Microorganisms - Moulds

Moulds are a large group of fungal species. They can be found in the division of zygomycota and ascomycota. Best known for food spoilage and multicoloured detrimental alterations of food, e. g. bred, fruit and vegetables. On the other hand, they can be quite useful in foodtechnology and biotechnology.


Moulds are growing on food and other objects in large numbers, in different colours with fluffy threads on the surfaces. These threads are made from hyphae, a kind of fine filaments. A network of hyphae is called mycelium. A mycelium can be very big. In most cases the mycelium is transparent.

Why do moulds appear in magnificent colours - red, orange, green, blue and black - when they are really transparent? The answer is that spores are colouring the mould. Spores are sitting at the end of the hyphal tips in large containers, so called sporangiophore, or they are free and forming chains, so called conidiophores. Mould spores are able to survive everywhere. They can be transported by air, sitting on humans, animals and other surfaces. Spores survive cold temperatures as well as high temperatures and dry environments. This is the moulds trick to survive in uncommon environment. When the conditions become better, spores build new hyphae and the mycel starts to grow.

Some moulds produce mycotoxins. Mycotoxins are a health risk and can be the source of cancer (aflatoxin from Aspergillus flavus), allergic reactions, respiratory and neurological problems. However, not all moulds are dangerous. Many are helpful in food technology, biotechnology and medicine. When Sir Arthur Fleming discovered the antibiotic penicillium from a Penicillium spp. it was just the beginning of great developments in biotechniques. Some mold species produce enzymes and aromatic chemicals like citrus acid. The aroma industry benefits from their capabilities. The food industry uses moulds for food fermenting (e. g. Aspergillus oryzae, soybeans), ripening of raw sausages, cheese production (Penicillium roquefortii) and brewing.

Moulds can be found in the bathroom, in the kitchen, in the air, on the surface of old books - they are ubiquitous. The knowledge of its species is important for their handling. Not every kind of mould is dangerous, but some are!



Figure 1: Penicillium spp. under a microscope (magnification: 1000x); [source: D. Graubaum, Berlin, Germany]










Figure 2: Schematic drawing of an apple with mould [source: D. Graubaum, Berlin, Germany]











This article was written by Prof. Diana Graubaum, Department of Food Microbiology, Beuth University of Applied Sciences Berlin, Berlin, Germany.

For further questions please refer to: graubaum@beuth-hochschule.de



           "Yeast and mold (mould) growing in petri dish"