Download Estimation of Proteins and Lactose in Milk

ESTIMATION OF PROTEINS AND
LACTOSE IN MILK.
376BCH
Nov 2008
OBJECTIVES
To estimate the total protein content of milk.
 To estimate the lactose concentration in milk.

INTRODUCTION
 major
constituents of milk are lactose, fats and
proteins
 The proteins include casein (a phosphoprotein
and 80% of total protein), lactoalbumin and a
little lactoglobulin
 There are also important amounts



Calcium
phosphorus
vitamin A , B2 B1, C , D3 and or iron
INTRODUCTION
 The
CONT..,
white colour of milk is due to
emulsified liquid and to the calcium salt
of casein.
 The fat content of human milk is similar
to that of cow’s milk but there is more
lactose and less protein, calcium and
phosphorus
INTRODUCTION


CONT..,
Colostrum is more yellowish and contains about
twice as much protein including
immunoglobulins
The protein content falls with time reaching
average levels after about one month. Fat and
lactose change little.
PRINCIPLE ( CASEIN )
 Total
protein in milk is estimated as
casein by the Biuret reaction.
 Under strongly alkaline conditions, such
compounds give violet coloured complexes
with cupric salts, which may be
spectrophotometrically estimated.
PRINCIPE ( LACTOSE )



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The diluted milk is added to sodium sulphate-copper
sulphate solution and protein precipitated by the
addition of sodium tungstate solution. The mixture
is centrifuged, and the supernatant liquid is then
added to alkaline tartrate.
Lactose present reduces the copper sulphate to
cuprous oxide.
Addition of phosphomolybdic acid solution oxidizes
the precipitated cuprous oxide to cupric oxide and is
itself reduced to molybdenum blue.
The absorbance of the resulting blue colour is taken
at 680 nm. From this the concentration of lactose in
the diluted milk may be found if parallel tests using
standard lactose solutions are carried out.