How Do Blood Oranges Get Their Color?

Blood oranges get their distinctive, dark, crimson red color from a mixture of nature and nurture. Although some varieties can have a tart taste, blood oranges are a member of the Citrus sinensis family, or sweet orange. Well-known in Italy and throughout the Mediterranean, blood oranges are also grown in Pakistan. In the United States, they are grown in California and Florida. Eat and juice blood oranges just as you would any other orange.

Origin

In a February 2007 interview with NPR, David Karp, an exotic fruit connoisseur and writer for "The New York Times," discusses the history and use of blood oranges. According to Karp, blood oranges date back to 1646 in a book called "Hesperides." Its author, a Jesuit priest, described tasting a strange, grape-flavored orange. Since then, many different varieties of blood oranges have evolved, including the Moro, Egyptian, St. Michael and Tarocco. The Moro has the darkest flesh color, nearly purple. According to Karp, the Tarocco blood orange is the finest eating orange in the Mediterranean. It tends to be sweeter than the Moro.

Anthocyanin

The unusual flesh color of blood oranges is due to the presence of anthocyanins, the same pigment present in red wine, red apples, cherries and other fruits and vegetables. On the Linus Pauling Institute's website, Ronald E. Wrolstad, a professor of food technology at Oregon State University, writes that anthocyanin is a type of flavonoid, antioxidants found in plants. According to Wrolstad, there is some evidence that flavonoids may have some medicinal benefit and play a disease-prevention role.

Mutation

In addition to the presence of anthocyanin, blood oranges also have a gene mutation. Most oranges contain one gene responsible for creating a red pigmentation. Blood oranges contain two such genes. In the United States, the blood orange made a surprise appearance in 1988 in the backyard of a California woman who mistakenly believed that her neighbor had been poisoning her Valencia orange tree. It wasn't poison, but rather a gene mutation. Many blood oranges currently grown in the United States trace their origin to the seeds from that mutated Valencia tree.

Growing Conditions

Despite the gene mutation and the presence of anthocyanin, blood oranges need one more ingredient to allow their coloring to fully develop: cold air. In his book, "The Biological Activity of Phytochemicals," David R. Gang, an associate professor of biological chemistry at Washington State University, writes that cold weather, combined with the gene mutation, allows an enzyme to be produced in greater quantities than normal. The enzyme, dihydroflavonol 4-reductase, regulates the production of anthocyanin. When more dihydroflavonol 4-reductase is present, more anthocyanin is produced.