Question

Write short notes on lactose and maltose.

Answer 1

Lactose

• Lactose, which is made up of glucose and galactose, is the most common reducing disaccharide.

• It comes in two forms:$\mathrm{\alpha }-$anomer and $\mathrm{\beta }-$anomer.
• Lactose is a reducing sugar since it has one free hemiacetal hydroxide.
• It gives positive benedicts test as the acetal is reduced to hemiacetal.
• The lactose synthase (LS) enzyme complex converts two precursors glucose and UDP-galactose into lactose in the Golgi apparatus of mammary epithelial cells (MEC). Galactosyltransferase builds the enzyme complex, which is related to $\mathrm{\alpha }-$lactalbumin.

• Lactose is a disaccharide with poor solubility when compared to other disaccharides.
• Lactose has $30\%$ of the sweetness of sucrose

Maltose or malt sugar:

• Maltose is made up of two glucose molecules joined by a -$\mathrm{\alpha }-1,4$ glycosidic bond.
• One of the glucose's aldehyde groups is left free, providing the disaccharide its reducing characteristics and allowing it to take the $\mathrm{\alpha }\&\mathrm{\beta }$form.
• Maltose has a free hemiacetal hydroxide, hence it undergoes mutarotation. It exists as both $\mathrm{\alpha }\&\mathrm{\beta }$-Maltose.
• It gives a positive test with Benedict’s and Tollen’s reagent.
• Maltose is formed when removing a water molecule from two glucose molecules

• It is mildly sweet and water-soluble, and it is formed when the carbon $1$ of $\mathrm{\alpha }-\mathrm{D}$-glucose ($\mathrm{\alpha }-$glycosidic bond) is bound to the carbon $4$ of another $\mathrm{D}-$glucose.