Abstract

This study focused on the effects of several pretreatments on the microstructure and chemical composition of Kenyan green coffee beans. Initially, the green coffee beans were soaked in water for 30, 60, 120, and 180 min in advance. Subsequently, the beans with different moisture content underwent four pretreatments as hot air drying, freeze-drying, short-time heating & puffing, and microwave & puffing. The color change (ΔE*), porosity, content of caffeine and chlorogenic acid of the treated green coffee beans extracts were then measured, and the microstructure of the beans was observed using the scanning electron microscopy. The study found that with longer soaking in water, the microstructure of pretreated coffee beans becomes more porous, especially in freeze-dried and microwave & puffed beans, which led to a higher extraction efficiency of caffeine and chlorogenic acid in the solvent. These pretreatments altered the bean color only slightly, with the exception for the treatment of short time heating & puffing. Freeze-dried beans pre-soaked for 120, 180 min, as well as microwave & puffed beans, exhibited significantly higher porosity ranging from 21.5%-32.6%.

Keywords: Green Coffee Beans; Modification; Freeze-Drying; Microwave & Puffing; Flavor Compounds