled with GC-MS, Yunnan and Fujian oolong teas, green tea, black tea, and Pu-erh tea were collected from major tea estates across China. Their main water-soluble and volatile compounds were identified and measured. The total polysaccharide, caffeine, and catechin content of Yunnan oolong tea was found to be different from that of Fujian oolong tea, a result suggesting that the kinds of tea leaves used in Yunnan and Fujian oolong teas were naturally different. However, according to their aroma compounds, principle component analysis (PCA) and cluster analysis (CA) of the volatile compounds showed that the two types of oolong teas were similar and cannot be clearly distinguished from each other; they are also different from green, black, and Pu-erh teas, a result indicating that the same oolong tea processing technology applied to different tea leaves results in consistent aroma characteristics. The PCA analysis results also indicated that benzylalcohol, indole, safranal, linalool oxides, β-ionone, and hexadecanoic acid methyl ester highly contributed to the distinct aroma of oolong tea compared with the other three types of teas. This study proved that the use of the same processing technology on two kinds of tea leaves resulted in a highly consistent tea aroma.3. Using HPLC, Folin-phenol method, phenol sulfuric acid method, and fully automatic HS-SPME coupled with GC-MS, volatile and water-soluble compounds in 4 types of teas were determined.40 black, green, Pu-erh and oolong tea samples were analyzed and established a quality evaluation model. The results showed that, in 40 tea samples, green teas had the highest contents of (+)-catechin, (-)-epicatechin, (-)-epicatechin gallate ester, (-)-epigallo catechin, and (-)-epigallo catechin gallate; there was not significant difference (P>0.05) in the polyphenol contents of tea samples; and the polysaccharide content of black teas was the highest among the tea samples; in different types of tea, aroma components and quantities have significant differences (P<0.05); ECG, EGCG, hexanal, linalool, β-onone, indole and 1,2,3-trimethoxybenzene can be used to identify green tea, black tea, Pu-erh tea and oolong tea. Therefore, the main water-soluble components and volatile components can be the value index to classify the different types of tea and builded their own characteristics models, which provides some new ideas for the quality control of tea products.4. In addition, we determined the antioxidant properties of oolong tea, green tea, black tea and Pu-erh tea by FRAP and DPPH, and studied the relationship between the main water soluble components and antioxidant properties in different types of tea. The results showed that the content of polysaccharide in different tea leaves increased from 10.31 mg/g to 18.52 mg/g; the content of polyphenols in different tea increased from 121.71 mg/g to 124.68 mg/g; The order of antioxidant capability and the contents of catechins is green tea> oolong tea>Pu-erh tea> black tea. It suggested that catechins, in tea was the major antioxidant components. |
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