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.
Cider apple
Polyphenols are an important component of ciders, contributing astringency, bitterness, colloidal stability and colour. The content in apples varies depending on cultivar, production practices, and part of the fruit, with the peel of an apple having more polyphenols than the flesh. The primary polyphenol in apples is procyanidins, followed by hydroxycinnamic acids in the flesh and flavonols in peel. Much of the polyphenols in the fruit are not pressed into the juice, because they bind to polysaccharides in the fruit cell wall, becoming bound to the pomace, when the cell wall is ruptured during the pressing process. Procyanidins are especially prone to binding to the pomace with about 30% extracted into the juice. Cider apples can have five times the total phenolic content compared to dessert apples, but there is a limited supply of bittersweet and bittersharp apples in the U.S. to meet the needs of the fast-growing cider industry. Some cider makers add exogenous tannins to improve phenolic characteristics, and researchers are working on improving polyphenol extraction technology. In countries with more well-established cider industries, such as the U.K. and France, there is an adequate supply of high tannin cider apples. About one half of the apples processed for cider in Europe are bittersweet fruit.