Problem:
Which liquid do you think will prevent the food from turning brown the best? Why?
Materials
- Baking sheet or wax paper
- Labeling tape
- Pen or marker
- Tongs
- Bowl
- Knife
- Lemon juice
- Vinegar
- Clear soda
- Olive oil
- Water
- Saltwater
- Potato
- Apple
- Banana
- Avocado
- Any other liquid you want to test
- Any other fruit or vegetable you want to test
- Camera (optional)
Procedure
- Use the tape to create labels for each type of liquid you will test.
- Place your labels on the baking sheet or wax paper. This is where you will set down your samples for observation.
- Cut each fruit or vegetable into slices at least 1-cm thick. Make sure you have as many slices of each food item as you do liquids to test, plus one morefor a control. Have an adult help you cut your samples!Why should the food samples be cut?
- Set out a slice of each food item on the baking sheet or was paper under the heading “Control.”Why is it important to have a control?
- Fill the bowl with enough liquid to fully submerge each sample.
- For each fruit or vegetable you are testing, dip a slice into the liquid with tongs. Be sure to cover the whole slice! Let the extra liquid drip off before placing it under the correct label on the baking sheet or wax paper.
- Rinse out the bowl and repeat until you have made samples with each liquid.
- Record all your observations, taking note of the time. You can also take pictures to document how the food turns brown over several hours.
Results
Lemon juice, Vinegar, clear soda will all prevent food from turning brown quickly. These liquids are acidic, so they will lower the pH of the food surface. Olive oil, will also prevent food from browning, but is less effective than the acids. Water and salt water will also slow the browning of foods.
Lemon juice is the most effective, and by chance, also the most delicious!
Why?
Having a control group is necessary because it is important to know how long the food samples will take to turn brown without any liquid added.
The food’s skin protects the inside “meat” of the fruit or vegetable from damage and debris. When a fruit or vegetable is dropped and the skin is poked or broken, the food often goes bad faster. The reason fruits and some vegetables go brown when they are cut is because the part containing the oxygen-reactive enzyme is exposed. There is then a lot of surface area for the air to come in contact with the food. For the most part, brown fruits and vegetables still taste fine, they just do not look very appetizing.
Acids prevent browning because they react with the oxygen that comes into contact with the surface of the sample. Once all the acid (or whatever else is covering the surface) has reacted with the oxygen or the acid hasdegraded or washed off, then the sample will start to brown again. Stronger acids, like lemon juice, can evendenaturethe enzyme. This means that the enzyme can no longer perform its original function because of its environment.
Digging Deeper
Why doesn’t dried fruit turn brown? What about the fruit drying process prevents enzymatic reaction with oxygen?
FAQs
Have you ever bitten into an apple, set it down for a few moments, and found that it has turned brown? This is caused by an enzyme (polyphenol oxidase and catechol oxidase are two common examples) that reacts with oxygen in the air and an iron or copper cofactor in the fruit.
What causes apples to turn brown? ›
When an apple is cut, oxygen is introduced into the plant tissue and a chemical reaction called oxidation occurs. Apples contain an enzyme called polyphenol oxidase (PPO). When this enzyme comes in contact with oxygen, it turns colorless compounds into a brown pigment called melanin.
Why do apples turn brown in the experiment? ›
It has to do with a chemical reaction called oxidation. The ascorbic acid (vitamin C) in the lemon juice creates a barrier between the apple slice and oxygen in the air. Without the acid, the enzymes in the exposed apple slices would react with oxygen (oxidation) and start turning the apple brown.
Is an apple turning brown a physical or chemical change? ›
Change of apple's colour into brown is a chemical change.
Why do apples turn brown kindergarten? ›
Have you ever bitten into an apple, set it down for a few moments, and found that it has turned brown? This is caused by an enzyme (polyphenol oxidase and catechol oxidase are two common examples) that reacts with oxygen in the air and an iron or copper cofactor in the fruit.
Is there a gene that causes apples to turn brown? ›
Browning occurs when phenolic compounds are oxidised by the enzyme polyphenol oxidase (PPO) which causes brown pigments to be generated (Queiroz et al., 2008). PPOs belong to a large gene family and of these, ten PPO genes have been mapped to the 'Golden Delicious' apple genome (Di Guardo et al., 2013).
What is the hypothesis on apples turning brown? ›
The apple slices turn brown because
When polyphenol oxidase comes in contact with atmospheric oxygen, it turns the phenolic compounds present in the apple tissues into brown-coloured products which impart brown colour to the freshly cut apple.
What liquid will keep apples from turning brown? ›
Method #1: Lemon Juice
Therefore, when you apply lemon juice to apple slices, it helps to prevent the oxidation process. To use this method to prevent apples from turning brown, create a water bath for your apple slices with a ratio of 1 tablespoon of lemon juice to 1 cup of water.
How does temperature affect the browning of apples? ›
Explain how these results support the hypothesis that enzymes cause browning in apples. 40°C is the optimum temperature for enzyme reactions. At temperatures of lower than 40°C, enzyme reactions will be slower. At temperatures greater than 60°C, the enzymes will be denatured and the reaction will not occur.
What is the chemical reaction when fruit turns brown? ›
Oxygen in the air can cause sliced fruit to brown, a process called enzymic browning (an oxidation reaction). Phenols and the enzyme phenolase are found in the cells of the apple, and when these are exposed to oxygen in the air, for example through slicing, the oxygen causes a reaction.
In that case, the apples placed into the acidic solution of pH 2 will exhibit a slower rate of oxidation over the course of 180 minutes by appearing less brown. Apples placed in a solution of pH 6 will also display a slower oxi- dation rate than the basic pH 10 solution due to it being mildly acidic.
How to avoid apples from turning brown? ›
Here's the short version: The best way to prevent browning is to soak the cut fruit in a saltwater solution (half a teaspoon of kosher salt per cup of water) for 10 minutes, then drain and store until ready to use.
Will apples turn brown in a Ziploc bag? ›
If you're storing sliced apples in a plastic container or baggie where there's no way for any residual moisture to evaporate out of them, then those slices will dry out quickly, which will cause them to turn brown.
Is it safe to eat apples that have turned brown? ›
Is it safe to eat apples that are browning? Yes! While aesthetically brown apples are not the most pleasing fruits, there is no safety concern. It's simply a natural reaction to the fruit's flesh being exposed to oxygen.
What is a common remedy to prevent apples from turning brown? ›
Any type of citrus juice—lemon, lime, or orange juice—will work here; pineapple juice will do the trick too. These fruit juices contain citric acid, which slows the chemical reaction and prevents browning. (You can also sprinkle the fruit with powdered citric acid, but it may leave a strong sour flavor.)
How do grocery stores keep sliced apples from turning brown? ›
Packaged apples found at McDonalds or in your local produce section are usually treated with a solution of calcium ascorbate (a blend of calcium and vitamin C) or citric acid (found in citrus fruit) to maintain freshness and color. Both are very safe to use on fruit that will be consumed.
How long does it take for a cut apple to turn brown? ›
It's a chemical reaction that happens when the sugar in apple slices reacts with oxygen. This process is called oxidation. It can be prevented by storing apples with their skin on and using them quickly. But if they are cut open or bruised, it will only take about 5 minutes for them to start turning brown.
