Our results showed that CGA isomers in green coffee beans will react to Frémy’s salt, an inorganic stable radical, to a degree that is specific to the isomer. On the contrary, MRP generated partly from CGA transformation during roasting had stronger reactivity with the TEMPO radical, compared with Frémy’s salt. Thus, the complex chemical composition of coffee brew being the basis for different atoms each possessing distinct electron densities, will ultimately govern the absolute response in different antioxidant assay measurements used to evaluate activity. Factors that include the variety or source of the coffee bean, exact roasting conditions and brewing times and procedures collectively influence the final composition of the coffee brew. These factors in turn might react differently