Ultrasound-assisted green technology for decaffeination of Gayo Arabica coffee: Process parameter optimization and kinetic modelling

Caffeine reduction in Coffea arabica has become increasingly important due to growing health concerns related to excessive caffeine intake. This study investigates ultrasound-assisted extraction (UAE) as a green, solvent-free method for the selective decaffeination of Gayo Arabica coffee, using water as the extraction medium. The effects of extraction time (2–12 min), feed-to-solvent (F/S) ratio (0.100–0.150 g/mL), and temperature (40–70 °C) were evaluated. Kinetic modeling was performed using six models: first-order, second-order, hyperbolic, power law, Elovich, and Weibull. The extraction exhibited biphasic behavior, with an initial fast-release phase (2–10 min) followed by a slower diffusion-controlled phase (10–12 min). Among the models tested, the power law model provided the best fit, with R² values up to 0.9881 and RMSE as low as 0.0017, demonstrating strong predictive accuracy. Optimal conditions were achieved at 60 °C, 10 min, and an F/S ratio of 0.125 g/mL, yielding 66–68 % caffeine recovery. Under these conditions, the power law constants ranged from B = 0.6247–0.7152 and n = 0.1456–0.1891, indicating enhanced mass transfer due to ultrasonic cavitation. Statistical validation via ANOVA (R2 = 0.9968) and residual analysis confirmed the model's robustness. Compared to conventional methods, UAE showed significant improvements in energy efficiency, extraction speed, and preservation of bioactive and sensory properties. This research advances sustainable decaffeination technologies and offers a scalable kinetic framework for other plant-based bioactive extractions.