TOPIC: The Study of Contents Responsible for Flavour of of Tea
This is to certify that Shreya Sharma of class XII has successfully completed the project work on chemistry for class XII practical examination of the Central Board of Secondary Education in the year 2011-2012. All the three experiments in the project were performed by the student. It is further certified that this project is the individual work of the candidate.
Signature:
Date:
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I would like to express my special thanks of gratitude to my teacher Ms. Sonali Khanvilkar as well as our principal Ms. Sudhi Mattoo who gave me the golden opportunity to do this wonderful project on the topic the Study of Contents Responsible for Flavour of Tea, which also helped me in doing a lot of Research and I came to know about so many new things. I am really thankful to them. Secondly I would also like to thank my parents and friends who helped helped me a lot in finishing this project within the limited time. I am making this project not only for marks but also to increase my knowledge.
THANKS AGAIN TO ALL WHO HELPED ME.
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1.
The study of contents responsible for the flavour of tea -
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Introduction
2.
Tea Chemistry
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3.
The components of tea - Caffeine - Tea fibre - Carbohydrates
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Amino Acids Lipids and fatty acids Anthocyanidins Organic acids
4.
Tea and Health
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5.
Experiments carried out - Experiment 1
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Experiment 2
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Experiment 3
6.
Conclusion
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7.
Bibliography
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The Study of Contents Responsible for Flavour of Tea
Tea is the most commonly and widely used soft beverage in the household. It acts as a stimulant for central nervous system and skeletal muscles. That is why tea removes fatigue, tiredness and headache. It also increases the capacity of thinking. It is also used for lowering body temperature. The principle constituent of tea, which is responsible for all these properties, is the t he alkaloid-caffeine. The amount of caffeine in tea leaves varies from sample to sample. Originally it was thought that caffeine is responsible for the taste and flavour of tea. But pure caffeine has been found to be a tasteless while substance Therefore, the taste and flavour of tea is due to some other substance present in it. There is a little doubt that the popularity of the xanthenes beverages depends on their stimulant action, although most people are unaware of any stimulation. The degree to which an individual is stimulated by given amount of caffeine varies from individual to individual. Tea is made from the young leaves and buds of the tea plant. Besides caffeine, tea leaves contain tannic acid and colouring matter, such as polyphenolic compounds. The relative amounts of
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these substances are different in different varieties of tea leaves, that is why, their taste and flavour are different. The brownish colour of the tea is due to the presence of polyphenolic compounds and some inorganic icons like Mn 2+, Fe 3+ etc. some simple experiments can be carried out to study the components that are responsible for the variation in tea flavour in various brand of tea.
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Chemical Composition of Fresh Tea Shoot Compounds %
Dry weight
Total Polyphenols
25 - 30
Contribution
Astringency
Flavanols (-) Epigallocatechin gallate
8 - 12
(-) Epicatechin gallate
3-6
(-) Epigallo catechin
3-6
(-) Epicatechin
1-3
(+) Catechin
1-2
(+) Gallocatechin
3-4
Flavonols and flavonol glycosides
3-4
Leuco anthocyanins
2-3
Polyphenolic acids and depsides
3-4
Caffeine
3-4
Theobromine
0.2
Theophylline
0.5
Amino acids
4-5
Organic acids
0.5 - 0.6
Monosaccharides
Briskness
Brothyness
4-5
Polysaccharides
14 - 22
Cellulose and Hemicellulose
4-7
Pectins
5-6
Lignin
5-6
Protein
14 - 17
Lipids
3-5
Chlorophylls and other pigments
0.5 - 0.6
Ash (minerals)
Colour and Appearance
5-6
Volatiles
0.01 - 0.02
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Aroma
Biochemical
compounds responsible for colour
Compounds
Colour
Theaflavins
Yellowish brown
Thearubigins
Reddish brown
Flavonol glycosides
Light yellow
Pheophorbide
Brownish
Pheophytin
Blackish
Carotene
Yellow
Biochemical compounds responsible for taste Compounds
Taste
Polyphenol
Astringent
Amino acids
Brothy
Caffeine
Bitter
Theaflavins
Astringent
Thearubigin
Ashy and slight astringent
Biochemical compounds responsible for flavour Compounds
Flavour
Linalool, Linalool oxide Geraniol, Phenylacetaldehyde Nerolidol, Benzaldehyde, Methyl salicylate, Phenyl ethanol Trans-2-Hexenal, n-Hexanal, Cis-3-Hexenol, Grassy, b-Ionone
Sweet Floral Fruity Fresh flavour
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Caffeine Caffeine is a purine derivative, which is 1,3,7-tri-methyl xanthine. Caffeine content in black tea is around 3 - 4% of dry weight. It has stimulating property and removes mental fatigue. The contribution of caffeine to the infusion is the briskness and creamy property resulting from the complex formed by caffeine caf feine with polyphenols. Briskness is a taste and sensation while creaming is the turbidity that develops from a good cup of tea when cooled. On the contrary their excessive use is harmful to digestion and their long use leads to mental retardation.
Tea fibre The leaf cell wall, containing cellulostic materials surrounded by hemi-cellulose and a lignin seal, prevents the penetration of hydrolyzing enzymes. The reduced succulence in the matured shoot is believed to be due to structural bonding between phenolic components of lignin, polysaccharides and cutin of cell wall.
Carbohydrates The free sugars found in tea shoot are glucose, fructose, sucrose, raffinose and stachyose. Maltose in Assam variety and rhamnose in china variety appeared special. Pectic substances contain galactose, arabinose, galacturonic acid, rhamnose and ribose. Free sugars are 8
responsible for the synthesis of catechins in tea shoot, formation for mation of heterocyclic flavour compounds during processing of black tea and contributing towards water-soluble solids in tea liquor. Cellulose, hemi-cellulose, pectins and lignins are responsible r esponsible for the formation of crude fibre content in black b lack tea.
Amino acids Aspartic, glutamic, serine, glutamine, tyrosine, valine, phenylalanine, leucine, isoleucine and theanine (5-N-ethylglutamine) were found to be the principal amino acids present in tea leaf. Theanine alone contributed around 60% of total amino acid content. Asparagine was formed during withering. The amino acids play an important role in the development of tea aroma during the processing of black tea.
Lipids and fatty acids The neutral, glyco and phospholipid contents and their fatty acid composition varied in Assam, China and Cambod varieties and also during different stages of black tea manufacture. Total lipid contents(%) and total fatty acids (µg/g) at different stages i.e. green leaf, withered leaf, rolled leaf, fermented leaf and black teas are about 6.5, 5.7, 4.5, 4.3 and 2.8 and 9.8, 8.4, 6.6, 4.8 and 3.7 respecttively. The major fatty acids available in tea are linolenic, linoleic, oleic and palmitic.
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Anthocyanidins Delphenidin and cyanidin were the major anthocyanidins present in tea leaf. Anthocyanin contents were higher in tea shoots from pruned than those of unpruned bushes. Role of anthocyanins on the quality of black tea however, has not been found to be significant.
Organic acids Citric, tartaric, malic, oxalic, fumaric and succinic acids were detected in Assam leaf. Role of organic acids towards the biochemical influence on the quality of black tea is not yet reported.
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A large body of scientific evidence indicates the benefits of tea drinking for its wide range of medicinal properties. Tea prevents coronary heart disease, hypertension, blood sugar and tooth decay. Tea has also been reported to have antiviral and germicidal activity.
The most important medicinal value of tea is that it is anticarcinogenic and antimutagenic. The anticarcinogenic activity contributed by the antioxidant polyphenols in tea has been shown to be in very low concentration even in consumer dosages. Thus tea offers tremendous scope of emerging as practical chemipreventive included in a healthy diet for protection of the general consumers by lowering the risk of different dif ferent types of cancer.
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Experiments Carried Out
Aim: Compare the water soluble polyphenol content in the various samples of tea leaves.
Requirements: Beakers, conical flasks, funnels, heating arrangement, tea bags of of different brands of tea.
Theory: Tea contains up to 30% of the water soluble polyphenols. These are largely responsible for the flavour of the tea. To estimate the extent of these compounds in a given sample, the tea leaves are immersed in hot water for equal time and loss in the weight of tea leaves in determined.
Procedure: 1. Weigh the different samples of tea and place them in tea bags. 2. Take three or four conical flasks and put 100ml of hot water to each of them. 3. Put tea bags of different samples of tea t ea in the different conical flasks. After 10 minutes remove the tea bags and dry them by placing in an oven. 12
4. When the tea bags become dry, reweigh them. 5. Note the flavour of the tea solution obtained.
Tea bag
Observations: S. No.
Brand name of tea
Initial weight (gms)
Final weight (gms)
Loss of weight (gms)
% of water soluble component
1.
Brooke Bond (Taj Mahal) Homewood Tea Twinings (green tea & lemon)
2.410
1.810
0.6
75.1 %
2.390 2.290
1.620 1.740
0.77 0.55
67.8 % 76 %
2. 3.
Result: The tea having better flavour has more polyphenol content.
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Aim: Compare the tannic acid content of various samples of tea.
Requirements: Beakers, conical flasks, funnel, heating arrangement, various samples of tea, calcium carbonate, conc. HCL.
Theory: The tannic acid present in tea leaves is precipitated as calcium tannate by treatment of aqueous solution of tea with calcium carbonate. Calcium tannate is then hydrolysed with conc. HCL and re-crystallised from water.
Tannic acid
Procedure: 1. Weigh 5g of each of the given samples of tea leaves. 2. Take 100ml of distilled water in a 400ml beaker and boil boi l it. Then add the first sample of tea leaves to it and boil for 10 minutes. Cool and filter the solution. 14
3. To the filtrate add about 2g of solid calcium carbonate and boil the contents. Tannic acid gets precipitated as calcium c alcium tannate. Separate the precipitate of calcium tannate by filtration. 4. Calcium tannate obtained is hydrolysed by warming with 45ml of conc. HCL. The tannic acid obtained is crystallized from water and weighed. 5. Repeat the steps 2, 3 and 4 with the other samples of tea and record the observations.
Observations: S. No.
Brand name of tea
Weight of tea leaves taken (gms)
Weight of tannic acid obtained (gms)
% of tannic acid
1. 2.
Red Label Waghbakri Tea
5.800 5.810
1.466 0.973
25.3 % 16.7 %
Result: The tea sample containing higher percentage of tannic acid gives better flavour.
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Aim: Compare the caffeine content of the different samples of tea.
Requirements: Beakers, Conical flasks, heating arrangement, different samples of tea, sulphuric acid and chloroform.
Theory: Tea contains caffeine up to 4%. It is more soluble in chloroform than in water. Therefore, it can be extracted from the aqueous extract of the tea with chloroform. However, tannic acid and lead interfere in the extraction and these have to be removed first. Tannic acid is removed as calcium tannate and lead as lead sulphate. After the removal of tannic acid and lead, caffeine is extracted with chloroform.
Formula of caffeine
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Procedure: 1. To the filtrate from Experiment 2 add about 1ml of dil. H 2SO 4. Lead gets precipitated as lead sulphate. 2. Remove the ppt. by filtration and extract the filtrate with chloroform 3-4 times. 3. Combine the chloroform extract and remove the solvent by heating on a stream bath. The residue left behind is caffeine. 4. Weigh the residue left behind. 5. Similarly, determine the amount of caffeine in other samples of tea.
Observations: S. No.
Brand of name of the tea
Weight of tea leaves taken (gms)
Weight of caffeine obtained (gms)
% of caffeine
1. 2.
Red Label Waghbakri Tea
5.800 5.810
0.197 0.168
3.4 % 2.9 %
Result: The tea sample containing higher percentage of caffeine gives better flavour.
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Tea is made from the young leaves and buds of the tea plant. Besides Besides caffeine, tea leaves contain tannic acid and and colouring matter, such such as polyphenolic compounds. The relative amounts of these substances are different in different varieties varieties of tea leaves, which is why, their taste and flavour are different. The brownish colour of the tea is due to the presence of polyphenolic compounds and some inorganic icons like Mn 2+, Fe 3+ etc. Tea contains up to 30% of the water soluble polyphenols. These are largely responsible for the flavour of the tea. tea. It contains caffeine caffeine up to 4%. It It is more soluble in chloroform than in water. Therefore, it can be extracted from the aqueous extract of the tea with chloroform. However, tannic acid and lead interfere in the extraction and these have to be removed first.
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Tea acts as a stimulant for central nervous system and skeletal muscles and removes fatigue, tiredness and headache. The principle constituent of tea, which is responsible for all these properties, is the alkaloid-caffeine. alkaloid-caffeine. The amount of caffeine in tea leaves varies from sample to sample.
The conclusions from the three experiments are as follows: 1. The tea having better flavour has more polyphenol content. 2. The tea sample containing higher percentage of tannic acid gives gives better flavour. 3. The tea sample containing higher percentage of caffeine gives better flavour.
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Websites:
www.google.com
www.wikipedia.com
www.fmltea.com
coffeetea.about.com
www.tocklai.net
Books:
Comprehensive practical chemistry
Investigatory projects on chemistry
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