Fresh strawberries are a quintessential flavour of summer. But how do you retain their freshness and nutritional value , while also ensuring that they are free from any pesticides used when they were growing, and so safe to eat?
The use of pesticides in the production of crops such as strawberries is widespread. But they can leave residues, including harmful micro-organisms, which need to be removed before human consumption.
Cooking by applying heat kills most harmful micro-organisms in some foods, but it does not work well for many others. For instance, we cannot cook a strawberry to kill harmful organisms, and still enjoy its fresh flavours. Nor can we wash them in the factory like some other fruits and vegetables, because this damages soft fruits.
So, how do we ensure that the strawberry remains safe, while also remaining "fresh-like"? This is what researchers have been trying to answer over the last two decades.
At our laboratory in Dublin Institute of Technology (DIT), we developed 'cold plasma technology to allow for the elimination of harmful micro-organisms on foods while retaining their flavour and nutritional value.
So, what is cold plasma? Well, there are three states of matter: solid (such as ice), which, when heated, turns into liquid (water) and when further heated or energised, turns into a gas (steam).
When a gas is further energised by heat or using electromagnetic fields (or simply electricity), it will breakdown into ions, electrons, energetic molecules, ultraviolet and/or visible light. This ionised state of the gas is called plasma and it exhibits distinctive properties, which earns it the honour of 'the fourth state of matter'.
We all have seen plasmas - the sun, cloud-to-ground lightning, polar lights, incandescent lamps, decorative plasma balls and plasma televisions.
The sun and lightning are examples of 'hot (or thermal) plasmas' in nature, the polar lights (aurora) are natural 'cold plasma', while the last three examples represent man-made cold plasmas which are generated using electricity.
From a food safety point of view, the most interesting feature of cold plasma is their ability to kill most micro-organisms harmful to humans.
For the purposes of our research, we produce the cold plasma inside a sealed plastic package which contains the food, such as strawberries. We transform the air inside the package into plasma by applying a high voltage (60 to 80 kilo volts) across the package for about two minutes, which is long enough to kill the micro-organisms.
Our results show that using this process, fresh produce, such as strawberries, retain a high quality, while any pesticide levels also decrease.
The technology is relatively inexpensive - it does not use water, requires low power similar to a 100-watt light bulb - and does not leave any harmful chemical residues.
It is currently being tested by industrial partners in the EU.
Dr Nrusimha Nath Misra, a former Irish Research Council Embark Fellow at DIT, is currently a food scientist at General Mills, Mumbai, India.He is the lead editor of the upcoming book 'Nonthermal plasma for food processing' to be published by Elsevier Academic Press.