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The method determines the titratable acidity of:
acid caseins.
The titratable acidity of acid caseins: the volume in millilitres, of a 0,1 mol/1 standard sodium hydroxide solution required to neutralize an aqueous extract of 1 gram of the product.
An aqueous extract of the sample at 60 o C is obtained and filtered. The filtrate is titrated against standard sodium hydroxide using phenolphtalein indicator.
Any water used in the method procedure or in the preparation of reagents shall be freed from carbon dioxide by boiling for 10 minutes before use.
As described in Section 1.2 of the General Provisions.
Weigh about 10 grams of the test sample (6.1) to the nearest 10 mg and transfer it to the conical flask (5.2).
Using the 250 ml measuring cylinder (5.6), add 200 ml of freshly boiled and cooled water, previously heated to 60 o C. Stopper the flask, mix by swirling and place in the water bath at 60 o C (5.8) for 30 minutes. Shake the flask at intervals of about 10 minutes.
Filter, and cool the filtrate to about 20 oC. The filtrate must be clear.
Transfer 100 ml of the cooled filtrate into the conical flask (5.5), using the pipette (5.3). Add 0,5 ml of the phenolphtalein indicator solution (4.2), using the pipette (5.4). Titrate with the standard volumetric sodium hydroxide solution (4.1), until the appearance of a faint pink colour, persisting for at least 30 seconds. Determine and record the volume used to the nearest 0,01 ml.
The titratable acidity of the acid casein is given by:
where:
is the volume, in millilitres, of the standard volumetric sodium hydroxide solution (4.1) used;
is the strength of the standard volumetric sodium hydroxide solution (4.1) in mol/1;
is the mass, in grams, of the test portion.
Calculate the titratable acidity to two decimal places.
The difference in results between two determinations carried out simultaneously or in rapid succession on the same sample, by the same analyst, under the same conditions, shall not exceed 0,02 ml of 0,1 mol/1 sodium hydroxide per 1 gram of product.
This repeatability interval should be achieved in 95 % of the times that the method is correctly carried out.