UHPLC-PDA-ESI-TOF/MS metabolic profiling of aqueous extracts of Arabica and Robusta Coffee Silverskin: not only natural antioxidants.

Coffee wastes and by-products from coffee industry are a source of contamination and a serious environmental problem, being mainly unutilized, discharged to the environment or burned. This promoted the interest of researchers in the characterization of wastes and by-products as coffee silverskin (CS, the tegument covering the coffee beans) to evaluate the possibility of reusing them. The high content of caffeine (CAF) and chlorogenic acids (CGAs) in CS and a significant antioxidant activity make them attractive for the recovery of natural antioxidants to be used as food supplements, dietary additives or cosmetic ingredients. The presence of phytotoxins and miycotoxins in green and roasted coffee beans, in CS and in dietary supplements containing green coffee (GC) extracts has recently been reported suggesting that a deeper knowledge of the metabolic profile of CS is required in order to evaluate advantages and risks associated with its consumption. In the present study, a comprehensive UHPLC-PDA-ESI-TOF/MS metabolic profiling of aqueous extracts of Arabica (CS-A) and Robusta (CS-R) CS was carried out. CS-A and CS-R were also characterized in terms of total polyphenols, flavonoids and antioxidant activity. The results were compared to those of Arabica GC aqueous extracts. Caffeic acid (CA) derivatives were found as the main CGAs in GC and CS, and the content of both CAF and CGAs followed the order GC >> CS, with CS-R > CS-A. Furokauranes as mozambioside and mascaroside, not previously reported in CS, were found and their levels in CS-A were much higher than in CS-R. The aglycone of mozambioside, not previously reported in coffee, was also evidenced. Atractyligenin and differently glycosilated derivatives were detected in GC and CS, the estimated content being CS-A >> CS-R.