Acids Prevent Browning

Using a little lemon juice helps to keep pesto from turning brown. It's actually the ascorbic acid (also known as Vitamin C) in the lemon juice that keeps the basil from oxidizing. This same trick can be used for other recipes where a fruit or vegetable might turn brown. Try using lime juice in guacamole – the flavor of limes and avocado together is perfect and the avocado will stay bright green.