Caffeine (1,3,7-trimethylxanthine) is a purine alkaloid and is largely present in several beverages. Hence it becomes essential to quantify the caffeine in various food items.
The beverages such as tea, coffee and soft drinks are the most widely consumed in the world have caffeine. The amount of caffeine in soft drinks varies among brands which are regulated by the US Food and Drugs Administration (FDA) to no more than 6 mg/oz fluid or 200 mg/L. Therefore, analysis of caffeine is required to ensure proper caffeine levels in beverages and to meet regulatory standards
It is important to monitor caffeine in beverages and food by establishing a more precise, simple, fast and low-cost analytical method in order to study its physiological
Due to the wide occurrence of caffeine in the variety of products and interference of the matrix elements of sample, a large number of extraction methods have been proposed for the caffeine. In these methods the aqueous solution of tea or beverages is extracted with the solvents like dichloromethane, chloroform, acetone
In the modified method using solid-phase extraction, the interfering tea pigments were effectively removed by passing the sample through a Sep-Pak C18 cartridge filter
Several chemical and physical methods have been developed for the determination of caffeine in coffee and other beverages. The most widely used methods for the determination of caffeine in beverages include various analytical techniques such as Fourier Transform infrared,
Different samples of green tea and black tea (Lipton Tea, Himalayan Tea, Taaza Tea, Nice Tea) and soft drinks (Thums Up, Pepsi) were purchased from the local market in Hapur. The green tea sample of Lipton was in the form of a tea bag whereas Nice black tea was in the form of dried leaves. The details of samples with their brands and category are given in
All the chemicals used were of analytical grade. The chemicals like chloroform (Fisher), caffeine 99.9% (Sigma Aldrich), sodium carbonate anhydrous (Merck), de-ionized water (Merck) was used.
For the UV/Visible study the spectrophotometer model Specord-210 Plus from Analytical Jena, Germany is used.
S. No. |
Category |
Name of Brand |
1 |
Green Tea |
Lipton Green Tea |
2 |
Himalayan Green Tea |
|
3 |
Black Tea |
Taaza Tea |
4 |
Nice Tea |
|
5 |
Soft Drink |
Thums Up |
6 |
Pepsi |
A standard stock solution of caffeine is prepared at 100 ppm. Several standards of caffeine from the stock solution were prepared from the range of 2-30 ppm. The UV spectrum is obtained by scanning the standards from the range 250 nm to 400 nm. The maximum absorbance is obtained at 273 nm.
500 mg of tea (dried, ground and sieved) was placed in a 250 mL beaker, and 100 mL of boiling distilled water was added to it. The solution was kept on a boiling water bath for 5 min at temperature 90-100oC instead of 40oC mentioned in previous method
Pipet an appropriate soft drink sample (Thums Up, Pepsi) about 5 ml (after degassing) into a 125-ml separatory funnel. Add 10 ml of distilled water, 1 ml of 20% aqueous Na2CO3 followed by 10 ml of chloroform (due to more solubility of caffeine in it), instead of Carbon tetrachloride used previously by Tautua A et al
The spectrum for the various standard solutions of caffeine (2-30 ppm) were recorded with the help of UV Visible spectrophotometer. The maximum absorbance of caffeine is found out at 273 nm. The absorbance values for standard caffeine solutions at 273 nm are used to plot the calibration curve. The calibration curve for the caffeine is constructed from 2 to 30 ppm show the value of regression coefficient 0.99 given in
S. No. |
Category |
Name of beverages |
Caffeine content in this study |
Caffeine content reported by other researchers |
1 |
Green Tea |
Lipton Green Tea |
23.60 mg/g |
13.672mg/g (Rehman R et al) |
2 |
Himalayan Green Tea |
25.30 mg/g |
7.856mg/100g (Letić NG et al) |
|
3 |
Black Tea |
Taaza Tea |
30.50 mg/g |
7.826mg/100g (Letić NG et al) |
4 |
Nice Tea |
45.60 mg/g |
---- |
|
5 |
Soft Drink |
Thums Up |
0.178 mg/ml |
10.69 mg/L-42.17mg/L (Khalid A et al) |
6 |
Pepsi |
0.161 mg/ml |
19.9 mg/L (Rehman R et al) |
The higher caffeine content reported by us from the local samples of green tea, black tea and soft drink may be due to the modified method with the help of UV-Visible spectrophotometry. In the previous studies the factors like temperature and brewing time were ignored. Since in our study, the higher temperature and longer brewing time result the higher caffeine content. UV Visible spectrophotometric method applied in this study for the quantitative analysis of the caffeine concentrations of green tea, black tea and soft drink is sensitive, precise and correct method. It is also an inexpensive and time saving technique instead of HPLC and other analytical techniques.
The author is highly thankful to the department of Science and Technology (DST), New Delhi for providing the grant for the research facilities in the College through DST-FIST program ref. SR/FST/College-318/2016(C).