Food Safety Hazards

The term food safety has no universally accepted definition. In fact, it is sometimes used, wrongly, in relation to defects in food commodities that are much more to do with food quality than with safety. For example, microbial spoilage of food may make it unattractive, or even inedible, but if neither the microorganisms concerned, nor the by-products of their growth and metabolism have any adverse effect on health, then it is not strictly a food safety issue, but one of acceptability. For the purposes of this book, food safety can usefully be defined as the practice of ensuring that foods cause no harm to the consumer. This simple definition covers a broad range of topics, from basic domestic and personal hygiene, to highly complex technical procedures designed to remove contaminants from sophisticated processed foods and ingredients.

Essentially, the practice of food safety can be distilled down to three basic operations:

• Protection of the food supply from harmful contamination.

• Prevention of the development and spread of harmful contamination.

• Effective removal of contamination and contaminants.

Most food safety procedures fall into one, or more than one, of these categories. For example, good food hygiene practice is concerned with the protection of food against contamination, effective temperature control is designed to prevent the development and spread of contamination, and pasteurisation is a measure developed to remove contaminants.

A food safety hazard can be defined as any factor present in food that has the potential to cause harm to the consumer, either by causing illness or injury. Food safety hazards may be biological, such as pathogenic bacteria, chemical, such as a toxin produced during processing, or a physical object, like a stone or piece of metal. In other words, hazards are the factors that food safety practice seeks to protect against, contain and eliminate from foods. In order to be effective, food safety practice must be informed about the nature of these hazards, and food safety procedures must be science-based. A thorough understanding of biological and chemical hazards is the first essential step in their control. This is less important for physical hazards, which also tend to have a much lower potential impact on public health. Physical hazards are not considered further here.

It is generally biological hazards that pose the greatest immediate food safety threat to the consumer. For example, the ability of food-poisoning bacteria to cause large outbreaks of acute illness within a short time is a threat with which most food businesses are likely to have to contend. There are few foods that are not vulnerable to biological hazards at some point in their manufacture, storage and distribution.

Technically, biological hazards may include larger organisms, such as insects and rodents. However, these rarely present a direct threat to health and are not considered further here. It is microorganisms and certain food-borne parasites that are of most concern as food safety hazards.

A significant number of bacterial species can be classified as food safety hazards. Some of these, such as Salmonella and Listeria monocytogenes, are very well known and familiar to consumers, whereas others are much less common and less well understood. Examples include Vibrio parahaemolyticus, a comparatively rare cause of food poisoning associated with seafood, and Yersinia enterocolitica, a cause of gastroenteritis that predominantly affects young children. Campylobacter is another example of a less well known cause of food-borne illness. Few consumers have heard of this organism, yet it is now the cause of more reported cases of food poisoning than any other agent, including Salmonella. Campylobacter is also less familiar to the food industry and there are still many unknowns surrounding its transmission to humans. This underlines the importance of continued research and scientific investigation for increasing our understanding of biological hazards.

Bacterial food safety hazards fall into one of two categories according to the mechanism by which they cause illness.

Most food-borne bacterial pathogens cause illness by multiplying in the gut after ingestion of contaminated food. They may then provoke symptoms by invading the cells lining the intestine, or in some cases, invading other parts of the body and causing more serious illnesses. Salmonella, Campylobacter and E. coli O157 are all examples of bacteria that cause infective food poisoning. This type of food poisoning is usually characterised by a delay, or incubation time, of at least 8–12 hours (sometimes much longer) before symptoms develop.

This category also includes some bacteria that produce symptoms by multiplying in the gut and producing toxins, rather than by actively invading the tissues. An example of this type is Clostridium perfringens, a food-poisoning bacterium usually associated with cooked meat products.

There are a few food-borne pathogenic bacteria that produce illness not by infection, but by intoxication. These organisms are able to grow in certain foods under favourable conditions and produce toxins as a by-product of growth. The toxin is thus pre-formed in the food before ingestion and in some cases toxin may still be present even after all the bacterial cells have been destroyed by cooking. Bacillus cereus and Staphylococcus aureus are examples of bacteria able to cause intoxication, but the most important and potentially serious cause of intoxication is Clostridium botulinum. Intoxications usually have much shorter incubations times than infections, because the toxins are pre-formed in the food.

Viral gastroenteritis is very common worldwide. There are a number of viruses that are capable of causing food-borne infections, although in most cases, other forms of transmission are more common. Perhaps the best known are noroviruses and hepatitis A, which has been responsible for a number of serious food-borne disease outbreaks, often as a result of poor personal hygiene by infected food handlers.

‘New’ viruses may also pose a threat to food safety. For example, highly pathogenic avian influenza viruses primarily affect birds, but in some cases may be transmitted to humans and cause serious disease. So far, there is no direct evidence that this transmission can be food borne, but these viruses are a source of great concern to the poultry industry and there is still much to learn about them.

A wide range of intestinal parasites can be transmitted to humans via contaminated foods, although for most, faecal–oral, or water-borne transmission are more common. These organisms are much more prevalent in developing countries with poor sanitation, but the increasingly global nature of the food supply chain may increase their importance in the developed world. Currently, protozoan parasites are the most important, but other types also need to be considered as food safety hazards.

The protozoan parasites that can cause food-borne illness in humans include several well known species, such as Entamoeba histolytica, the cause of amoebic dysentery, and Cryptosporidium parvum. However, in recent years, some unfamiliar species have emerged as threats to food safety, especially as contaminants in imported produce. An example is Cyclospora cayetanensis, the cause of several outbreaks of gastroenteritis in the USA associated with imported fruit.

Other types of food-borne parasite include nematode worms, such as Trichinella spiralis and the anisakid worms found in fish, and cestodes (tapeworms), such as Taenia solium. Although many of these are far less prevalent in developed countries than was once the case, thanks to improved sanitation, they are still significant causes of illness worldwide.

Prions are a relatively recent threat to food safety and are still not fully understood, but their probable involvement in potentially food-borne new variant Creutzfeldt–Jakob disease (vCJD), an invariably fatal brain disease, has lead to considerable concern.

The presence of chemical hazards in food is usually less immediately apparent than that of bacteria and other biological hazards. Acute toxicity caused by food-borne chemical contaminants is now very rare in developed countries. Of much more concern is the potentially insidious effect of exposure to low levels of toxic chemicals in the diet over long periods. In some cases this can lead to chronic illness and there is also the risk that some contaminants may be carcinogenic.

There is potential for an enormous range of chemical contaminants to enter the food chain at any stage in production. For example, agricultural chemicals, such as herbicides and insecticides, may contaminate fresh produce during primary production, some commodities may contain ‘natural’ biological toxins, and chemicals such as detergents and lubricants may enter food during processing. It is also possible for chemical contaminants to leach out of packaging into foods during storage.

Some of the main classes of chemical contaminant important in food safety are as follows:

• Agricultural chemicals, pesticides etc.

• Veterinary drugs

• Natural biological toxins

  • Fungal toxins

  • Plant toxins

  • Fish toxins

• Environmental contaminants (e.g. dioxins and heavy metals)

• Contaminants produced during processing (e.g. acrylamide)

• Contaminants from food contact materials (e.g. plasticisers)

• Cleaning and sanitising chemicals

• Adulterants (e.g. illegal food dyes)

The total number of potentially harmful chemicals that may contaminate food is very large. For example, UK legislation contains maximum residue levels (MRLs) for over 28000 pesticide/commodity combinations. It is therefore not practical to cover pesticides here in anything but the most general terms. Fortunately, the use of pesticides is very strictly controlled in many countries and residues in imported foods are regularly monitored. Links are provided in the “Sources of Further Information” section for readers needing specific information on pesticides.

The list of potential adulterants is also an extensive one. Almost by definition, adulterants are often compounds that would not be expected to be present in foods and little may be known about their health significance if present in the diet. Recent examples include synthetic Sudan dyes found in imported spices and other commodities in the EU. These are illegal for food use, but the health effects of low levels in foods are uncertain, and there has been some discussion over their food safety significance. For these reasons, it is not practical to cover potential adulterants here, with one notable exception. The industrial chemical melamine has been found in food commodities and ingredients, especially from China. Its presence in foods has been found to cause potentially serious kidney damage in animals and humans and it was responsible for a very large outbreak of illness among Chinese infants, which lead to at least six deaths. Because of the seriousness of this incident, the widespread nature of potential contamination and the known health hazard, melamine is included here.

The Chemical Hazards section focuses on contaminants that are known to be food safety hazards, and which have received some attention from food safety researchers and regulators to establish the level of risk they carry.

In recent years, the problem of food allergy has been growing in importance for the food industry as the number of people, particularly children, affected by allergy symptoms has increased. Food manufacturers have been encouraged to respond to this development, particularly in terms of labelling foods clearly. Along with clear allergen labelling comes a responsibility to ensure that such labels are accurate. When foods are labelled as not containing specific allergens, it is extremely important that they do not become contaminated with those allergens during production. This is vital for allergens such as peanuts, which may cause life-threatening anaphylactic reactions in sensitive individuals. The presence of undeclared allergens in foods is a growing cause of product recalls in the EU, North America and elsewhere.

The control of allergens in food is now a rapidly developing aspect of food safety, which many manufacturers will need to be concerned with. Fourteen specific major food allergens are currently recognised by EU legislation, although many more foods are likely to be capable of causing allergic reactions in sensitive individuals.

These are:

• Celery

• Crustaceans

• Egg

• Fish

• Lupin

• Milk

• Molluscs

• Mustard

• Peanuts

• Soya

• Sesame

• Sulphur dioxide and sulfites

• Tree nuts

• Wheat

It is probable that food allergies will continue to grow in importance in the coming years, and that further allergens will be recognised in legislation.

In most countries, the safety of the food supply is regulated by national and local authorities. Food businesses are required to meet the demands of food safety regulations, at the very least, in order to protect consumers from hazards in food. These are likely to include the setting up of an effective food safety management system, such as hazard analysis critical control point (HACCP). In addition, many food businesses will need to meet the requirements of their customers, such as large retail chains, or will need to comply with the food safety provisions of third party audit schemes. Most of these will expect more extensive food safety measures than are required by relevant legislation.

Most businesses will find it necessary to adopt a risk assessment and HACCP-based approach to addressing food safety, and there is considerable assistance and support available to help with this. Nevertheless, it is important that every food business develops at least a basic understanding of the specific food safety hazards that may be relevant to their products and processes. Only then can food safety management systems operate effectively. The following pages are designed to help provide that basic understanding.