Effect of Roasting Degree on Total Polyphenol Content, Antioxidant Activity (DPPH and ABTS), Caffeine Concentration, and Sensory Acceptance of Highland Arabica Coffee (Coffea arabica L.) from West Sumatra, Indonesia

Abstract

Coffee roasting is a complex thermal transformation process that fundamentally determines the sensory, nutritional, and functional profile of the beverage. Arabica coffee from the highlands of West Sumatra grown at elevations of 1,000–1,600 m above sea level and processed by wet/washed methods represents a premium segment of the Indonesian specialty coffee market. Despite growing consumer interest in the health-promoting properties of coffee, systematic data integrating polyphenol content, dual antioxidant evaluation (DPPH and ABTS), caffeine quantification, and sensory profiling across a full roasting gradient for West Sumatran highland arabica remains limited. This study evaluated the effect of five roasting degrees green (unroasted), light (8 min), medium (10 min), dark (12 min), and very dark (14 min) at an initial drum temperature of 170°C on weight loss, moisture content, colorimetric lightness (L*), total polyphenol content (TPC), DPPH and ABTS antioxidant activities, caffeine content, and snsory acceptability of the resulting brew. Roasting degree significantly influenced all measured parameters (p < 0.001). Weight loss increased progressively from 12.1% (light) to 20.3% (very dark), while moisture and L* decreased monotonically. Total polyphenol content exhibited a characteristic biphasic curve increasing from 52.4 mg GAE/g (green) to a peak of 64.8 mg GAE/g at light roast, then declining to 44.3 mg GAE/g at very dark roast. DPPH radical scavenging followed the same pattern (peak 41.5% inhibition at light roast; nadir 24.6% at very dark), while ABTS values showed relatively minor variation across roasting degrees (11.20–11.62 mmol TE/L), confirming differential sensitivity of the two assays. Caffeine content increased relatively from 10.4 to 11.9 mg/g owing to concentration by mass loss. Sensory evaluation by 30 semi-trained panelists identified medium roast as the most preferred treatment for overall acceptability (4.2/5.0). Medium roasting degree is recommended as the optimal balance among antioxidant preservation, flavor development, and safety considerations related to acrylamide formation.