This standard specifies two determination methods: insolubility index method and solubility method.
The first method of this standard is applicable to the determination of the insolubility index of milk powder containing no soybean component and the second method is applicable to the determination of the solubility in foods and milk powder for infants and young children.
Method I Determination of Insolubility Index
2 Term and Definition
insolubility index
milk powder or milk powder product is reconstituted under the conditions specified in this standard, and centrifuged to obtain the the volume of the precipitate, expressed by mL.
3 Principle
Add the sample to water at 24℃ or 50℃, then use a special stirrer to restore it, keep it for a period of time (as specified), centrifuge a certain volume of the reconstituted milk in a graduated centrifuge tube, remove the upper liquid, add the same amount of water as the recovery temperature to suspend the precipitate, centrifugate it again and record the volume of the resulting precipitate.
Note: Spray-dried products are reconstituted with water at a temperature of 24℃, and some drum-dried products are reconstituted with water at a temperature of 5℃.
4 Reagents and Materials
Unless otherwise specified, all reagents adopted for this method are analytically pure and water is Grade 3 water specified in GB/T 6682.
4.1 Silicone defoamer: the mass fraction of silicone emulsion is 30%.
The suitability of the silicone defoamer was tested according to the procedure described in 6.4.5 (without sample). After the end of the test, the silicone liquid at the bottom of the centrifuge tube shall not be larger than 0.01 mL.
