A slice of apple left on a table slowly goes brown due to an enzymatic reaction. Dipping the apple slice in lemon juice prevents it from browning Which of the following best explains this result?
A.
Lemon juice has enzymes which reverse the browning reaction
B.
Lemon juice has a pH which inactivates the enzymes
C.
Lemon juice functions to bleach the brown material
D.
Lemon juice functions to dilute the brown material
The correct answer and Explanation is :
The correct answer is B. Lemon juice has a pH which inactivates the enzymes.
Explanation:
The browning of apple slices is primarily due to a biochemical process known as enzymatic browning, which involves the enzyme polyphenol oxidase (PPO). This enzyme catalyzes the oxidation of phenolic compounds in the apple when the fruit is exposed to oxygen, leading to the formation of brown pigments called melanins.
Lemon juice contains citric acid, which lowers the pH of the solution when applied to the apple slices. This acidic environment is unfavorable for the activity of the polyphenol oxidase enzyme. Enzymes have specific pH ranges in which they function optimally; outside of this range, their activity diminishes significantly. The acidic conditions created by lemon juice denature the enzyme, reducing its ability to catalyze the browning reaction. As a result, the formation of brown pigments is inhibited, and the apple slices maintain their fresh appearance for a longer time.
Other options can be dismissed for the following reasons:
- A. Lemon juice has enzymes which reverse the browning reaction: This is incorrect because lemon juice does not contain enzymes that reverse the browning process; rather, it inhibits the enzyme responsible for browning.
- C. Lemon juice functions to bleach the brown material: While lemon juice may have some bleaching properties, its primary function in this context is to alter the pH, not to bleach existing pigments.
- D. Lemon juice functions to dilute the brown material: This is also incorrect as the primary mechanism at play is the inhibition of the enzyme rather than dilution of the pigments.
In conclusion, the key reason lemon juice prevents the browning of apple slices is its ability to create an acidic environment that inactivates the enzymes responsible for the browning reaction, thus preserving the apple’s color and freshness.