Dairy Chemistry And Biochemistry

64 DAIRY CHEMISTRY AND BIOCHEMISTRY

CU”

0

\c/H

I

HO-C-H

H

II

I

C-OH

H-C-OH

I

I

I

H-LOH

Galactose -C-H Alkali - Galactose -C-H

HO-C-H I HO-C-H

CH2OH I CHaOH

LaCtW enediol

COOH

I

I

I

Red I

I

HO-C-H

H-C-OH

Heat

CuzO - CuOH Cu’ + Galactose -C-H

HO-C-H

CHIOH

Figure 2.37 Oxidation of lactose by alkaline copper sulphate (Fehling’s reagent).

One millilitre of 0.04 N thiosulphate is equivalent to 0.0072 g lactose
monohydrate or 0.0064 g anhydrous lactose.
The sample is deproteinized and defatted using phosphotungstic acid.

2.7.3 Colorimetric methods

Reducing sugars, including lactose, react on boiling with phenol (2.2) or
anthrone (2.3) in strongly acidic solution (70%, v/v, H,SO,) to give a
coloured solution.

0

P”

2.2 0 2.3