Extraction kinetics, analysis of caffeine, and total acid contents of coffee at different roasting conditions

Abstract

Green coffee beans contain important components like total acids that were labile of temperature effects and can be affected by roasting. So, it is important to investigate effects of coffee roasting conditions classifying as light, medium and dark roasting on the caffeine and total acid contents of coffee from Jimma, Ethiopia. To investigate the effect of roasting, coffee samples were weighed properly and roasted at three different roasting conditions adapting traditional coffee roasting and classified as light, medium and dark. The roasted coffee beans were evaluated for quality attribute at all degree of roasting by five professional cuppers and by the so called regular users (four in number). During the experiment, the amount of total acidis determined by titration method whereas caffeine content was measured using UV-Visible spectrophotometer. The extraction efficiency of caffeine was performed from extraction kinetics study. Based on cupping evaluation, medium roasted was selected as very important roasted condition and assumed as a common roasted coffee type in Ethiopia. The light roasted coffee was found to have higher concentrations of total titratable acids than that medium and dark. The caffeine content of the three different types of roasted coffee (light, medium and dark) ranged from 1.1 – 1.15% (w/w). For kinetic study, the experimental data fitted first order kinetics with linear regression equation of (R2 =0.944). The caffeine extraction rate decreased with increasing extraction time.