Chlorogenic acids (CGA), a major family of phenolic compounds that represent 6–12% of coffee constituents in mass, are known to be responsible for coffee pigmentation and astringency. The thermal degradation of chlorogenic acids during roasting will result in formation of phenolic substances that contribute to bitterness and aromatic compounds like phenols,
which are undesirable to cup quality. Additionally, CGA participates in colour formation through its incorporation
into the backbone of melanoidins. The major CGA classes in coffee are the caffeoylquinic acids , feruloylquinic acids and dicaffeoylquinic acids, with at least three isomers per class. Caffeine is a xanthine derivative that gives a bitter characteristic taste to coffee. Trigonelline is a pyridine derivative known to contribute indirectly to the formation of desirable and undesirable aroma compounds during roasting. Trigonelline content has also been correlated to good cup quality. Sugars, particularly sucrose, which is the most abundant simple carbohydrate in coffee, act as aroma precursor, originating several volatile substances during roasting such as furans, aldehydes and carboxylic acids. In the last few years, CGA, caffeine and trigonelline have also been the subject of several investigations in view of their
potentially positive biological effects in humans.