1. Lemon juice prevents cut apples from turning brown.
2. Squeezing lemon juice on fruit like apples and bananas will prevent oxidation (turning brown).
Hoax or Fact
The messages claim that Lemon juice prevents fruits like Apples and Bananas from oxidation and turning brown. It is a fact.
Light colored fruits like Apples and Bananas generally turn brown after they are sliced, cut or peeled because of the activity of enzymes in the fruit. This process is called oxidative browning, and happens when the pigments in the food oxidize and trigger the enzymes, which in turn accelerates chemical reactions in the food. Cut or sliced apples must be covered and refrigerated when they are not eaten within 2 hours. This not only reduces the browning of apples, but also maintains the quality of it. The browning of apples can be avoided by treating them with anti-oxidant preservatives like Ascorbic acid (Vitamin C) and Citric acid which halt and slow down the process of oxidative browning.
Lemon juice is a dilute and natural solution containing both the ascorbic and citric acids, and therefore acts as an effective anti-browning agent in case of cut or sliced apples. Bottled or fresh lemon juice can be used for this purpose, in the ratio of 6 teaspoons in a litre of water. A best way to preserve the cut apples is to dip them in a bowl containing the lemon juice, and then shaking off the excess. These preserved apples can be stored in an air tight container and refrigerated, especially when they are not going to to be used soon. But it is important to note that this will add lemony taste to the apples, and if you are using larger amount, it may mask the natural flavor of apple.
If lemon juice is not available, even Orange or Pineapple juice can be used to prevent the browning of apples. A more effective preservative for apples is the pure crystalline Ascorbic acid that you can buy from food stores or pharmacies.