Change in lifestyle and working patterns have a huge impact on food intake. Lack of time has introduced a trend for convenient, ready to eat or ready to cook foods. There is also an increase in demand for nutritious and healthy food. However, preservation and processing techniques like Pasteurisation, sterilisation, treatment with chemicals, food additives etc. have a negative effect on the nutritional quality of food , due the exposure of heat causing destruction of heat labile nutrients. To overcome such problems, novel technologies are introduced to enhance the keeping quality, nutritional availability, quality and structural integrity of foods.
Cold plasma technology is a unique technology that uses plasma for the sterilisation of products thus, improving the shelf life of the product. Since the process occurs at ambient temperature, there is no loss of heat liable nutrients.
PLASMA – DESCRIPTION AND MECHANISM
The term ‘plasma’ was first employed by Irving Langmuir in the year 1928. Plasma is defined as the 4th state of matter, referring to fully ionised gas composed of photos, electrons, free radicals and radiations of varying length in the UV and visible range. It has a neutral charge with atoms in an excited state. It is produced by passing an inert gas (helium/argon/nitrogen) through an electric field with a constant or varying amplitude and high frequency. Cold plasma is developed in an atmospheric or vacuum pressure with an ambient temperature of 30 – 60 °C using electrical or electromagnetic waves. Plasma is discharged by the following techniques: Corona discharge, Dielectric barrier discharge, Gliding arc discharge and radio frequency plasma.
Plasma works on the following mechanism: Material is removed from the surface by etching and ablation by plasma or material is added on the surface in the form of a thin film by the process of plasma enhanced vapour deposition or surface is modified physically and chemically during the exposure to plasma.
POTENTIAL AREAS OF APPLICATION OF COLD PLASMA TECHNOLOGY IN FOOD INDUSTRY
Inactivation of microorganisms:
Cold plasma technology is an alternative to heat and chemical treatment of inactivation and removal of surface microorganisms in fresh produce. Activated species present in plasma bombard the microbial surface causing lesions that the cells cannot repair. This process is called etching. The free radicals present cause denaturation of the microbial DNA causing an antimicrobial effect. Effective on bacteria, moulds, yeast, virus and vegetative spores.
Prevention of enzymatic browning:
It is another cause for post-harvest losses in fresh produce. Browning is caused due to the action of polyphenol oxidase and peroxidase on phenols forming hydrogen peroxide that causes off flavour development and is one of the biggest problems faced in the packaging of cut fruits and vegetables. Plasma inactivates these enzymes thus reducing browning.
Influence on seed germination:
Treatment with plasma has led to early germination of seeds. Active particles in plasma penetrate through the seed coat and influence the cells inside leading to breakdown of seeds dormant stage, thus increasing the germination rate.
Modification of starch:
Traditional processing involved in modifying starches includes chlorine treatment and enzymatic reactions. Treatment of starch with plasma involves structural changes which in turn alters the functional properties without any worry of deposition of toxic residues of chemicals. Plasma modified starches show an increased efficiency in food preparations.
Cold plasma is used for the decontamination of packaging material and improving the surface properties like adhesion, polymerisation and printability. Therefore, changing the interaction of the package with the product, improving the shelf life. Also involved in easy cleaning of irregular shaped package material as plasma can reach all the nooks and corners.
Cold plasma is an emerging and a novel technology that is gaining fame due to its unique characteristics of low or ambient temperature and short period of exposure. This helps in maintaining the textural, functional and structural properties and quality of the product. It is proved to be effective for surface sterilization and retarding enzymatic browning. More and more researches are being conducted to understand its potential and uses. Thus, it is a promoting technique for food processing in the near future.