GREEN TO ROASTED: EVALUATING THE EFFECTS OF ROASTING CONDITIONS ON COFFEE'S BIOACTIVE COMPOUNDS

Abstract

This study evaluates the influence of roasting degree and time–temperature profiles on the physicochemical properties and bioactive compound composition of Coffea arabica. Two specialty coffee samples differing in post-harvest processing (wet and dry) were subjected to five roasting conditions: light, medium, dark, low-temperature long-time (LTLT), and high-temperature short-time (HTST), with green coffee serving as control (n = 16). Statistical evaluation was performed using analysis of variance (ANOVA, α = 0.05), and multivariate relationships were explored by Principal Component Analysis (PCA). Roasting significantly affected all monitored parameters. pH decreased from green coffee (5.33–5.38) to light and medium roasts (4.66–4.92), followed by an increase in dark roasts (5.51–5.74), reflecting the formation and subsequent degradation of organic acids. Dry matter increased from approximately 90.5% in green coffee to ~98% in roasted samples, while water activity decreased from 0.49–0.52 to ~0.19–0.23. Total antioxidant capacity declined with roasting intensity (from ~85–88% DPPH inhibition in green coffee to ~58–61% in dark roast), whereas total polyphenol content showed variability depending on processing method. Chlorogenic acids exhibited substantial degradation, decreasing from ~25–28 g·kg⁻¹ DM in green coffee to ~7–12 g·kg⁻¹ DM in dark and HTST samples, while caffeine content remained relatively stable (~7.5–9.1 g·kg⁻¹ DM). Roasting dynamics significantly influenced compound retention. LTLT roasting preserved chlorogenic acids (~9.4–9.6 g·kg⁻¹ DM) and antioxidant capacity at levels comparable to medium roast, whereas HTST resulted in the highest degradation (~60–75% loss). PCA confirmed roasting conditions as the primary factor driving compositional variability, with secondary contributions from post-harvest processing. These findings demonstrate that peak temperature is the dominant factor governing bioactive compound stability and highlight the potential of controlled roasting strategies to optimize coffee quality.