Nutritionist > Dairy
Fungal growth
Moulds grow by producing long filaments called hyphae, which are important for the survival and dispersal of fungi. The hyphal network is responsible for cementing kernels together, which in stored grain or feed can result in clumps of grain that cannot be separated. Grain-mould fungi also produce spores (conidia) capable of aerial dispersal in the field as well as within a grain storage bin. It is usually masses of these spores that give the mould a characteristic colour. Spores can lay dormant for months or years until the proper conditions for fungal development are available.
Fungal species are often divided into two groups:
- Field fungi
- Storage fungi
Storage fungi (also called storage moulds) are those that invade grains or seeds during storage. They need less moisture than field fungi (13-18%) and usually do not present any serious problem before harvest. Storage fungi include species of Aspergillus and Penicillium.
While the field/storage terminology is generally used to indicate the differences in temperature and moisture required by various fungi, in fact the proper conditions for growth of a specific organism can occur in either the field or storage bin. Ideal conditions for fungal growth depend on the species, but normally moulds require high temperature and moisture.
Mycotoxins are produced as secondary metabolites. Under field conditions, stress and subsequently reduced vigour often predispose plants to infestation and colonisation by toxigenic fungi. In stored grain, toxigenic fungal infection and mycotoxin production result from a complex interaction among moisture, temperature, substrate, oxygen (O2) carbon dioxide (CO2) concentration, fungal abundance and insect presence (insects can influence a differentiation on fungal species, that is a specific insect determines the presence of a specific fungal species).
On one side plants can modify the concentration of mycotoxins due to different enzymatic systems. On the other side, it seems that they can move substances from the site of production to the hull and the stem, then to the leaves. Mycotoxins can so be found in forage.
In general, most fungi need at least 1-2% oxygen and usually grow at temperatures between 20 and 30°C. It is important to note that if the grain is at high temperature at harvest, it can maintain that high temperature for several days or weeks after harvest unless the storage facility has cooling capabilities. Normally, in storage conditions fungi grow at 13-18% moisture. However, in case of grains with high levels of oil (e.g. peanuts) fungal growth occurs at moisture contents as low as 7%.
