Solved: The mystery of the blood orange
These are blood and blonde varieties of sweet orange (Citrus sinensis). The anthocyanin pigments that provide the "blood" color of blood oranges are not produced in significant amounts unless the fruit is exposed to cold conditions during its development or post-harvest. No cold exposure means poor anthocyanin production and the loss of the entire crop. This means that blood oranges can be grown in many areas of the world, but they are most likely to be exposed to the correct temperature conditions in only a few regions, including their major area of production in Sicily. Solving the mystery of why cold exposure causes anthocyanin production would benefit both agriculture and health; like many other anthocyanin-rich foods, blood oranges have notable human health benefits. Indeed, blood oranges have the healthful vitamin C, fiber, and carotenoids of regular "blonde" oranges, with the added antioxidant punch provided by anthocyanins. However, unreliable production limits...