Ever wondered why apples turn brown when you cut them up? It’s all thanks to a naturally occurring enzyme called polyphenol oxidase (PPO). This enzyme is released when the fruit’s cells are ‘broken’ and it reacts with other parts of fruit cells turning the fruit brown. Once this reaction has taken place, nothing can be done to reverse it and quite often the fruit is thrown away.

You can destroy the PPO enzyme through cooking or reduce enzymatic browning by covering the fruit. Another popular way to stop further browning is to put lemon juice on it. This works because the ascorbic acid in lemons delays the PPO enzyme reaction.

We took a different approach to stop browning. First, we isolated the genes that encode the PPO enzyme, then we constructed an anti-PPO gene. Inserting this gene into plants blocks the production of PPO and therefore stops the browning.

War on food waste

Australians are throwing out over 4 million tonnes of food each year. That’s over $1000 of food wasted by the average Australian household. This waste not only hurts our bank accounts, it also hurts our world, with global food loss and waste generating 8 per cent of total greenhouse gas emissions annually. Sounds like a big problem, doesn’t it? And we haven’t even mentioned its impact on global food security and our growing waistlines. As with any complex problem, the solution involves a number of different tactics. One of which is trying to keep food fresher for longer.

This month, a special kind of apple slice will go on sale at select US supermarkets and, thanks to our research, these apples won’t turn brown when they’re cut, bitten, or bruised.

USA getting a slice of the action

Arctic® apples have been developed by an innovative Canadian biotech company, Okanagan Specialty Fruits Inc. (OSF). Their first product will be bags of fresh Arctic® Golden apple slices, with more nonbrowning varieties expected in future years, including Arctic® Granny and Arctic® Fuji. Neal Carter, the company’s founder, began working on the apples in the mid-1990s.

“I came across research from CSIRO that had managed to ‘turn off’ browning in potatoes,” explains Carter. “As an apple grower, I was very aware that apple consumption had been declining for decades while obesity rates had simultaneously been sharply rising. My wife and I felt that we could help boost apple consumption through a similar biotech approach with apples, as nonbrowning apples would be more appealing and convenient. Additionally, we felt this small genetic change could also significantly reduce food waste, as nearly half of all apples produced end up wasted, many due to superficial bruising.”

Arctic® apples will be sold through select US outlets beginning in October 2017; while there is limited supply this year, as plantings mature resulting in increased volume, sales will expand throughout the U.S. and Canada.

While there may be other sliced apple products already on the market, these are often coated with vitamin C and calcium to prevent browning and to preserve crispness, and this can change their taste.

I heard it on the grapevine

Ian Dry and Simon Robinson were our scientists working on this project in the 1990s.

“We heard about a naturally occurring Sultana grapevine mutant that produced sultanas that were light golden in colour instead of dark brown and we tried to find out why,” explained Ian.

“We discovered the sultana was light in colour because of a mutation in the grape PPO gene. It was then that we realised the potential of this discovery to be applied to other fruits and vegetables. We tested anti-PPO technology on potatoes and managed to produce Australia’s first non-browning potato,” he said.

The anti-PPO gene in the apples does not come from another species. It is made from DNA sequences from four of the apple’s own genes, and insertion of this anti-PPO gene is aided by commonly relied upon biotech tools.

Waste not, want not

This non-browning technology has potential to reduce waste not only in apples and potatoes but also in other important horticultural crops, such as beans, lettuce and grapes where produce with only small injuries could still be sold.