Real-Time Quantification of Aromas using PTR-MS

IONICON PTR-MS is a rapid screening system designed for quantifying complex aromas. Soft ionization helps obtain rich chemical fingerprints and high throughput is achieved through real-time sampling. The IONICON PTR-MS systems are perfect for chemometric data-mining techniques.

Image Credit: IONICON Analytik

Aroma Real-Time Quantification with PTR-MS

The Challenge

Buying decisions can be influenced by aroma and its perception. Therefore, it is crucial for the industry to understand what users smell and taste when, for example, enjoying a piece of chocolate or drinking a cup of coffee, immediately the flavor molecules hit the receptors.

Taste and flavor of food can also differ over time, based on production processes or raw materials etc. However, the aroma quality of food should remain stable in order to achieve a consistent brand image.

Coping with demands such as very high time resolution, direct and real-time air samplings are the main challenges to conventional analytical techniques.

IONICON PTR-MS – Ultra Sensitive for Real-Time Trace VOC Analysis

IONICON delivers real-time VOC analyzers so as to provide the industry and Scientists with a better understanding of sensory perception, and is the market leader in PTR-MS (Proton Transfer Reaction – Mass Spectrometry).

The main advantages are as follows:

• Head-space analysis of products without sample preparation
• Direct mouth- & nose-space air analysis
• Chemical fingerprints of food samples in real-time
• Monitoring of real-time variations in aroma
• Fast screening of complex aroma systems due to high-resolution mass spectrometry and soft chemical ionization
• Ideal for chemometric data-mining

IONICON PTR-MS offers results that could improve research, flavor and fragrance development, quality control and facilitate process monitoring in food and flavor industries.

Advantages of High-Resolution PTR-TOFMS for Food & Flavor Analysis

Usually, Researchers encounter extremely complex matrices in food and flavor science. Thus, in order to isolate compounds of interest from other compounds which share the same nominal m/z but have a different chemical composition (isobars), extremely high mass resolution is of paramount importance.

The Full Width at Half Maximum (FWHM) mass resolution of an IONICON PTR-TOF 6000 X2 with over 6200 m/Δm (Figure 1) was determined by introducing trichlorobenzene from a certified gas standard.

Figure 1. Mass resolution of an IONICON PTR-TOF 6000 X2 with over 6200 m/∆m (FWHM). Image Credit: IONICON Analytik

The nosespace of a person who had taken some freshly brewed coffee was analyzed in order to demonstrate the advantage of this exceptional resolution. It is well known that 4-ethylguaiacol and vanillin are vital isobaric aroma compounds at nominal m/z 153 (protonated molecules).

Yet, from the mass spectrum around m/z 153 as shown in Figure 2, one can see that there are indeed four ions which share this nominal mass (black line). In the case of a low-resolution instrument, all four ions would be combined into one wide mass spectral peak and it is possible to measure only the intensity of the sum of them.

The high mass resolution of the PTR-TOF 6000 X2 allows separation of all four ions. IONICON's advanced data processing software enables automatic deconvolution (grey and blue lines; the orange line is the sum of the deconvoluted peaks, which perfectly reproduces the original data) of intensities and independent quantification of 4-ethylguaiacol and vanillin, with no parasitic influence of the two extra isobars.

Figure 2. Nose-space air analysis of coffee flavor demonstrates high mass resolving power of PTR-TOF 6000 X2. Image Credit: IONICON Analytik

High sensitivity plays a key role when quantification of compounds of very low abundance has to be done using high time resolution. The nosespace of a person before (blank) and after drinking freshly brewed coffee was analyzed utilizing the high sensitivity PTR-TOF 6000 X2. Figure 3 shows the concentration values of 3-mercapto-3-methylbutyl formate at m/z 149.063 during this experiment with a time resolution of 700 ms. This significant aroma compound is present only in trace concentrations below 1 ppbv. However, the low limit-of-detection and high sensitivity of the PTR-TOF 6000 X2 facilitate online quantification of the aroma development across various breath cycles after the coffee is swallowed in real-time.

Figure 3. Quantification of 3-mercapto-3-methylbutyl formate at m/z 149.063 with a time resolution of 700 ms and a concentration < 1 ppbv. Image Credit: IONICON Analytik

Coffee Head-Space Analysis

This novel and efficient approach of characterizing the aroma of coffee blends by on-line analysis may cut down the time needed for the development of new products and improve quality control in a more objective and automated manner.

Sensory profiling and analytical studies are carried out on different commercially available espresso coffee products. On-line analysis with IONICON PTR-MS is used to acquire chemical information about difference in composition of the coffee headspace characterizing the different coffee blends. Moreover, an expert panel trained for coffee tasting describes each sample by scoring 10 major flavor attributes on a 10-point scale.

Figure 4. Image Credit: IONICON Analytik

The overall sensory description of each sample is correlated with the differences in chemical composition that were analytically obtained to develop a statistical tool in order to predict the sensory profile according to analytical data. In a second step, the prediction is substantiated using a new series of coffee blends, which vary in the aroma profile and which are not a part of the development of the predictive tool.

The overall sensory prediction of the latest blends based exclusively on the analytically produced data shows a good match with the sensory profiles independently achieved by the expert panel.

When PTR-MS Tastes Coffee

Instrumental Approach to Predict the Sensory Profile of Espresso Coffee

Image Credit: IONICON Analytik

A major step forward with respect to correlation of sensory with instrumental results has been acquired by Lindinger et al of the Nestlé Research Center in Switzerland employing IONICON PTR-MS.

The Scientists were able to develop a reproducible and robust model for predicting the sensory profile of espresso coffee from instrumental headspace data.

Real-Time Flavor Release

Online measurement abilities of the PTR-MS allow Researchers to quantify compounds in the nose-space air of test persons. A high time resolution and extremely low detection limit allow for real-time aroma-release analysis. A better understanding of flavor research and aroma design can be achieved through correlations between measured in-nose aroma concentration and individual food perception.

Results of PTR-MS Measurements - Mastication of Strawberries

Figure 5. Image Credit: IONICON Analytik

The graph displays a peak of isoprene (red line), an endogenous compound formed in the body, with each exhalation occurring roughly every 8 seconds. When strawberries are chewed (start after 80 seconds), aroma compounds such as methy-2methyl-butanoate, are discharged and can be measured in each exhalation.

In order to carry out the real-time analysis of flavor compounds in nose-space air, IONICON has exclusively designed the N.A.S.E., an inlet system for PTR-MS to be best utilized for this application.

Food Quality

PTR-MS in Saffron Quality Control

Image Credit: IONICON Analytik

PTR-MS can be employed in the quality control of saffron, a spice derived from the flower of Crocus sativus. Saffron is among the world's most costly spices by weight. Although attempts were taken for standardization and quality control, an extensive history of saffron adulteration, especially among the cheapest grades, are present even today.

Researchers monitored the VOCs from a small amount of sample (35 mg) over a 5 week period and have discovered that the VOC safranal (m/z 151), which was at first predominant, gradually decreased. Nenadis et al. further report that inspection of calculated and recorded fingerprints for several admixtures demonstrated that PTR-MS VOCs analysis, in combination with chemometrics, could be employed to screen for the presence of lower quality saffron in a commercial product in a few minutes. PTR-MS can be employed in a complementary fashion, adding to the battery of sophisticated analytical techniques available to address the authenticity and quality issues of saffron.

Thanks to the IONICON autosampler, high-throughput screening of food and flavor samples is now even faster and more comfortable.

Freshness of Food in the Consumer's Perceptions

Depending on the individual experiences, consumers have a distinct appreciation of what constitutes freshness. For food and flavor science, PTR-MS can be the perfectly suited tool to link objective fingerprinting of food volatiles with descriptive sensory analysis. Scientists* have proved that for bread an objective understanding of the freshness can be derived by linking consumer freshness judgments to sensory descriptive analysis and volatile composition.

Reference

* Heenan S., Dufour J.-P., Harvey W., Delahunty C., University of Otago

This information has been sourced, reviewed and adapted from materials provided by IONICON Analytik.

For more information on this source, please visit IONICON Analytik.