Impact of Coffee Bean Roasting on the Content of Pyridines Determined by Analysis of Volatile Organic Compounds.

Anna Oniszczuk,Maciej Combrzyński,Robert Rusinek,Yousef Darvishi,Wacław Roman Strobel,Sylwester Tabor,Marek Gancarz,Alaksandra Żytek,Urszula Malaga-Toboła,Daniel Ćwikła,Hamed Karami,Bohdan Dobrzański

doi:10.3390/molecules27051559

Abstract

The aim of the study was to analyze the process of roasting coffee beans in a convection–conduction roaster (CC) without a heat exchanger and a convection–conduction–radiation roaster (CCR) with a heat exchanger for determination of the aroma profile. The aroma profile was analyzed using the SPME/GC-MS technique, and an Agrinose electronic nose was used to determine the aroma profile intensity. Arabica coffee beans from five regions of the world, namely, Peru, Costa Rica, Ethiopia, Guatemala, and Brazil, were the research material. The chemometric analyses revealed the dominance of azines, alcohols, aldehydes, hydrazides, and acids in the coffee aroma profile. Their share distinguished the aroma profiles depending on the country of origin of the coffee beans. The high content of pyridine from the azine group was characteristic for the coffee roasting process in the convection–conduction roaster without a heat exchanger, which was shown by the PCA analysis. The increased content of pyridine resulted from the appearance of coal tar, especially in the CC roaster. Pyridine has an unpleasant and bitter plant-like odor, and its excess is detrimental to the human organism. The dominant and elevated content of pyridine is a defect of the coffee roasting process in the CC roaster compared to the process carried out in the CCR machine. The results obtained with the Agrinose showed that the CC roasting method had a significant effect on the sensor responses. The effect of coal tar on the coffee beans resulted in an undesirable aroma profile characterized by increased amounts of aromatic volatile compounds and higher responses of Agrinose sensors.

Highlights

The mode of heat transfer in coffee bean processing has a considerable impact on the taste of brewed coffee [1,2]
Organic coffee beans roasted in the conduction–radiation roaster (CCR) and conduction roaster (CC) roasters
The process of roasting five coffee bean varieties from different regions of the world in the CC roaster was characterized by increased content of pyridines in the aroma of the coffee beans, in comparison with the CCR roaster equipped with the exchanger

Summary

Introduction

The mode of heat transfer in coffee bean processing has a considerable impact on the taste of brewed coffee [1,2]. In the coffee roasting process, heat can be transferred to coffee beans via three methods: convection, conduction, or radiation [3]. The most important variables for each type of roasting are the type of roaster, the temperature of the coffee beans, and the duration of the roasting process [4]. Roasters based only on conduction heat do not ensure a homogeneous temperature distribution in the coffee beans due to their non-homogeneous contact with the drum surface in the roasting process. Heating via radiation is based on the emission of light and heat waves that penetrate the coffee bean; very little energy is lost during the process, rendering this heating method the most efficient

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