Tea (Camellia sinensis L.) is one of the most widely consumed beverages in the world. One of the most important beneficial effects of tea is the antioxidant activity and free radical-scavenging ability of the polyphenol components. There are three kinds of teas divided by the degree of fermentation process, non fermented (green and white tea), partially fermented (red, pouchong and oolong tea) and completely fermented (black tea). Therefore, the objectives of this research were to study the physico-chemical properties and sensory evaluation of tea infusions which used tea leaves from the plant of Camellia sinensis L. cultivar Shy-jih-chun with different fermentation times: green tea, pouchong tea, oolong tea and black tea.
A tea infusions sample was prepared by 5 grams of tea leaves, infused with 150 grams of boiled water for 5 minutes, and then filtered through tea strainer. Four kinds of tea infusions were analyzed the physico-chemical properties, taste components, antioxidant activity, antioxidant components, antimicrobial activity and consumer sensory evaluation. The decrease of pH of tea infusions was found when tea leaves passed the process of fermentation. The color result of green tea infusion showed that the green tea was the most greenish and yellowish. Black tea’s color was the darkest with red and yellow in color as a result of the concentration of theaflavins (TFs), which are a group of yellow-orange pigments produced as a result of enzymatic oxidation of tea polyphenols in the fresh leaf. Thearubigins (TRs), a group of red pigments converted from TFs under the action of peroxidase.
The soluble sugars found included fructose, glucose and sucrose. Fructose was found in the highest contents in all tea infusions, which found in green tea > oolong tea > pouchong tea > black tea (42.94 > 40.52 > 34.67 > 25.70 mg/100 ml, respectively). The most abundant amino acid was theanine which is a unique amino acid. The contents of free amino acids of tea infusions were expressed as oolong tea (2.010 mg/100 ml) and green tea (1.927 mg/100 ml) contained significantly more total contents of free amino acids, whilst black tea was 0.618 mg/100ml due to the fact that during process of fermentation, the amino acids were transformed to carbonyl compounds.
With regard to the antioxidant properties of tea infusion, antioxidant activities of the tea infusions were more effective than that of ascorbic acid. The reducing power of the tea infusion was in descending order of green tea > oolong tea > pouching tea > black tea. Tea infusions had the good ability for scavenging free radical due to the presence of polyphenols, EGCG and ECG. During oxidation, much of the catechin content of green tea was converted to oxyproducts, along with a loss of antioxidant capacity. The ability to chelate Fe2+ and scavenge free radicals renders the flavonoids very good antioxidants, the main antioxidant activity resides in ring B. That caused the values of chelating ability were in the descending order: black tea > green tea > oolong tea > pouchong tea. For total catechins contents, the values were in the descending order: 124.60 > 84.00 > 77.26 > 62.97 mg/100 ml which were found in green tea > oolong tea > pouchong tea > black tea, respectively. The results obtained indicate that EGCG, epigallocatechin gallate was in the highest concentration in catechins. All types of tea have the alkaloids caffeine and theobromine but in varying amounts.
The antimicrobial activity exhibited that green tea infusion was the most effective against Staphylococcus aureus. From the hedonic scores for tea infusion, color, aroma and overall of oolong tea was higher than others tea. The taste of oolong tea, black tea and pouchong tea did not differ significantly. In conclusion, different fermentation times resulted in tea leaves with different physico-chemical, sensory and antioxidant properties.

TABLE OF CONTENTS iii
LIST OF FIGURES vi
LIST OF TABLES vii

CHAPTER 1 Literature Reviews 1
1.1 Introduction of tea 1
1.2 Classification and methods for making tea 2
1.3 Chemical composition of tea 6
1.4 Chemistry of color and taste of tea 17
1.5 Functional effects of tea 19
1.6 Antioxidant properties 23
1.7 Antimicrobial properties 36
CHAPTER 2 Materials and Methods 40
2.1 Experiment material 40
2.1.1Tea samples 40
2.1.2 Chemicals 44
2.2 Experiment methods 46
2.2.1 Sample preparations 46
2.2.2 Analysis of physical and chemical properties 46
2.2.2.1 pH value 46
2.2.2.2 °Brix value 46
2.2.2.3 Conductivity value 46
2.2.2.4 Soluble solids in tea infusion 46
2.2.2.5 Color analysis 47
2.2.3 Characterization of flavor 47
2.2.3.1 Soluble sugar (Ajlouni et al., 1995) 47
2.2.3.2 Free amino acid 48
2.2.4 Analysis of antioxidant properties 49
2.2.4.1 Determination of antioxidant capacity (conjugated diene method, AOA) (Lingnert et al., 1979) 49
2.2.4.2 Determination of free radical scavenging activity on 1,1 - diphenyl -2- picrylhydrazyl hydrazine group (Shimada et al., 1992) 50
2.2.4.3 Determination of reducing power (Oyaizu et al., 1986) 51
2.2.4.4 Determination of chelate ferrous ions (Dinis et al., 1994) 51
2.2.4.5 Determination of Trolox equivalent antioxidant capacity (Re et al., 1999) 52
2.2.5 Analysis of antioxidant component 52
2.2.5.1 Determination of ascorbic acid (Wang et al., 2006) 52
2.2.5.2 Determination of total phenolic content (Taga et al., 1984) 53
2.2.5.3 Determination of total flavonoid content (Tsai et al., 2008) 53
2.2.5.4 Determination of polyphenols and purine alkaloids contents (Liang et al., 2003) 54
2.2.6 Analysis of antimicrobial properties 54
2.2.6.1 Test organisms 55
2.2.6.2 Inhibition zone 55
2.2.6.3 The minimum inhibitory concentration and minimum bactericidal concentration (Teke et al., 2007) 55
2.2.7 Consumer sensory evaluation (Comsumer preference test) (Lin et al., 2002) 56
2.2.8 Statistical analysis 57
CHAPTER 3 Results and Discussion 58
3.1 Analysis of physical and chemical properties 58
3.2 Characterization of flavor 66
3.3 Analysis of antioxidant properties 73
3.4 Analysis of antioxidant component 96
3.5 Analysis of antimicrobial properties 102
3.6 Consumer sensory evaluation (Consumer preference test) 107
CHAPTER 4 Conclusion and Recommendation 109
CHAPTER 5 References 110

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