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Preventing oxidation of an apple

Postby Ntaylor » Mon Feb 27, 2012 4:42 pm

My daughter is doing a project to see if the ph level of a liquid has anything to do with its ability to prevent/slow down an appe from browning. we used vinegar, lemon juice, saltwater and orange juice. Although vinegar has a the same ph as lemon and has a lower ph than salt water an orange juice, the appe treated with vinegar started to oxidize first...her hypothess is totally unsupported based on these findings... Why is this.

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Re: Preventing oxidation of an apple

Postby sunmoonstars » Tue Feb 28, 2012 2:39 pm


That's a great project! When analyzing your scientific data, it is okay to get results that don't support your hypothesis. So perhaps there is something more going on in the browing process. In the report, it is important to have the background research. I found a good explanation of browning given by Heather in a past post:

"Apples turn brown because of an enzyme called tyrosinase. This enzyme exists in many different organisms, including plants, animals, and fungi... 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."

Perhaps the presence of these compounds is more important to browning speed than their concentration (which would affect pH).


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Re: Preventing oxidation of an apple

Postby robertpak » Wed Feb 29, 2012 9:57 am

Hi Ntaylor.

Tonya gave some really great advice.

Confounding Variables:
Your project is testing "the effects of pH on browning of the apple." Ideally, you would use a strong acid, dilute it to varying levels of pH, and then measure the rate of browning. As Tonya pointed out, vinegar is essentially acetic acid and water, while lemon juice and orange juice contain vitamin C which helps protect the apple even more than just the sole protective effects of pH.
-As long as you note this in the discussion, it should be fine
-also since this is elementary school project, you can note the limitations of actually getting a strong acid and diluting it for your experiment

pH strips and base:
I would recommend that you get pH strips to get the relative pH of each solution. In addition, I would add a base solution to your experiment, like milk. That way, you can note the effects of basic condition on browning, along with your data on acidic and neutral conditions.

Best Wishes

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Re: Preventing oxidation of an apple

Postby HeatherL » Sat Mar 03, 2012 4:30 pm

Hi Ntaylor,

Thanks to Tonya for giving you some of the background information! Bob has also given you some great insight into why you may have seen these confusing results.

It is true that a low pH (acidic conditions) inhibits tyrosinase, so it is somewhat surprising that the vinegar (acetic acid) browned first. What kind of vinegar did you use? As Bob pointed out, it's difficult to compare the different acids rather than dilutions of the same one, but it's a great learning experience.

I hope we've helped you to better interpret the results. Please post again if you have more questions!


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Re: Preventing oxidation of an apple

Postby davidtilghman » Tue Jun 19, 2012 2:59 am

I heard that to prevent oxidation of apple rub some salt on the surface or put it in the water with salt and vinegar.I think it is a good project.

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Re: Preventing oxidation of an apple

Postby KrishnaPatel » Sun Oct 21, 2012 12:23 pm

Re: Preventing oxidation of an apple

Post by davidtilghman » Tue Jun 19, 2012 4:59 am
I heard that to prevent oxidation of apple rub some salt on the surface

Salt does prevent the oxidation of apples because Salting places the cells of an apple in a hypertonic environment (the environment is saltier than the inside of the cells). When a cell is placed in a hypertonic environment, the cell looses water due to osmosis (the movement of water in and out of a cell/membrane) in an attempt to equalize the concentrations of salt and water inside and outside of the cell (the water goes out of the cell to try and dilute the outside to the same level as the inside of the cell). But, in this process, the cell looses so much water that it shrivels up and becomes inactive. Since the cells are inactive, tyrosinase (look at Tonya's post above :D ) cannot function because even though the cell is damaged, it is also inactive, and this enzyme functions inside of the cell, which means that it would also be rendered inactive, keeping the apples from browning.
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