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. Proper potassium levels are also needed for good 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.
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. 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.