Critical roasting level determines bioactive content and antioxidant activity of Robusta coffee beans

Indonesian Lampung Robusta coffee green beans were roasted at eight roasting levels (green bean, early yellow, brown, 1st crack done, very light, light, medium, and dark), followed by grinding and brewing. The physical properties of ground coffee and chemical properties of brewed coffee were analyzed. The resulting data were mapped in order to investigate the critical roasting level. It was observed that major alterations for physicochemical properties of coffee happened after "first crack" roasting level (when water activity (Aw) of bean decreased from 0.22 to 0.15). This cracking is defined as popping sound of the bean during roasting. Continuous formation of melanoidins under low Aw (< 0.15) was followed by slow degradation of chlorogenic acid (5-CQA) and total phenolic compounds. Caffeine was stable during roasting, while antioxidant activity slightly decreased. The "first crack" was determined to be the critical roasting level to produce roasted coffee beans containing high concentrations of phenolics.