40. Why does dipping an apple slice in lemon juice prevent it from browning through an enzymatic reaction?
Answer: A
Lemon juice has a pH that inactivates the enzymes.
Dipping an apple slice in lemon juice prevents it from browning because the acidity of the lemon juice inactivates the enzymes responsible for the browning reaction.
A) Lemon juice has a pH that inactivates the enzymes.
This option is correct as the low pH of lemon juice effectively denatures the enzymes such as polyphenol oxidase, which are responsible for the browning of cut apples. By lowering the pH, the enzymatic activity is inhibited, thereby preventing the browning process.
B) Lemon juice has enzymes that reverse the browning.
This option is incorrect because lemon juice does not contain enzymes that reverse browning. Instead, it contains citric acid, which prevents browning by inactivating the enzymes involved rather than reversing their effects.
C) Lemon juice functions to dilute the brown material.
This option is incorrect as lemon juice does not dilute the brown material; rather, it acts on the enzymes that cause the browning. Dilution would not effectively prevent the enzymatic reaction and subsequent browning of the apple slices.
D) Lemon juice functions to bleach the brown material.
This option is incorrect because lemon juice does not bleach the brown material. While lemon juice can lighten the color due to its acidity, it does not chemically remove the brown pigments; it prevents their formation by inhibiting the enzymes.
Conclusion
The correct answer is A because the acidic nature of lemon juice effectively inactivates the enzymes that cause browning, thereby preserving the apple's color. Other options fail to accurately describe the mechanism of how lemon juice prevents browning, focusing instead on incorrect or irrelevant processes.