Determination of 3-Alkyl-2-methoxypyrazines in Green Coffee: A Study To Unravel Their Role on Coffee Quality

Abstract

Although a high concentration of some 3-alkyl-2-methoxypyrazines in green coffee has been associated with an off-flavor described as potato taste defect (PTD) or “peasy” defect, affecting the product quality, the natural concentration of these compounds in good quality coffee beans has never been the subject of a detailed study. 3-Isobutyl-2-methoxypyrazine (1), 3-sec-butyl-2-methoxypyrazine (2), 3-isopropyl-2-methoxypyrazine (3) concentrations were determined on a range of selected, good quality green coffees of different botanical species (arabica and robusta) and geographical origin. The presence of the three methoxypirazines was confirmed in all samples; the concentration of compound 1 was significantly higher than those of compounds 3 and 2, showing a geographical-origin-dependent variability. This whole set of experimental data was then used as a reference to ascertain the PTD occurrence in “suspected PTD” and insect-damaged samples. Compound 3 was the main indicator of defectiveness, with a main variability in its concentration in insect-damaged samples, suggesting that the insect-induced damage is not a sufficient condition to induce the off-flavor. The analysis in fresh potatoes, carried out to disclose the origin of the term used to describe the PTD in coffee, showed a very low concentration of 3-alkyl-2-methoxypyrazines. However, the relative prevalence of compound 3 on the total of 3-alkyl-2-methoxypyrazines could be related to the characteristic “potato” flavor frequently evoked to describe the sensory perceived defect in coffee.

Analytical Determination of the Severity of Potato Taste Defect in Roasted East African Arabica Coffee

“…7 Surprisingly, the overall concentration of methoxypyrazines in these two suspected PTD batches was consistent with the natural baseline established for the geographic region and only inter-batch variability in the concentration of IPMP was seen for the suspected beans from Rwanda. 7 Given that these recent studies have focused on quantifying these methoxypyrazines in green coffee beans, the effect of PTD on roasted coffee beans remains an open question. Furthermore, due to the sensitivity and chemical selectivity provided by HS-SPME-GC-MS, 16 the total volatile analyte profile of roasted coffee beans affected by PTD can be closely examined to provide additional insight into this understudied defect.…”

“…14 Both mechanisms can explain the occurrence of PTD in coffee beans with and without visible insect damage. 7 Alterations to the sensory properties of coffee due to the presence of defects have been observed in a coffee sample's chemical profile, especially in the vapor headspace. 4,15 Headspace solid-phase microextraction gas chromatography− mass spectrometry (HS-SPME-GC-MS) is the prominent technique for studying the volatile analyte composition of defective coffee beans because of its sensitivity in extraction and detection.…”

“…3,4,6,15 Recently, HS-SPME-GC-MS was utilized to quantify the natural concentration of IPMP and IBMP in green coffee bean samples from different botanical species and geographical origins. 7 However, this study only analyzed two suspected PTD samples, in which one batch was from Ethiopia and the other was from Rwanda. 7 Surprisingly, the overall concentration of methoxypyrazines in these two suspected PTD batches was consistent with the natural baseline established for the geographic region and only inter-batch variability in the concentration of IPMP was seen for the suspected beans from Rwanda.…”

“…7 However, this study only analyzed two suspected PTD samples, in which one batch was from Ethiopia and the other was from Rwanda. 7 Surprisingly, the overall concentration of methoxypyrazines in these two suspected PTD batches was consistent with the natural baseline established for the geographic region and only inter-batch variability in the concentration of IPMP was seen for the suspected beans from Rwanda. 7 Given that these recent studies have focused on quantifying these methoxypyrazines in green coffee beans, the effect of PTD on roasted coffee beans remains an open question.…”

Effect of Ground and Roasted Parameters on Both the Microstructure of Arabica Coffee Beans and Coffee Infusion – An Imagistic Study

“…The surface and the section of green and roasted Arabica coffee beans were analyzed. The coffee beans were cut by hand with a razor blade [30], and the pieces of coffee beans were mounted on carbon tape placed onto support stubs, then sputter covered with a layer of gold for better conductivity, allowing surface and section imaging with a Quanta 200 system (FEI Company-Thermo Fisher Scientific, Oregon, USA; 30 nm as resolution) with secondary electron detector. All samples were examined in Low-Vacuum mode using an accelerating voltage (HV) of 15 kV [31] and 10 nm as working distance (WD).…”