High-precision analytics - In Bayreuth, Germany, additives and contaminants are made visible using imaging tech-niques
Imaging mass spectrometry provides highly precise information on the spatial distribution of substances in many areas. A study conducted in cooperation with the Bavarian State Office for Health and Food Safety shows the great potential of this process, especially with regard to consumer protection. For example, researchers at the University of Bayreuth have succeed-ed in making an additive in dairy products and a production-related contamination in baked goods visible. Ingredients in fruit, vegetables and sausages that influence food quality can also be detected.
Ingredients of a kiwi: Green = sugar, blue = polyphenol, red = lipid. (Photo: © Oliver Wittek)
From natamycin in cheese to acrylamide in gingerbread
Where conventional food analysis methods have reached their limits up to now, imaging mass spectrometry (MS imaging) could show its strengths in the future. It combines the in-formation gained about molecules with spatial information: By scanning a sample surface and irradiating a different spot pixel by pixel, a mass spectrum can be recorded for each point that the laser has hit.
The team led by Prof. Dr. Andreas Römpp at the University of Bayreuth has now succeeded in making natamycin visible in cheese. The background: To protect cheese wheels or even smoked sausages from mould infestation, the surfaces are often treated with the fungicide. An EU regulation sets a limit of one milligram per square decimetre for this and also stipulates that natamycin must not penetrate deeper than five millimetres into a treated cheese wheel. However, current methods cannot describe this penetration depth in detail. With MS imaging, natamycin molecules can be tracked from the rind to the inside of the cheese wheel. "Build-ing on this newly developed approach, it may be possible to reduce consumer exposure to preservatives in the future," says Römpp, who holds the Chair of Bioanalytics and Food Anal-ysis at the University of Bayreuth.
The process also makes the acrylamide distribution in traditional gingerbread visible. To do this, the scientists had to cool the samples to less than minus 60 degrees Celsius and then produce gingerbread slices around two millimetres thick using an electric microsaw. This en-abled them to detect very small amounts of acrylamide. The background here: As it is a can-cer-promoting substance formed from sugar and the amino acid asparagine at low humidity and temperatures above 120 degrees Celsius, the EU prescribes specific measures for cer-tain foods to reduce the acrylamide content.
MS imaging of a cross-section through a Gouda wheel. (Photo: © Julia Kokesch-Himmelreich)
Useful in the fight against food fraud
The work of Römpp and his team also shows that MS imaging is equally suitable for analyses of processed meat products. In white sausages, water-soluble and fat-soluble components become recognisable, so that low-fat and high-fat regions can be clearly distinguished. Like-wise, it becomes visible where substances of plant origin are found that come from admixed herbs.
"MS imaging not only enables the localisation of ingredients in meat products, but also helps in investigations of 'glutinous meat' or so-called hydrolysate additives, which are intended to simulate a higher quality when they are not declared on the packaging. It could therefore be useful for detecting consumer deception in meat products and for better protecting consum-ers in this respect as well," says Römpp.
From the scientists' point of view, MS imaging has the potential to complement the already established methods of food analysis. It offers new insights into the spatial distribution and relative proportions of ingredients. It has the advantage that the molecules of the ingredients need not be marked with dyes or other labelling processes.
"At the university, we will - as part of the newly established Faculty VII for Life Sciences: Food, Nutrition and Health - will continue to work in the future on refining the analytical possi-bilities of imaging mass spectrometry, combining it with other food analysis instruments and applying it to ingredients that have not been investigated so far. In this way, we can make important contributions to consumer protection," says Römpp.