The constituents of coffee that are important in making a good beverage are the flavor substances, the bitter substance and caffeine which responsibilities for the stimulating effect of the drink. Caffeine is a methylxanthine with bitter characteristics; however, it is responsible for no more than 10% of the perceived of the coffee bitterness.
The caffeine content of a cup of coffee (150 ml) is about 100 mg. Most people consume three cups of coffee a day and thus 300 mg of caffeine.
Protein is subjected to extensive changes when heated in the presence of carbohydrates. There is a shift of the amino acid composition of coffee protein acid hydrolysates before and after bean roasting.
Several organic acids are present in the aqueous extract from green coffee beans, the predominant being chlorogenic acid and the least acetic acid. Amino acids particularly alanine, glutamic acid and leucine are relatively increased.
The roasting process affects chemical composition because compounds break down or interact as they are heated for different lengths of time and at different temperatures. During roasting, formic and acetic acid are increased and chlorogenic and other acids like citric and malic partially destroyed.
Trigonelline is an alkaloid biologically derived from enzymatic methylation of nicotinic aid. It contributes to the bitterness of the brew and is a precursor for the formation of different classes of volatile compounds during roasting such as pyrroles and pyridines.
Chemical composition of coffee
