Q.Explain the following :
Browning of cut apple can be prolonged by applying lemon juice.

Step 1. Recall what slows browning. Section 16.1.2.1 states the enzymatic browning reaction 'can be slowed down using reducing agents such as SO2, ascorbic acid (vitamin C) or by change of pH by adding edible acid such as lemon juice (citric acid) or vinegar.'

Step 2. Apply this to lemon juice. Lemon juice's active acid is citric acid, an edible acid. Applying it to the cut surface of an apple changes (lowers) the local pH away from the value the browning enzyme works best at. …

Applying the pH-change browning-prevention mechanism of Section 16.1.2.1 to the spec …

• Claiming lemon juice 'kills the enzyme' rather than the more accurate description in the text -- it changes pH, which reduces (not necessarily eliminates) the enzyme's catalytic activity. …