Lactobionic acid (4-O-β-galactopyranosyl-D-gluconic acid) is a sugar acid. It is a disaccharide formed from gluconic acid and galactose. It can be formed by oxidation of lactose. The carboxylate anion of lactobionic acid is known as lactobionate.

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Lactobionic acid

Names
IUPAC name (2R,3R,4R)-2,3,5,6-Tetrahydroxy-4-[ [(2S,3R,4S,5R,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)-2-tetrahydropyranyl]oxy]hexanoic acid
Other names Galactosylgluconic acid
Identifiers
CAS Number	96-82-2 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:55481
ChemSpider	7040 N
ECHA InfoCard	100.002.309
E number	E399 (antioxidants, ...)
PubChem CID	7314
UNII	65R938S4DV Y
CompTox Dashboard (EPA)	DTXSID3048861
SMILES O[C@@H]1[C@H](O)[C@@H](O)[C@H](O[C@@]([C@H](O)CO)([H])[C@H](O)[C@@H](O)C(O)=O)O[C@@H]1CO
Properties
Chemical formula	C12H22O12
Molar mass	358.296 g·mol−1
Appearance	Syrup[1]
Solubility in water	Freely soluble[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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As an acid, lactobionic acid can form salts with mineral cations such as calcium, potassium, sodium and zinc. Calcium lactobionate is a food additive used as a stabilizer. Potassium lactobionate is added to organ preservation solutions such as Viaspan or CoStorSol to provide osmotic support and prevent cell swelling. Mineral salts of lactobionic acid are also used for mineral supplementation.

Lactobionic acid is also used in the cosmetics industry as an antioxidant^[2] and in the pharmaceutical industry as an excipient for formulation. For example, the antibiotic erythromycin is used as the salt erythromycin lactobionate when intravenously delivered.