Second newsflash

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Submillimetre and THz spectroscopy: an effective tool for monitoring the freshness of foods of various kinds?

During the first period of the Terafood project (https://terafood.iemn.fr/) several relevant freshness indicator gasses have been identified via lab tests on Atlantic salmon (Salmo salar) (more info available in first Terafood newsflash [1]. Now the gasses indicating early spoilage are known a new approach is used to analyse surrounding gasses in order to determine the microbial activity (and linked to that the freshness) of a packaged target food product. For this purpose submillimeter and THz absorption spectroscopy is potentially a very attractive solution, as it allows to obtain extremely clear signatures (at least at low pressure) of the different gasses in complex mixtures.

In principle, the THz and submillimetre wavelength offers excellent selectivity in gas detection. To detect and identify the gasses tracers with a strong dipole moment to be suitable for trace detection are needed. To illustrate this, an existing spectrometer developed at the ‘Physico-Chimie Laboratory of the Atmosphere’ in Dunkerque has been adapted for the temporal monitoring of a target molecule within a gas mixture. The principle of the experiment is shown in Figure 1. A microwave source multiplied in frequency is used to cover the frequency range of 100 to 900 GHz (3 to 0.333 mm wavelength). An absorption cell ensures the interaction between the radiation and the gas under study. A Schottky diode at room temperature is used for signal detection. The sweeping frequency of the radiation source and the detection of the associated signal allow to reveal absorptions at characteristic frequencies of the target molecules present in the gas cell (see Figure 2).

Figuur 1

Figure 1 : Experimental setup to measure molecular absorption in the submillimeter THz range

Provided that the spectroscopic parameters of the target molecule are known, it is then possible to deduce its concentration. In this example, formaldehyde was clearly identified and quantified at the ppm level. In order to improve the signal-to-noise ratio of this technology a frequency modulation technique with a second harmonic demodulation can be used. The next step in the project consists of carrying out a feasibility experiment on a sample of Atlantic salmon measuring the identified spoilage gas molecules in the head space of a packaged sample in order to improve the technology and to propose a first prototype of the system.

Figuur 2

Figure 2: Absorption signal of formaldehyde in a complex mixture

With support of the European Regional Development Fund

Terafood

[1] Available on http://food2know.org/en/news/terafood-eng

First newsflash

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Focus on spoilage – volatile organic compounds (VOCs) in food quality monitoring

Spoilage of highly perishable food products such as fresh fish is typically due to microbial activity that leads to the generation of volatile organic compounds (VOCs). These compounds could be used as spoilage indicators and thus for quality monitoring of the packaged food product. The TERAFOOD project is investigating innovative analytical techniques for the identification and quantification of potential food spoilage indicators.

Food spoilage is a major economic and ecological concern in the modern society. In industrialized countries, more than 40 % of all yearly food losses has been estimated to take place at the retail or consumer level (FAO, 2011). A great part of food waste originates from refrigerated products that have a very short shelf life, such as fresh seafood. In this case, spoilage is usually due to microbial activity and the consequent generation of volatile organic compounds (VOCs) in the package headspace. Even though spoiled food does not necessarily pose an infection risk, offensive off-odors and other unpleasant changes in the sensory quality render the product unfit for consumption. Development of innovative quality monitoring systems thus calls for the identification of VOCs that indicate food spoilage.

The TERAFOOD project, coordinated by the CNRS (Institute of Electronics, Microelectronics and Nanotechnology, Lille) and involving several academic and industrial partners, aims at the development of a compact and low-cost commercial terahertz-sensor that can be used for monitoring the quality of packaged food products by VOC detection (Flanders’ FOOD, 2017; UGent, 2017). Introducing the sensor in food packages allows real-time quality monitoring at any time during storage without opening the package and has thus the potential to greatly reduce food waste. However, every food product has its characteristic spoilage processes that depend on several intrinsic and extrinsic factors. To allow efficient quality monitoring, information is thus needed about VOCs and their concentration levels in different food products as well as under different packaging and storage conditions. Identification and quantification of VOCs that indicate food spoilage is carried out at the Department of Food Safety and Food Quality at Ghent University.

During the first semester of the project, spoilage of Atlantic salmon (Salmo salar) packaged under different gaseous atmospheres was examined (Fig. 1).

Fig. 1. The experimental setup of Atlantic salmon.

Microbiological, chemical and sensory changes were analyzed on a regular basis throughout storage time. VOCs produced in the package headspace were monitored with selected-ion flow-tube mass spectrometry (SIFT-MS) that allowed fast and sensitive quantification of VOCs directly from the actual food packages. The obtained results show that the evolution of the VOC profile and the emerging off-odors depend on the applied storage conditions and that several VOCs can be considered as potential spoilage indicators of Atlantic salmon. For the sensor development, the results provide with essential information about spoilage-related VOCs and highlight the sensitivity levels needed for their detection. During the next semester of the project, advanced multivariate statistical analyses will be carried out to further enhance the characterization of most potential spoilage indicators. Furthermore, the developed experimental setup and methods will be extended to new food products.

More information:

Lotta Kuuliala – Lotta.Kuuliala@UGent.be

If you are interested to become a member of the advisory board of this project, you can contact Isabelle Sioen – Isabelle.Sioen@UGent.be

 

Terafood