Chemical Characterization of Capsule-Brewed Espresso Coffee Aroma from the Most Widespread Italian Brands by HS-SPME/GC-MS

Abstract

Coffee capsules market is on the rise as it allows access to a wide selection of coffee, differing in taste and brand. However, few data about the chemical characterization of the capsule-brewed coffee aroma are available. In this work, an untargeted approach using headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography–mass spectrometry (GC-MS) and combined to chemometrics was performed to study and compare aroma profile from 65 capsule-brewed espresso coffees (ECs) commercialized by five of the most representative brands in Italy. Volatile profiles obtained from ECs were subjected to multivariate statistical analysis, which generally did not show a significant variability among coffees belonging to the same brand, except for those modified after the addition of specific flavor additives or aromatic substances (such as caramel, chocolate, etc.). Similarities may be related to the starting coffee brew or the processing method, which is likely the same for each individual brand. Additionally, partial least squares discriminant analysis (PLS-DA) showed that capsules from a specific brand contain the highest concentration of pyrazines, thus characterized by an intense and characteristic aroma, and a stronger note than those from the other brands. This study supports that the chemical analysis in conjunction with chemometric tools is a useful approach for assessing flavor quality, even if the need remains to identify volatile markers of high-quality beverages.

Integrating a Low-Cost Electronic Nose and Machine Learning Modelling to Assess Coffee Aroma Profile and Intensity

“…There were non-significant differences ( p > 0.05) between samples for compounds C2, C5, C7, C8, 12, C27, and C31; all other compounds presented significant differences ( p < 0.05) between the coffee samples. In Table 3 , it can be observed that most of the volatile compounds are associated with coffee, cocoa, and nutty aromas, which have also been reported in other published studies, some of these are furans such as 2,5-dimethylfuran (C2), 2-methoxymethyl furan (C8), 2-acetyl furan (C12), 2,2-methylenebisfuran (C31), furfuryl propionate (C32); pyrazines such as 2-methylpyrazine (C7), 2-ethylpyrazine (C13), coffee pyrazine (C20), and nutty pyrazine (C36), among others [ 12 , 13 , 56 ]. The most abundant compound based on the peak area for all samples was furfuryl acetate (C18), which has been related to fruit, banana, and ethereal aromas ( Table S1 ); other authors have also found this compound in arabica [ 57 ], and robusta [ 58 ] coffees and they have associated this compound also with a floral aroma.…”

“…To ensure that the final products (brewed coffee) will be acceptable by consumers, different techniques are used to assess their quality traits. Traditional methods to assess aromas in coffee consist of either instrumental techniques using gas-chromatography/mass-spectroscopy (GC/MS) [ 12 , 13 ], or most commonly through sensory analysis using descriptive sensory panels [ 14 ] and methods such as quantitative descriptive analysis (QDA ® ), or expert panels. The latter tend to be less reliable as sensory panels are often subjected to more biases, such as the habituation error [ 15 ].…”

Characterization of the Aroma Profile and Main Key Odorants of Espresso Coffee

“…They are classified by chemical classes into pyrazines, furans, aldehydes, ketones, and pyrroles. These compounds are present together with phenols, hydrocarbons, acids and anhydrides, esters, alcohols, sulfur compounds, and others [37,38]. Quantitatively, the main two chemical classes in coffee are furans and pyrazines, while qualitatively, sulfur-containing compounds together with pyrazines are considered the most significant to coffee flavor [25,39].…”

“…These compounds exhibit variable changes in concentration and sensory potency, which explains why different coffee types may have such unique and specific flavors [46]. It was reported that espresso coffee (EC) contains volatile components belonging to different chemical classes such as furans, pyrazines, aldehydes, ketones, phenolic, and sulfur compounds [37,[47][48][49].…”

“…These results concerning the levels of furan were in accordance with other authors for EC [53][54][55][56], although it was reported that furan levels could change from sample to sample, due to many factors, for example, type of extraction method, brewing temperature, and the type of fiber used during sample preparation and roasted coffee beans. Lolli et al studied the aroma profile of 65 capsules brewed EC belonging to five commercial brands sold in Italy, and eight furanic compounds were found in all samples, except for vinyl furan, which was present at the lowest concentration between these compounds [37]. In 1995, the International Agency for Research on Cancer (IARC) classified furan as type 2B-"possibly carcinogenic to humans" due to their methyl furan metabolites which are considered to be toxic.…”