High-moisture grain preservation in view of feed and food safety

Moulds can either invade certain parts of the growing crop in the field or can cause deterioration in storage when harvest moisture content exceeds 14 %. Both, field and storage fungi, cause significant nutrient losses and have a detrimental effect on hygienic quality by the formation of mycotoxins. These undesired substances may enter the food chain via contaminated feed grain, thereby not only posing a risk to farm animals, but also to consumers.

With coming into effect of REGULATION (EC) 183/2005 (Feed Hygiene Regulation), feed business operators (e.g. compound feed manufacturers) as well as farmers feeding food-producing animals “shall take measures and adopt procedures to keep the risk of biological, chemical and physical contamination of feed …. as low as reasonably achievable”. This is certainly the first time ever in the EC that a significant share in the responsibility for food safety is hold by the primary production of feed, meaning the farmer. As additional protective measure to minimize the potential health hazard related to mycotoxins exposure in the EC, not only maximum tolerable levels for certain mycotoxins in foods have been implemented. Also guidance values for the mycotoxins deoxynivalenol (DON), zearalenone, ochratoxin A, T-2 and HT-2 as well as fumonisins in products intended for animal feeding have been proposed in COMMISSION RECOMMENDATION 2006/576/EC. These actions clearly stress necessity and responsibility for every person involved in food and feed production to prevent formation and accumulation of mycotoxins in the food chain.

The pattern of mycotoxin production on growing crops in the field is always similar irrespectively of grain type. Numerous studies have shown that the longer the mature plant is left in the field the higher is the risk for and the degree of mycotoxin contamination. Results of a study which our company carried out in collaboration with researchers of a Chamber of Agriculture in the German State Lower Saxony (see graph) confirmed those findings for grain maize. The concentration of the Fusarium toxin DON significantly increased with delayed harvest date, but starch accumulation was already completely at a rather early stage of maturity and changed only slightly over the whole experimental period.

A strategically desirable approach is to harvest grain when starch accumulation is completed and mycotoxin contamination is still low, even if moisture content is higher than 14%. However, such material must be preserved. Otherwise it will rapidly undergo fungal deterioration in storage by moulds of the genera Penicillium and Aspergillus.

Drying has been the most widely used technology to protect cereals from spoilage. However, it is no longer an option for feed grain due to significantly increased costs for energy and additional investments into drying capacities. High-moisture grain preservation by organic acids with antimycotic activity is an attractive and interesting alternative to drying. This preservation method has been in use since the early 70ies, when the first oil crisis hit the world. Nowadays, it is frequently employed by farmers and will become even more important in the future because of higher flexibility in harvest date, comparatively low investment costs in technology and storage facilities and simple equipment requirements.

Preservation of damp grains with propionic acid is well researched and documented. Care needs to be taken on the application of the required dosage of preservative which depends on moisture content at harvest and intended length of aerobic storage. Major obstacles in making farmers choose chemical grain preservation with pure propionic acid have been its pungent odour as well as its corrosivity on skin, concrete and metal. Partial buffering of the acid with ammonium propionate or other salts can significantly reduce corrosivity but unavoidably results in higher application rates than those for pure propionic acid. More recent developments in the field of commercial preservatives have led to unique formulations containing sodium benzoate. This substance which has long and safely been used in food preservation is an even more potent fungal inhibitor than propionic acid. Sodium benzoate containing products have the advantage of being as effective as pure propionic acid in terms of application rate, but are not corrosive on skin.

The technology of chemical preservation of high-moisture grain offers further advantages. Using home-grown cereals is the only way for farmers to admix feeds of known origin and quality to animal diets. This makes total traceability possible and increases feed and food safety. Finally, productivity of livestock farming can be significantly reduced by feeding preserved damp grain since purchasing of such feed materials on the market is typically linked with higher prices than the production costs.

The following conclusions can be drawn for farmers based on current state of knowledge, aforementioned risks and new EC legislation:

• To keep fungal infestation in the field at low level, grain must be harvested at optimal stage of maturity irrespective of weather conditions.
• Adherence to this strategy will lead to variable proportion of grain which is harvested at moisture contents too high for safe storage and, therefore, needs to be preserved.
• Preservation of feed grain by drying will not be an option in the future due to its enormous energy demand and increased energy costs.
• Chemical preservation of high-moisture grain is a safe, proven and comparatively cheap alternative to drying. The extent of use can easily be adapted to variable, weather-depending demand, which is, among other things, due to simple equipment required and low fix costs.
• There are very efficient commercial chemical preservatives available, which are easy to use and entirely harmless to animal and consumer. Their application makes feeds and foods even safer than ever as they protect from risks of inferior feeding hygiene.
• High-moisture grain preservation offers the great advantage of storing and using home-grown feed, thereby allowing total traceability within the food production chain. This technology is the best way to guarantee that only cereals of high hygienic quality are fed.
• Chemical preservation of damp grain improves profitability of livestock production because of lower prices for grain that would otherwise have to be purchased at higher costs from commercial traders as such or as component of compound feed.