Chemical Characterization of Green Coffee Beans and Determining the Effect of Roasting Temperature on the Content of Caffeine

Abstract

Coffee is one of the most popular drinks in the world. The quality of coffee depends on post harvesting process, agricultural practices, agro ecology conditions and chemical composition of coffee beans. Hararghe is among the major coffee producing areas in Ethiopia. However, the chemical profiles of Hararghe coffee beans have never been reported. The objectives of the present study was to determine pH value, total acidity and total polyphenols of Hararghe green coffee beans and also evaluates the effect of roasting temperature on caffeine content. Fifteen coffee bean samples were collected from different areas of Hararghe, Ethiopia. Total polyphenols were determined using the Folin-Ciocalteu reagent. The pH value was measured by a pH meter. The total acidities were determined by titrating with NaOH. The caffeine content from roasted coffee beans was measured using a UV-Vis spectroscopy. The lowest (5.26) and the highest (5.66) pH values showed by the coffee bean samples collected from Jarso and Gurachae, respectively. On the contrary, the lowest (1.44 ml of NaOHg^-1) and highest (2.3 NaOHg^-1) total acidity values revealed by Gurache and Jarso coffee green beans, respectively. Likewise, the lowest and the highest total polyphenols content exhibited by Girawa (7.22 mg GAE/g) and Kobo (20.96 mg GAE/g) coffee beans, respectively. The caffeine content in coffee bean samples roasted at different temperatures varied from 2.36 (w/w %) to 6.09 (w/w %). The content of caffeine increased from low temperature - long ranged time roasted coffee beans to intermediate temperature - intermediate ranged time. However, it was gradually decreased from intermediate temperature - intermediate ranged time to high temperature - short ranged time.

Keywords: Coffee, Caffeine, UV-Vis spectroscopy, total acidity, total polyphenols.

DOI: 10.7176/CMR/11-8-03

Publication date:October 31^st 2019