Comparative evaluation of phenolics and antioxidant activities of hot air and superheated steam roasted coffee beans (Coffea canephora)

As no investigation has so far been made to study the effect of superheated steam (SHS) roasting in comparison to that of hot air (HA) roasting on bioactive compounds acting as antioxidants in roasted coffee beans, changes in phenolic compounds and antioxidant activities of robusta coffee beans undergone HA and SHS roasting at 210-250 degrees C to reach a light, medium or dark roast level were investigated. Total phenolics as well as 5-, 4- and 3-CQA contents and ABTS, DPPH and FRAP antioxidant activities significantly decreased, whereas the flavonoid content remained unchanged or even increased with an increased roast level. Highest and lowest caffeic acid contents were noted in medium and dark roasted beans, respectively. All the aforementioned variables belonging to dark roasted beans significantly decreased with decreased roasting temperature, particularly at 210 degrees C. However, CQAs and caffeic acid contents tended to increase in dark roasted beans when SHS was applied, instead of HA for roasting at 210 degrees C.