Cross contamination is the transfer of pathogens from a source to a high risk meals. If the high risk items are allowed to remain at ambient temperature, the bacteria can grow and illness can result. Sources include raw meats and vegetables with soil contamination, hygiene handlers, pets, packaging and pests..all safety hazards. There are four main contaminants, they are:
- Microbial, which are the living microscopic organisms such as bacteria, viruses, fungi and protoctists
- Chemical, such as pesticides, agricultural residues, excessive additives / preservatives, vehicle fumes, perfumes and aftershaves.
- Physical reflectors to foreign body contamination such as glass or wood from the inside of kitchens, parts of kitchen equipment, packaging materials, bones and shells from products being prepared and items from staff or customers such as jewelery, cigarette ends, plasters, tissues, pen tops, drawing pins, buttons, etc.
- Allergenic contamination is the fourth hazard, this includes:
Cereals containing gluten, crustaceans, eggs, fish, peanuts, soybeans, nuts, celery, mustard, sesame seeds, sulfur dioxide and sulfites. Cross contamination can occur when raw products are placed next to high risk items, which is called direct cross contamination. Indirect cross contamination is when high risk meals are contaminated by a vehicle which has been in direct contact with the source. The vehicles can include hands, cloths, knives, forks, containers, preparation boards, work surfaces. When raw meat juices drip onto high risk eats in a fridge, this is another form of direct contamination which affects operations. The ten major causes of food poisoning include:
- Preparation too far in advance of service and storage at room temperature
- Improper cooling to within the temperature danger zone
- Insufficient reheating to less than 75C
- Processed or canned meals already contaminated
- Inadequate cooking to less than 75C
- Insufficient thawing
- Raw ingredients consumed
- Improper hot holding at less than 63C
- Infected hygiene handlers attending the workplace without informing the supervisor.
Food preservation works on the promise of removing one or more of bacterial requirements for growth. Bacteria require protein, moisture, warmth and time to grow. One method is by controlling warmth. Use of heat advances growth and will, in most circumstances kill bacteria lead to safety. Cooking to 75C kills bacteria, both pathogens and spoilage microbes. Pasteurisation to a temperature exceeding 63C kills all pathogens, but spores can remain, especially fungal spores which causes milk, of example, to go off even if left unopened in a fridge. Ultra heat treatment (UHT) is very high for a very short period of time (135C for 1 second) This kills all microorganisms and spores and is why UHT products do not have to be refrigerated until opened. The canning industry uses commercial sterilization to kill all microorganisms and spores, especially important with Clostridium botulinum, which, if the spores survived, would germinate and vegetate and release Botox.
This extremely poisonous neurotoxin could kill within minutes if the can's contents was ateen cold. (Cooking to 75C deactivates Botox). Commercial sterilization, or the Botulinum Cook is 121C for> 3 minutes, depending on the thickness of the can and product. Autoclaves, used in hospitals and dentists, use the same temperature for 15 minutes to sterilize their instruments. Cold temperatures can also prevent microbial growth such as -18C or 1 to 4C. At freezing temperatures there is no moisture available for growth, it is held in ice crystals. Most pathogens do not grow in refrigeration temperatures, apart from E coli 0157, Listeria, Yersinia and C botulinum. Spoilage bacteria prefer warmer temperatures for enzymatic activity to occur and to compromise food safety. Most bacteria will not grow in an acidic environment, a pH of below 3.8 is required to prevent growth. The pH scale goes from 1 to 14, where pH 7 is neutral. 1 is classed as very acidic and 14 as very basic (alkaline) Human blood, for example, has a pH of 7.4. So the use of acids such as vinegar, acetic acid, lime or lemon juice are very good preservatives. Microbes require moisture, so if this is removed by dehydration, there will be no growth of spoilage or pathogenic bacteria. Dehydration can be achieved by drying or the addition of salt / sugar to the ingredients.
Salt and sugar use a biological process termed osmosis, where liquid is transferred from an area of high solute concentration to an area of low solute concentration through a semi-permeable membrane. The salt and sugar are the high concentrations and therefore "suck" liquid from a food material. This process is used in curing pork into bacon. Also, if strawberries are covered in dry sugar, liquid will be drawn from the strawberries, making them more firm (The best way to prepare them for strawberry jam, by the way!) Vacuum packing removals oxygen and aerobes will not grow. However, Closridia, which are anaerobes, could grow and there before vacuum packs must be refrigerated to prevent growth and affect operations. Smoking food releases chemicals such as esters, aldehydes and alcohols which act as preservatives. Smoking also dries the surface of food that preventing oxidization and growth of microbes. Chemical preservatives are used in regulated amounts in foodstuffs such as salami, bacon, bottled drinks, etc. For example Potassium Sorbate and Sodium Benzoate.
For further information go to Food Safety .