Tuesday, December 21, 2010


Food processing is ideally a balance between the need for preservation from spoilage and maintaining the sensory quality and nutrition of the food almost on par with their fresh counterparts. But in practice some compromise has to be struck wherein the eating quality may have to be compromised to some extent. Of the major process technologies, thermal processing using high temperature conditions is known to cause maximum damage to the end product, especially in terms of texture and some times flavor. Innovative developments in food technology are invariably targeted at evolving an ideal process that can accomplish preservation at ambient conditions and there are already a few such technologies like gamma radiation, use of chemical preservatives, etc which, of course have their own limitations when it comes to universal acceptance. It is in this context that the new innovation, recently reported involving use of non-thermal plasma for achieving food decontamination at low temperatures, has to be considered.

Gas plasma decontamination, produced by discharges at atmospheric pressure and low temperature, could make it a practical and inexpensive process for product preservation. Non-thermal plasmas can be generated by microwave, radio-frequency, pulsed and other power sources. Suitable systems that have been studied include the resistive barrier discharge (RBD), which can generate gas plasma at atmospheric conditions. Several mechanisms are thought to be responsible for microbial inactivation and depend on plasma characteristics and the type of microorganism. The electrical and chemical emissions of the plasma devices can be measured and used to calculate the electron number density of the plasma, while emission spectra can also be used to determine the rotational and vibrational temperatures of the plasma. Gas plasma could have potential for the decontamination of foods such as shell eggs that are difficult to sanitize by conventional methods, but further investigation is needed into the use of cold plasma in the food industry. A study by Ragni et al.1, describes the development and evaluation of a prototype RBD plasma device. The plasma glow was analysed by optical emission spectroscopy while the discharge was electrically characterized. The surface decontamination of shell eggs, experimentally inoculated with Salmonella enteritidis and Salmonella typhimurium, was assessed over different decontamination times and gas conditions. The RBD device generated a low-temperature, after-glow gas mixture able to reduce the populations of both microorganisms on shell eggs. The plasma emission showed the presence of OH radicals, NO radicals and other reactive species involved in the microbial reduction. Treatment times of around 90 minutes were feasible for the poultry industry, with no significant negative effects on egg quality traits.

Though the development is in an early stage, the gas plasma technology for preservation may revolutionize the industrial processing of foods in the coming years, if it can be applied to many foods, especially those vulnerable to pathogenic infection. Limited studies on egg preservation offer some encouraging results and there is a long way to go before it becomes a reliable means of ensuring safety of perishable foods. One of the limitations could be the long exposure time required to achieve a satisfactory kill of pathogens which may make it difficult to make the process continuous. Also to be ensured is the safety of artifacts produced in the food, if any, during the process on human health.


No comments: