Emerging food safety risks from biological contamination

BĂ©atrice Conde-Petit, 22 Mar 2017

Food safety is one of the largest challenges facing the global food system. It is not only about supplying enough to eat for a growing population, but also about ensuring the integrity of food in terms of safety, nutrition and wellbeing.

Emerging food safety risks of biological origin

Since early days, mankind had to find ways of overcoming the potential harmful effects of biological contamination of food, leading to spoilage, poor quality and, even worse, to illness and death. Today’s world relies on industrial food processing and a global supply chain in order to nourish a growing urban population, but food safety remains a constant challenge. Food safety hazards of biological origin still count to the main risks around the globe.

Mycotoxins are a silent threat for humans and animals

The Food and Agriculture Organization of the United Nations (FAO) estimates that 25% of food crops are contaminated by mycotoxins. These are poisonous chemicals formed by fungal mould which grows on crops like maize, wheat, rice and other grain staples. Also nuts, in particular peanuts, and dried fruit are frequently affected. Mycotoxin contamination of feed and food is the third most frequent hazard reported in the European Rapid Alert System for Food and Feed (RAFFS). Globally, 80% of animal feed is contaminated, because mycotoxins are concentrated in the side streams from grain processing which are diverted into feed[1]. Although mycotoxin is considered a chemical hazard, the route cause is fungal growth on raw material on the field or during storage due to poor agricultural practices, insect infestation and poor post-harvest handling. Many fungi are known to form mycotoxins under hot and humid conditions, and overall more than 300 of these toxic compounds have been described.

Climate change increases the risk of aflatoxin, the most toxic mycotoxin. The risk map shows the estimated prevalence on maize for Europe for three different climate scenarios (a) present, (b) +2°C, (c) +5°C. Image from reference[2].

Aflatoxin is the most toxic mycotoxin and maximum limits exist around the world for feed and food in the range of 0.1 to 20 μg/kg, while the contamination of raw materials may be 10 to 100 fold higher. Also cow milk may be affected by aflatoxin as a result of carryover of contaminated cattle feed. Acute intoxications of humans by high levels of aflatoxin leading to death are rare. However, prolonged exposure to this tasteless and colourless compound is a silent threat for humans and animals, as aflatoxin is the most potent natural carcinogen known. Around 4.5 billion people, mainly in developing countries, are continuously exposed to cereals contaminated with aflatoxin and other mycotoxins like fumonisin and deoxynivalenol.

It is estimated that aflatoxin accounts for up to 150 000 cases of liver cancer, mainly in Asia and Africa[3]. An emerging concern is the role of mycotoxins as factor contributing to stunted child growth[4] on top of poor nutrition and infections. Stunting of children is manifested by impaired infant growth and diminished cognitive and physical development. The World Health Organization (WHO) judges childhood stunting is one of the most significant impediments to human development, globally affecting approximately 162 million children under the age of 5 years. Likewise, livestock health and productivity is severely impaired by the continuous exposure of animals to mycotoxin contaminated feed.

Mycotoxin prevention means post-harvest protection of crops

Mycotoxins are relatively heat stable compounds which cannot be eliminated by thermal processing. Containing the risk of mycotoxins means preventing fungal growth on the field and in storage. Aflatoxin is a typical storage mycotoxin, and the most effective prevention is drying of crops directly after harvest, as fungal moulds stop growing at moisture levels below 14%. Furthermore, safe storage that protects the crop from rain and pests is necessary.

An effective measure to reduce the level of mycotoxins is the removal of highly affected grain fractions. The uneven distribution of aflatoxin is a typical feature of this kind of contamination, where a few highly contaminated grains within 10 000 grains destroy the value of a lot. Eliminating the highly contaminated grains by cleaning and sorting is a key measure for safe food. The cornerstone of mycotoxin reduction is high capacity optical grain sorting to identify and remove the discoloured, shriveled and broken grains, which are the typical signs of fungal infection. For moderately contaminated grain it allows processors to recover over 95% of a lot for safe feed and food.

Nuts, spices and cereals may carry harmful bacteria

Most foodborne diseases are caused by bacteria, viruses and parasites causing around 230 000 deaths per annum according to WHO. The public health burden is highest for low income regions and for children under the age of 5. Microbial contamination of food can also strike more affluent societies. In Europe 23 million people fall ill and 5 000 die every year. The Center of Disease Control (CDC) estimates that in the United States 48 million people get sick and 3 000 die of foodborne diseases. According to the US Department of Agriculture (USDA) foodborne illnesses cost USD 15.6 billion each year.

Food of animal origin and water are still the main vehicles of contamination. However, in the past 15 years foods of plant origin have increasingly been associated with foodborne illnesses due to microbial contamination. Besides fresh fruit, sprouts and vegetables, dry foods like nuts, sesame, spices, cereal flour and chocolate are today seen as potential carriers of harmful bacteria like Salmonella spp., Listeria monocytogenes, E. coli, etc. High profile foodborne outbreaks and product recalls in Europe and the United Stated could be traced back to these ingredients by applying modern methods of DNA fingerprinting. New scientific evidence has led to a reassessment of food safety risks related to dry plant-based foods[5]. It is known today that many raw food materials can be contaminated with pathogenic bacteria trough unclean water, birds, rodents or unhygienic handling. Although the number of harmful bacteria may be small, they pose a hazard as they may well survive in dry environments and start multiplying in contact with moisture. The threat is even higher where the infectious dose leading to illness is as low as a few cells, which has been documented for fat-rich products like peanuts, almonds or chocolate contaminated with Salmonella spp. Modern urban lifestyle features ready-to-eat foods for snacking on the go and convenience in the kitchen. A good example are snack bars based on dry fruit, nuts, seeds, cereal flakes and chocolate, all these ingredients being potential vectors of microbial contamination.

The biggest risk for global public health are pathogenic bacteria that carry antimicrobial resistances (AMR). They mainly evolve due to overuse of antibiotics in livestock production, and are spreading into the whole food supply chain. When humans are infected with AMR bacteria, antibiotics fail to cure, resulting in the death of 25 000 people every year in Europe and the United States. It is estimated that by 2050, more than three million will lose their lives to one bacterial infection: drug-resistant E. coli[6] which is primarily transmitted by contaminated food.