Documentation on Enzymatic Browning of Apples
Objective:
Participants will examine the process of apples turning brown due to chemical
reactions.
Time to complete the activity: 1hr and 30 minutes.
Background:
Tons of fruits and vegetables are produced, processed, and shipped daily, specifically
to the market. However, some of it never makes it into the stores. The reason is fruits and
vegetables turn brown rapidly when they are damaged. The primary culprits are air, moisture,
light, temperature, mechanical stress (fall, cut), and microbial growth. Furthermore, people will
often reject them due to their browning and bruises. This reaction is called Enzymatic
Browning.
Enzymatic browning happens when the chemical reaction of fruit is exposed to oxygen,
resulting in browning, and may affect the taste, flavor, and nutritional value. The enzyme
responsible for browning is called polyphenol oxidase (PPO). Due to the presence of oxygen,
the PPO changes its substances to phenolic compounds via oxidation into quinones compounds.
Thus, the quinones react with other substances to form melanin. In addition, PPO has the
presence of 𝐻2 𝑂2which induces melanin. For this reason, it affects the loss of color and the
modification of taste, flavor, and nutritional properties.
It can be simplified into:
Polyphenol oxidase + 𝑂2 → Melanin (Brown color)
Apples are one of the most consumed fruits. They are rich in minerals and vitamins.
They contain high phenolic compounds that elicit protective effects against chronic and
degenerative diseases. Hence, it acts as an anti-oxidants that potentially limits the damage to
cells and tissues. The phenolic profile of an apple has five major phenolic groups found in most
cultivars: hydroxycinnamic acids, flavanols-3 and procyanidins, anthocyanins, flavanols, and
dihydrochalcones. Furthermore, phenolic compounds may vary depending on the fruit's
maturity and climatic/ environmental conditions. Therefore, in each apple, the phenolic
composition and the activity of various enzymes are critical to understanding, as they may
influence the potential for browning.
Questions:

Which Test solution will prevent browning the most?
Hypothesis:
If we add a slice of an apple in various five test solutions and Controlled treatment. Then apple
will act differently with different test solutions. Furthermore, time and temperature may affect
the enzymatic browning of apples.
Variables:



Independent Variable: Slices of apple and Different Five Test Solution
Dependent Variable: Time taken for apple slices to turn brown.
Controlled Variable: The freshness of apple before the experiment, type of an apple
(Red Delicious), The temperature, and Amount of time monitoring the apple slices.
Introducing the experiment:
This experiment involves dipping slices of apple in a variety of test solutions. These include
Distilled water + salt (Acetic acid), Vinegar (Acetic acid), Distilled water (Water soak),
Calamansi (Citric acid), Celine ascorbic acid syrup + distilled water (Ascorbic acid), and
Controlled Apple slice (No treatment). Lastly, slices of red delicious apple.
Slicing an apple.
Dipping the apple slices and soaking the apple slices:
Putting the apple slices on paper towel:
Parts of an apple:
Observation on Level of Browning Data:
After 10 minutes:
After 10 minutes of observation in the treatment group of apple slice that was dipped in
Distilled water (Water Soak) and Salt +water (Acetic acid), it had some slight browning, but
not as much as the Control (No treatment). The distilled water restricts the amount of oxygen
in fruit tissues, and the PPO reaction decreases. Thus, it slows down the production of melanin
in fruit. While the control apple slices with no treatment turned light brown. Moreover, the
treatment group of apple slices dipped in the calamansi; and Celine ascorbic acid syrup +
distilled water shows a sign of scant brown patches around the apple. In comparison, vinegar
shows no sign of browning because the 4.5% ph. level of acidity inactivates the browning of
enzyme.
After 20 minutes:
Observation
The Vinegar (Acetic Acid) still shows
no sign of browning, even the injured
part, which we poked using a fork.
In Calamansi (Citric acid), the poke
holes in the hypanthium flesh part turn
light brown rapidly.
Celine ascorbic acid has a slight
browning of the skin in the apple.
Thus, there is a mushy texture in the
mesocarp part.
In the Control treatment, the endocarp
(Core) of the apple becomes light
brown.
Picture
In salt+ water treatment, the apples
were pale white. The poke holes turn
light brown in hypanthium flesh.
The Water-soak treatment has a slight
medium shade of brown in the
endocarp of the apple.
After 30 minutes:
Observation
The hypanthium fresh part of the
vinegar treatment is pale white, and the
exocarp lining and endocarp parts were
turning brown.
In Calamansi (Citric acid), the poke
holes and hypanthium fresh of apples
are still the same shade and have not
darkened.
Picture
In Celine ascorbic acid, the skin of the
apple is still the same. It keeps a
mushy texture in the mesocarp part.
Furthermore, the poke holes and
exocarp lining turn light brown. Hence,
the color of the apple started turning a
bit yellow.
In the Control treatment, the endocarp
(Core) of the apple is still the same.
The apple's mesocarp and bruises on
the hypanthium flesh turn light brown.
The color of the apple becomes a
yellowish-brown color
In salt+ water treatment, there are no
changes in appearance.
The apple in Water-soak treatment
started turning brown.
After 40 minutes:
Observation
The hypanthium fresh and mesocarp
part of the vinegar treatment is pale
white, and the exocarp lining and
endocarp parts were both deep browns.
In Calamansi (Citric acid), the poke
holes and hypanthium fresh of apples
are still the same shade, and the color
of the apple has not darkened.
In Celine ascorbic acid, the skin of the
apple is still the same. It keeps a
mushy texture in the mesocarp part.
Furthermore, the poke holes and
exocarp lining are a light brown shade.
Hence, the color of the apple is a bit
yellowish-brown.
In the Control treatment, the endocarp
(Core) of the apple is still the same.
The apple's mesocarp and bruises on
the hypanthium flesh turn a medium
brown shade. The color of the apple
becomes a 90% yellowish-brown color
and a 10% light brown shade.
Picture
In salt+ water treatment, there are no
changes in appearance. The two poke
holes turn light brown.
The apple in the Water-soak treatment
is still the same. The skin of the apple
is a brown shade.
After 50 minutes:
Observation
The hypanthium fresh and mesocarp
part of the vinegar treatment is white,
and the exocarp lining and endocarp
parts were both deep browns.
In Calamansi (Citric acid), the poke
holes are deep brown shade, and
hypanthium fresh is still light brown.
Picture
In Celine ascorbic acid, the exocarp
(skin) of the apple is still the same. It
keeps a mushy texture in the mesocarp
part. Furthermore, the poke holes and
exocarp lining are in deep brown
shade. Hence, the color of the apple is
a bit yellowish-brown.
In the Control treatment, the endocarp
(Core) of the apple is still the same.
The apple's mesocarp and bruises on
the hypanthium flesh turn a medium
brown shade. The color of the apple
becomes a 90% yellowish-brown color
and a 10% light brown shade.
In salt+ water treatment, there are no
changes in appearance. The two poke
holes turn deep brown.
The apple in the Water-soak treatment
is fully light brown.
After 60 minutes:
Observation
The hypanthium fresh and mesocarp
part of the vinegar treatment is white,
and the exocarp lining and endocarp
parts were both deep browns. There are
brown linings around in hypanthium
fresh.
In Calamansi (Citric acid), the poke
holes are a deep brown shade, and
hypanthium fresh is still light brown.
There are a lot of spotted patches.
In Celine ascorbic acid, the skin of the
apple is still the same. It keeps a
mushy texture in the mesocarp part.
Furthermore, the poke holes and
exocarp lining are in deep brown
shade. Hence, the color of the apple is
a bit yellowish-brown.
In the Control treatment, the endocarp
(Core) of the apple is still the same.
The apple's mesocarp and bruises on
the hypanthium flesh turn a medium
brown shade. The color of the apple
becomes a 90% yellowish-brown color
and a 10% light brown shade.
Picture
In salt+ water treatment, there are no
changes in appearance. The two poke
holes turn deep brown.
The apple in the Water-soak treatment
is fully light brown. The exocarp lining
becomes medium brown.
In Conclusion:
The hypothesis was accurate since the apple browning was differently affected by
various test solutions and controlled treatments. In conclusion, the acetic acid found in vinegar
reduces the browning by lowering the ph. level of an apple below 3.0, and it inhibits the
polyphenol oxidase enzyme. Although vinegar is effective, it is not commonly used as a fresh
preservative because it dramatically changes the taste of an apple due to its sour and pungent
smell. Furthermore, our second option will be the calamansi; the citric acid also lowers the ph.
level of the apple. It is an easy way to prevent browning and does not negatively affect the
taste. Lemon juice is commonly citric acid used to preserve apples because it has a chelating
agent that causes metal ions to react with other molecules to form a ring structure. Citric acid
inhibits the polyphenol oxidase enzyme by binding up metal ions in the enzyme. Therefore, it
inhibits enzymatic browning. Lastly, the salt + water, known as acetic acid, slows down the
browning because chloride ions in the salt inhibit the polyphenol oxidase (PPO) enzymes, and
the water shields the cut-off enzyme from the air, which contains oxygen.