Food safety issues: biological contaminants in fruits and vegetables

Yengkhom Bijen Kumar / Sunil Kumar Chongtham / Ngangkham Umakanta *

Pix - Society for Agriculture, Food and Innovation

Food safety is "the assurance that food will not cause harm to the consumer when it is prepared and/or consumed according to its intended use". Food hazard can be "a biological, chemical or physical agent in food or condition of food with the potential to cause an adverse health effect on the consumer".

Foodborne illness or injury is at best unpleasant and can be fatal at worse condition. Food hazards may be hidden and go undetected until the product has been consumed. Market-oriented, successful food production must focus on the safety of the final consumer. The aim of fruit and vegetable production is to deliver a safe and wholesome final product to the consumer.

Nevertheless, fresh fruits and vegetables have recently been identified and confirmed as a significant source of pathogens and chemical contaminants that pose a potential threat to human health worldwide. This is mainly because almost all the fruits and most of the vegetables are consumes raw whereby chances of eliminating contaminants by any processing methods is not there. An understanding of the agents that affect fresh fruit and vegetable safety and quality makes it possible to develop practices to minimize potential negative impacts. In this article, an attempt has been made to define and highlight some of the potential biological hazards associated with fresh fruit and vegetables.

Biological hazards in fresh fruits and vegetables are caused by pathogenic microbes such as bacteria, fungi (yeasts and moulds), protozoans, viruses and helminthes (worms), which can also be termed microbes. In some cases, microbial contamination is indirectly introduced by pests. The term pest generally refers to any animals of public health importance, such as rodents, birds, insects (e.g. cockroaches, flies and their larvae), that may carry pathogens and have potential to contaminate food.

Micro-organisms capable of causing human disease may be found in raw produce. Sometimes they are part of the fruit or vegetable microflora as incidental contaminants from the soil and surroundings. In other instances, they are introduced into or on food by poor handling practices in agricultural production or post-harvest processes.

The primary sources of microbial contamination of fresh fruits and vegetables are:
o Human and animal faeces, for example untreated manure or municipal bio-solids and sewage fluids.
o Water contaminated with pathogenic microbes
o Contaminated soil, dust, surroundings and farm equipment
o Poor sanitary practices throughout the production chain (contamination by humans or animals).

To take precautionary measures, it is necessary to aware of what we are dealing with and it will help in dealing with the problems. Following are the brief information of the various pathogenic microbes and their characteristics.

Bacterial Hazards: Bacteria pose a common food safety risk due to their presence at every place in our environment. Pathogenic bacteria potentially contaminate fruit and vegetables in all stages of the production chain. The number of individual bacteria that must be present to cause actual human disease varies with the type of organism as well as the age and condition of the host. The followings are some of the important bacterial pathogens, their characteristics and impact on human health that are reported to be associated with fresh produce.

Bacterial pathogen, its main characteristics and effect on human health

Camphylobacter spp.: These are one of the most common bacteria responsible for serious diarrhoeal illness in human being. It is commonly found in the intestinal tracts of animals or untreated water. Symptoms of infection include fever, abdominal cramps and diarrhoea (often bloody).
Escherichia coli O157:H7: This is a highly pathogenic strain of the bacterium Escherichia coli. It produces a powerful toxin that can cause severe illness. This infectious strain is commonly found in intestines of ruminants and may contaminate soil and water and its infection can cause severe bloody diarrhea and abdominal cramps.
Listeria monocytogenes: Listeriosis is a serious foodborne infection caused by Listeria which is found in animal intestines, soil and water. Fresh fruits and vegetables may become contaminated from the soil or from manure used in crop production. Common symptoms of Listeriosis are fever, muscle aches and serious gastrointestinal problems.
Salmonella spp.: Salmonella bacteria are the most frequently reported cause of foodborne illness. The bacteria live in the intestinal tracts of infected animals and humans.Salmonellosis is an infection causing diarrhoea, abdominal cramps and fever within 8 to 72 hours after ingestion of the contaminated food.
Shigella spp.: Shigella infections may be food borne and are usually passed on fresh produce by improper hygiene of foodhandlers or contamination in fields due to infected human sewage and crop production water. Common symptoms of Shigellosis include diarrhoea, fever and stomach cramps starting 1-2 days after exposure. Shigellosis usually resolves in 5 to 7 days.
Staphylococcus aureus: It is the causing agent for the gastrointestinal illness referred to as staphylococcus food poisoning. It is caused by contamination of foods with bacterial toxins that are resistant to heat and therefore cannot be destroyed by cooking.

Viral hazards: Viruses are very small organisms that are unable to reproduce and multiply outside a living cell and that cannot therefore grow on or inside food as bacteria do. However, raw fruit and vegetables may become contaminated by viral particles with exposure to contaminated water, soil, dust or surfaces. The virus could then infect the consumer of the product if it is consumed raw. The infective dose of most viruses is extremely small (sometimes as few as 10 viral particles), so prevention of contamination is essential. The following are the main viruses reported to be associated with food borne illness.

Viral pathogen, its main characteristics and effect on human health

Noroviruses: These are a group of viruses that cause gastroenteritis. They are found in the intestines of infected persons, who can easily pass them on. The symptoms of Norovirus illness usually include nausea, vomiting, diarrhoea, stomach cramps, low-grade fever, chills, headache and muscle aches. The illness often begins suddenly, and the infected person may feel very sick.
Rotaviruses: It is the most common viral cause of severe diarrhoea among children worldwide. The primary mode of transmission is faecal–oral. Because the virus is stable in the environment, transmission can occur through ingestion of contaminated water or food and contact with contaminated surfaces. The disease is characterized by vomiting and watery diarrhoea for 3-8 days, and fever and abdominal pain occur frequently.
Hepatitis A: The Hepatitis A virus can be transmitted from one infected person to another by contamination of food or water. Foodborne cases of Hepatitis A are recognized to occur worldwide and can mainly be prevented by proper hygiene practices during handling of fresh food.

Parasitic hazards: Parasites are organisms that derive nourishment and protection from other living organisms known as hosts. Parasites are of different types and their sizes may vary from tiny, single-celled protozoa to large multi-cellular worms like helminths. Several parasites have emerged as significant causes of food and water borne disease. They may be transmitted from host to host through consumption of food or water, or by oral contact with infected surfaces. Some of the most prominent pathogenic parasites that can be associated with fresh produce are listed as below.

Pathogenic parasite, its main characteristics and effect on human health

Entamoeba histolytica: This is a very common protozoan parasite in developing countries that causes Amebiasis, both food and water borne in nature. Symptoms are quite mild and include loose stools and stomach pain and cramps. Amebic dysentery is a severe form of Amebiasis associated with stomach pain, bloody stools and fever.
Giardia intestinalis: It is a protozoan parasite that lives in the intestines of infected humans or animals and is commonly found in soil, water or surfaces that have been contaminated with faeces of infected hosts. It occurs in every region throughout the world and considered as one of the most common causes of water borne (and occasionally food borne) illness. This parasite causes diarrhoeal illness (Giardiasis), typical symptoms being diarrhoea, stomach cramps and nausea.
Toxoplasma gondii: Toxoplasmosis is the disease caused by the protozoan parasite Toxoplasma gondii. This parasite can only carry out its reproductive cycle within members of the cat family. In this parasite–host relationship, the cat is the definitive host. The infective stage (oocyst) develops in the gut of the cat and then spreads to the environment via cat faeces, a common source of food and water contamination. Toxoplasmosis brings on "flu-like" symptoms. Infants may develop severe toxoplasmosis, which can result in damage to eyes or brain.

Fungal Hazards: Fungi are mostly responsible for the spoilage of many kinds of food, where some molds can even produce harmful toxins. Usually moulds can be easily seen with the naked eye. There are both beneficial and harmful moulds. Harmful ones can make food unattractive and spoil it. We should not eat mould, except where it has been used intentionally.

Strategic measures to prevent to contamination by pathogenic microorganisms

Strategic measures to prevent the hazardous levels of these pathogenic microorganisms from our food are necessary to avoid any harmful effect from these contaminants. Some of important measures that will help in providing safe food are highlighted as follows:

For prevention of hazardous levels of bacterial contamination in fresh produce we should:
o Prevent bacteria from reaching the product surface and / or keeping their initial numbers low
o Ensure prevention of further growth of any bacteria present in food

Although vegetative bacteria may be resistant to low or even freezing temperatures, they can be killed by high temperatures, such as those reached during cooking. Some types of bacteria, however, have the ability to form spores, which protect the bacteria from unfavorable conditions. Since spores are so difficult to destroy, it is important to cook, cool, and reheat food properly.

For prevention of hazardous levels of viral contamination in fresh produce we should prevent contamination of product as viruses can pose serious health hazards in very low concentrations. For this
o Proper sanitation and hygiene measures during food handling in agricultural and post-harvest operations
o Proper washing and sanitizing of produce before final packing

For prevention of hazardous levels of viral contamination in fresh produce, the following strategies must be applied at all the stages of production:
o Prevention from any contact with water or soil contaminated with human or animal faeces
o Infected people should not engaged in handling the food products
o Avoidance of any contact between animals (pests) and fresh produce
o If present in our food, proper cooking and freezing of food items will kill the parasites

In case of fungal pathogens, that is, mold cells and spores, they can be killed by heating them but, some toxins are not destroyed by normal cooking methods. Food with molds that are not a natural part of the product should always be discarded.

Microbial pathogens pose the greatest threat to the food safety of fresh produce. Microbial contaminants are responsible for the majority of food borne illness.

Understanding how microorganisms grow, reproduce, contaminate food, and infect humans is critical to understanding how to prevent the food borne illnesses they cause. The principles of "prevention is better than cure" should always be borne in mind during any horticultural operation to combat with microbial contamination of food. This is because once a product is contaminated; removing or killing the pathogens on the produce is very difficult.