Every day, I eat an apple for lunch. After all, an apple a day keeps the doctor away! No doubt, fruit is good for you. But, as my apple has to be cut up due to the unfortunate metal device called braces, it often browns a little bit if I don’t eat it before I get home. So why does it do that?
One site writes, “When an apple is cut (or bruised), oxygen is introduced into the injured plant tissue. When oxygen is present in cells, polyphenol oxidase (PPO) enzymes in the chloroplasts rapidly oxidize phenolic compounds naturally present in the apple tissues to o-quinones, colorless precursors to brown-colored secondary products. O-quinones then produce the well documented brown color by reacting to form compounds with amino acids or proteins, or they self-assemble to make polymers.” Wait, what? You know how your blood isn’t always red? How when it has no oxygen it’s blue? Well, like blood, which automatically turns red when it is exposed to oxygen, plant tissues, yes, plants are living things, are also exposed to oxygen. Once this happens, PPO, or, more generally (And very unscientifically) stuff in the chloroplasts, combines with oxygen the phenolic compounds already found in the apple with, as said before, “… o-quinones, colorless precursors to brown-colored secondary products.” This makes the brown color by reacting with more stuff, like proteins.
Okay, you say, now finally understanding my really over-complication of the already-complicated explanation. So why do some brown faster?
So, you know that stuff in the chloroplasts, the PPO? This varies within fruits and even types of apples. Other conditions, like growing conditions or maturity can also affect PPO. This, in turn, affects the browning time. One site writes, “One approach the food industry employs to prevent enzymatic browning is to select fruit varieties that are less susceptible to discoloration—either due to lower PPO activity or lower substrate concentration.”
So for all you at-home apple-eaters, all you have to do is coat your freshly sliced apple in sugar or syrup, which can reduce the amount of oxygen access, and slow down browning. So can pineapple or lemon, which are more acidic, which lowers the pH, which lowers the PPO. Another method includes, “Heating can also be used to inactivate PPO enzymes; apples can be blanched in boiling water for four to five minutes to nearly eliminate PPO activity. (Be warned that cooking will affect the texture of the product.)”
Not only does browning occur in apples and other fruits, but in tea and coffee as well. And I know multiple people that eat or drink these items mentioned. That’s why everyone needs to know about the process of browning, and that, to prevent browning, all you need is more sugar! (because I’m sure you all need more of that! 🙂 )
Happy New year everyone!
So ta ta for now and I hope to see your chemical reaction soon!