Apple Browning: How Can It Be Prevented?

Problem: A woman noticed that when she peeled some apples and left them standing, they turned brown. Design and perform an experiment to find the conditions that can be applied to prevent the browning of apples.

Title: Apple browning: how can it be prevented?

Part 1: Identification of the Problem

In this experiment, the problem being investigated is to determine whether it is possible to prevent the browning of apples. In this case, apple pieces will be put in various different conditions to verify this. The browning of apples is a natural process which occurs when the inner fleshy texture of the apple is exposed to air, which occurs in a relatively short period of time. This exposure occurs due to damage to the apples protective other tissue either by the apple being dropped from a height for example it falls from its tree or by being cut with a knife or bitten. In other words, this is known as the bruising of an apple, since the same darkening effect occurs when human skin is bruised. Apple browning is caused by enzymes mostly polyphenol oxidase and catechol oxidase that react with oxygen in the atmosphere and the iron or copper component which is present in the fruit and which is necessary for the enzymatic reactions to occur. The fruit starts to oxidize, when electrons are lost to the air, and the food turns brown. (http://www.education.com/science-fair/article/stop-cut-fruits-vegetables-turning-brown/) (http://chemistry.about.com/od/demonstrationsexperiments/ss/appleenzyme.htm)

This aerial oxidation can be prevented or slowed down by not allowing oxygen to get to the surface of the fruit. Since this may sometimes be difficult to achieve, it is also possible to prevent browning by putting the apple pieces in solutions of different pHs for example neutral, acidic, alkaline to see if browning occurs or not. Then the apple pieces are compared with each other to determine in which solution browning does not occur. Also, the apple pieces will be put in test tubes with water at different temperatures. Then the degree of browning will be observed at different time intervals.

The apple pieces which will be put in different solutions with different pH’s will end up as follows: apple pieces put in the neutral solution will turn brown, apple pieces put in the alkaline solution will turn brown and apple pieces put in the acidic solution will not turn brown. This is because enzymes are affected by pH, since some enzymes are denatured or become inactivated in a certain pH range. In this case polyphenol oxidase and catechol oxidase are inactivated in an acidic pH, hence the apple piece will not turn brown.

The apple pieces which will be put in different temperatures example, temperatues from 0-30oC will eventually turn brown. Temperature from 30-45oC will turn brown at an even faster rate but temperatures greater than 50oC, the apple pieces will not turn brown. This is because enzymes are affected by temperature. A rise in temperature increases the rate of an enzyme –controlled reaction; but above 45-50oC, the enzymes are denatured – the shapes of their active sites are changed and they can no longer combine with the substrate, so the reaction slows down and stops.

Part 2: Experimental design

To perform this experiment, the following apparatus and materials are needed to make the experiment as accurate as possible.

Apparatus and Materials:

• Beakers

• Tripod

• Gauze

• Bunsen Burner

• Matches

• Test Tubes

• Test Tube Rack

• Forceps

• Spatula

• Lids

• Knife

• Mass Balance

• Camera

• Thermometer

• Chopping Board

• Pipettes

• Apple

• Ethanoic Acid

• Hydrochloric Acid

• Distilled Water

• Sodium Hydroxide Solution

• Ammonia Solution

Method:

1) A fresh apple will be obtained and it will be equally divided into eight fresh apple pieces using a knife.

2) The apple pieces will be weighed on the mass balance to make sure that their weight is equal and only a difference of ±3g will be accepted as this won’t affect the results.

3) Five different solutions which are: hydrochloric acid, ethanoic acid, distilled water, sodium hydroxide and an ammonia solution will be prepared and poured into five different test tubes, where one test tube will contain only one type of solution. Two pipette-fuls of each solution will be added in each test tube.

4) Five out of eight apple pieces will be put into the five test tubes, each containing one type of solution.

5) The apple pieces will be left to stand in the test tubes and will be observed the following day to check if browning will occur.

6) The other three fresh apple pieces will be put into three beakers containing water at different temperatures. One beaker at room temperature, other at 40oC and the other at 60oC.

7) The beakers will be covered with lids to prevent heat loss and will have a thermometer in them to measure the temperature.

8) Measurements and observations will be recorded in a table.

9) After approximately 15 minutes, the apple pieces were removed from their beakers and the colour of the apples pieces is observed and recorded.

10) Photos will be taken to record the colour of the apple.

Precautions:

1) Care will be taken not to damage the apples before conducting the experiment especially with the knife.

2) Equal pieces of apple will be cut from the same apple for fair testing.

3) Equal