Vitamin C and Citrus Juices

Vitamin C and Citrus Juices

Vitamin C, ascorbic acid, is one of the most important vitamins found in citrus juices, including orange juice. Testing for vitamin C levels in different forms of orange juice is also a favorite science project for many students. Due to the limited available references on vitamin C levels in citrus juices and how it degrades over time, this web site will attempt to provide some information on the subject to help students find additional references for their science projects.

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:

Production factors and climate conditions
Maturity state and position on the tree
Type of citrus fruit (species and variety)
Parameters used for processing into different products
Type of container
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. This was due to residual oxygen and vitamin C reacting with the tin. Glass packed orange juice provides poor retention of vitamin C, losing 10% after 4 months of storage. Older cardboard cartons lost up to 20%. (Today, most cartons have specially designed multi-layered oxygen and light barriers to protect both loss of vitamin C, flavor, and to enhance shelf-life.) FCOJ packed in foil-lined cardboard cans retained greater than 90% of their vitamin C after 12 months at -20°C.

Handling and storage: Oxygen is the most destructive ingredient in juice causing degradation of vitamin C. However, one of the major sugars found in orange juice, fructose, can also cause vitamin C breakdown. The higher the fructose content, the greater the loss of vitamin C. Conversely, higher acid levels of citric and malic acids stabilize vitamin C. Orange juice must be stored at proper cool temperatures with oxygen barriers for best retention of vitamin C levels. When fresh citrus is stored at 38°F for 12 weeks, there was no loss of vitamin C, but when stored at high temperatures, the loss was great.

To test for vitamin C, or ascorbic acid, concentration in single strength citrus juices, here is a Vitamin C Determination Method that you can try.

Some useful links:

Ten-Year Study of Orange and Grapefruit Juice Yields Verdict on Vitamin C

Citrus Physiology and Nutraceutical Program - Citrus fruit contain several phytochemicals and /or nutraceuticals including vitamin C that have antioxidant properties and reportedly reduce the risk of cardiovascular dieseases and some forms of cancer. There are several factors have the effect on the components of pytochemicals, such as the preharvest factors (growth regulators, rootstocks, climate, season and fertilizer practices). From Texas A&M University Phytochemicals in Fruits and Vegetables web site.

Here is some nutritional information on Florida Citrus, including vitamin C contents.

The Orange Book - JUST RELEASED: Great New book! - The Orange Book follows the complete journey of orange juice. A must have book for the processor and grower who wants to know everything possible about The Orange!

Much of the information on this page came from these references which you can look up at your local University Library:

AN: 80-07-J0965
TI: Vitamin C contents of citrus fruit and their products: a review.
AU: Nagy, Steven
AD: Florida Dep. of Citrus, Agric. Res. & Education Cent., Lake Alfred, Florida 33850, USA
PY: 1980
SO: Journal-of-Agricultural-and-Food-Chemistry; 28 (1) 8-18, many ref.
LA: En (English)
SC: J Fruits-vegetables-and-nuts
AB: Variability in vitamin C (ascorbic acid) contents of citrus fruit and their products is influenced by var., cultural practice, maturity, climate, fresh fruit handling, processing factors, packaging, and storage conditions. Aerobic and anaerobic mechanisms are mainly responsible for destruction of vitamin C in processed products. The mode of breakdown of vitamin C can best be explained by a 1st-order reaction but a significant quadratic time effect was determined by polynominal regression calculations. Plots of log rate (loss of vitamin C) vs. 1/T for canned orange juice showed 2 distinct Arrhenius profiles, whereas canned grapefruit juice showed only 1. Retention of vitamin C is greater in canned than bottled juices because of the reducing activity of the tinplate.

AN: CAIN 779021809
TI: Temperature and storage effects on percent retention and percent U.S. recommended dietary allowance of vitamin C in canned single-strength orange juice
AU: Nagy,-S; Smoot,-J-M
SO: J-Agric-Food-Chem, Jan/Feb 1977, 25 (1): 135-138. Ref.
PA: USDA
PY: 1977
LA: English
PT: Article
ID: United-States

More publications and abstracts of interest that you might be able to find in an University Library can be found in this text file.

I want to acknowledge the assistance of Kevin L. Goodner of the USDA Citrus and Subtropical Products Research Laboratory in Winter Haven, Florida, and Pamela K. Russ of Citrus Research & Education Center in Lake Alfred, Florida, without whose assistance, this web site would not be possible.

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