Why Do Apples Turn Brown

Eating fresh apples everyday is always good for health, and the nutritional facts associated with it are amazing. You must have come across the proverb "An apple a day keeps the doctor away". This proverb is not only to urge people to include apples in their daily diet, but is also definitely a very nutritive fruit. The dietary fibers, vitamin A and C, potassium, pectin, water, sugar and antioxidants it contains, makes it the most ideal fruit to be consumed daily. But these apples have to be consumed right away after cutting them into pieces or slices, you can't really store them. The delicious red, crisp apples do not taste the same if you cut and store them. They turn brown when exposed to air for some time. Even though apples that have turned brown are safe for consumption, one does not enjoy its taste like the original one. Find out why does this happen in the section below.

Why Do Apples Turn Brown When They are Cut

Apple is a pomaceous fruit with seed chambers inside and the outer part being fleshy and juicy. Apart from vitamins A and C, potassium, fiber, water and many other nutrients, apples contains enzymes called "polyphenol oxidase (PPO) or tryosinase". These enzymes in particular are responsible for the brown coloration of the apple.

Apples turn brown when cut open due to the chemical process of oxidation. This oxidation process is being driven by the enzyme polyphenol oxidase (PPO) or tryosinase, present in apples. Now, when apples are sliced or bitten into or bruised, the enzymes present in this fruit are exposed to air, where they react with the oxygen in the air, thereby oxidizing the phenolic compounds in the apple tissues to o-quinones. O-quinones then produce brown colored secondary products which discolors the apple from its original color to brown. Therefore, the process in which the naturally present phenolic compounds are changed to quinone compounds, gives the apple its brown color, when cut.

Preventing Apples from Turning Brown

The level of PPO activity and the concentration of substrate vary from apple to apple, depending upon the maturity of the apple and its growing conditions. Sometimes, it is necessary to cut and store apples, in particular when apples are used for garnishing or apple slices are to be presented to the guests. Therefore, it becomes essential to prevent them from turning brown. Here are a few ways you can actually reduce or prevent the apples from turning brown when cut.

• An approach which the food industry follows to prevent these enzymatic brown coloration of the apple is to choose fruits that are low on PPO activity and low on substrate concentration. Though this being a very commercial approach, the other points mentioned here are a few easy ways to prevent apples from turning brown.
• The easiest way to prevent apples from turning brown is to brush the cut apple pieces with lemon juice or pineapple juice. Both these juices being acidic in nature, (lower pH) cause the PPO activity to slow down, thus preventing the apples from turning brown.
• Sprinkling powered sugar or brushing the exposed part of an apple with sugar syrup or salt water, helps prevent the apples from turning brown. This act reduces the oxygen diffusion and slows down the browning process.
• Dip the apple slices in ascorbic acid or lime-lemon soda. Both of these act as anti-browning solution. Wrapping in plastic or heating them in boiling water (blanching) also prevents apples from turning brown after being cut.
• The best way to prevent the browning reaction is to place these apple slices in apple juice, the acid in the apple juice prevents the oxidation process and retains the taste of the apple.

Now you know why do apples turn brown when cut open, and the above tips on preventing apples from turning brown will also help to store apples after peeling, slicing or cutting.