Red and green and everything in between

Mini-experiment 3: Oxidation with red and green apples

Background:  Whether an apple is cut or bitten into, there is an oxidation process that occurs which makes the fruit begin to turn brown and deteriorate.  Polyphenol oxidase is the enzyme within cells that is triggered to oxidize compounds in the presence of oxygen.  There were several questions that arose among researchers:

Do red apples brown faster than green ones?

Does a smaller piece of apple brown quicker than a larger comparison? 

And lastly, would the enzymes in human saliva catalyze the oxidation deterioration in apple?

The saliva is actually comprised of about 97-99.5% water, but the rest is made up of enzymes.  The three enzymes found in the human saliva are salivary amylase, lingual lipase, and an antibacterial compound called lysozymes (Niedziocha, 2011).  There are many types of apples, and researchers examined if there would be a difference between two types: red delicious and granny smith.  Research was aimed to observe not only the difference between apples, but the effect of enzyme variation. 

There were two hypotheses:  

-          Human saliva would increase the deterioration of the apple from oxidation

-          Red delicious apples will oxidize faster than granny smith apples

Null hypotheses:

-          Human saliva will have no effect on the deterioration of the apple from oxidation

-          There will not be a significant difference between the oxidation of red and green apples

Independent variables:

-          Presence of human saliva/not

-          Type of apple

Dependent variables

-          Oxidation level of apples

I will standardize:

-          Browning time

o   30 minutes

-          Depth of apple slice

o    

-          Exposure to alpha-amylase

o   10 seconds in my mouth

Results

Granny smith (L) Red delicious (R)

Oxidation after 5 minutes

Oxidation after 30 minutes

Regular red delicious apple (L) Saliva apple (R)

Regular granny smith apple (L) Silva apple (R)

The slice of apple in contact with 10 seconds of human saliva was found to oxidize slower than the apple which was not in contact with the human saliva.  The granny smith apple was found to oxidize more significantly over 30 minutes compared to the red delicious.  A limitation involved in this experiment were the age/ripeness of the apple.  

Discussion

Both of the hypotheses were disproved in this experiment.  It cannot be said that the null hypotheses can be accepted because there was a clear change in the opposition of what was predicted.   After 5 minutes the apples still looked similar in oxidation level, but after 30 minutes it was clear that the granny smith apples were browning faster and the saliva exposed apples were not oxidizing.  Although it seemed to make sense that the addition of another enzyme which breaks down food would aid in the deterioration process, it clearly denatured some aspect of the processes.  According to World’s Healthiest foods, “Flavonoids like quercetin found in apples can inhibit enzymes like alpha-amylase” (whfoods.com, 2014).  As alpha-amylase is found in the human saliva it then makes sense that those apples would not oxidize similar to the other samples.  Also, it was hypothesized that the sourness of the granny smith and thus seemingly more acidic pH would decrease oxidation over the course of a 30 minute time span.  The pH of these two particular apples was determined to be around 6.2 for each one, so that would nullify that particular hypothesis.


Sources

http://www.scientificamerican.com/article.cfm?id=experts-why-cut-apples-turn-brown

http://www.livestrong.com/article/423200-what-are-the-digestive-enzymes-in-the-stomach-mouth-called/

http://www.whfoods.com/genpage.php?tname=foodspice&dbid=15