Readers: We are pleased to introduce you to a key member of OSF’s staff. Science team lead John Armstrong grew up spending summers in British Columbia’s Okanagan Valley, and returned there to live and to work for OSF in 1999. He earned his doctorate in molecular biology from the University of Manitoba in 1993. When not applying his impressive credentials in the lab, John is an avid outdoorsman. This is his first appearance here, but not his last! – Julia
I’m often asked why we chose a nonbrowning apple as our first project. In fact, the food science community began studying enzymatic browning in apples and other foods long before our little company came on the scene. In apples, browning negatively impacts flavor, texture and nutrition, and precludes the use of minimally processed apples (ever seen a fresh-cut apple on a buffet?).
Three primary factors are involved in the enzymatic browning process: (1) the food’s phenolic content; (2) the food’s levels of the enzyme polyphenol oxidase (PPO); and (3) the compartmentalization or separation within the food’s individual cells that keeps the phenolics and PPO from mixing. When those cells are ruptured, such as by bruising, biting or slicing, that triggers the chemical reaction that leaves behind brown-toned melanin (which we’ve written about here).
Since food processing – including simple slicing and dicing – inherently involves rupturing the food’s cells, it’s simply not possible to control compartmentalization to prevent browning. That left the science community to look at phenolics and PPO for solutions to the browning problem.
Over the years, science has measured the levels of phenolics and PPO in apple varieties around the world, and found the levels of both can vary widely, from almost none to buckets. For example, traditional cider varieties of apples, which are very high flavored, tend to have higher overall phenolic content too. But breeding apple varieties with no phenolics to prevent browning isn’t desirable. Apple trees need phenolics for various plant growth and protection purposes, and they confer flavor, aroma, nutritional and other benefits we want in the fruit. So the only remaining viable solution is to look at PPO.
To date, efforts to address the “PPO problem” have focused on finding plants that produce low PPO, or applying an industrial solution – both with limited success. Naturally low-PPO apple varieties aren’t necessarily nonbrowning; typically browning is only delayed. That’s likely because, as we’ve found, all of apples’ PPO genes must be silenced to yield a truly nonbrowning apple. The chances of conventionally breeding for what we scientists refer to as “down regulation” of all four of the browning genes is incredibly slim and would be very time consuming (think: decades). By using biotechnology’s modern science tools, we’ve in effect been able to precision breed a truly nonbrowning apple in significantly less time with significantly more accuracy.
Meanwhile, industrial solutions such as antioxidant treatments are expensive, can impart an off flavor to the fruit and chemical treatments generally aren’t popular with consumers. (By the way, using lemon juice – a natural antioxidant – isn’t an option in food processing; it imparts a tart flavor, and couldn’t be applied fast enough in large enough quantities to stop processed apples from browning.)
Our Arctic® apple solution harnesses the very natural process of gene suppression or silencing – generally referred to today as “RNA interference” (described rather technically here) – to silence all four of apples’ browning genes to produce apple varieties with very low PPO. Plants already use RNA interference to control aspects of their development and as part of their immune response to a virus. We’ve simply harnessed this process to make the apple varieties you like, know and want to eat nonbrowning, rather than asking you to change which apples you eat.
What’s the takeaway? Accessibility. Apples are currently underutilized – in fresh cut, traditional processing, foodservice, and at home, you name it – because they brown. Our goal is to put more apples in more peoples’ hands, in a way that does away with the need for chemical treatments. At the end of the day, increasing apple consumption is a goal everyone should be able to support.