Less mold, more food
Foods like fruit, vegetables and dairy products often get attacked by mold or fungus and therefore must be discarded. If we can extend the shelf life just a few days, we can save a lot of food from being thrown out. SDU researchers are trying to contribute to that.
Green mold spots on the cheese are a clear signal that it should go in the bin, and if you’ve only eaten some of it, that is a shame.
This is also the case for many other foods that can be attacked by mold and fungus; they must be discarded and thus transformed from food to food waste.
Many foods can actually last quite a long time before mold starts to develop, and this is often because they have been treated with an anti-fungal agent. One such agent is Natamycin (with the e-number 235).
In Denmark it is used to treat the surface of matured cheeses, cheese products and certain meat products while other countries use it for for the preservation of milk, yoghurt, wine, juice, sausages, bread, fruits, vegetables, etc.
Breaks down in sunlight
But even though Natamycin is both effective and suitable for food protection, there are limits - after 3-4 weeks the first mold spots on the cheese may start to appear.
What if you could prolong the effect of Natamycin? Or make it more efficient? Certain conditions, such as sunlight, make Natamycin less effective, and just a few days more shelf life could make a huge difference for producers and consumers, said Daniel Wüstner, who leads a research group at the Department of Biochemistry and Molecular Biology.
One of the group's current areas of interest is studying Natamycin by directly observing it using advanced microscopes, thereby gaining better insight into exactly how this fungicide keeps mold and fungus down.
- If we can find out precisely what is happening, then perhaps we can also modify Natamycin to become more effective - and this holds the potential to increase the shelf life of foods treated with Natamycin, he explains.
Fungicide produced by soil bacteria
Natamycin is a fungicide produced by a commonly occurring bacterium that lives in the soil.
It was discovered in a South African laboratory in 1955, and since then the bacterium (S. natalensis, named after the KwaZulu-Natal province) has supplied the global food industry with Natamycin – and incidentally also pharmacies, because Natamycin is also prescribed as a medicine against fungal infections in humans.
Natamycin’s advantages are that you cannot smell, see or taste the substance after a food item has been treated with it. This is done, for example, by dipping the food in a solution containing Natamycin, so that the surface is protected against attack by mold and fungus.
The question that occupies Wüstner's research group, is; what exactly happens when Natamycin kills a fungus?
If we can modify Natamycin to become more effective, this holds the potential to increase the shelf life of foods
The group knows that the interesting components in the process are the so-called polyenes. Polyenes are a group of substances found naturally in certain bacteria, where they function as part of their innate defense system. If you - as from the South African bacteria - extract polyenes, you can use them in medicine against fungal infections and to treat food with.
What the researchers do not know is how the polyenes get through the fungal cell's membrane and on to the target in the cell. The target is the cell's ergosterol, which is a subset of steroids, and the question is how do the polyenes bind to and interact with ergosterol?
Wüstner's group has teamed up with colleagues Peter Reinholdt and Jacob Kongsted, who do research in theoretical and computational chemistry (also at SDU) and also work together with two German research teams from Leipzig University and Humboldt University Berlin. The group has described their latest study of polyenes in this scientific article.
Daniel Wüstner mentions three examples of why it is interesting to improve Natamycin by modifying the substance chemically:
1. It breaks down in daylight, and therefore treated foods must be stored preferentially in the dark.
2. It is not soluble in water, and therefore other solvents must be used when mixing it up for treatment.
3. It is the only agent approved as an antifungal medicine for humans in the United States and several other countries, and this increases its use coming with the risk of fungi becoming resistant to it.
More on mold: Can't I just scrabe the green mold off?
Mold on food is a fungus that can form mycotoxins, which can, for example, cause stomach aches or be carcinogenic in the long term. Often, food is attacked by fungal spores that are commonly found around us.
The Danish Veterinary and Food Administration recommends that you always throw out these foods when you can see mold on them: Bread (may have spread to the whole bread, even if you can't see it), nuts, seeds and kernels, juicy fruits and vegetables, liquid "sauces" (such as pesto, jam, tomato puree, mustard, mayonnaise), meat, milk, liquid milk products such as yoghurt and sour cream.
You can eat these foods if you cut away visibly moldy areas: Mushrooms “(the white fur” is the mushroom's own mycelium), hard cheeses, firm fruits, firm vegetables and tubers.
Meet the researcher
Daniel Wüstner is an associate professor and Principal Investigator at the Department of Biochemistry and Molecular Biology.