BASIC CHEMISTRY OF TEA

 

Components of Green Leaf

INSOLUBLE ELEMENTS

-Inorganic components

K,Ca, Ph , Mg , Mn , Fe , S ,Al , Na , Si , Zn , Cu

-Proteins

Contribute to dry weight of green leaf

-Carbohydrates

They account for 34% of green leaf

-Caffeine

They constitute 3-4% of unwithered leaf on a dry weight basis

Chemically, caffeine is a member of the xanthine family. Caffeine is odorless, has a bitter taste and is highly soluble in hot water. Caffeine occurs naturally in coffee, tea, cocoa, kola nuts and a variety of other plants.

In moderation, caffeine has beneficial effects on the body: it increases alertness, stimulates metabolism and contributes to an increase in dopamine levels in the blood, which improves mood.

-Lipids & Fatty Acids

3-4% of dry weight of green leaf

 

 

 

 

 

-Carotenoids Yellow pigments in green leaf Carotenoid content of tea leaves ranges from 36 to 73 mg/100 g dry weight, and is dominated mainly by β-carotene, lutein and zeaxanthin. Among the cultivars, China contained the maximum and Assam clone the least. Carotenoid fractions were found to degrade to different extents at different stages of tea processing. The carotenoid content was as low as 25 mg/100 g in the made tea. Only a small quantity was leached into the brew, the remaining being retained in the infused leaf/tea residue. The high stability of carotenoid in tea is mainly due to the presence of antioxidants, such as polyphenols and catechins. Carotenoid degradation was found to be greater in the CTC (Crush, Tear, Curl) process than the orthodox process, greater in withered than unwithered, and in the order β-carotene > zeaxanthin > lutin. Vitamin A value was greater in orthodox tea than CTC tea and it varied with clones. The carotenoid degradation was found to yield large quantities of desirable aroma volatiles in made tea, giving a high grown flavour status. An increase in endogenous carotene content enhanced all the quality parameters of tea, the VFC (volatile flavour compounds) index, almost being doubled. The tasters' evaluation also revealed the same trend. It was found that a 1:1 NK application at the rate of 300 kg/ha/year enhanced the carotenoid content of green leaves in the second week after application, with subsequent decline.

 

 

 

 

 

 

 

 

SOLUBLE ELEMENTS

-Polyphenols

6 main polyphenols are Catechin , Epicatechin , Epicatechin gallate , Epigallocatechin gallate , Gallocatechin , Epigallocatechin

Tea polyphenols are chemical compounds such as flavanoids and tannins found naturally intea. Depending on how the tea is harvested, handled, processed, and brewed, the polyphenol level in the tea can vary. These chemical compounds are believed to be beneficial to human health, and they are the basis of many claims made about the health benefits of tea. As with many natural compounds which appear to be beneficial to human health, it is difficult to isolate and study tea polyphenols on their own, and some researchers have suggested that their actions in the body may actually be the result of several compounds working together.

Polyphenols are most definitely antioxidants, which means that they can reduce the risk of developing coronary artery disease and a number of other health problems. The polyphenolsfound in tea have also been linked with cancer reduction, as they appear to block the action of some enzymes linked with cancer. Because cancer is so complex and it can be influenced by many environmental and genetic factors, scientists are reluctant to say that tea polyphenolswill categorically prevent cancer, although cancer rates do seem to be lower in tea drinkers after controls for other obvious factors like diet are used to evaluate the data.

Tea also contains small amounts of flavonols (kaempferol, quercetin and myricitin) in the form of glycosides. The flavonol content is less affected by processing, and flavonols are present in comparable amounts in green and black teas

 

-Enzymes

Polyphenol oxidase

Peroxidase

 

 

 

 

 

 

-Amino acids

Theanine contributed to 60% of total amino acid content

Theanine , also gamma-glutamylethylamide or 5-N-ethyl-glutamine, is an amino acid and a glutamic acid analog commonly found in tea (infusions of Camellia sinensis), primarily in black tea, and also in the basidiomycete mushroom Boletus badius and in guayusa.^] Theanine is an analog toglutamine and glutamate, and can cross the blood–brain barrier.^[4] It is sold in the US as a dietary supplement, and is classified by the FDA as agenerally recognized as safe (GRAS) ingredient.^[5] However, the German Federal Institute for Risk Assessment (Bundesinstitut für Risikobewertung, BfR) has objected to the addition of isolated theanine to beverages

-Minerals (ash)

-Gummy matter

-Stimulants like theine , theobromine, theophylline & caffeine

 

 

 

 

 

 

 

 

 

WITHERING CHEMISTRY

-PPO Enzyme activity decreases during withering as a result of moisture loss but can be restored when withered leaf is rehydrated .Activity of the enzyme also decreases at temperatures above 35degC

-Carbohydrates breakdown into simple sugars .This increases during withering and maybe incorporated into amino acids to form volatile flavor compounds

-Caffeine increases during physical wither

-Lipids & fatty acids breakdown to form volatile compounds which have a detrimental effect on flavours

-Carotenoids –yellow pigments in green leaf which help in photosynthesis .During withering they degrade to form volatile flavor compounds

-Amino acids – Asparagine formed during withering

Measurement of :

-Chlorophyll fluorescence

-Ph

-Chloroform test

-

 

 

 

 

 

 

 

During Fermentation

Catechins are first formed into orthoquinones which are then oxidized to form theaflavins

Catechins react to form 6 theaflavins :

Theaflavin / Theaflavin 3 monogallate / Theaflavin 3’ 3’ digallate/ Theaflavin 3’ monogallate / Isotheaflavin / Neotheaflavin

TFs are unstable and further oxidize to form TRs – TRs are largely responsible for flavor , aroma , and colour of liquor – some make it brighter and brisker and some make it dull

TRs reduce black tea brightness , provides colour and body

Volatile carbonyl compounds formed from amino acids during processing :-

Glycine   à formaldehyde

Alanine  à acetaldehyde

Valine  à isobutyraldehyde

Leucine à isovaleraldehyde

Methionine à methional

Phenyl alanine à phenlyacetaldehyde

 

 

 

 

 

 

 

During Drying

-Chlorophyll breaks down to form dark colour

In the final stage of black tea processing following chemical changes take place:

· By the deactivation of enzyme like Polyphenol Oxidase (PPO), Peroxidase (PO), etc. almost all the biochemical reactions are brought to an end. However, as the temperature rises to the level for destroying enzymes, the particular enzymes get activated and faster reaction takes place in the initial stage of drying. If the temperature is raised slowly, TR is likely to be formed.

· Chlorophyll is degraded to pheophytin and pheophorbide at elevated temperature during drying contributing towards the blackness of made tea.

· At elevated temperature, by binding with proteins, Polyphenols make complex chemicals, which brings down the level of astringency.

· Interaction between carbohydrates with amino acids at elevated temperature leads to the formation of flavour components.

 

 

 

 

 

 

 

 

 

 

 

 

How to measure TR in tea ?

The absorbance measured on a UV visible spectrophotometer

6ml of black tea extract (100mg/10ml) was mixed with 6ml of 1% 1% (W/V) aqueous solution of anhydrous disodium hydrogen phosphate and the mixture was extracted with 10ml of ethyl acetate by quick repeated inversion for 1 min. The separated bottom layer was drained ,and the remaining ethyl acetate layer (the TF fraction) was diluted with 5ml ethyl acetate .Optical densities E1, E2 , and E3 were obtained on extracts prepared as follows :

1. 2.5ml of TF extract (100mg/10ml) was diluted to 25ml with methanol (E1)

2. To 0.25ml (100mg/10ml) of black tea extract 2.25ml of water was added and made up to 25ml with methanol (E2)

3. To 0.25ml (100mg/10ml) of black tea extract 0.25ml of aqueous oxalic acid (10% w/v) and 2ml of water was added and made up to 25ml with methanol ( E3). Optical densities of E1 ,E2 and E3 were measured at 380 and 460 nm

At 380nm %TF = 2.3* E3

%TR = 7.06 (4E3-E1)

At 460nm total colour = 6.25 * 4E2

% total brightness = E1/4E2 * 100

 

 

 

 

MEASURING STRENGTH OF TEA

How Do You Take Your Tea? Make a Simple Electronic Device to Measure the Strength of Tea

Experimental Procedure

Making Your Light-measuring Device

1. Wrap the sides of one of the plastic cups with aluminum foil. Leave the bottom uncovered.

2. Secure the aluminum foil with electrical tape. Use a minimal amount of tape to hold the aluminum foil in place.

3. Bend the wires on the photoresistor, where they are attached.

4. Tape the photoresistor under the cup, described as follows, and shown in Figure 1.

a. First cover the foil with electrical tape so that the metal wires from the photoresistor do not touch any foil (Figure 1.A.). The foil would cause a shortin the photoresistor.

b. The part with the squiggly line should face into the cup. See Figure 1.C.

 

Figure 1. A photoresistor is taped to the bottom of a clear plastic cup covered with aluminum foil. The metal leads from the photoresistor are protected from the foil with electrical tape (1.A.). The photoresistor is taped in place with electrical tape (1.B.). The whole bottom of the cup is covered with electrical tape to hold the photoresistor in place and to block stray light (not shown). The cup is turned over and taped to a waterproof counter. The squiggly surface of the photoresistor (the light-sensitive side) faces the inside of the cup (1.C.).

 

5. Tape the photoresistor in place with electrical tape. (Figure 1.B). If there is a dot or other obstruction in the middle of the bottom, locate the face of the photoresistor away from the obstruction.

6. Now cover the entire bottom of the cup with electrical tape. This will hold the photoresistor in place and block stray light.

7. Turn the cup right-side up.

8. When you get to the “Measuring the Strength of Tea” section you will place the testing cups inside the cup with the photoresistor. Don't pour liquid into the cup with the photoresistor attached.

9. Use electrical tape to secure the cup with the photoresistor to a kitchen counter surface. The surface should be waterproof.

10. Place a lamp on the counter so that the light shines into the cup. If the cup can be illuminated with other kinds of existing light in the room instead, such as track lighting, that is fine, too.

11. It is very important that the light source stays the same for all of the tests. Once you start a series of tests, do not move the lamp or change its brightness or position.

Making the Tea

1. Label five mugs 1–5 with the masking tape and permanent marker.

2. The five mugs will hold the following samples:

o Mug #1: Water only

o Mug #2: Tea, 10-seconds (sec.) brewing time

o Mug #3: Tea, 30-sec. brewing time

o Mug #4: Tea, 90-sec. brewing time

o Mug #5: Tea, 270-sec. (4 1/2 minutes) brewing time

3. Place a tea bag in mugs 2–5.

4. Heat water to boiling in a teapot. The temperature of the water should be the same for each test. Start each sample with boiling water.

5. Pour 200 mL of hot water into the liquid measuring cup or beaker. The measuring cup/beaker is used to obtain accurate volumes for each sample. The volume of the water should be the same for each test.

6. Use the thermometer to measure the temperature of the water in the beaker. Write down the temperature. All future trials should start with water that is the same temperature. Heat or cool the water as needed to achieve the same temperature each time. Plus or minus two degrees is fine.

7. Pour the hot water from the measuring cup into mug #1. Mug #1 is a negative control. Controls are samples with known ingredients that should give clear results. They are used to test the procedure. In a negative control, there should be no "signal." Plain tap water is a suitable negative control in this experiment, because it has no tea.

8. Pour 200 mL of hot water into the measuring cup.

9. Pour the hot water from the measuring cup into mug #2.

10. Remove and discard the tea bag after 10 seconds. Use the stopwatch to keep track of the time.

11. Re-boil the water to keep the starting temperature constant. Pour 200 mL of hot water into the measuring cup.

12. Pour the hot water from the measuring cup into mug #3.

13. Remove and discard the tea bag after 30 seconds.

14. Pour 200 mL of hot water into the measuring cup.

15. Pour the hot water from the measuring cup into mug #4.

16. Remove and discard the tea bag after 90 seconds.

17. Re-boil the water to keep the starting temperature constant. Pour 200 mL of hot water into the measuring cup.

18. Pour the hot water from the measuring cup into mug #5.

19. Remove and discard the tea bag after 270 seconds (4 1/2 minutes).

20. Allow all of the teas to cool to room temperature.

Measuring the Strength of the Tea

1. To keep the light constant, block any sources of sunlight. Be careful not to let your shadow affect the readings.

2. Attach the wires from the multimeter to the wires of the photoresistor. For more information about using a multimeter, visit the Science Buddies pageElectronics Primer: Using a Multimeter.

3. Turn the multimeter on. Make sure the multimeter is set to measure resistance, and that the leads are in the correct holes in the multimeter.

4. Tape the wires from the multimeter to the surface of the counter to keep them in place.

5. Label five other plastic cups 1–5. These are the testing cups.

6. Pour the water from mug #1 into the empty plastic cup #1.

7. Place the plastic cup with the water in it into the cup with the photoresistor. Don't pour liquid into the cup with the photoresistor attached.

8. Read the resistance of the photoresistor with the multimeter. Remember to record all data in your lab notebook. Note: You may need to experiment with the correct range.

 

Figure 2. Experimental setup for measuring the strength of tea. The multimeter is set to read resistance. The cup in the middle has the photoresistor taped to the bottom. Two samples are shown on the right side of the figure.

 

9. Repeat the readings for testing cups 2–5.

10. To get duplicate readings, measure the resistance for each cup again.

11. Repeat Making the Tea and Measuring the Strength of the Tea, with clean and fresh materials, at least two more times. This ensures that your results are accurate and repeatable.

Analyzing Your Results

1. Make a data table with the resistance readings for each sample.

2. Calculate the average resistance for each brew time.

3. Subtract the value of the negative control (cup of water) from the other values.

4. Graph the average resistance, in ohms, on the y-axis vs. time (in seconds) on the x-axis.

5. Discuss the shape of the curve. Is it a straight line or does it curve?

 

 

Introduction

 

 

 

Color Perception

 

Ten million! That is the number of different colors that we can distinguish. No wonder we cannot remember colors well enough to  identify a particular shade.  However, the  quality criterion “color” is becoming more and more important in every industry. Uniform color influences customers’ likes and dislikes. This is of particular importance when the individual components of the final product  are manufactured at different company sites, or even more complicated when several suppliers are involved. Neverthe- less, in the end the color must be right.

Visual color perception is influenced by different color sensitivities from person to person (mood, age, etc.), varying environments such as lightness and color, as well as the deficiency to communi- cate and document color and color differences.

 

These shortcomings can only be solved by using color instrumen- tation with internationally specified color systems. This guaran- tees objective description of colored objects. Color perception is dependent on the interaction of three elements:

 

SolID Color

 

light source

observer

 

 

 

 

 

 

 

 

object

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

light Source

 

Color changes with the light source. Therefore, standard  illumi- nants have to be agreed  upon and used. The prerequisite of a light source to be usable for color evaluation is to continuously emit energy throughout the visible spectrum (400 to 700 nm).

 

 

 

 

 

 

 

 

 

 

 

White daylight dispersed into the spectral colors (rainbow)

 

The CIE (Commission Internationale de l’Eclairage) standardized light sources by the amount  of emitted energy at each wave- length (= relative spectral power distribution).

In practice, important illuminants are: Daylight D65, C

Incandescent light A

Fluorescent light F2, F11

Together they stimulate the brain to produce the impression of color. To determine the sensitivity of the receptors,  systematic visual tests were done by the CIE in 1931 and 1964. Based on the results, the 2° and 10° observer were standardized,  representing a small and large field of view, respectively.

 

Observer

 

2° Standard Observer

 

 

 

 

 

 

 

10° Standard Observer

 

 

 

 

 

 

When viewing a sample, the eye integrates over a large area, which correlates best to the 10° observer.

 

S(λ)

 

D65

S(λ)

object

A

Light source and observer are defined by the CIE and their spectral functions are stored within color instruments. Optical properties of an object are the only variables that need to be measured. Modern color instruments measure  the amount  of light that  is

400 700 nm

 

 

S(λ)  F2

 

 

 

 

 

400 700 nm

 

 

observer

400 700 nm

reflected by a colored sample. This is done at each wavelength and is called the spectral data.

For example, a black object reflects no light across the complete spectrum  (0% reflection), whereas  an  ideal white specimen reflects nearly all light (100% reflection).

All other colors reflect light only in selected parts of the spectrum. Therefore, they have specific curve shapes or fingerprints, which are their spectral curves.

In the following graphs, typical spectral curves for a red, blue and green sample are shown.

 

Without an observer there  would be no color. Reflected light from a colored object enters  the human  eye through  the lens and strikes the retina. The retina is populated with three different types of light-sensitive receptors: one which reacts to red light, another to green light, and a third to blue light.

R(%)

 

 

 

 

 

400 700 nm

R(%)

 

 

 

 

 

400 700 nm

 

R(%)

 

 

 

 

 

400 700 nm

 

 

 

 

 

 

 

72  BYK-Gardner GmbH • Lausitzer Strasse 8 • 82538 Geretsried • Germany • Tel +49 8171 3493-0 • Fax +49 8171 3493-140

Color Systems

 

Color systems combine data from three elements:

■ light source

■ observer

■ object

The same ΔE* value can be obtained for two sample sets, and yet look completely different:

 

They are the tools to communicate and document color and color differences.

The system which is recommended  by the CIE and widely used

Sample Set 1

Sample Set 2

 

Sample  Set 1  Sample  Set 2

today, is the CIELab system.

 

 

L* = 100

ΔL* 0.57 0.0

Δa* 0.57 0.0

Δb* 0.57 1.0

ΔE* 1.0 1.0

 

 

 

 

 

- a*

+ b*

 

 

 

h°

 

C*

 

+ a*

To determine the actual change in color, the individual colorimet- ric components ΔL*, Δa*, Δb* or ΔL*, ΔC*, ΔH* need to be used.

The calculation and interpretation  of the differences are done as follows:

 

 

- b*

∆ = Sample – Standard

 

 

L* = 0

 

It consists of two axes a* and b* which are at right angles and represent  the hue dimension or color. The third axis is the light- ness L*. It is perpendicular to the a*b* plane.Within this system, any color can be specified with the coordinates L*, a*, b*. Alter- natively L*, C*, h° are commonly used. C* (= Chroma) represents the intensity or saturation of the color, whereas the angle h° is

 

-∆a* +∆a*

 

 

 

 

-∆b* +∆b*

 

+∆L*

 

 

 

 

-∆L*

 

 

-∆C*

 

 

 

-∆H*

 

 

 

 

 

+∆H*

 

+∆C*

another term to express the actual hue.

 

To keep a color on target  a standard  needs  to be established and the production run is compared  to that standard;  a typical customer / supplier situation. Therefore, color communication is done in terms of differences rather than absolute values.

The total change of color, ∆E*, is commonly used to represent a

color difference.

The color differences that can be accepted must be agreed upon between  customer and supplier. These tolerances are dependent both on demands and technical capabilities.

 

 E* = B(  L*)2  + (  a*)2 + (  b*)2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BYK-Gardner GmbH • Lausitzer Strasse 8 • 82538 Geretsried • Germany • Tel +49 8171 3493-0 • Fax +49 8171 3493-140  73

Color Instrumentation

 

In industry, there are two classes of instruments used to measure color: 45/0 and sphere geometry.

 

Control  color as you see it

The 45/0  geometry uses 45° circumferential illumination and 0°

viewing perpendicular to the sample plane.

The circumferential illumination  is essential to achieve repeatable measurement results on directional and structured surfaces.

Control  the hue of your color

A sphere geometry illuminates the sample diffusely by means of a white coated integrating sphere. Baffles prevent the light from directly illuminating the sample surface. Measurement  is done using an 8° viewing angle.

 

 

 

Detector

8° viewing

 

 

 

 

 

Light Source

 

Detector

0° viewing

Baffles

 

 

 

Baffles

 

Light source Diffused Illumination

 

 

 

 

 

Sample

 

 

 

The 45/0 geometry simulates the normal condition used for color evaluation. For example, when we read a glossy magazine we position it to avoid the gloss from coming into our eye.

A high gloss sample with the same pigmentation is visually judged

A sphere instrument may be operated  under two different meas- urement conditions:

specular included (spin) or specular excluded (spex)

In the “spin” mode, the total reflected light is measured: Diffuse reflection (color) + direct reflection (gloss)

Color is measured  independent  of the sample’s gloss or surface texture.

darker  by the  eye when  compared  to  a matte  or structured sample.

This is exactly what a 45/0 instrument measures:

Differences in gloss / texture →x

Color differences

 

Differences in gloss / texture → Color differences

 

On the automotive interior plaque, you will get a difference be- tween the two structured sides: ΔE* = 3

Applications where it is necessary to have the agreement with the visual assessment are:

■ Batch to batch comparison in production

■ Assembly of multi-component products using different materials

 

 

 

 

 

 

 

 

 

 

 

 

Example: Automotive interior plaque – one material with different structures.

On the automotive interior plaque, you will get no difference

between  the two structured sides: ΔE* = 0

 

Applications for measurements taken in “spin” mode:

■ Color strength depending on dispersion time

■ Weathering and temperature influence on color

■ Color matching

 

In the “spex” mode, a gloss trap is used to capture  the directly reflected light (gloss). This configuration simulates the 45/0  ge- ometry. In case of medium to low gloss samples, deviations will occur between the 45/0 and the sphere spex configuration as the gloss trap does not completely exclude the specular component.

 

Summary

 

Only measurements taken under the same conditions can be com- pared. Therefore, it is necessary to note the following information in a color measurement report:

■ Color instrument (geometry)

■ Illuminant / observer

■ Color system

■ Sample preparation

 

BYK-Gardner offers a complete line of benchtop  and portable spectrophotometers for color measurement.

-Impact of fermentation on Ph

The pH of tea varies widely depending on the strength of the tea, and the type of tea used. Some green teas, such as chun mee, which have a sour flavor, are naturally slightly more acidic. 

The more strongly you brew tea (meaning, the more leaf used per amount of water, and the longer the steeping time), the more acidic the tea will be, and thus, the lower the pH will be. 

There are many sources that state the pH of ordinary black tea is normally from 6.0 - 6.6, but one scientific study measured it as low as 4.9. Even this lower figure is still within the normal range of mild food and drink. Soft drinks, by comparison, have a much lower pH. For comparison, pure lemon juice has a pH of around 2. The pH of tea is high enough that it is not a matter of health concern for anyone.
Ph is due to tannic acid , so Ph during fermentation is between 4.5-5 , and should be more during withering during the early stage of formation of tannic acid

-Correlation of gas and resistance to fermentation

As a first step, an electronic nose needs to be trained with qualified samples so as to build a database of reference. Then the instrument can recognize new samples by comparing volatile compounds fingerprint to those contained in its database. Thus they can perform qualitative or quantitative analysis. This however may also provide a problem as many odours are made up off multiple different molecules, this may be possibly wrongly interpreted by the device as it will register them as different compounds, resulting in incorrect or inaccurate results depending on the primary function of a nose.^[10]

Tannic acid is astringent in nature .It is formed from polyphenol and is a weak acid intrinsically compared to citric juices or even coke.