The purpose of the document is to establish a general and uniform method for the determination of the insolubility index in milk powder.
2.0SCOPE
This standard testing procedure is suitable for the determination of the insolubility index in milk powder samples.
3.0RESPONSIBILITY
The expert and trained chemist are responsible for following this procedure. The technical manager is responsible for implementing this procedure.
4.0REQUIREMENTS
4.1 Apparatus
4.1.1 Thermometer
4.1.2 Water bath
4.1.3 Analytical Balance
4.1.4 Electric mixer
4.1.5 Magnifying lens
4.1.6 Centrifuge, electric, with speed indicator with vertical-loading swing-out cups for accommodating the centrifuge tubes
4.2 Glassware
4.2.1 Mixing jar, made of glass, of capacity 500 ml, as supplied for use with the mixer. The mixing jar (clover-leaf pattern).
4.2.2 Measuring cylinder made of plastic material, of capacity 100 + 0.5 ml (at 20°C).
4.2.3 Stirring rod, made of glass, of length 250 mm and diameter 3.5 mm.
4.2.4 Centrifuge tubes, glass, conical, with the shape, dimensions, and graduation scheme
4.3 Reagent
4.3.1 Silicone antifoaming agent, for example, an aqueous emulsion containing 30 %(m/m)of silicone
5.0 PROCEDURE
5.1 Sample preparation: Transfer the sample to a clean, dry container
5.2 Preparation of the mixing jar, According to whether the insolubility index is to be measured at 24°C or at 50°C. adjust the temperature of the mixing jar to 24.0+0.2°C or 50.0 + 0.2°C, respectively, by standing the jar in the water bath, with the water level near the top of the jar, for a sufficient period of time, Weigh, to the nearest + 0,01g, in the scoop or the sampling paper, test portion of
· 13,00 g in the case of dried whole milk, dried partly skimmed milk, and infant food based on either;
· 10.00 g in the case of dried skimmed milk and dried buttermilk;
· 7, 00 g in the case of dried whey.
5.3 DETERMINATION
5.3.1 Remove the mixing jar, from the water bath, quickly wipe dry the outside of the jar, and using the measuring cylinder add to the jar 100 + 0.5 ml of water at 24.0 + 0.2°C or 50.0 + 0.2°C as appropriate
5.3.2 Add 3 drops of the silicone antifoaming agent to the water in the mixing jar and transfer the test portion to the jar, using the brush if necessary so that the entire test portion falls onto the surface of the water.
5.3.3 Fit the mixing jar to the mixer, switch on the mixer, and after the mixer has operated for exactly 90 s, switch it off. If the mixer is of the type with a non-synchronous motor, speed control, and speed indicator, bring the rotational frequency of the impeller to 3600 + 100 min -1 within the first 5 s of the 90 s mixing period.
5.3.4 Remove the mixing jar from the mixer (allow a few seconds for liquid on the impeller to drain into the jar), and leave the jar to stand, at laboratory temperature for not less than 5 min and not more than 15 min
5.3.5 Add 3 drops of the silicone antifoaming agent to the mixture in the mixing jar thoroughly mix the contents of the jar by stirring (not too vigorously) for 10 s with a spoon spatula and immediately pour sufficient of the mixture into a centrifuge tube to fill the tube up to the 50 ml mark, i.e. until the top level is coincident with the 50 ml mark.
5.3.6 Place the centrifuge tube (counterbalanced) in the centrifuge, bring the centrifuge as quickly as
possible to the rotational frequency producing an acceleration of 160 g at the internal bottom of the tube and then spin the tube at this rotational frequency for 5 min, at 20 to 25°C.
5.3.7 Remove the centrifuge tubs from the centrifuge and, using a spoon spatula, remove and discard any top layer of fatty material in the tube.
5.3.8 Add water at 24°C or 50°C as appropriate to the centrifuge tube until the top level is coincident
with the 30 ml mark, completely disperse the sediment with the stirring rod, tap the bottom of the rod against the inside of the tube to collect adhering liquid, and add more water at the same temperature until the top level is coincident with the 50 ml mark.
5.3.9 Close the centrifuge tube with a rubber stopper, and invert the tube slowly five times so as to mix its
contents thoroughly, remove the stopper (draw the bottom of the stopper across the rim of the tube to collect adhering liquid), and then spin the tube in the centrifuge for 5 min at the required rotational frequency and temperature,
5.3.10 Remove the centrifuge tube from the centrifuge, hold the tube in a vertical position against a suitable background with the top of the sediment at eye level, and, using the magnifying lens, read the volume of Sediment to the nearest 0.05 ml if the volume is less than 0.5 ml and to 0.1ml if the volume is more than 0.5 ml.
5.3.11 Estimate the volume if the top of the sediment is sloping. If the top of the sediment is uneven, leave the tube in a vertical position for a few minutes; the top of the sediment will usually become less uneven and the volume of sediment can be read more easily. Record the Temperature of the water used for the reconstitution.
5.3.12 The difference between two single values for the insolubility index should not exceed 0,138 M. where M is the mean of the two values.
6.0 CALCULATION:
The insolubility index of the laboratory sample is equal to the volume, in milliliters, of sediment Recorded, Report the result with the temperature of the water used for reconstitution.
7.0REVISION /CHANGE HISTORY
8.0 ATTACHMENTS
· Appendix-1: FLOW CHART FOR INSOLUBILITY INDEX
9.0 REFERENCES
· IS 12759:1989;RA 2010
END OF THE DOCUMENT
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