If brown apple slices are getting you down, think twice before reaching for a box of baking soda to stop the discoloration. The results of soaking browning apples in a bowl of sodium bicarbonate are likely to disappoint. The reasons relate to the pH of the solution -- whether it's acid or alkaline.
Apple browning is caused by a chemical reaction known as enzymatic oxidation. When a cut apple comes in contact with the oxygen in air, polyphenol enzymes begin to break down. It is this enzyme breakdown that results in browning. This reaction may be a natural defense mechanism used by plants to guard against pest invasion when the fruit becomes blemished. Although this chemical reaction cannot be reversed, you can slow it down.
The chemical reaction that occurs when cut apples meet oxygen can be slowed by the introduction of an acid. Ascorbic acid and lemon juice are traditional additives to prevent apples browning. You can also use vinegar, but its taste is too strong for apples. These items have a low pH, which slows down the enzymatic reaction and reduces the rate of browning.
Unlike acidic items, baking soda is alkaline -- it has a high pH -- making it ineffective for slowing the browning of apples. Exposing an apple to an alkaline item, like baking soda, speeds up the browning. This is because items with a high pH contain higher amounts of oxygen. The more oxygen there is to react with the polyphenol enzymes, the more browning you will see on the apples.
Stop the browning reaction in its tracks by dipping apple slices in a bowl of lemon, orange or apple juice before storing them in the fridge. Spritzing the slices with a small amount of ascorbic acid before refrigerating also works well. You can also buy commercial anti-browning products at the supermarket. After dousing the apple slices with the acid, place them in an airtight container, cutting off as much oxygen as possible.
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