Time for coffee and tea
Caffeine in a cup of coffee
There are many reasons that people love coffee, some love the taste, some love its aroma, but for many the main benefit of coffee is its stimulatory effect: Caffeine. But if you are drinking coffee how do you know how much caffeine that you get? There are large differences in the amounts of caffeine that are present in decaffeinated coffee and an espresso.
Caffeine is soluble in water and is neutral over a large range of pH's. Caffeine has been measured by HPLC, CE and its solubility allows the MEKC to be used. Recently a new technique using a Pi-complex to add charge to the running buffer has been proposed. The results showing the amount of caffeine in coffee is given below.
Caffeine is found in coffee beans and are associated with esters of trans-cinnamic and quinic acids known as chlorogenic acids. as caffeine is able to travel through the membranes of cells and accumulate within them (by complexing with chlorogenic acids), it was thought that this was a good basis for measuring with CE.
By using either caffeate or 3,4-dimethoxycinnamate in the running buffer allowed the measure of caffeine in instant, ground and decaffeinated coffees. The results were very similar to what were seen when measuring caffeine by the more traditional HPLC method. So how much caffeine is in a cup of coffee? The results of the caffeine measurements are given below:
1. Instant coffee: Average caffeine content: 32.5 mg per gram of coffee
2. Ground coffee: Average caffeine content: 13.5 mg per gram of coffee
3. Decaffeinated coffee: Average caffeine content: 0.7 mg per gram of coffee
It can be seen that a cup of instant coffee has a much higher content of caffeine than ground or decaffeinated coffee but bear in mind that you will use a much higher amount of fresh ground coffee than instant to make a cup of coffee. An average cup of espresso will have about 2 to 3 times as much caffeine cup as an instant cup of coffee, whereas a decaffeinated cup will have about a fifth of the caffeine content of an instant cup of coffee.
Nogueira and do Lago (2007). Determination of caffeine in coffee products by dynamic complexation with 3,4-dimethoxycinnamate and separation by CZE. Electrophoresis. 28: 3570 to 357