Processes

Many manufacturing processes can contribute to an improved food safety. From sterilisation to sterile filtration, go through the currently available processes.

STERILISATION
Sterilization eliminates all microorganisms by treating a product at temperatures of 100-180°C (212-356°F). This process became popular during the 19th century and is still used by the food industry for fruits, vegetables, meat, soups, sauces and RTE meals and in pet food production, although it has some negative effects on sensory quality. The process is internationally standardised: ISO 17665-1 (vapour, replace ISO 11134), EN 554 (vapour).

PASTEURISATION
Pasteurisation involves heating a foodstuff to 70-85°C (158-185°F) for a preset time before rapid cooling to below 4°C (39°F). This process destroys most heat-sensitive microorganisms and limits the growth of surviving germs. Initially invented for wine treatment, pasteurisation preserves most of the sensory qualities and ‘freshness’ of food. This makes it popular for sensitive products such as beverages, honey, jams, syrups, milk, liquid eggs, concentrated vegetable and fruit juices, and pastes.

The efficacy of pasteurisation is highly dependant on the foodstuff to which it is applied. A low pH may reduce the heat resistance of microorganisms, although some heat-resistant pathogenic spores can survive this process.

TYNDALLISATION
For this moderate heat treatment, heat is applied discontinuously at low temperature, generally below 60°C (140°F), over the course of 24 hours. During each cycle, heat-resistant spores can swell (germinate) and grow, before being eliminated in the next heat treatment. Although quite effective for batch-to-batch production, this progressive process is too lengthy and impractical for use on most modern, fast turnaround food production lines.

ULTRA HIGH TEMPERATURE (UHT)
Ultra high temperature treatment (UHT) involves the rapid heating of food to 140-150°C (284-302°F), at which it is maintained for a few seconds to kill bacteria. The product is then cooled rapidly and placed in sterile, airtight containers to prevent recontamination. This treatment is widely used to produce long-life milk and fruit juices.

A disadvantage of this high temperature treatment is that heat-sensitive proteins and vitamins such as vitamin C are destroyed and the sensory qualities are modified. In fruit juices, the vitamins are replaced after treatment.

HIGH PRESSURE (HPP)
The knowledge that high hydrostatic pressure could destroy bacteria dates back to 1895 but it was not used by industry until 1991 in Japan. It consists of applying high iso-static pressure of 100-800Mpa at ambient temperature (<50°C/122°F) to a food product, normally wrapped in flexible packaging, for 5-30 minutes. The pressure causes a uniform temperature increase inside the food product.

As the pressure does not modify the chemical structure of small sensitive molecules such vitamins or flavour compounds, most of the food’s sensory qualities are maintained. The depressurisation may, though, modify the structure of large molecules such as proteins, fibres, sugars and nucleic acids.

Most vegetative bacteria, yeast and moulds are destroyed above 200MPa, but bacteria spores can resist the treatment up to 1000MPa.

FOOD IRRADIATION
Food irradiation covers several techniques where packaged and sealed food products are bombarded with high-energy gamma rays emitted by a radioactive source such as cobalt-60, by X-rays or by fast-moving electrons. The aim is to kill bacteria, fungi and insects and, in some cases, to delay fruit ripening. When used at high energy or high exposure time, these methods may impact polymer molecules, mostly at the surface of the product, and partially modify sensory qualities.

Widely used in pharmaceutical production and for medical equipment, these methods are also used to treat added value foodstuffs such as spices, nuts and dry fruits. Electron beams can be used to treat small products, such as ground beef, fruits and vegetables. Although irradiation is effective in killing contaminating microorganisms, it does not eliminate insect carcasses, faeces or toxins and, thus, may not be sufficient to ensure high food safety. This process is now internationally standardised: ISO 11137 & EN 552 (irradiation)

UV LIGHT
Ultraviolet light irradiation (from a germicidal lamp)  ranging from 100-400nm can alter the DNA of a living microorganism, making it unable to reproduce. This is useful only for the sterilisation of surfaces and objects able to absorb UV. It is ineffective is shaded areas or under dirt.

Each waterborne microorganism, from small bacteria to larger algae and protozoa, requires specific UV radiation exposure to penetrate microorganism cell walls and disrupt DNA. This makes the method superior to ozone or chlorine/bromine water treatment as it leaves no residues and is harmless to animals. However, UV light does not discriminate in its cidal action and can also kill good bacteria, limiting its use to sterilising pure clear pools of water.

STERILE FILTRATION
Mechanical filtration is suitable for sensitive liquids or solutions that would be damaged by heat, irradiation or chemical sterilisation, notably in pharmaceutical and biological production processes.  Sterilisation takes place by filtration through a 0.2µm pore (bacteria) or 20nm pore (virus), generally in an atmosphere with highly filtered air (HEPA filtration).

To prevent airborne contamination, HEPA filtration systems used in the medical sector incorporate high-energy ultra-violet light units to kill off the live bacteria and viruses trapped by the filter media. These measures restrict the number of particulates within the atmosphere and inhibit growth. However, prions are not removed by sterile filtration.