Fourier-Transfrom Infrared Spectroscopy

Achim Kohler

Fourier-transform infrared (FT-IR) spectroscopy has been used to analyse biological materials since the 1980s. There are several applications of the technique, such as e.g. the characterisation of tissue samples and the differentiation of microorganisms. Some of the advantages of the FT-IR technique are that it is easy to use, rapid and cost-effective.

Content in this page:
1. FT-IR facts
2. Research and applications
3. Cooperation and development
4. Publications FT-IR (at Campus Ås)
5. Contacts and related links


1. FT-IR facts

Introduction
The mid-IR region covers the range from 4000 to 400 cm-1. The basic principle of the IR technique is that various organic functional groups absorb infrared light at specific wavelengths. Thus, since every organic molecule has an unique chemical composition, it also has an unique infrared spectrum. Biological samples are composed of proteins, carbohydrates, lipids and nucleic acids. Since these molecules contain functional organic groups, the IR spectrum consists of bands from all these components.

The infrared spectrum is very complex, and it contains a large amount of information. To evaluate the data, it is necessary to use multivariate statistical analysis. MATFORSK has a FT-IR instrument equipped with several devices: a bio-module, a microscope and a focal plane array detector. Each device is suited for specific applications:

Bio-module
The bio-module was developed for the automatic measurement of microorganisms. In this technique, the microorganisms are suspended in water, dried on an IR transparent crystal before acquisition of the spectra.

FT-IR Microspectroscopy
FT-IR microspectroscopy combines a light microscope with a FT-IR spectrometer thus providing a very powerful technique of measuring vibrational spectra of e.g. microbial cells (e.g. as microcolonies) or individual morphological components of tissues. The FT-IR microscope enables the acquisition of spectra with a spatial resolution in the micrometer range, i.e. spectra from e.g. single fibres or connective tissue can be obtained, where an IR spectrum reflects the overall molecular composition of the specific tissue structure.

FT-IR Imaging
Fourier-transform infrared (FT-IR) imaging, employing focal plane array (FPA) detectors is a relatively new and promising technique for rapid food analysis. In contrast to conventional FT-IR microscopy, the FPA assembly allows the simultaneous collection of spectra at 4096 pixels enabling the rapid spectroscopic and spatial discrimination of a sample area.


2. Research and applications

The research tasks of our group employing different FT-IR spectroscopic techniques are the following:

- Classification and differentiation of food-relevant microorganisms, e.g. differentiation of lactic acid bacteria at different taxonomic levels (e.g. species and strain level).
- Detection of specific bacterial cell components such as capsular polysaccharides in Campylobacter jejuni.
- Use of FT-IR imaging as a new technique to assess the quality of meat. In a pilot study, FT-IR imaging was used to monitor the denaturation process during four different heating temperatures (raw, 45 °C, 60 °C and 70 °C) spatially resolved in beef cryosections from two different muscles (longissimus dorsi and semimembranosus). The infrared images were recorded from regions in the tissue that contained both myofibers and connective tissue. From Fig. 1 it is evident, that the infrared images of longissimus dorsi allow visualising the denaturation process. The scales on the right side of each infrared image are increasing from raw to 60 °C indicating an increasing denaturation level. These results demonstrate that infrared imaging can be used to monitor the denaturation process in both tissues. Interestingly, the connective tissue spectra showed a higher b-sheet content indicating a more extensive denaturation in this tissue.
- Investigation of hydrolysed by-products from the fish-industry.
- Monitoring of fermentation processes under varying process conditions.


3, Cooparation and development

MATFORSK has been working with FT-IR spectroscopy since the beginning of the year 2002, but has very long experience with spectroscopic techniques like fluorescence spectroscopy and NIR spectroscopy and with multivariate data analysis. The use of FT-IR spectroscopy for applications in food science fits very well in this tradition.
In the short period MATFORSK has been working on FT-IR spectroscopy, collaboration with different relevant research groups has been established.



Updated: 17.11.03
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