When my friends find out about my work with Arctic® apples, invariably one of the first questions they ask is: How’d we do that? That is, how’d we “make” a nonbrowning apple? Here’s what I tell them:
First, a quick biochemistry lesson. When the cell of a typical apple is ruptured – for example, by biting, slicing or bruising – polyphenol oxidase (PPO) found in one part of the cell mixes with polyphenolics found in another part of the cell. (PPO is a plant enzyme. Polyphenolics are one of the many types of chemical substrates that serve various purposes, including supplying its aroma and flavor.) When PPO and polyphenolics mix, brown-toned melanin is left behind.
Arctic® apples produce practically no PPO so that enzymatic browning reaction never occurs. This means Arctic® apples’ polyphenols aren’t burned up when the apple is bitten, sliced, or otherwise bruised. No chemical reaction, no yucky brown apple left behind. So how’d we “make” a nonbrowning apple? The small number of genes (four, to be exact) that control PPO production were identified several years back, when the apple’s genome was mapped. To create a nonbrowning Arctic® version of an existing apple variety, our science team uses gene silencing to turn down the expression of PPO, which virtually eliminates PPO production, so the fruit doesn’t brown. This genetic transformation is aided by modern science tools. (We’ll explain what we mean by “modern science tools” in a later post.)
This transformation takes place in a laboratory in a petri dish, with a small sample of apple tissue. We confirm the genetic transformation was successfully completed before growing the tissue out into a tiny plantlet and eventually moving it to an orchard. (We’ll explain how we confirm the transformation in a later post, too.)
Personally, I was amazed to find out how “simple” this transformation process is. (I put the word in quotes out of deference to the head of our science team, Dr. John Armstrong, who knows best how much hard work and brain power went into making this process look simple to me.)
The end result of all this science is just an apple tree, now with very low PPO production to prevent enzymatic browning in its fruit. Our Arctic® apple trees grow and behave in the orchard, blossom and bear fruit just like their conventional counterparts. We’ve got almost 10 years of test orchard experience to document that. Arctic® apples are also compositionally and nutritionally similar to conventional apples, further indicating that lower levels of PPO aren’t consequential to the tree or the fruit. It’s only when one of our apples is bitten, sliced or cut that the Arctic® apple difference becomes clear.
What role does PPO play in the plant, you might ask? In some plants, PPO plays a defensive role – for example, tomatoes produce high levels of PPO when attacked by pests or pathogens. In contrast, apples produce very low levels of PPO, and only in very young fruit. Its presence is probably left over from apples of ages ago, playing no role in today’s apples.
I always close my talk with friends with this intriguing sidebar to the story: When eaten by humans, polyphenolics may have health-promoting benefits. For example, phenolics are believed to act as antioxidants, fighting the well-documented damaging effects that oxidation can have on the heart, other organs and throughout the body. Not enough is known yet about phenolics for the health community to suggest a recommended intake amount, as for other vitamins and nutrients such as Vitamin C (the best-known antioxidant), fiber and so on – but they are certainly worth watching!