*2.2.3 Trigonelline*

Trigonelline, a nitrogenous compound is derived from the methylation of the nitrogen atom of nicotinic acid (niacin) and an alkaloid that has a chemical formula, of C7H7NO2 and molecular weight of 137.138 g/mol [55]. Trigonelline is a major source in discriminating between Arabica and Robusta coffees during roasting [56]. Arabica has trigonelline levels ranging from 0.88% to 1.77% dmb whereas *C. canephora* species levels range from 0.75% to 1.24% dmb [53]. Trigonelline is a vitamin B6 derivative with 100% solubility in water and contributes to bitterness

in coffee [54]. Degradation of trigonelline during roasting results in niacin, nicotinamide and a wide range of aroma volatiles, that include pyridines and pyrroles which in turn influence flavour [6, 53].

### *2.2.4 Chlorogenic acids*

Chlorogenic acids (CGA) are the highest occurring polyphenols in coffee and form a significant part of coffee antioxidants [57, 58]. CGA belongs to hydroxycinnamic acids classes that comprise caffeic acid (3,4-hydroxycinnamic acid), ferulic acid (3-methoxy-4-hydroxycinnamic acid), p-coumaric (4-hydroxycinnamic acid), and sinapic acid (3,5-dimethoxy-4-hydroxycinnamic acid) [59]. CGA varies from 4% to 8.4% in Arabica coffee and between 7% to 14.4% in Robusta coffee whereas Arabusta hybrids have intermediate levels [60]. Maillard and Strecker's reaction cause chlorogenic acids to form pigments that affect taste and flavour [61].
