Browning is the process of food turning brown due to the chemical reactions that take place within. When fresh fruits and vegetables are peeled or cut open, the enzyme called polyphenol oxidase (also called tyrosinase) contained in the cells is exposed to and reacts with the oxygen in the air. The reaction that occurs, which is called oxidation, is what turns the fruits and vegetables brown.
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Prevent Fruits from Turning Brown
Some of the fruits that turn brown are apples, pears, peaches, and bananas. There are several techniques that can be used to prevent fruit from browning.
1. Prevent browning by brushing the surface of the fruit with juice from citrus fruits, such as lemons, limes, oranges, and grapefruits. Lemon juice is often used for this purpose.
Lemon or pineapple juices, both of which naturally contain antioxidants, can be used to coat apple slices and slow enzymatic browning. In addition, both fruit juices are acidic and the lower pH that they bring about causes polyphenol oxidase to become less active.
2. Use lemon juice in the water for soaking fruits and vegetables. Do not over soak fruit. Do not allow fruit to soak for no more than 3 to 5 minutes. Drain and pat dry before using.
3. Another method to prevent browning is to mix them with acidic fruits like oranges, tangerines, grapefruit and other citrus fruit or pineapple. Prepare the acidic fruit first. Then, cut the other fruits, mixing them within the acidic fruit. Cover and refrigerate cut fruit until ready to serve.
4. The best way to prevent browning is to soak the cut fruit in a saltwater solution (half a teaspoon of kosher salt per cup of water) for 10 minutes, then drain and store until ready to use. The mild salt flavor can be rinsed off with tap water before serving. The best part is that even after rinsing, the browning is still just as effectively reduced.
5. Coating freshly cut apples in sugar or syrup can reduce oxygen diffusion and thus slow the browning reaction.
6. Heating can also be used to inactivate polyphenol oxidase enzymes; apples can be blanched in boiling water for four to five minutes to nearly eliminate polyphenol oxidase activity. (Be warned that cooking will affect the texture of the product.)
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Prevent Vegetables from Turning Brown
Some of the vegetables that turn brown are potatoes, sweet potatoes, and artichokes etc. There are several techniques that can be used to prevent vegetables from browning.
1. When the potato is completely peeled, place it in cold water immediately until ready to cook or ready to cut to desired size. The cold water will prevent the outer surface of the potato from discoloring.
2. Juice from other citrus fruits, such as limes, oranges, and grapefruit can also be used. Use lemon juice to cold water. Place the vegetables in the water and allow them to soak until ready to use. Vinegar can also be used in place of the lemon juice.
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