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.
Proanthocyanidin
Proanthocyanidins are present in fresh grapes, juice, red wine, and other darkly pigmented fruits such as cranberry, blackcurrant, elderberry, and aronia. Although red wine may contain more proanthocyanidins by mass per unit of volume than does red grape juice, red grape juice contains more proanthocyanidins per average serving size. An serving of grape juice averages 124 milligrams proanthocyanidins, whereas a serving of red wine averages 91 milligrams ("i.e.", 145.6 milligrams per 8 fl. oz. or 240 mL). Many other foods and beverages may also contain proanthocyanidins, but few attain the levels found in red grape seeds and skins, with a notable exception being aronia, which has the highest recorded level of proanthocyanidins among fruits assessed to date (664 milligrams per 100 g).