Analysis of sugars and chlorogenic acid in coffee harvested at different ripening stages and after processing

Abstract

Compounds such as sugar and clorogenic acids, accumulated during the ripening of coffee beans, have an important role in beverage quality, which is ascribed not only to their high concentration, but also to the changes occurring during roasting. The predominant sugars present in coffee beans are glucose, fructose and sucrose. Chlorogenic acids may be responsible for a loss in beverage quality, since they suffer intense thermal degradation during bean processing. The objective of this study was to evaluate the behaviour of the chemical compounds during the post-harvest steps in coffees harvested at different ripening stages, using High Performance Liquid Chromatography (HPLC). With respect to the chlorogenic acid monoisomers, the 5-CQA content tended to increase during the bean processing, despite being unstable during sun drying. The three batches studied (batch 1: 90% cherry + 10% unripe; batch 2: 100% cherry; batch 3 85% floaters + 10% cherry + 5% unripe) presented significantly different 5-CQA contents, batch 2 presenting the highest concentration. During the roasting process and elaboration of the beverage, a reduction in the 5-CQA contents occurred. The levels of the isomers 3 and 4 showed no defined tendency to increase or decrease during processing. With respect to the sugars, the sucrose content tended to increase and the fructose and glucose contents decreas during processing. A higher concentration of sucrose was found in batch 3. After roasting, the levels of sucrose, fructose and glucose decreased drastically, glucose and fructose not being detected in the roasted beans. The method chosen to determine the sugar and clorogenic acid contents was considered efficient during validation of the methods, due to the results obtained.