Variability of Total Polyphenol Contents in Ground Coffee Products and Their Antioxidant Capacities through Different Reaction Mechanisms

Coffee is one of the most popular non-alcoholic drinks consumed daily by millions of by millions of individuals worldwide. It is characterized by varieties and processing, which cause changes in chemical compositions and biological activities. This study aimed to evaluate the effects of roasting degrees during the processing period (light, medium, and dark) on the total polyphenol contents (TPCs) inground coffee products of arabica, robusta, and liberica and their trolox equivalent antioxidant capacities (TEACs) through various chemical reaction mechanisms (DPPH, ABTS, FRAP, and CUPRAC). The analytical methods were conducted based on spectrophotometric principle after the microwave-assisted liquid extraction. The results of the TPCs followed the descending order of robusta (34.3-48.23 mg GAE g(-1)) > liberica (31.5-34.37 mg GAE g(-1)) > arabica (27.1-44.11 mg GAE g(-1)). Moreover, robusta coffee generally performed greater TEACs than liberica and arabica. Besides, the TPCs and TEACs varied regarding different roasting degrees, in which the medium roasting mostly exhibited the highest values due to the balance between the degradation of phenolic compounds and the generation of new antioxidant compounds mainly from the Maillard reactions. Strong correlations between TPCs and antioxidant capacities (R-2 > 0.6), indicating rich phenolic compounds played key roles in TEACs of coffee.