When buying apples, look for those that are firm and brightly colored. Shiny red for Macintosh, Rome and red Delicious. Clear green for Granny Smith and golden yellow for Delicious. Always avoid bruised apples. When an apple is damaged, the injured cells release polyphenoloxidase, an enzyme that hastens the oxidation of phenols in the apple, producing brownish pigments that darken the fruit. It's easy to check loose apples. If you buy them packed in a plastic bag, turn the bag upside down and examine the fruit.

Store apples in the refrigerator. Cool storage keeps them from losing the natural moisture that makes them crisp. It also keeps them from turning brown inside, near the core, a phenomenon that occurs when apples are stored at warm temperatures. Apples can be stored in a cool, dark cabinet with plenty of circulating air.

Check the apples from time to time. They store well, but the longer the storage, the greater the natural loss of moisture and the more likely the chance that even the crispest apple will begin to taste mealy.

When preparing apples, do not peel or slice an apple until you are ready to use it. When you cut into the apple, you tear its cells, releasing polyphenoloxidase, an enzyme that darkens the fruit. Acid inactivates polyphenoloxidase, so you can slow the browning (but not stop it completely) by dipping raw sliced and/or peeled apples into a solution of lemon juice and water or vinegar and water or by mixing them with citrus fruits in a fruit salad. Polyphenoloxidase also works more slowly in the cold, but storing peeled apples in the refrigerator is much less effective than immersing them in an acid bath.

When you cook an unpeeled apple, insoluble cellulose and lignin will hold the peel intact through all normal cooking. The flesh of the apple, though, will fall apart as the pectin in its cell walls dissolves and the water inside its cell swells, rupturing the cell walls and turning the apples into applesauce. Commercial bakers keep the apples in their apple pies firm by treating them with calcium while home bakers will have to rely on careful timing.

To prevent baked apples from melting into mush, core the apple and fill the center with sugar or raisins to absorb the moisture released as the apple cooks. Cutting away a circle of peel at the top will allow the fruit to swell without splitting the skin.

Red apple skins are colored with red anthocyanin pigments. When an apple is cooked, the anthocyanins combine with sugars to form irreversible brownish compounds. Apples can be process by drying. To keep apple slices from turning brown as they dry, apples may be treated with sulfur compounds but that may cause serious allergic reactions in people allergic to sulfites.

Besides, apple could also be made into juice. Clear apple juice has been filtered to remove the pulp. Ninety-eight percent of all juices, including apple juices, sold in the United States are pasteurized to stop all natural enzyme action that would otherwise turn sugars to alcohols, eventually producing the mildly alcohol beverage known as apple cider (non alcoholic cider is plain apple juice). Pasteurization also protects juices from potentially harmful bacterial and mold contamination.

Apples also have medical benefits. They are use as an antidiarrheal. The pectin in apple is a natural antidiarrheal that helps solidify stool. Shaved raw apple is sometimes used as a folk remedy for diarrhea, and purified pectin is an ingredient in many over-the-counter antidiarrheals.

Apples can also be used to lower cholesterol levels. Soluble fiber (pectin) may interfere with the absorption of dietary fats, including cholesterol. The exact mechanism by which this occurs is still unknown, but one theory is that the pectins in the apple may form a gel in your stomach that sops up fats and cholesterol, carrying them out of your body as waste.