Page 164 - Analytical method for food addtives

E249–50: Nitrites 109

conical flask for at least 15 min, but not longer than 1 h. Then filter through a filter
paper, collecting the filtrate in a 250 mL conical flask (see notes under ‘Extraction
and deproteination: whey cheese’).

Extraction and deproteination: dried whey
Add progressively 136 mL of preheated water at 50–55 °C to the test portion.
Disperse the test portion by stirring with a glass rod or by shaking the conical flask.
Cover the conical flask with aluminium foil or a watch glass and place it in the
water bath with boiling water for 15 min. Remove the flask from the water bath and
wait until the temperature has dropped to between 55 °C and 60°C. Add in the
following order, swirling thoroughly after each addition, 12 mL of zinc sulphate
solution, 12 mL of potassium hexacyanoferrate (II) solution and 40 mL of buffer
solution and mix.
In order to obtain a clear filtrate, leave the mixture in the conical flask for at least
15 min, but not longer than 1 h. Then filter through a filter paper, collecting the
filtrate in a 250 mL conical flask (see notes under ‘Extraction and deproteination:
whey cheese’).

Extraction and deproteination: caseins and caseinates
Add progressively 136 mL of preheated water at 50–55 ºC and 10 mL of buffer
solution to the test portion. Disperse the test portion by stirring, using the magnetic
stirrer. Add in the following order, swirling thoroughly after each addition, 12 mL
of zinc sulphate solution, 12 mL of potassium hexacyanoferrate (II) solution and
30 mL of buffer solution and mix. In order to obtain a clear filtrate, leave the
mixture in the conical flask for at least 15 min, but not longer than 1 h. Then filter
through a filter paper, collecting the filtrate in a 250 mL conical flask (see notes
under ‘Extraction and deproteination: whey cheese’).

Extraction and deproteination: cheese
Add progressively 144 mL of preheated water at 50–55 ºC to the test portion. Mix in
the mixer or homogeniser until the test portion is well suspended. Add in the
following order, swirling thoroughly after each addition, 6 mL of zinc sulphate
solution, 6 mL of potassium hexacyanoferrate (II) solution and 40 mL of buffer
solution and mix. In order to obtain a clear filtrate, leave the mixture in the conical
flask for 3 min. Then filter through a filter paper, collecting the filtrate in a 250 mL
conical flask (see notes under ‘Extraction and deproteination: whey cheese’).

Extraction and deproteination: whey cheese
Add progressively 134 mL of preheated water at 50–55 ºC to the test portion. Mix
in the mixer or homogeniser until the test portion is well suspended. Add in the
following order, swirling thoroughly after each addition, 12 mL of zinc sulphate
solution, 12 mL of potassium hexacyanoferrate (II) solution and 40 mL of buffer
solution and mix. In order to obtain a clear filtrate, leave the mixture in the conical
flask for at least 15 min, but not longer than 1 h. Then filter through a filter paper,
collecting the filtrate in a 250 mL conical flask.