The Effect of Potential Hydrogen on the Oxidation of Apples : The Effect of Potential Hydrogen on the Oxidation of Apples By: Nicolas Perdomo, Luisa Sanchez & Andres Olivero Introduction : Introduction We have all experienced moments when we are about to eat an apple, forget about it for a while, then come back to find it covered in a gross brown color. Biologically, what is occurring is the oxidation of the apple causing it to turn brown. Therefore, for our experiment we decided to experiment and observe the effects of acids and bases on the rate of browning of apples when they are cut and the enzymes inside them are exposed to the oxygen in the air. Hypothesis : Hypothesis Different substances containing different levels of pH do not affect the rate of oxidation in cut apples. Body : Body A. Bibliographical Research:
1. Oxidation in ApplesIn apples, there is a specific enzyme contained in the fruit that causes oxidation, which is called polyphenal oxidase (PPO). This enzyme exists in the cell and is released when the skin of the apple is broken. The polyphenal, called monophenol in the diagram below, then reacts with the oxygen in the air to form diphenol, which is also colorless. This diphenol then reacts again with the oxygen once again to form the complex brown polymers, which is what we perceive to be ëbrown stuffí. (Helmenstine, 2010), (Scientific American, 2007)(Burnskill, 2009)
2. Effect of Vitamin C in Oxidation of ApplesVitamin C, also known as ascorbic acid, is known to slow down the oxidation process in apples. Since vitamin C is a highly reactive anti-oxidant it reacts with the oxygen in the air to protect the enzymes in the apple from being oxidized. (Pollick, 2009), (Home Science Tools, 2010) Slide 5: B. Experimental Design:
1. Equipment and materials used:
Baking Soda Solutionï
Milk of Magnesia Solution
Petri dish Slide 6: 2. Procedure:
1. Label the cups: Vinegar, Lemon Juice, Baking Soda Solution, Milk of Magnesia Solution, and Water.
2. Add a slice of apple to each cup.
3. Pour 50mL of each substance over the apple in its labeled cup. Swirl the liquid around the cup to make sure the apple is completely coated.
4. Record your immediate observations of the apples appearance.
5. One day later, observe what has occurred to the apples and record your observations. Slide 7: 3. Experimental Group:
The pieces of apple coated with different substances with different pHís that are not 7. Slide 8: 4. Control Group:
The piece of apple in water, since water has a neutral pH. Slide 9: Variables:
Independent Variable: the different pH’s we coat the apples with.
Dependent Variable: The browning (oxidation) of the apples. Slide 10: Constant Factors:
Type of apple
Quantity of substance that is used to coat the apple Slide 11: C. Experimental Data & Results
GRAPH 1: THE EFFECT OF OXIDATION OF THE APPLE MEASURED IN A SCALE OF OXIDATION (1-10)
Here we can observe that all the substances oxidized considerably on our scale except, the specimen containing lemon juice. This tells us that lemon juice has some property that helps retard oxidation TABLE 1: THE EFFECT OF POTENTIAL HYDROGEN ON THE OXIDATION OF APPLES : TABLE 1: THE EFFECT OF POTENTIAL HYDROGEN ON THE OXIDATION OF APPLES GRAPH 2: THE EFFECT OF OXIDATION OF THE APPLE MEASURED IN A SCALE OF OXIDATION (1-10) : GRAPH 2: THE EFFECT OF OXIDATION OF THE APPLE MEASURED IN A SCALE OF OXIDATION (1-10) In the graph below, it is apparent that all the specimens oxidized to a point, except the one containing lemon juice which oxidized considerably less than the others. TABLE 2 : THE EFFECT OF POTENTIAL HYDROGEN ON THE OXIDATION OF APPLES : TABLE 2 : THE EFFECT OF POTENTIAL HYDROGEN ON THE OXIDATION OF APPLES GRAPH 3: THE EFFECT OF OXIDATION OF THE APPLE MEASURED IN A SCALE OF OXIDATION (1-10) : GRAPH 3: THE EFFECT OF OXIDATION OF THE APPLE MEASURED IN A SCALE OF OXIDATION (1-10) In the graph below we can observe that only the specimen containing lemon juice didn’t oxidize at all compared to all the other ones. TABLE 3 : THE EFFECT OF POTENTIAL HYDROGEN ON THE OXIDATION OF APPLES : TABLE 3 : THE EFFECT OF POTENTIAL HYDROGEN ON THE OXIDATION OF APPLES Conclusion : Conclusion The level of acidity or alkalinity has no effect on the rate of oxidation of apples.
Lemon juice is a good retardant of oxidation in apples Photos! : Photos! Andres preparing the lemon juice and taking measurements of the baking soda Slide 19: The different substances used to see if pH has an effect on the oxidation of an apple and Luisa and Nicolas preparing the apples in each petri dish in order to add the different substances. Slide 20: The whole experiment set on day 1. Slide 21: The results on day 2, showing that only the apple with lemon juice stayed fresh and the others oxidized. Lemon Juice vs. Vinegar (Day 2 for both specimens) : Lemon Juice vs. Vinegar (Day 2 for both specimens) Clearly, the apple with lemon juice on day 2 looks much fresher than the one that had vinegar, even though they are both acids. Therefore, lemon juice had to have a property that retarded oxidation that vinegar didn’t have.