Organic apples not oxidising

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Organic apples not oxidising

Postby rafaelajean » Mon Jul 26, 2010 7:30 am

I'm doing a project on how the period of time for which an apple is submerged in boiling water will affect how much it oxidizes subsequently.
However, none of the apples I experimented with oxidized, even after trying many different brands and leaving them overnight in the open. Perhaps there are explanations such as genetic modification, but that doesn't account for the organic apple not oxidizing. Even my control which was not blanched did not show any browning at all. Is there any reason that organic apples would not oxidize?
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Re: Organic apples not oxidising

Postby aelin » Wed Jul 28, 2010 6:30 am


That is an interesting question. The control apple should definitely be turning brown. What type of apple did you use? Perhaps the type of apple may have made the browning hard to see or distinguish.

Another possibility is that the conditions for browning were not met. The enzyme responsible requires oxygen, light, and high temperature. What kinds of conditions did you leave them in overnight?

Hope this helps!
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Re: Organic apples not oxidising

Postby sunmoonstars » Wed Aug 18, 2010 4:58 am


This sounds like a great project! I would love to have a way to keep apples from browning when I serve them.

You didn't mention if you cut the apples before setting them out to brown. The apple peels won't brown - only the meat inside the apple will brown (as Aaron said, when exposed to light and air). Can you let me know if you you cut them or not? If not, try cutting them in half before leaving them overnight and the control apple should brown along the cut edge, where the meat of the apple is exposed.
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Re: Organic apples not oxidising

Postby soccergate » Fri Aug 20, 2010 4:10 pm

You most definitaly have an interisting science fair project idea!
now the apples may not have turned brown because they dont have any pesticides on them..were the ones you bought store bought or picked right off a tree?
because the psticides may have contributed to it..just a thought.
8th grader!!!
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Re: Organic apples not oxidising

Postby heatherL » Thu Sep 23, 2010 11:39 am

Hi Rafaela,

I know you posted this awhile ago, but I wanted to give you some more information about why apples turn brown, and why you may have seen the results that you saw.

Apples turn brown because of an enzyme called tyrosinase. This enzyme exists in many different organisms, including plants, animals, and fungi. It is actually the enzyme that speeds up the production of pigments, including melanin. Melanin is what makes your skin darker in the sun. People and animals who lack tyrosinase are called albino, and cannot produce any pigment.

In apples, tyrosinase is activated by cell damage. So, cutting your apples roughly will help you see oxidation more quickly.

There are many inhibitors to tyrosinase, including sodium benzoate (a preservative seen in many foods), citric acid (which is why people put lemon or lime juice on guacamole to keep it from browning), ascorbic acid (Vitamin C, which is what McDonald's uses to prevent their pre-cut apples from browning), and heat. I'm not sure why you are boiling your apples, but heat denatures (changes the shape) of the enzyme tyrosinase, and can prevent it from working. That may be why you didn't see any oxidation! Interestingly, the heat-sensitivity of tyrosinase is what gives Siamese cats their distinctive color. They have more pigment in the fur where their bodies are cooler (the ears, paws, and tail), and less pigment where their bodies are warmer. I think the heat was de-activating your tyrosinase and preventing oxidation.

Hope that helps!

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