July 23, 2017

24/07/2017: Preserving feed by getting a grip on moulds

by Dr Eckel Animal Nutrition GmbH & Co. KG

One of the most critical factors in global feed and food production remains to be the prevention of post-harvest losses
Image credit: James Lee on Flickr

The post-harvest system encompasses the delivery of a crop from the time and place of harvest to the time and place of consumption, ideally with minimum loss and maximum efficiency. Even under optimal growing and harvest conditions, losses immediately post-harvest are common.

According to estimates by the FAO, up to 3.5 percent in central Europe and 30 percent in tropical areas are lost due to spoilage and pests. Efficient preservation methods for crops and feeds with organic acids are therefore of special interest for all parties involved in food and feed production.

There are multiple factors leading to spoilage in feed and food, including moisture content, temperature, storage conditions and the naturally occurring microbial contamination (Table 1).

Table credit: Dr Eckel

Nutrient losses
Moulds in feed are a serious economic problem because they consume the main nutrients and affect the palatability of the feed. Losses of nutrients caused by moulds can occur in magnitudes of up to 10 percent.

The crude fat content of grains is especially affected by mould growth during storage, even more so than proteins and carbohydrates. Losses in metabolisable energy from maize may even reach 25 percent necessitating the use of additional costly sources of energy in the formulation, for instance fat and oil. Spoilt raw materials therefore reduce the efficiency of animal production.

The danger of mycotoxins
Apart from these nutrient losses, moulds also produce mycotoxins, threatening animal and human health. Many studies in the literature show the detrimental effects of mycotoxins on animal health and performance.

The sensitivity for these effects is dependent on animal category, age, health status and also duration and level of exposure. Antonissen et al. (2014) described how the mycotoxin Deoxynivalenol might act as a predisposing factor for necrotic enteritis in chickens. Aflatoxins can be transferred into animal tissues and therefore pose a serious risk for the consumer (carry-through-effect).

Feed preservation is key
Prevention is the recommended method to avoid the problems arising from nutrient losses and mycotoxin contamination due to mouldy feeds. This means minimising the microbial spoilage from time of harvest to the final use of the material.

Several methods are possible to preserve raw materials and feed in practice. These methods include drying, oxygen deprivation, cooling and the application of chemical preservatives. The use of organic acids to prevent feed and food spoilage is widespread. To get the highest preservation success the right choice for preservative and the correct application are imperative.

Choose the right preservative
Due to its lipophilic character, propionic acid and its salts are especially effective against moulds making it the organic acid of choice when contemplating feed preservation. As a result of its pKa value of 4.8, propionic acid is also active at a more neutral pH, which closely matches the native pH value in grain and feed.

Organic acids cause inhibition of microorganisms by rapid diffusion of the undissociated molecule into the cell. Dissociation (release of the H+ Ion) of these molecules in the cell of the bacteria causes acidification of the cytoplasm thereby preventing growth (Lambert & Stratford, 1999).

This is typically more effective at a low pH when – depending on the respective pKa - a higher proportion of the acid is undissociated. Furthermore, propionates have been shown to prevent the formation of Ochratoxin A by Aspergillus sulphureus and Penicillium viridicatum (Tong & Draughton, 1985). Shekar et al. (2009) described a reduction of Aflatoxin in post-harvest maize by propionic acid and sodium propionate.

The efficacy of different preservatives may easily be tested with the so-called CO2 test. In this test, the volume of carbon dioxide formed by microorganisms is measured in vitro. As moulds grow, they consume oxygen from the air and produce CO2.

The higher the amount of CO2, the higher the contamination with moulds in the substrate. As shown in figure 1, the application of a propionic acid based preservative (MoldCid) decreases the CO2 production in grain, giving a clear indication that the microbial activity was reduced.

Read the full article, HERE.

Visit the Dr Eckel website, HERE.

The Global Miller
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which is published by Perendale Publishers Limited.

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