Reed Mangels, PhD, RD
QUESTION: If you juice oranges or other foods such as carrots, how long is it until the vitamin C content is reduced? Is there a difference between leaving the juice out and putting it in the refrigerator?
M.R., via e-mail
ANSWER: Freshly squeezed orange juice is an excellent source of vitamin C with about 120 milligrams of vitamin C in an 8-ounce glass. To help put this in perspective, the recommended dietary allowance (RDA) for vitamin C is 90 milligrams per day for adult men and 75 milligrams for adult women. The amount of vitamin C in a cup of orange juice, 120 milligrams, is an average value and can be affected by many factors, including the type of orange, season, growing region, and preparation and storage conditions. Carrot juice has less vitamin C than orange juice; one source reports 20 milligrams per cup.
Vitamin C is lost from foods when the foods are exposed to oxygen. Since oxygen is everywhere, this means that the more quickly freshly squeezed juice is used, the more vitamin C will be present. Keeping unused juice in a tightly closed container will reduce the amount of vitamin C lost1.
One study has found that about 2% of the vitamin C in orange juice is lost for each day of storage1. Storing juice at cooler temperatures, such as in the refrigerator, slows the loss of vitamin C2. This study was done using orange juice reconstituted from frozen concentrate but the rate of vitamin C loss for freshly-squeezed orange juice would be similar. If you're trying to maximize the amount of vitamin C in your juice, it would be best to drink it immediately after it is made, rather than storing it. If you must store it, keep it refrigerated and in an opaque container.
Juice is not the only way to get vitamin C. Eating the whole fruit or vegetable eliminates the need to worry about vitamin C losses due to processing and has the added benefit of fiber. Citrus fruits have long been recognized as good sources of vitamin C. Less well-known sources include broccoli, Brussels sprouts, cabbage, and bell peppers as well as cantaloupe, kiwis, strawberries, and tropical fruits like papaya, guava, and pineapple. It's not surprising that most studies show that vegetarians have higher intakes of vitamin C than do non-vegetarians and that vegans have higher intakes than lacto-ovo vegetarians.
Our bodies cannot store vitamin C, so it is important to have plenty of good sources of vitamin C every day.
1Johnston CS, Bowling DL. 2002. Stability of ascorbic acid in commercially available orange juices. J Am Diet Assoc 102:525-529.
2Squires SR, Hanna JG. 1979. Concentration and stability of ascorbic acid in marketed reconstituted orange juice. J Agric Food Chem 27:639-641.