Amino acid
Amino acids are organic compounds containing amine (-NH) and carboxyl (-COOH) functional groups, along with a side chain (R group) specific to each amino acid. The key elements of an amino acid are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), although other elements are found in the side chains of certain amino acids. About 500 naturally occurring amino acids are known (though only 20 appear in the genetic code) and can be classified in many ways. They can be classified according to the core structural functional groups' locations as alpha- (α-), beta- (β-), gamma- (γ-) or delta- (δ-) amino acids; other categories relate to polarity, pH level, and side chain group type (aliphatic, acyclic, aromatic, containing hydroxyl or sulfur, etc.). In the form of proteins, amino acid residues form the second-largest component (water is the largest) of human muscles and other tissues. Beyond their role as residues in proteins, amino acids participate in a number of processes such as neurotransmitter transport and biosynthesis.
Blood orange
The distinctive dark flesh color is due to the presence of anthocyanins, a family of antioxidant pigments common to many flowers and fruit, but uncommon in citrus fruits. Chrysanthemin (cyanidin 3-"O"-glucoside) is the main compound found in red oranges. The flesh develops its characteristic maroon color when the fruit develops with low temperatures during the night. Sometimes, dark coloring is seen on the exterior of the rind, as well, depending on the variety of blood orange. The skin can be tougher and harder to peel than that of other oranges. Blood oranges have a unique flavor compared to other oranges, being distinctly raspberry-like in addition to the usual citrus notes.
The blood orange is a natural mutation of the orange, which is itself a hybrid, probably between the pomelo and the tangerine,
Within Europe, the "arancia rossa di Sicilia" (red orange of Sicily) has Protected Geographical Status. In the Land of Valencia, it was introduced in the second half of the 19th century.