Result
PROJECT FINAL REPORT COVER PAGE
GROUP NUMBER W6
PROJECT TITLE
SPECTRUM & EXTINCTION COEFFICIENTS OF TEA LEAF EXTRACT
DATE SUBMITTED April 29th, 2002
ROLE ASSIGNMENTS
ROLE GROUP MEMBER
FACILITATOR…………………………….Chalothorn Vashirakovit
TIME & TASK KEEPER………………..…Lesleigh Redavid
SCRIBE………………………………...…..Zaishao Cheng
PRESENTER……………………………….Jamil Beg
SUMMARY OF PROJECT
Spectronic Genesys 5 spectrophotometer was used to determine the influence of brewing tea in different environments such as different pH, temperatures, deionized and tap water. 3 main types of tea, black, green and oolong were used. Also varying grades of tea were compared. Brewing tea in different pHs and in tap water causes a change in the peak absorbance of the wave spectra. At pH of 6 and 8, the peak absorbance was lower than when brewed in deionized water. In tap water, the shape of the curve as well as the peak absorbance is changed. Hence, brewing the tea in tap water or solutions of different pH affect the taste of tea. By comparing the wave spectra patterns of high-grade and low-grade teas brewed at 500C, it was found that high-grade tea had a lower peak at absorbance than low-grade tea. This could be because in the processing of high-grade tealeaf, compounds that are deemed low grade are removed, resulting in a low peak absorbance. Both caffeinated and decaffeinated black and green teas were tested and the molar extinction coefficients of the extracted caffeine were determined to be 0.89 + 0.086 mol/L.cm and 0.84 + 0.067 mol/L.cm, respectively. The 2 molar coefficients of caffeine extracted from tea, ε1 and ε2, were found to be statistically similar to that of the molar coefficient of pure caffeine solution, ε3 (0.93 + 0.023 mol/L.cm), at 95% confidence. Also, Caffeine concentration in black tea is 33.3% higher in black tea, with a caffeine concentration of 0.0064 + 0.0000149 g/L compared to 0.0048 + 0.0000111 g/L in green tea.
Objectives:
The original objectives of this experiment were to determine if different brewing temperatures and brewing solutions (deionized water, tap water, phosphate buffer solutions of pH 6 and pH 8) would affect the compounds extracted from tea, to determine the molar extinction coefficient of caffeine extracted and compare it to that of a pure caffeine solution, and to determine if higher grades of tea contained more polyphenols than lower quality teas. Additional objectives were to see if tea extracts could behave as buffers and to find an ideal buffer, which would not react with the tea.
Proposed Specific Aim:
Our specific aim was to determine the molar extinction coefficient of caffeine from tea extract to be statistically similar to the molar extinction coefficient from a pure caffeine solution at 95% confidence.
Background:
Tea
There are three types of tea: green, oolong and black. Black tea is fully fermented, oolong tea is partially fermented and green tea is not fermented. The characteristic compounds of tealeaves are polyphenols. The oxidative fermentation process converts polyphenols into thearubigens, which changes the chemical structure of the tealeaf. Hence, green tea would have the highest percentage of polyphenols and black tea would have the least. Fermentation allows the key flavor characteristics to emerge, which is why each type of tea has a different flavor.
Caffeine
Caffeine is present in tea, approximately 0.2% dry weight[1]. Caffeine increases pulse rate because it increases the strength and frequency of heartbeats, which can lead to high blood pressure. Caffeine also acts as a mild and harmless diuretic and taken in excess could lead to dehydration. The half-life of caffeine is 4-5 hours so it takes about 10-12 hours for the body to dispose of.
Absorption Spectrophotometry
In absorption spectrophotometry, when a light source scans a solution in the cuvette, some of the UV light is absorbed, which causes a decrease in the intensity of the initial light source. This decrease in intensity depends on the molecular composition of the material.[2] The Spectronic Genesys 5 Spectrophotometer can measure the absorbance for every wavelength, in this experiment the range was 200 to 400nm. Once the absorption spectra were plotted at a fixed wavelength and the concentrations of the solutions were calculated, the molar extinction coefficient was determined using the Beer-Lambert law: A=ε(λ)Cl.
Hypothesis:
The hypotheses remained the same throughout the experiment. One of the hypotheses for this experiment was that for tea brewed at temperatures ranging from 70 to 90oC the wave spectra pattern would have one major peak at 273nm, and at temperatures ranging from 30 to 40oC the wave spectra pattern would have multiple peaks, clustering around 273nm, with lower absorbance values. Another hypothesis was that the ions in tap water (Cl-, F-, Ca2+, Pb2+) and changes in the pH of the brewing solution would affect the compounds extracted from the tea, thus changing the wave spectra. The remaining hypotheses were that a higher quality tea would contain more polyphenols, and therefore have a higher absorbance value and that black tea would have the least amount of polyphenols when compared to oolong and green teas, due to the fermentation process.
Apparatus and Materials:
1. Spectronic Genesys 5 Spectrophotometer
2. Hot plate
3. 100 ml graduated cylinder
4. 150 mL beakers
5. Stopwatch
6. pH meter
7. Electronic Balance: Mettler PB303 (50 to 300+0.01g)
8. Tea: decaf/caffeinated green & black, oolong, gourmet black/green/oolong
9. Coffee Filters
10. Mercury thermometer
11. Pipette man – 1000, 200, 20 μl
12. Phosphate buffer solution (pH6 & 8)
13. Pure caffeine solution
14. 1cm cuvettes (λ ................
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