Restaurants keep apples from turning brown by soaking the sliced apples in a salt water solution and also by using lemon juice or a citric acid solution and even by using controlled atmosphere packaging.
These methods that restaurants use to keep apples from turning brown, slow down the oxidation process that causes the browning and the controlled atmosphere packaging method creates an environment which minimizes the oxygen exposure to the apples.
The best liquid to keep apples from turning brown is salt water.
You can soak the apple slices in some salt water solution for a couple of minutes and then rinse the apples, which is a very good and effective way of preventing browning of the apples, while also minimizing any impact on the taste of the apples.
Lemon juice can also be added to apple slices or other fruits to keep them from turning brown.
Lemon juice is a common liquid used on fruit salads to keep them from turning brown as well.
Apples turn brown as a result of a chemical reaction called enzymatic browning.
And when the flesh of the apples are exposed to oxygen, an enzyme called polyphenol oxidase reacts with polyphenols, which causes them to oxidize and turn brown.
Salt water helps to prevent the reaction by inhibiting the enzyme activity and also potentially create a barrier to the oxygen.
To use saltwater for preventing apples from turning brown, dissolve 1/8 teaspoon of salt in 1 cup of cold water and then soak the apple slices for around 5 minutes and then rinse and dry them.
Lemon juice is also effective but it can alter the taste of the apples, and salt water instead has a minimal impact on the flavor of the apples.