Tuesday, November 01, 2011: 12:07:33 PM

Food Processing Guest Column

Cold sterilisation: The simple way - Dr VH Potty, Diversified Food Technologies (Mysore)

Sterilisation of food continues to be a challenge for many in spite of several new developments in the industry

Sterilisation of food products at ambient conditions is a dream every food scientist entertains and if this can be achieved in sealed packs it can be a bonus. Of course the Gamma Radiation or ionising radiation technology is readily available for the food industry to be tapped and optimum dosage levels for different foods have been worked out long ago. Unfortunately, this technology is shunned by the user industry because of fear of consumer backlash from misapprehensions about the safety of foods irradiated and government policies have not helped the cause of this extremely efficient technology to take roots. One single most crucial impediment is the discriminatory labelling rules that make it mandatory for irradiated foods to be declared on the label though genetically modified foods can be marketed without the consumers knowing about through distinct labelling.

 
Plasma field
 
There are other similar processes which deploy pulse electric fields or ultra high pressure to achieve sterilisation and it is a question of time before these technologies find industry wide application. A relatively new entrant to this field is Plasma Field sterilisation, which has hit the headlines recently. Though it may take years before the limited studies in this area can become an accepted technology, there is excellent potential for it to become an industry standard eventually. What is interesting in this case is that unlike other similar technologies, Plasma Field technology may not be investment intensive and energy guzzling and even SMEs may be able to afford the process easily. One of the uncertainties that can cloud any futuristic expectations is that adequate efforts have not been made to calibrate the process using different food products and probably wide scale studies with a variety of products may be undertaken world wide because of the commercial potential this technology has.
 
The spark for development of plasma energy for food preservation seems to have been provided by scientists at Purdue University in the US who found a way to eliminate bacteria in packaged foods such as spinach and tomatoes to make them safe for use in products like salads. The facilities for achieving such a feat consist of a set of high-voltage coils attached to a small transformer that generates a room-temperature plasma field inside a package, ionising the gases inside. The process was found to kill many harmful bacteria such as E. coli and salmonella, which have caused major public health concerns, in some parts of the world. If the concept can be effectively exploited, it should be possible to sterilise any packed food within a package exposing them to a Plasma Field.
 
The Plasma Field is created easily, at least under the laboratory conditions, by placing two high-voltage, low-watt coils on the outside of a sealed food package. A plasma field is formed which is a charged cloud of gas where oxygen is ionised and turned into ozone. According to available information, the treatment time can vary from 30 seconds to about 5 minutes depending on many variable factors. It is well known that ozone gas can kill many pathogenic bacteria and the kill rate is proportional to the time the gas remains ionised. The life time of ozone so formed is limited and it gets back to molecular oxygen in no time once the Plasma Field is removed. Interestingly, the process uses only 30-40 watts of electricity while the temperature remains almost same as room temperature, with only a few degree rise outside the treatment chamber, not sufficient to heat the packed product or alter its quality characteristics. Naturally, if ozone can be used directly in the pack, same effect can be achieved. But such treatments require packing the product in an ozone atmosphere which has its own logistical difficulties. It is interesting that the technology is suitable for many containers that include glass, plastic bags, plastic bottles and cartons.
 
Though the scientists who came up with this development have every right to indulge in claims regarding their discovery, the ground reality is that they have been able to establish a concept only with its technical feasibility. There is a long way to go before commercial models with large capacity, beyond the small gadget designed by them, are built for treating not a few grams of the product but in tons on a continuous mode. The effect of Plasma Field on the quality of the products is still unclear though it is claimed that nothing untoward happens to them. As many food products have different composition, their vulnerability to exposure to ozone may also be varying and these aspects need to be explored. On the legal side, ozone is a permitted water treatment chemical but its use for preserving food does not seem to have any official sanction and this aspect requires attention.
 
Dr VH Potty is a renowned food technologist and the chairman of Diversified Food Technologies (Mysore)

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