Cold lightning keeps food fresh for longer

Thanks to this new technique perishable food items now last for weeks…
19 March 2019

Interview with 

Kirsty Bayliss, Murdoch University in Perth


A fresh avocado cut in half


How much food did you throw away this week? Well if you're anything like Izzie Clarke and Chris Smith it was probably a sufficient amount. Thankfully scientists in Australia might have an answer. The reason we usually throw food away is because those tasty-looking fruits and vegetables that we picked up cheap at the supermarket last week have since turned into miniature mould factories. The reason this happens is that microbes are everywhere, so everything you buy is naturally covered in them; and they like to eat your strawberries just as much as you do! But, at Murdoch University in Perth, Western Australia, Kirsty Bayliss has found a way to use just room air and electricity to make perishable food items last for weeks…

Kirsty - The FAO (Food and Agricultural Organisation) say that globally 30% of all food is lost or wasted, which is equivalent to 1.3 billion tons. And a large part of that occurs at what we call the post-harvest stage, so it's after it's left the farm and before it reaches the consumer, or even at the stage of the consumer.

Chris - Some figures I've seen suggest that even in households people are buying stuff, they put it in the fridge and then they just grow it as a mould culture and then they just put in the bin. I mean a lot of that waste actually happens because people overbuy.

Kirsty - That's exactly it. A produce like avocados, people take them home, they turn black, they go ‘oh I'm not eating that’ and they throw it in the bin. Same with strawberries, you have them for a couple of days, they start to grow that grey fluff... ‘oh I'm not eating that’, gets thrown in the bin. So that's what we wanted to address, how do we actually stop that mould growing and reduce the amount of food waste that's occurring. So we've developed a  technology which we call cold plasma or cold lightning and actually stops that mould occurring.

Chris - Completely?

Kirsty - Completely.

Chris - How does it work?

Kirsty - Cold plasma is an ionised gas. If you think back to your high school science days it's the fourth state of matter and we produce it by applying an electrical current to a gas. The gas that we use is just the air that we breathe and when we produce the plasma it leaves a coating over the surface of the fruit vegetables. So it's little reactive ions, electrons, reactive oxygen and nitrogen species, and all of those things together are anti microbial so they actually stop the spores that are in the mould from germinating, and if they don't germinate they can't infect the food.

Chris - So you basically apply a strong electric field to some air, strip off the electrons from some of the molecules that are in there so you end up with this plasma? This then, you pass that over the food, it decorates the surface of the food and and then you've protected the surface so that if there is anything resident on there from the air - fungus, bacteria, whatever, it will killed?

Kirsty - That's right. So all those little electrons and ions and things that are produced in the plasma, they directly attack any mould that is on that food. And it can be mould, so that's the fungal pathogens, but it can also be bacteria and also viruses as well.

Chris - Why does it attack the microbes but it doesn't attack the food?

Kirsty - Yeah, that's interesting. That's the real science behind it so that's something that we want to look into. We actually do think it has an effect on the food, particularly on fresh produce and we actually think what it might be doing is boosting the immune response of the fruit and vegetables so there's actually a two-fold effect there. So that's one of the stages of research that we’d like to do next, to actually look at the science behind that and confirm that theory.

Chris - And it doesn't actually affect the flavour, and it doesn't affect the integrity or the safety of the food item?

Kirsty - No, that's correct. We've had in our lab avocados, strawberries, we’re doing mangoes, citrus and corn at the moment. After we've treated them we have row of students lining up to test these - students always like free food - but it hasn't change the taste. We've also looked things like the firmness of the fruit so we look at whether it's softening or anything like that, but is all unaffected. The colour doesn't change, the weight of the fruit doesn't change either. So that's a major benefit, it's not impacting on the actual quality or taste of the fruit either.

Chris - So if I took an average strawberry or an average avocado, both of which I love very much, but also does the fungus trying to grow in my fridge based on what I threw away last week, how much longer would that last in my fridge after it's been treated via your technique compared with if I just took the same batch of strawberries and put them straight in my refrigerator?

Kirsty - Okay. So avocados have been our biggest achievement. When we've treated avocados with plasma normally they would last about five days if you're lucky. We've had them about three weeks old and they're still nice and fresh. There's a bit of variation there but to extend that shelf life by three weeks is a huge achievement and the growers are really excited about that.

Chris - I'm not surprised because, of course, that means they're going to a lot more produce isn't it? I mean, in financial terms, how much do you think you can save the market?

Kirsty - Yeah, there hasn't actually been a lot done on that. But there is a figure that says for every dollar spent on reducing food waste there is a fourteen-fold return. So that’s in general for whatever treatment it is, so that's sort of what we're hoping to achieve by doing it with plasma.

Chris - Now is this scalable, because when you've got literally millions of tonnes of food flowing to consumers, is it feasible to subject it to plasma treatment using the technique you've developed?

Kirsty - In the next six months what we want to do is to test it in the pack house. We’re working with a local avocado grower and we're going to go into his pack house and look at where we can apply it on the conveyor belt. So as the avocados come in out of the orchard we are looking at can we apply the plasma across the conveyor belt, or do we even apply it in water when they washed the avocados. So that will confirm that we can actually scale it up out of the lab. There's no reason why it won't work, we're just going to confirm it.


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