Grain storage and spoilage prevention and control

Feed Processing Articles >> Biosecurity

The feed hygiene Regulation (EC) No 183/2005 presents a legal foundation for the production of safe feedstuffs. The regulation applies to primary production and puts the spotlight clearly on grain storage since grain is an important potential source of contamination in the food chain with the risk of exposure of consumers to the contaminants. The Regulation says that cereals operators must control hazards (mites, moulds, mycotoxins, …) with the potential to compromise feed safety.

Good Storage Practices (GSP) is the primary mechanism to control and reduce hazards in cereals. On the other hand, all GSP recommends the use of suitable and approved preservatives, for example Myco CURB® range of products, because preservatives are beneficial for cereal to avoid heating and moulding. Safe grain is a requisite for safe food. Furthermore, high levels of animal performance can only be achieved with hygienically safe grain.

INTRODUCTION

It is widely recognized that grains are always contaminated with moulds and always susceptible to mite infestation. Grains are ideal substrates for mould growth and they can initially be contaminated by so-called “field moulds” such as Fusarium, whilst developing on the plants in the field. Under storage conditions, “storage moulds” such as Aspergillus and Penicillium become the predominant spoilage organisms. “Storage moulds” can grow at relatively low moisture content (mc).
These various mould species can produce several toxic metabolites known as mycotoxins.

THE SPOILAGE SYSTEM

Biodeterioration is the result of numerous interacting spoilage agents.

The factors which primary contribute to biodeterioration (including mould growth) are moisture, temperature and pests. Moulds can grow over a wide range of temperatures and, in general the rate of mould growth will decrease with decreasing temperature and available water. In grains, moulds utilize inter-granular water vapor (free water). For a given moisture content, different grains afford a variety of water activities and, consequently, support different rates and type of mould growth. Typical water activities which are necessary for mould growth range from 0.65 to 0.97; the water activity, and the propensity for mould growth increases with temperature. Maize, for example, can be relatively safely stored for one year at a moisture level of 14 per cent and a temperature of 10°C. However, the same maize stored at 30°C will be substantially damaged by moulds within two months.

Insects and mites (arthropods) can also make a significant contribution towards the biodeterioration of grain because of the physical damage and nutrient losses caused by their activity, and also because of their complex interaction with moulds and mycotoxins. The metabolic activity of insects and mites causes an increase in both the moisture content and temperature of the infested grain. Arthropods also act as carriers of mould spores and their faecal material can be utilized as a food source by moulds. Furthermore, moulds can provide food for insects and mites but, in some case, may also act as pathogens.

Another important factor that can affect mould growth is the proportion of broken kernels in a consignment of grain. Broken kernels, caused by general handling and/or insect damage, are predisposed to mould invasion of the exposed endosperm.

Mould growth is also regulated by the proportions of oxygen, nitrogen and carbon dioxide in the inter-granular atmosphere. Many moulds will grow at very low oxygen concentrations. Interactions between the gases and the prevailing water activity also influence mould growth.

The grain surface absorbs atmospheric moisture, mainly in winter, increasing significantly the mc and mycotoxin production. Moisture content fluctuation can create important wet spots. It is due to the natural convection currents originating from the head space. It depends on the ERH of the head space air, the grain mass and temperature.

Moulds consume nutrients and oxygen and produce carbon dioxide, water and heat. The water and heat cause the humidity of air surrounding nearby kernels to increase above 65% to 70% and results in further mould growth.

Condensation of the grain surface and underside of the roof also occurs when weather conditions fluctuate.

THE CONSEQUENCES OF BAD STORAGE

Mould growth will reduce the nutritional value of the grains. The balance of essential nutrients such as vitamins and amino acids will be disturbed and the energy content reduced. Feeding animals on moulded grains will lower the animal performance.

Moulds produce mycotoxins which will also have a significant impact on animal performance and productivity. Furthermore mycotoxins are considered to be one of the most important food contaminants due to their negative impact on food safety and public health.

Mite infestation during grain storage is also a common occurrence. Storage mites are extremely small but widely distributed. These insects are of increasing concern with reported allergenic effects to humans and well-documented detrimental effects to livestock causing loss of nutritional quality and reduction of palatability. Mites can cause dermatitis, digestive and respiratory disorders in farm animals and humans. Mites act as carriers of mycotoxins, mould spores and bacteria such Salmonella, and their faecal material can be utilized as a food source by moulds.

INFORMATION FOR STORAGE STRATEGIES

There is a basic need for information before any storage strategy can be designed. Information relating to storage conditions can be categorised according to the following checklist:

Grain type
Storage period
Grain moisture
Kind of storage, bag or bulk
Kind of material of bags and silos
Ambient temperature range through the storage period
Ambient humidity range outside the stores
Ambient humidity range inside stores
Stores proofed against rodents, flying insects and water

STORAGE PESTS

Grains are susceptible to pest infestation.

Insect and mite storage pests belong to the most successful animal group on earth.

The majority of grain storage pests are small beetles, moths and mites and in a lot of cases is very difficult to see them. It is important to know the local insect and mite species and the temperature and moisture requirements for each species.

The commonest species are:

Pest BEETLES in stored grain and grain stores

Grain Beetles (Oryzaephilus, Cryptolestes, Sitophilus and Ahasverus species)
Lesser Grain Borer (Rhyzopertha dominica)
Clover Weevil (Sitona sp)
Ground Beetle (Carabidae)
Mould and fungus beetle (Mycetophagidae, Typhaea, Lathridiidae and Cryptophagus species)
Rove Beetle (Staphylinidae)
Spider Beetle (Ptinus fur)

Pest MOTHS in stored grain and grain stores

White-Shouldered House Moth (Endrosis sarcitrella)
Grain Moth (Sitotroga cerealella)
Brown House Moth (Hofmannophila pseudospretella)
Mill/flour Moth (Ephestia kuehniella)

Pest MITES in stored grain and grain stores

Grain Mite (Glycyphagus destructor)
Predatory Mite (Cheyletus eruditus and Gamasina)
Flour Mite (Acarus siro)
Cosmopolitan Food Mite (Lepidoglyphus destructor)

DETECTING AND MONITORING PESTS

Detecting insects in grain enables corrective action to be taken.

Monitoring pests assesses effectiveness of control measures.

Samples sacks help to determine the infestation status of the grain, and visual inspection is extremely useful too.

Insect monitoring traps have been used for many years. Results from trapping can be reliable because traps operate continuously. If the trap incorporates a lure, there is a considerable positive attraction factor. Bait bags are attractive to most storage beetles.

Traps are not very effective for quantifying insect infestations but can indicate population trends.

Visually detecting insects in bulks of grain is in some cases almost impossible.

Sampling is a poor method for detecting insects and mites. Even a single insect in a 1 kg sample may represent potentially serious infestation.

Mites can be monitored by using mite traps or by sieving.

Mites are most likely to re-infest a grain surface when it absorbs moisture from the atmosphere in winter.

GOOD STORAGE PRACTICES

Prevent losses from insects, mites and moulds by storing grain, oilseed and pulse crops properly; preventing infestations is easier, safer and less expensive than curative interventions.
Prepare the bin before storing the new crop. Stores must be clean, dry and well ventilated. Handling equipment must work properly to reduce damage grain.
Install an aeration system to reduce grain temperatures and to reduce moisture migration.
Drying. Tough or damp crops are more likely to become mouldy or infested with insects and mites than dry crops. There are two basic methods of drying grain: heated air and bulk drying.
Cooling after drying to stop insects breeding, prevent pest increase and reduce relative humidity.
The use of a suitable, approved preservative, for example Myco CURB, is beneficial for cereals to avoid heating and moulding as storage conditions change in the course of the storage period.
The preservative should be applied promptly with appropriate application equipment to provide even coverage of the whole batch of grain being treated.
Monitoring and control moisture and temperature as these two factors interact to provide favourable conditions for growth of moulds and mites. As a result of monitoring, eventually apply corrective actions.
Monitoring pest and rodents and eventually apply corrective actions.

KEMIN GRAIN TREATMENT (GT) PROGRAMME

Preventing loss of grain quality from mites and moulds during storage grains, cereals, oilseed, and pulse crops is easier, safer and less expensive than any remedial or curative programme to improve spoiled grain.

The goal of effective grain storage is to avoid quality losses from the time the grain is stored until the time it is used. For this purpose, it is crucial to keep the mould contamination of grains as low as possible.

A practical and widely used method to control mould in stored grain is through the Grain Treatment Programme from Kemin.
This Programme has been developed by Kemin for the safe storage and management of cereals, oilseeds and pulses used in animal feeds.

The GT Programme will contribute to the production of a safe, wholesome food supply for the consumer.

The safe storage methods that the GT Programme promotes are based on sound management practices and expert knowledge of moulds and mites and the GT Programme is an essential tool to deal with Feed Hygiene and Food Safety issues. The GT Programme puts the consumer’s safety first and is a valuable example that when Industry and Kemin cooperate, important problems can be solved.

Preventive measures to maintain good grain quality during harvesting and storage are clearly necessary. The major hazards in grain can only be controlled by strict application of Good Storage Practices and Hazard Analysis and Critical Control Point (HACCP) plans. The GT Programme paves the way for implementing efficient GSP systems as well as the new regulatory requirements.

Good Storage Practices includes the use of a mould inhibitor as Myco CURB®, which controls mould and mites. Kemin’s GT Programme, with Myco CURB®, should be used to treat storage structures and grain and it plays a useful role in GSP.

by Kemin Europa N.V.

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