Abstract: The bitterness can directly affect the quality and consumer acceptance of coffee. The bitter taste receptor family (TAS2Rs) from taste cells can perceive bitter substances. The bitterness of coffee is mainly attributed to the presence of alkaloids, as well as the formation of oxidation products of chlorogenic acid and Maillard reaction products during roasting. Alkaloids are the main source of bitter substances in green coffee beans. The oxidation products of caffeoylquinic acid and the Maillard reaction products formed during roasting are important flavor constituents of roasted coffee. At present, combination of instrumental physicochemical analysis and sensory evaluation is mostly used for the identification of new bitter substances found in coffee. This paper presents a review of the formation pathways, sensory characteristics, and physicochemical identification techniques of coffee bitter substances, and the impact of bitterness on the consumer preference for coffee, which will be useful for the quality control of coffee products and optimization of the roasting process.

Key words: coffee, bitterness, chlorogenic acid, Maillard reaction, threshold