The enzymatic browning of my Avocado.

Mini-experiment 2 – The enzymatic browning of my Avocado.

Today we are going to take a closer look at one of my fruits, the avocado. The Avocado is a rich source of 

mono-unsaturated fat, which according to the American Heart Association, can reduce bad cholesterol levels in your blood and lower risk of heart disease. Besides being healthy Avocados are also delicious and 

I have been eating Guacamole since I was  young

especially when eaten fresh.  Avocados unfortunately have the tendency to turn brown after sometime they are cut open. Harold McGee explains in his book "On Food and Cooking: The Science and Lore of the Kitchen" that avocados have a naturally high metabolism and deteriorate fast than lethargic fruits.  The brown pigmentation  is the work of the enzyme polyphenol oxidase.  Straightdope.com explains that this enzyme works on phenolic compounds in the flesh of the avocado, changing their chemical structure and thus their color.  My mini experiment today will test if exposure to air influences the browning process and thus the enzymatic activity in the avocado.  I hypothesized that avocado that is exposed to more direct air will brown more than avocado that is exposed to less air. The independent variable is air exposure and the dependent variable is the browning process. 

The experiment
For this experiment I decided to use one avocado and cut it in half. I then used the two halves and placed one half in a Zip-lock bag. Both halves were placed on a yellow plate and I timed how long it took for the 

avocados to turn brown. Since I used the same avocado for both subjects is was able to standardize the flesh and presence of approximately the same amount of enzymes in the avocado. 

Initial experiment

Both halves were exposed to the same temperature (68 F) and other influences such as light. After several hours the browning process was not as significant as we expected so we decided to take the avocado out of its skin so the fruit can be exposed to air from top to bottom. I photographed the avocados at the start of the exposure to air as shown on the right. 

Avocados without the skin to have
a better look at the browning (3 hours in) 

The avocados did not brown as fast as I anticipated, however. Some online research had me belief that the browning would be clearly visible after a couple hours but even after 7 hours of exposure the browning was minimal. I decided to leave the avocado on the counter over night to add some time to the experiment and hopefully provide stronger support for my hypothesis.
As the picture on the right shows the avocado that remained in the Zip-Lock bag over night did in fact brown less than the avocado directly exposed to air. I can thus support my hypothesis with the observations I made this morning. Less exposure to air does slow down the enzymatic browning process, so to avoid the pigmentation of your avocados you should store them in some sort of closed vacuum environment. 

The difference in browning after 17 hours.
The avocado in the Zip-Lock bag
 (right) showed less enzymatic browning

Discussion
If we will look at the enzymatic browning of guacamole under certain circumstances for our group project the information gained from this project is helpful. the working enzymes in the avocado can be stimulated depending on some variables that we will carefully have to standardize. We will have to decide how we are going to make the guacamole and with what ingredients. There are special guacamole mixes than can simply be added to avocados which might provide preservatives. Today's experiment showed that it is important to consider how exposure to air can be promoted by simply removing the avocado from its skin. Our group experiment will provide more statistical data and a more detailed overview of enzymatic browning of avocados.
 


Dinner time
After the experiment I decided that is was time to actually eat the avocadoes.  I made some guacamole which will be the center of our group project later this month. Guacamole goes great with burgers, so I decided to make a salsa burger with guacamole, sour cream, pineapple salsa, and a bacon cheddar ground beef patty. Yummy!

Salsa burger I made 

Home-made Guacamole

For some more information on enzymatic browning and the health benefits of monounsaturated fats visit these sources. 

• http://www.straightdope.com/columns/read/2210/does-leaving-the-avocado-pit-in-the-guacamole-keep-the-stuff-from-turning-brown
• http://www.heart.org/HEARTORG/GettingHealthy/FatsAndOils/Fats101/Monounsaturated-Fats_UCM_301460_Article.jsp
• On Food and Cooking: The Science and Lore of the Kitchen by Harold McGee, 1984.