‘Pulsed light’ refers to a type of broad-spectrum radiation delivered as intense intermittent short duration pulses. The technique has been gaining popularity as a non-thermal food processing technique that involves the discharge of high voltage electric pulses (up to 70 m kilovolts/cm). It is one of the emerging technologies, which are replacing traditional thermal pasteurisation process. It is effective for sterilisation of surfaces and highly transparent liquids such as water.
Process of treatment
The pulsed light processing can be described as a sterilisation or decontamination technique used mainly to inactivate surface micro-organisms in food, packaging material, and equipment. The system is composed of a pulse generator (comprising a high voltage DC power supply) and a treatment chamber. The capacitor stores a high voltage electric power provided by the power supply. Reflectors are used to maximise the radiant energy received by the target material. In order to avoid lamp overheating, the treatment chamber also includes an air or water cooling system.
Pulsed light treatment is being used to treat eggs. It successfully terminates the Salmonella cells on the egg surface. It is also being used to treat chicken. A continuous flow of pulsed light is effective for bacterial inactivation in fruit juices and milk. Fresh slices of mushrooms treated with pulse light witnesses a significant increase in shelf life as compared to untreated samples. This technique is also being used to decontaminate packaging material and food contact surfaces.
This technology, as a sterilisation solution, was patented by Hiramoto in Japan in 1980 and extended to the US in 1984. In 1996, Joseph Dunn proposed this treatment for food products and packaging materials and this technology was subsequently adopted by the US Food and Drug Administration (FDA).
The intensity of light in this technology that lasts for only a second is 20,000 times brighter than sunlight but there is no thermal effect and hence, the quality and nutrient content of food items are retained. It is an effective tool against a great variety of pathogenic and contaminating agents. Moreover, this technology is also used to decontaminate food packaging materials.
A possible problem of this preservation method is that folds or fissures in certain food items may protect microbes from being exposed to the pulsed light. There might be some strains of micro-organisms that are resistant to this treatment. The low penetration power of this technology is an added disadvantage.