We have dedicated this article to an article that has attracted our attention. Our customers who have known us for a long time know very well what espresso means to us. It is our most beloved product that we have established the foundation of best for years, serving with 3 different types of espresso in our shops. In this study, which we will summarize and comment on, the In Vitro and In Vivo aroma release analysis of three different espresso coffees was examined by performing one elemental and one sensory analysis. The first thing that draws attention when buying and consuming coffee is aroma. Aroma is the most important feature that both reveals the character of the coffee and easily catches clues about its quality, and directs the tendency to consume coffee towards it. The so-called "retronasal perception (behind-the-nose perception)" is initiated by the VOCs (volatile-organic-compounds = organic volatile compounds) in the exhaled air after swallowing, reaching the olfactory (smell nerve) system that reaches the nose. In both aroma perceptions, VOCs meet the olfactory bulb in the nose. However, the interpretation of odor perception depends on factors related to the path followed by volatiles, physical properties of aroma compounds, food composition, interactions with texture and matrix components, and consumer physiology. In the study, we mentioned two different analysis methods, elemental and sensory analysis. Sensory, i.e. Retronasal (or in vivo) aroma release monitoring was performed using APCI-MS, PTR-MS or SIFT-MS, also known as "nosespace analysis". In the study, proton-transfer-reaction mass spectrometry (PTR-MS) was first used to monitor coffee aroma release by intraoral and nasal area measurements. Immediately afterwards, these studies focused on differences between consumers and release mechanisms. PTR-MS was later used to investigate the effect of coffee foam on organic volatile compound release in espresso coffees, to examine interindividual differences in coffee aroma release, and to examine the relationship between time-dependent aroma release and retronasal perception. The PTR-MS device is a frequently used device in scientific research, which has provided the opportunity to distinguish between Arabica and Robusta coffees or between different Robusta blends based on their geographical origins in the study of coffee science. The main objective of the study was to verify whether it is possible to distinguish espresso coffees based on their nose area profiles. The same products were also examined with headspace analysis (a technique used to sample and examine volatile compounds associated with a solid or liquid sample, the actual measurement is made with gas or vapor above the sample). This allowed a detailed comparison between in vivo and in vitro aroma release. In the study, two Arabica espresso coffees, a naturally low-caffeine coffee, a single-origin Ethiopian coffee and a granulated coffee were analyzed. PTR-ToF-MS was able to identify differences between the three espresso coffees and highlighted the differences in composition of aroma compounds and release profiles that were important differentiators between in vitro and in vivo.
Green C. arabica var. laurina beans (geographical origin: El Salvador) and Ethiopian coffees were roasted with Probat at 2 different roasting degrees. The biggest reason for choosing Ethiopia in the study is the aromaticity that comes from the natural chemistry of the bean (due to its high monoterpene content). Before moving on to the study results, I wanted to open another topic due to this series of experiments. We had previously mentioned panels and sensory analyses that have started to be used frequently in coffee science studies. Now, not only elemental analysis methods but also sensory analyses have a great place in coffee science studies because tasting is the main subject for everyone. Trying to measure these tastings and aromas is the most important subject of coffee science these days. Because coffee, with its enormous complex structure, winks at us with many aroma profiles but also hides itself quite a bit.
The summary of the study is in the image below. This image explains the operation of many experiments on aromas.
Since I will also include experimental studies and our own studies on this subject from now on, I would like to briefly summarize how nasal area analysis is performed in order to visualize it. Nasal area analysis is a sensory analysis method performed with multiple participants and where the criterion is that the participants have previously contributed to other studies. In this study, 5 separate sessions were conducted with 3 panelists (2 males and 1 female, aged between 29-39) and 3 espresso coffees were tasted per panelist in each session. In this way, 45 trials were tried by different panelists. Considering the previous experiments in the study, it was proven that these subjects produced reproducible NS release profiles; therefore, they were asked to participate in this study. All panelists participated in each session and three freshly prepared espresso coffees were served to each panelist in turn. Before each analysis session, the coffees were freshly prepared and served individually to each panelist. After preparation, 10 mL coffee extracts without cream were presented to the panelists in a polystyrene cup with the lid closed and with a pipette at 55 °C. The analysis sessions were performed according to a predefined protocol, which I will add in the table below: 30 seconds of free breathing (mouth closed), taking the sample in the mouth and swallowing (10 seconds in total), 2 minutes of free breathing, rinsing the mouth with water (20 seconds). Exhaled air was sampled through an ergonomic glass nose piece (let's summarize here, when I say nose piece, I mean exhaled breath into a glass piece) directly connected to the PTR-ToF-MS inlet and heated to 110 °C. Each analysis session lasted approximately 220 seconds; the first 150 seconds were used for data analysis.
PLS-DA confusion analysis and score plot
In the analysis table, it was seen that the participants were wrong once in the coffee A and coffee B results. As we know that coffee E is Ethiopian coffee, it is not expected for a good taster to be surprised by Ethiopian coffee, so we can say that the results are compatible for us. (By the way, the accuracy rate of the study was measured as 93-100%) Now that we have explained the nose space analysis part, we can move on to summarizing the results of the study.
The table below is a list containing information of 15 mass picas that are significant during PLS-DA analysis and have a VIP (Variable Importance in Projection) value greater than 1.5, a statistical measure used to determine the contribution of a variable. A high VIP value indicates that the relevant variable is more important in providing separation between classes. Mass picas are the picas that make the greatest contribution to the separation of coffee samples. The table includes the total formula for each mass pica, provisional definition and average concentration information for each coffee sample. This information can be used to understand the differences between coffee samples and to separate coffees.
This table summarizes the differences between coffee samples and the characteristic compounds of coffee E. Specific mass picas such as m/z 137.134 and 153.130 represent compounds that contribute to the characteristic fruity and citrus notes of Ethiopian coffee. This is consistent with previous studies showing that Ethiopian coffee is rich in terpenes and that these compounds play an important role in coffee discrimination. These studies were repeated in 2 sets in total, but these 2 sets were also analyzed in more detail.
The comparison between the HS (headspace analysis) and NS (noisespace analysis) datasets is represented by a circular plot (above) for each coffee. In each plot, the inner circle represents the NS data; mass picas are labeled with their respective fractional mass values and sorted by chemical class. Within each class, the values increase counterclockwise according to relative abundance. Similarly, the outer circles represent the HS data; each pixel is represented by a dot, and if the HS mass pica is also present in NS, the dot is filled and a line is drawn connecting the two data points. Empty dots represent HS mass picas not detected in NS. Chemical classes are represented by the different coloring of the two circles. This plot shows us that the chemical groups abundant in HS are also prevalent in NS. For example, the figure above shows that carbonyls are the chemical class with the highest number of entries in both HS and NS. Carbonyls are the most abundant class of compounds, accounting for more than 50% of the total peak area. The relative abundances of chemical groups in HS followed the same order for coffee A and E, with compounds being carbonyls, esters/acids, furans/pyranones, alcohols, pyridines, pyrrole, pyrazines, sulfur compounds, and phenols. Similarly, the relative abundances of these chemical groups in NS followed the same order for coffee A and E, with compounds being carbonyls, furans/pyranones, pyridines, pizazines, pyrrole, esters/acids, and phenols, but a different order was observed for coffee B, with compounds being carbonyls, pyridines, furans/pyranones, pizazines, pyrrole, esters/acids, and phenols.
According to the study results, changes in the concentration of different volatile compounds may be due to several factors. These include dilution by saliva in the mouth, which is important for small liquid samples, absorption of volatile compounds by nasal epithelium and interaction with oral mucosa and lung channels, dilution of volatile compounds by breath, and biotransformation of compounds by salivary or nasal mucus enzymes. This study presents a comprehensive workflow for measuring aroma release in vitro and in vivo using PTR-ToF-MS. It includes comparison of headspace (HS) and nosespace (NS) data sets along with data processing and analysis. PTR-ToF-MS successfully provided a detailed profile of three coffees in both analytical modes and distinguished the products with ≥92% accuracy. Comparison between HS and NS data revealed that NS represents the coffee aroma profile in a simplified manner.
The study found that some compounds quantitatively represented in the coffee nosespace, such as pyrazines, play an important role in determining coffee aroma, while some furans have minimal sensory effects. Future research with larger sample sizes or panelists and comparing instrumental and sensory data with physiological parameters of individual panelists will provide the greatest contribution to the sector.
Article Name; Monitoring In Vitro and In Vivo Aroma Release of Espresso Coffees with Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry, Andrea Romano 1, Luca Cappellin 1, Sara Bogialli 1, Paolo Pastore 1, Luciano Navarini 2 and Franco Biasioli 3
DUYGU KURTULUŞ
Co-Founder / Chemist / Nanotechnology Engineer / Hazardous Chemical Consultant / Chemical Evaluation Specialist