Preservation of meat - Gracey's Meat Hygiene - page 83

Products in Hermetically Sealed Containers, Codex
Alimentarius Commission of FAO/WHO).

Ultraviolet radiation
Ultraviolet rays occur at wavelengths of radiation
between 100 and 3000 Å and are invisible (the angstrom,
Å, is a unit of length equal to 10 −10 m or 0.1 nm). They
have a bactericidal action which is especially valuable for
destroying airborne bacteria and are utilised in storage
vats and other tanks to destroy micro-organisms on or
above the surface of foods. The penetrating effects of the
rays are generally considered to be low and are influ-
enced by factors such as the length of exposure, tempera-
ture, pH, relative humidity, light intensity and degree of
contamination.
The wavelength for maximum bactericidal activity of
ultraviolet rays is about 2500Å, which can be produced
by mercury-vapour lamps. As would be expected, spores
and moulds are more resistant than vegetative organ-
isms, yeasts being only slightly more resistant.
Ultraviolet rays are currently used in the ageing of
meat at relatively high temperatures to control the
growth of surface organisms. The bactericidal effect is
also due to shorter wavelengths which convert atmos-
pheric oxygen to ozone, an additional bactericide.

Other methods of meat preservation
Antioxidants
An antioxidant is defined in the UK Miscellaneous Food
Additives Regulations 1995 No. 3187 (as amended in
1997) as 'any substance which prolongs the shelf-life of a
food by protecting it against deterioration caused by
oxidation, including fat rancidity and colour changes.
Antioxidants often improve flavour in cooked meat
and some prevent colour changes.

Preservatives
A preservative is defined in the aforementioned regula-
tions as any substance which prolongs the shelf life of a
food by protecting it against deterioration caused by
micro-organisms.
Schedule 2 of the 1995 regulations gives a list of
permitted preservatives and antioxidants.
In the assessment of any additive for use in a food,
three criteria have to be considered:

1 Benefit or need accruing to the food industry, retailers
and customers
2 Safety in use
3 Satisfactory standard of purity of the chemical
Other substances are added to foods for specific purposes,
for example, emulsifiers, stabilisers, acids, non-stick agents,
air excluders, phosphates, humectants, sequestrants, firm-
ing agents, anti-foam agents, colouring agents, flavours
and solvents, in addition to nutritive substances such as
vitamins A, B 1 (thiamin), C and D, nicotinic acid and cal-
cium. While some of these additives contribute to the shelf
life, they are not normally regarded as true preservatives.
See also Food Additive Legislation, Guidance Notes
(www.food.gov.uk/multimedia/pdfs/guidance.pdf ).

Ionising radiation
Irradiation of food can be achieved by using either
gamma-rays produced by a radionuclide, usually
cobalt-60, or high-energy machines.
Both gamma-rays and electrons produce ions which
induce a sequence of chemical changes in the food, thus
causing the particular effect for which the irradiation
was applied, for example, the killing of bacteria. These
chemical changes are not unique to irradiation but are
also produced by other conventional processing meth-
ods such as heating and cooking.
Although the two sources of ionising radiation produce
similar reactions in a food, they may not be equally suita-
ble for all food applications because of their different pen-
etrating powers. High-energy electrons are less penetrating
than gamma-rays, the extent of penetration being influ-
enced by the energy (maximum permitted level is 10 MeV
(mega-electron volt)) and density of the product.
Double-sided irradiation allows an increase in the
effective thickness of a package, but electrons are not
suitable for treating large bulk packages although they
can be used for thin packs or for surface irradiation.
With gamma-irradiation, pallets of up to 1 m thickness
can be used.
The main features of an irradiation plant are the irradia-
tion room, which contains the source of ionising radiation,
and an automatic conveyor system, which transports the
food into and out of the room. Around this room is approx-
imately 2 m of concrete. In the case of a gamma-irradiator,

Irradiation
Electromagnetic radiation is known to inhibit the growth
of micro-organisms, and a considerable amount of work
has been expended in an attempt to use it for the sterili-
sation of foods. Close attention has been paid to the
effect on the nutritional value of the treated foods, as
well as the possible production of carcinogens and
induced radioactivity.

Infrared radiation
Infrared rays have been mainly used to dry fruits and
vegetables and for heat blanching in the same way as
high-frequency radiation. Infrared rays have a wave-
length of 3 × 10 −4 cm.