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Clinical pharmacy PharmD program Third level Phytochemistry-1 (PG-504)

3) Lactose = milk sugar

• It is absent from higher plants, but it is the sugar of mammalian milk.

• Chemically, it is: 4-O-(-D-Galactopyranosyl)-D-glucopyranose.

Preparation: It is prepared commercially from whey by evaporation to

crystallization. Whey is obtained as a by-product in the manufacture of cheese.

Properties:

• Lactose is a white crystalline solid, soluble in water, and is dextrorotatory.

• Its sweetness, in comparison with sucrose is about 1/6.

• Lactose is a reducing sugar, undergoes mutarotation, forms an osazone

(lactosazone) reduces Fehling’s solution but does not reduce Barfoed’s

reagent.

• It is not fermented by the common yeast.

• It is hydrolyzed by dilute acids or by the enzyme lactase, which is -

glycosidase, to an equimolecular mixture of D-glucose and D-galactose.

• It is readily converted to lactic acid by many micro-organisms.

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