Is alpha lactose is more soluble than beta lactose?

Lactose is a disaccharide that consists of a galactose unit and a glucose unit bonded together with a β glycosidic linkage. The glucose unit can exists in one of two isomeric hemiacetal forms as well as in a free aldehyde form. The isomeric hemiacetal forms, beta and alpha lactose, are anomers because the hemiacetal hydroxyl group gives diasteromeric products at the anomeric carbon.

Alpha and beta-lactose are able to change back and forth because of mutarotation, which is the change in specific rotation. The rate of this interchanging is influenced by a number of conditions including: the concentration of lactose, the temperature and the acidity, or pH, of the milk. At room temperature, the ratio of isomers is about 40% alpha to 60% beta.

The solubility of the two anomers is temperature dependent and therefore the equilibrium concentration of the 2 forms will be different at different temperatures. At room temperature (70°F, 20°C) the equilibrium ratio is approximately 37% α- and 63% ß-lactose. At temperatures above 200°F (93.5°C) the ß-anomer is less soluble so there is a higher ratio of α- to ß-lactose. The type of anomer present does not affect the nutritional properties of lactose.