Impact of water-soluble precursors leaching from green beans on aroma generation during coffee roasting

Abstract

In this investigation green Robusta coffee beans were pre-soaked with different time-temperature profiles before roasting in normal conditions and grinding to a standardized particle size. Aroma profile of roasted coffee beans and water soluble precursors such as sucrose and total protein content from soaking water were examined by using Solid Phase Micro Extraction-Gas Chromatograph Mass Spectrometry and Liquid chromatography– mass spectrometry and BCA Protein Assay Kit respectively. A significant impact of soaking time-temperature profile was observed on the yield of water-soluble precursors in the soaking water. The loss of these precursors significantly decreased aroma formation during roasting. The results also suggested that water-soluble precursors could modify the quality of Robusta coffee. Introduction Coffee species such as Arabica and Robusta are most common coffee varieties in the world, which account for 61% and 38% of the coffee production worldwide. Arabica, perceived as a smooth, and rich flavour is usually more desirable than Robusta, which is often described as having a muddy odour. Robusta coffee beans are often blended with Arabica coffee beans to create specific aroma profiles, enhance cream formation or reduce cost, but the maximum that can be included is often limited due to the loss of aroma quality [5]. Aroma formation in coffee is directly related to the chemical composition of the green coffee beans and typical coffee aromas are developed during the roasting process due to complex reactions such as, Maillard reactions, Strecker degradation, thermal degradation and oxidation [2]. A number of studies have improved the quality of Robusta coffee by passing the green Robusta beans through steam to remove substances such as 2-methylisoborneol, which is responsible for the muddy odour [1]. However, during this process important water soluble precursors such as sucrose and protein are leached into water, hence compromising the flavour generation potential of the roasted coffee. The amino acids and sugar are considered to be the main precursors in the aroma generation and colour formation during coffee roasting [3]. Therefore, the objective of this study was to investigate how much water-soluble precursors are lost during pre-soaking of green coffee beans and its impact on aroma generation during coffee roasting.