Chemistry Vitamin C

tamin C, ascorbic acid, is one of the most important vitamins found in citrus juices, including orange juice.

Often projects find that orange juices made from frozen concentrated orange juice (FCOJ) have the highest vitamin C levels as compared to freshly squeezed or not-from-concentrate (NFC) juices. This is probably due to the fact that vitamin C degrades over time in fresh and NFC, but doesn't degrade as much in FCOJ due to it being frozen until reconstitution. If one is comparing a NFC product that has been stored for about 3 weeks versus a newly reconstituted FCOJ, the FCOJ would almost certainly have a higher vitamin C concentration. Also another thing to consider is if the FCOJ is reconstituted to the same strength as fresh or NFC. If one doesn't add enough water, then the vitamin C (and other compounds) would be more concentrated. Another consideration is that the vitamin C content changes through the harvest season and orange variety also plays a part. Since most FCOJ is blended to a larger extent than some NFCs, it is entirely possible that the NFC is produced from a variety/season that has a lower vitamin C content.

According to Nagy and Smoot, temperature and storage time affects the percent of vitamin C content of orange fruits and orange juice. Different varieties of oranges also have different levels of vitamin C. The mid-season variety, Pineapple Orange had the highest levels, followed by the main early-season variety, Hamlin Orange. The late-season Valencia Orange had the lowest vitamin C content. Additionally, it was found that the longer the Valencia Orange fruit stayed on the tree, the lower the vitamin C level. (Additional details on these orange varieties can be found from links in The Story of Florida Orange Juice - From the Grove to Your Glass.) Nagy and Smoot also found that in orange juice containers, vitamin C loss was due to oxidation by a residual air layer trapped within the container during processing. The loss was faster in the first 2 weeks and was more evident at higher storage temperatures. Therefore, orange juice must be kept cool to prevent vitamin C degradation as it is excellerated at high storage temperatures.

Nagy, in his Review of Vitamin C Contents of Citrus Fruit and Their Products, investigated what factors affected the vitamin C contents of citrus fruits. Vitamin C levels depend on six main factors:

1. Production factors and climate conditions

2. Maturity state and position on the tree

3. Type of citrus fruit (species and variety)

4. Parameters used for processing into different products

5. Type of container

6. Handling and storage

Production factors and climate conditions: High nitrogen fertilizer rates can lower vitamin C levels in citrus fruits. Proper potassium levels are also needed for good vitamin C levels. Additionally, climate, especially temperature -- total available heat -- affect vitamin C levels. Areas with cool nights produce citrus fruits with higher vitamin C levels. Hot tropical areas produce fruit with lower levels of vitamin C. Environmental conditions that increase the acidity of citrus fruits also increase vitamin C levels.

Maturity state and position on the tree: Vitamin C decreases during the ripening process. Immature fruit has the highest levels. The position on the tree also affects vitamin C levels. Since sunlight exposure enhances vitamin C levels, fruit positioned on the outside of the tree and on the south side have higher levels. Shaded inside fruit has the lowest.

Type of citrus fruit (species and variety): Early maturing varieties have higher levels that late maturing types. Early Hamlin and Navel fruits have more vitamin C than the late maturing Valencia. Tangerines tend to have lower levels of vitamin C than oranges due to its lower acid levels. Studies have found that the peel had the highest levels of vitamin C followed by the pulp then the juice. Only 26% of vitamin C of a citrus fruit can be found in the juice. The peel had 53% and the pulp and rag had 21%.

Parameters used for processing into different products: Frozen concentrated orange juice (FCOJ) and reconstituted FCOJ almost always have higher levels of vitamin C and is above the 100% US RDA values. This is most likely due to blending of early-season fruit with late season fruit. Canned single strength orange juice will have lower vitamin C levels due to heating during the canning process. NFC, Not -From-Concentrate, will vary due to the varieties being processed.

Type of container: In cans, which are not used very much today, it was found that enamel-lined cans had higher losses of vitamin C than plain tin cans.