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Blog – control of Salmonella in soybean meal
Date: 04.08.2023

How to prevent Salmonella contamination in soybean meal

Soybean meal is the most important protein source used for animal feed worldwide, providing over two-thirds of protein products and with an export trade worth about US$30 billion per year.  Salmonella is one of the most dangerous pathogens that can contaminate animal feed. It can enter food supply chains at numerous points on the journey, from the farm cultivating soybean to the farm feeding the processed product to its livestock. It is widespread in the environment and occurs in the gut of mammals, birds, insects and reptiles. The main sources of human Salmonella infections are food animals such as pigs, poultry and cattle, especially raw food products derived from these animals. Preventing Salmonella from entering the food chain, from soybean production to human consumption of animal products, requires measures to prevent and control it at every link in the chain.

What is Salmonella?

Salmonella is a gram-negative rod-shaped bacterium in the family Enterobacteriaceae. It has a complicated classification of subspecies and serovars. There are two species of Salmonella bacteria, of which Salmonella enterica is the main risk to human health. 

Salmonella enterica has six subspecies, but enterica causes 99% of infections in humans and warm-blooded animals. There are over 2500 serotypes of Salmonella enterica subspecies enterica, some of which are highly virulent. The other serotypes are found mainly in the environment and cold-blooded animals and rarely in humans.

Salmonella is a hardy bacterium that is able to survive for several weeks in a dry environment and for months in water. 

Why is Salmonella a risk for food supplies?

Salmonella is one of the top-four causes of diarrhoeal diseases worldwide and one of the most frequently isolated food-borne pathogens. It is a major public health concern in both developed and developing countries because of the costs of surveillance, prevention and treatment of the disease. Livestock such as pigs, poultry and cattle are the main sources of infections in humans via both live animals and uncooked animal food products. In a study of Salmonella in the food chain in Poland,  160 Salmonella serovars were identified, with 124 in animals, 44 in food, 73 in animal feeds, and 15 in fertilisers.

Salmonellosis (the disease) can cause fever, abdominal pain, diarrhoea, nausea and vomiting. In most cases it is mild, but in children, the immunocompromised and the elderly, it is more likely to cause severe dehydration and become life-threatening. Different serotypes differ in their ability to cause infections in humans, but all have the potential to affect human health and some cause typhoid and paratyphoid, which are more often life-threatening. 

There is little data from South America, but In the EU, where cases are monitored, over 91,000 cases are reported each year and the economic cost is estimated to be up to €3 billion per year.

What are the causes of Salmonella contamination in soybean meal?

There are numerous opportunities for soybean meal to be contaminated with Salmonella before reaching the ship port. Businesses handling and processing animal feed materials must apply good practices such as HACCP principles and good hygiene and manufacturing practices (GHP and GMP) for import into countries such as the EU to comply with legislation related to animal feed. Sources of contamination include the following.

1. Contamination before processing: the soybeans can be contaminated during cultivation, harvesting and storage on the farm by coming into contact with contaminated water, soil, or animal faeces.
2. Inadequate storage conditions: Improper storage of soybean meal at the production facility or warehouse can lead to Salmonella growth and contamination. Factors such as high humidity and temperature, and poor ventilation create an environment that promotes bacterial growth.
3. Cross-contamination during processing: If proper hygiene and sanitation practices are not followed during the processing of soybean meal, cross-contamination can occur. This can happen when equipment, surfaces, or utensils come into contact with contaminated materials or are not adequately cleaned and sanitized between uses.
4. Pest infestation: Pests such as rodents, birds and insects can carry Salmonella bacteria and contaminate the soybean meal with their droppings, feathers, nesting material or from dirt on their bodies. Every facility storing or processing the product should have effective pest control measures in place to prevent infestations and remove the risk of contamination.
5. Poor handling practices: Improper handling of soybean meal during transportation and storage can result in contamination if containers or packaging materials are not clean or if there is a spillage or exposure to contaminated surfaces and materials.
6. Inadequate quality control measures: Poor quality control procedures, such as lack of regular testing for Salmonella or inadequate monitoring of production processes, can result in undetected contamination of soybean meal. It is crucial to implement good manufacturing practices (GMP) and HACCP to ensure stringent quality control measures.

How do you prevent Salmonella in soybean meal during shipping?

Controlling pathogens in bulk products in ship holds is essential to prevent the growth of harmful bacteria and fungi, which can lead to spoilage and contamination of the grain. In a study over 19 years of imports to Norway, 34% of samples collected during unloading of ships contained Salmonella, with 94 serotypes isolated, including major pathogenic serotypes. Some standard practices to prevent Salmonella are:

1. Pre-shipment inspection: an inspection should include visual checks for signs of damage, damp, mould, or insect infestation. Samples should also be collected and tested for Salmonella and other pathogens.
2. Proper cleaning: The ship hold should be thoroughly cleaned and disinfected before loading meal or grain. Any residual product, dust, or debris should be removed, and the hold should be treated with an approved disinfectant.
3. Temperature control: Salmonella thrives in warm and moist environments. The ideal temperature to prevent the growth of microorganisms is 10–20°C.
4. Moisture control: Salmonella can survive even in low moisture conditions, so it is essential to monitor the moisture level regularly and keep it below 12%. This also prevents the growth of other bacteria, mould and insects. 
5. Treating feed: A range of treatments are available to prevent the growth of Salmonella and eliminate it.
6. Storage and transportation: The grain should be stored and transported in clean, dry conditions. The hold should be well-ventilated to maintain the temperature and humidity levels, and the grain should be properly secured to prevent any movement.
7. Record keeping: All procedures related to the prevention of Salmonella should be documented, including pre-shipment inspection, cleaning, and any feed additives used. Records should be kept of the temperature, moisture levels, and any testing performed for salmonella.

What treatments can be used on soybean meal to prevent Salmonella during shipping?

Some specific treatments that can be used to control Salmonella include:

1. Thermal treatment: This involves exposing the grain to a high temperature for a specified period. The most common method is to apply hot air to the grain to raise the temperature to around 60-70°C for at least 30 minutes.
2. Fumigation: Fumigation with approved chemicals can be used to control insects and prevent contamination of food products. Fumigants such as phosphine, methyl bromide, and sulfuryl fluoride can be used, but their use requires strict safety procedures and should comply with both local regulations and guidelines and those of the country where the product is being shipped.
3. Irradiation: Irradiation involves passing the meal through a radiation chamber that exposes it to gamma rays, electron beams or Xrays to kill the bacteria. The dose of radiation required depends on the type of grain and the level of contamination. The meal does not come into contact with any radioactive materials and is not made radioactive.
4. Applying organic acids: The use of organic acids, such as formic acid, propionic acid and acetic acid, especially blends of the acids, is one of the most effective measures for controlling Salmonella. These acids lower the pH around and inside the bacteria, disrupting the cell membrane and cellular processes. Organic acids can also provide some residual protection against recontamination and prevent Salmonella infection in animals fed the product. Ecotec is a specialist in treating bulk commodities for Salmonella control .

Conclusion 

Salmonella is one of the most important pathogens that cause illness in animals and humans and is frequently found in bulk food products such as soybean meal, which is the main source of protein for animal feed worldwide. The production, processing, storage and transport of the meal all have critical vulnerabilities where Salmonella contamination could occur. 

Every business handling soybean meal must ensure good practices such as HACCP and GMP are observed to prevent contamination and eliminate the pathogen when it occurs, including maintaining proper storage conditions, following rigorous hygiene and sanitation protocols, implementing pest control measures, conducting regular testing for Salmonella, and treating the meal. One of the key treatments to prevent and eliminate contamination is treating with organic acids prior to shipping. This can be carried out by a specialist provider in the port.