There are a number of different products to use to prevent this naturally occurring process assuring a quality preserved product.
Ascorbic acid, also known as Vitamin C, is used as an anti-oxidant to keep fruit from darkening.
- Pure ascorbic acid crystals may be difficult to find at the retail level; a few supermarkets and drug stores may sell them, and it may be ordered online. Soak fruit immediately after cutting for 10 minutes in a solution prepared with 1 teaspoon of pure ascorbic acid dissolved in one gallon of cold water.
- Crushed Vitamin C tablets can also be used. Six 500-mg tablets equal 1 teaspoon of ascorbic acid. Vitamin C tablets may contain filler, which may turn the water cloudy, but this is not harmful. Use 6 finely crushed 500-mg vitamin C tablets in a gallon of water to make a holding solution while peeling fruit. A holding solution is used to control browning while the remaining fruit is being peeled.
- Erythorbic acid, also known as iso-ascorbic acid, is chemically identical to ascorbic acid, but because it is structurally different, has no Vitamin C activity. It does have similar anti-oxidant properties though and can be used the same way ascorbic acid is used to retain color.
Citric acid is used to preserve the color of fresh cut fruit or as a pre-treatment for frozen and dried fruit. It can be used either alone or mixed with other substances, such as ascorbic acid, erythorbic acid, N-acetylcysteine, glutathione, and EDTA.
Most people find it more convenient to use commercially prepared anti-oxidant formulations such as Fruit-Fresh® or Mrs. Wages® Fresh Fruit Preserver, which contains a mixture of citric and ascorbic acids as active ingredients.
Bottled lemon juice can be made into a holding solution to prevent enzymatic browning by mixing ½ cup lemon juice with 2 quarts of water.
Note: Citric acid and lemon juice are not as effective in preventing browning as ascorbic acid solutions.
Sulfites are sulfur-containing compounds used for centuries to prevent discoloration and reduce spoilage during the preparation, dehydration, storage, and distribution of many foods. In recent years, sulfites have been implicated as initiators of asthmatic reactions in some people. As a result, the Food and Drug Administration (FDA) has banned the use of sulfites on fresh fruits and vegetables for sale or served raw to consumers. Sulfites are still used as an antimicrobial agent and to help preserve the color of some dried fruit products. Because of potential health issues, the Penn State Food Safety Teamdoes not recommend the use of sulfites. Instead, use alternative methods for color preservation in home food preparation.
Food colors are available in both synthetic and natural forms. Although not necessary if good quality ingredients are used, there are several food grade food dyes available that are safe to use according to label directions. For example, red food coloring is an optional ingredient for canned cherry pie filling. Some highly colored fruits or vegetables can act as a natural color source. An example is beet juice which is often used to impart a red color to refrigerator pickled eggs.
Physical constraints include the application of heat while blanching, cooking, and steaming. Examples include blanching vegetables either by the boiling water method or by steaming to stop enzyme activity. Cooking potatoes (both white and sweet potatoes) destroys enzymes before using or freezing them. Cooking apples before making them into sauce destroys the enzymes that make freshly peeled apples dark. Processing canned goods applies heat that controls enzyme activity as well as microorganisms.
References:
Andress, E., & Harrison, J.; (reviewed 2019, August)."Preserving Food: Freezing Fruit".
LaBorde, L., Zepp, M., & Hirneisen, A.; (2019, September 3). "Let's Preserve: Ingredients Used in Home Food Preservation".
National Center for Home Food Preservation. (n.d.) "Maintaining Color and Flavor in Canned Food".
