Why the Arctic Apple Doesn't Turn Brown
There is so much controversy surrounding genetic modification of foods, from where the genes come from, to whether the genetic modifications can be transferred to other organisms, to whether producers should label genetically modified foods to alert consumers, and so on.
Controversy aside, I think it's important to understand the science behind genetic modification of foods, starting with one of the latest milestones: An apple that doesn't brown.
Why Do Apples Brown?
We can all blame the protein enzyme polyphenol oxidase, or PPO, for turning our apples brown when they are bruised or exposed to air. PPO transforms certain compounds in apple cells, like chlorogenic acid, into quinones, which assemble to produce compounds that are not only brown in color, but that also affect the flavor and nutritional value of the food.
This process is referred to as enzymatic browning and also occurs in other fruits and vegetables, like bananas, potatoes, and avocados.
Enzymatic browning isn't all bad, though: Coffee, cocoa, and certain tea leaves develop their characteristic dark color and flavor because of enzymatic browning. But in apples, enzymatic browning is frowned upon by growers and the average consumer.
Traditional Methods to Prevent Browning
There are steps we take in the kitchen to prevent browning. These techniques actually represent ways to reduce the activity of the PPO enzyme.
- Heat: By cooking the fruits and vegetables, PPO is denatured, rendering it inactive. Of course, cooking also greatly affects texture, flavor, and nutritional value.
- Acid: Coating the exposed flesh of fruits and vegetables with lemon juice inhibits the activity of PPO because PPO doesn't function well at low, acidic pHs.
- Antioxidant: Using vitamin C (ascorbic acid) to trap oxygen, which is essential to PPO function.
Geneticists have essentially tricked the Arctic apple into thinking that it's already made lots of PPO enzyme, when it hasn't, and therefore doesn't need to waste energy producing more — no PPO enzyme, no enzymatic browning. Arctic apples were modified to have extra copies of the PPO genes, and that excess of genetic material signals to the apple that it must not produce PPO. The genes introduced to the Arctic apple are genes from the apple's original genome, along with markers to verify the apple cells did indeed pick up those extra genes. Stop the apple from producing the PPO enzyme and you've stopped the enzymatic browning process.
The apple doesn't brown when bruised or exposed to air, thereby maintaining its color, preserving compounds like chlorogenic acid, along with their flavor and nutritional value.
Will you buy the Arctic apple, if/when it hits the market stands?