Development of plasma-assisted electrothermal reactor for coffee roasting and analysis of its roasting characteristics

Coffee roasting plays a critical role in determining coffee quality because it influences both aroma formation and the composition of bioactive compounds. In this study, a plasma-assisted electrothermal reactor was developed and applied to coffee roasting, and its roasting characteristics were compared with those of a conventional roasting method. The effects of roasting method on several major nonvolatile and volatile compounds in brewed coffee were also evaluated. Coffee beans were roasted using either plasma roasting or conventional roasting and classified into light, medium, and dark roast levels based on bean expansion and color. Plasma roasting resulted in a more rapid increase in bean dimensions than conventional roasting and achieved comparable roast degrees while reducing roasting time by 42%, 44%, and 81% for light, medium, and dark roasts, respectively. Chlorogenic acid content was significantly higher in plasma-roasted coffee than in conventionally roasted coffee at all roast levels, particularly under dark roast degrees. Differences were also observed in total polyphenol, caffeic acid, and caffeine contents, indicating altered compositional changes during roasting. In addition, aroma-related volatile compounds, including pyrazine, 2-methylpyrazine, and furfuryl alcohol, exhibited different formation behaviors depending on the roasting method. These results demonstrate that plasma roasting can achieve roast degrees comparable to those obtained by conventional roasting within substantially shorter processing times while producing distinct nonvolatile and volatile compound profiles. Plasma roasting may therefore represent a promising roasting technology that could complement conventional roasting technologies by diversifying coffee quality characteristics and differentiating coffee products.