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General information: D-Galactose is one of the products of the hydrolysis of -> lactose (milk sugar) which we ingest by eating or drinking milk products. In the liver, galactose is metabolized to become -> glucose. Some algal ingredients, used in food industry as thickening agents, consist of galactose and its relatives as basic molecules. These long chained substances (galactanes) build the basic mucilage of cell walls.

Dietetics: Galactose has no influence on the release of insulin. Shortly after its intake, it ends up in the liver. In the case of an inherited metabolic disease called galactosaemia, the enzyme galactose-1-phosphate uridyl transferase is missing. This enzyme is needed for the body to break down and use galactose. As a consequence, the sugar is converted to a sugar alcohol (galactitol), which affects the nervous system. Babies with this disease must neither drink breast milk nor any common milk products, because the lactose in the milk would be hydrolysed to glucose and galactose, the latter of which causes illness. The nourishment has to be completely converted to soy products (soy milk, also called soya milk, soybean milk, or soy juice).

Chemistry: Galactose is a monosaccharide and belongs to the hexoses that have six carbon atoms (elemental formula: C6H12O6).
Chemically, galactose is stereoisomeric to glucose, which means that the spatial arrangement of atoms is different in both molecules, without any difference in connectivity or bond multiplicity between the isomers. Soluted in water, galactose forms a cyclic hemiacetal like glucose; the open chain form and the cyclic form are at equilibrium. Long chained galactanes also contain L-galactose which is a mirror-image isomer of D-galactose (L means left-handed in the Fischer projection and D means right-handed).

Usage: Galactose is mainly used clinically; for instance in parenteral nutritions.