Cooking oil is glycerol esters of fatty acids. It may be of
animal or plant origins. Common types of cooking oil are peanut
oil, corn oil and lard. They are used as a heat-transfer medium
in frying to generate nicely cooked foods.
Changes associated with prolonged heating of cooking oil
In frying, cooking oil is heated to a temperature of 170-220
degrees Celsius. Upon heating, cooking oil may undergo chemical
reactions, hydrolysis, oxidation and polymerization. Degradation
products such as free fatty acids, hydroperoxides and polymerized
triglycerides may be formed. Besides, the viscosity of the
cooking oil will increase; its colour will go darker and rancidity
will also develop, giving rise to unpleasant flavour as a
result of oxidation.
Hazards associated with prolonged heating of cooking oil
The amount of degradation products increases with the duration
of heating of cooking oil at high temperatures. Some of these
may be used to indicate the degree of degradation of cooking
oil. The toxicity of these degradation products is of health
concern. However, there is no definite evidence showing that
the use of cooking oil with these degradation products will
lead to cancers in humans.
It has been reported that small amounts of acrolein, a toxic
substance to humans, may be found in repeatedly-heated cooking
oil. While its toxic effect associated with a long term intake
has yet to be determined.
Cooking oil may also has contaminants such as Polycyclic Aromatic
Hydrocarbons (PAHs). These contaminants, if present in cooking
oil, may be concentrated upon prolonged heating, or in some
cases, present in smoke from the heating process. Some PAHs
have been found to be potentially carcinogenic to humans.
Furthermore, peanut oil may be contaminated by Aflatoxin,
which is a kind of harmful substance in foods.
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How can the hazards be controlled?
In food business, the hazards can be controlled through the
adoption of Good Manufacturing Practice (GMP).
The purposes of GMP are to
optimise the useful life of cooking oil,
maintain food acceptability and wholesomeness,
avoid extensive oxidative decomposition,
avoid development of objectionable flavour and
avoid formation of polymeric compounds.
GMP includes the following points :
choosing cooking oil of good quality and consistent stability,
using properly designed equipment,
selecting the lowest possible frying temperature,
filtering cooking oil frequently to remove food particles,
shutting down and cleansing equipment frequently,
replacing cooking oil as needed to maintain high quality,
providing adequate training to personnel,
testing cooking oil frequently throughout the frying process.
Moreover, through its food surveillance programme, the Food
and Environmental Hygiene Department (FEHD) has monitored
the quality of cooking oil. Inspectors will take samples of
cooking oil for analysis to ensure they are suitable for cooking
and safe for human consumption. Public Health and Municipal
Services Ordinance also provides that sale of food not fit
for human consumption is an offence. Offenders shall be liable
to a fine of $50,000 and imprisonment of 6 months.
Enquiry
For further enquiries and information, please call FEHD's
Communication Resource Unit at 2319 8531 or the 24-hour enquiry
hotline 2868 0000.
Last
revision date:03-03-2003