Dairy Chemistry And Biochemistry

Skimmilk (Kjeldahl I)

II

Heat at loO°C x 20 min. Make to 12%

cool and acidify to pH 4.6,

filter

trichloroacetic acid,

filter

I

Acidify to pH 4.6,

filter

Precipitate Filtrate

(casein) (non-casein N:

serum proteins

non-protein N;

Kjeldahl 11)

Neutralize and

saturate with

filter

MgS04

Precipitate

(globulins)

Filtrate

(albumin and

non-protein N;

Kjeldahl V)

Total nitrogen = Kjeldahl I
Casein = Kjeldahl I - Kjeldahl II
Non-protein nitrogen = Kjeldahl 111

Precipitate Filtrate

(casein and (proteose peptone

heat-labile and non-protein N;

semm proteins) Kjeldahl IV)

I

Precipitate

(all proteins)

1

Filtrate

(non-protein

nitmgen;

Kjeldahl 111)

Proteose peptone N = Kjeldahl IV-Kjeldahl III

Serum protein = Kjeldahl 11- Kjeldalil IV

Figure 4.4 Scheme for quantifying the principal protein fractions in milk.