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.

3‐Alkyl‐2‐methoxypyrazines (MPs) are a very important class of volatile organic compounds (VOCs), intensively characterizing the aroma of several food products including fruits and vegetables. Due to the very low orthonasal sensory threshold, low amounts of MPs may act as key positive or negative aroma compounds. The analysis of these volatiles in foods is then remarkably important, and it may be very challenging as confirmed by the scarce literature focused on MPs, particularly with respect to quantitative data. In the attempt to fill this gap, in this work, presence and quantification of MPs in four different vegetables, namely, green bell pepper (Capsicum annuum L. var grossum), green pea (Pisum sativum L. and Pisum spp), carrot (Daucus carota subsp sativus), and cucumber (Cucumis sativus L.) have been investigated. Two different volatile extraction techniques (solid phase microextraction [SPME] and simultaneous distillation‐extraction [SDE]) in conjunction with VOC qualitative analysis by gas chromatography‐mass spectrometry (GC‐MS) methods were applied. Solid phase microextraction coupled with GC‐MS in single ion monitoring (SIM) mode showed the best performances in sensitivity to detect MPs on the different vegetable matrices. Therefore, a headspace (HS) SPME‐GC‐MS quantitative method was developed and optimized, and dominant MPs quantified. 3‐Isopropyl‐2‐methoxypyrazine (IPMP), 3‐sec‐butyl‐2‐methoxypyrazine (sBMP), and 3‐isobutyl‐2‐methoxypyrazine (IBMP) have been detected and quantified in all the vegetables. 3‐Isopropyl‐2‐methoxypyrazine was the prevalent MP in peas and cucumber while IBMP in bell pepper. These MPs were detected for the first time in carrot and cucumber. Finally, sBMP has been confirmed to be the most important MP in carrot. The developed method allowed to characterize the VOC pattern and, in particular, to quantify MPs in four vegetables. Results highlight the feasibility of further applications of the analytical approach to determine MPs in other food matrices where an excessive amount of these aromas may negatively affect their flavor (eg, coffee).

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