What is Safe Food?
CONTAMINATION OF FOOD
The main concern in handling, storing and preparing foods is possible contamination, which can adversely affect the healthfulness, taste and appearance of food, or worse yet, cause harm to the consumer. Kitchen processes and procedures are a key factor in avoiding food contamination, and must be carefully managed and monitored to ensure that all staff in a restaurant or other food facility follow correct procedure at all times.
Food can be contaminated in many different ways, some of which are discussed below.
Contamination from Cooking
Materials in some cooking utensils can find their way into foods:
Aluminium - If acidic foods are used with aluminium cookware (eg. saucepans), increased quantities of aluminium will contaminate food. If such foods are cooked in aluminium over long periods, or left sit in the container after cooking, the problem is increased. There is no conclusive evidence linking aluminium with health risks, but suspicions exist.
Copper – Similar problems to aluminium: cooking acidic foods will increase copper contamination, and copper can cause destruction of vitamin C in foods. Excessive copper in the body is a toxin.
The safest types of cookware include earthenware, glass, enamel and stainless steel.
Materials from fuels (eg. ash from a wood fire) may also find their way into foods:
Treated Pine - There have been reported cases of poisoning when people have used treated pine off cuts to cook a barbeque. The treatment used on pine to prevent it from rotting, when burnt, releases toxic chemicals. These may be inhaled, or may find their way into food. If using wood for a barbeque, make sure it is untreated.
Contaminants from Food Processing
Various materials used in processing foods can contaminate the foods, though the likelihood of a problem is low. These contaminants may include:
Chemical residues (eg. glues, solvents etc)
Other substances (eg. hair, insects, rodent excreta) that enter the food through unsanitary or careless practices probably pose the most obvious threat.
Most foods will become contaminated with pathogens (ie. microorganisms) after a period of time. This time period may be very short (eg. hours) for some foods, under normal room conditions. For other foods, spoilage may take weeks, months, or even years to occur.
Microorganisms including bacteria, moulds and yeasts may cause putrefaction, decay, fermentation or moulding of food. Small quantities of such microorganisms are common in the environment, and will almost inevitably be found on the surfaces of most foods. Under favourable environmental conditions, these organisms can grow and multiply at an alarming rate, feeding off the foodstuffs. If the surface of a food is damaged or broken, microorganisms are more readily able to penetrate the inside of the food, and can develop even faster.
Decomposition of food can also be hastened through the action of enzymes. Various enzymes occur in fresh foods that are part of the nature, controlling natural mechanisms such as the ripening of fruit. These enzymes will continue to affect the biochemistry of the food beyond peak condition, and in so doing they can contribute to deterioration. For example, fruit and vegetables that are not quite ripe may be acidic. Enzymes in the plant material will progressively assist changes of acid to sugar, hence bringing about a ripening. Eventually it will pass a stage where it is in optimum condition, and tissues will begin to deteriorate.
Physical or mechanical damage to food can cause deterioration. Damaged parts of food will then be more susceptible to attack by microorganisms (or other problems). Damage may come from bruising, cutting, tearing, puncturing, insects, birds or other pests, etc.
Ripening Of Fruit
As a fruit ripens, it undergoes a variety of different changes, and susceptibility to attack by microorganisms will increase as it progresses through these changes. These changes may include:
Changes in carbohydrate (ie. increase in sugar content)
Organic acid changes (decrease)
Change in colour
Change in respiration rate
Change in ethylene production
Change in tissue permeability
Change in protein content
Production of volatile oils
Development of wax on skin.
Consideration needs to be given to these different changes when considering storage and preservation of fruits.
Low Temperature Damage
Storing fresh foods (eg. fruit and vegetables) at low temperatures will slow deterioration by reducing the rate of respiration and metabolism, to a greater or lesser extent. Low temperature doesn't slow all metabolic processes though. Some metabolic processes (ie. cold labile enzyme systems) will stop completely if the temperature becomes too cold. Given that some reactions may still occur and others stop, an imbalance can develop where certain chemicals accumulate through some reactions producing them, but they are not disposed of because the elimination metabolism is stopped. The net result can be an accumulation of certain chemicals to toxic levels resulting in cells collapsing, and areas of tissue where this occurs becomes brown.
Chilling can occur in tissues exposed to temperatures below 15oC in some tropical plants. The critical temperature will be lower for other types of tissue. (Note: This is different to freezing injury where ice crystals are formed inside tissues at temperatures below zero). When plant tissue is damaged by chilling, various metabolic chemicals can be released from inside cells (eg. amino acids, sugars, salts etc). Floating freely in tissues, unprotected by the cell walls, these chemicals become a food for microorganisms, particularly fungi. For this reason, fruit may often be more susceptible to rot after cold storage than before (particularly the more susceptible tropical fruits).
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