GB/T 5413.29-1997 Determination of solubility of infant formula and milk powder
Some standard content:
GB/T 5413.29—1997
This standard provides two methods. Method 1 is the insolubility index method, which is equivalent to the International Dairy Federation standard IDF129A:1988 "Milk powder and milk powder products-Determination of insolubility index"; Method 2 is the solubility method, which modifies the text format of Method A.2 in GB5413-85.
Method 1 of this standard is the arbitration method.
This series of standards will replace GB5413--85 from the date of implementation. This standard is proposed by the China Light Industry Federation.
This standard is under the jurisdiction of the National Dairy Standardization Center. The responsible drafting unit of this standard: National Dairy Product Quality Supervision and Inspection Center. Participating drafting units of this standard: Food Hygiene Supervision and Inspection Institute of the Ministry of Health, Zhejiang Light Industry Research Institute, Harbin Morinaga Dairy Co., Ltd., Nestlé (China) Investment Service Co., Ltd. The main drafters of this standard: Wang Yun, Huang Min, Wang Xinxiang, Wang Xiaoyu. 339
National Standard of the People's Republic of China
Infant formula foods and milk powder
Determination of solubility
Milk powder and formula foods for infant and young children-Determination of solubility1Scope
This standard specifies the determination methods of insolubility index and solubility. GB/T5413.29-1997
Replaces GB541385
Method 1 of this standard is applicable to the determination of insolubility index of milk powder that does not contain soy ingredients, and method 2 is applicable to the determination of solubility of infant formula foods and milk powder.
Method 1 Determination of insolubility index of milk powder 2Definition
This standard adopts the following definitions.
Insolubility index is the volume of the precipitate in milliliters obtained by reconstitution of milk powder or milk powder products and centrifugation under the conditions specified in this standard. 3 Principle of the method
Add the sample to water at 24℃ or 50℃, and then use a special stirrer to reconstitute it. After a period of rest (as required), centrifuge a certain volume of reconstituted milk in a graduated centrifuge tube, remove the upper liquid, add water at the same temperature as the reconstitution temperature, resuspend the precipitate, centrifuge again, and record the volume of the obtained precipitate. Note: When reconstitute spray-dried products, use water at a temperature of 24℃. When reconstitute some drum-dried products, use water at a temperature of 50℃. 4 Reagents
All reagents, if the specifications are not specified, refer to analytical grade; all experimental water, if no other requirements are specified, refer to grade tertiary water. Silicone defoamer: The mass fraction of silicone emulsion is 30%. According to the steps described in Chapter 9 (without adding samples), check the applicability of silicone defoamer. After the test, the silicone liquid visible at the bottom of the centrifuge tube should not be greater than 0.01mL.
5 Instruments
Common laboratory instruments and:bZxz.net
5.1 Water bath: Working temperature is 24.0℃±0.2℃ and/or 50.0C±0.2℃, and can hold one or several stirring cups (5.8). 5.2 Thermometer: Can measure the temperature of 24℃ and/or 50℃, with an error of no more than ±0.2℃. Note: Since the recovery temperature is an important factor affecting the insolubility index, the accuracy of the thermometer used in 6.1 and 6.3 (and 6.4.8) should meet the requirements. 5.3 Smooth spoon, or clean and smooth sampling paper (size 140mm×140mm). Used to weigh samples. Approved by the State Administration of Technical Supervision on May 28, 1997 340
Implementation on September 1, 1998
5.4 Balance: Accurate to 0.01g.
GB/T 5413.29—1997
5.5 Plastic volumetric cylinder: capacity is 100mL±0.5mL (20℃). Note: Compared with glass volumetric cylinder, plastic volumetric cylinder has lower heat capacity, so the temperature change is minimal after adding water to the volumetric cylinder. 5.6 Brush: It can be used to brush away residual sample on the spoon or sample paper (5.3). 5.7 Electric stirrer, with the following characteristics: a) There are 16 blades (stainless steel) on the stirrer shaft, the shape and size are shown in Figure 1. The flat side of the blade is located at the bottom. For the stirrer rotating in a clockwise direction, the blades are tilted upward from right to left by 1. b) The angle between the blades is 30°, and the horizontal tooth spacing (circumference of the impeller) is 8.73mm (11/32 inches). These dimensions may change after a period of use, so they should be checked and maintained periodically. c) When the mixing cup is fixed on the stirrer, the height of the stirrer shaft (i.e. the distance from the lowest point of the blade to the bottom of the cup) should be 10 mm ± 2 mm, that is, the depth of the cup is 132 mm, the distance from the top of the cup to the lowest point of the blade is 122 mm ± 2 mm, and the distance from the top of the cup to the highest point of the blade is 115 mm ± 2 mm. The impeller should be located in the center of the cup. d) When 100 mL of 24 ° C water (with or without sample (6.2) is added to the mixing cup for mixing, the fixed speed of the impeller after the stirrer is turned on is 3600 r/min ± 100 r/min (reached within 5 s). The direction of rotation of the impeller should be clockwise (as shown in the figure). The speed of the impeller under load (as mentioned above) should be checked regularly using an electric tachometer, which is particularly important for old stirrers. For non-synchronous motors, the speed can be adjusted to 3600 r/min ± 100 r/min using a speed regulator or speed indicator (applicable to stirrers where the accuracy of the speed cannot be guaranteed).
5.8 Glass mixing cup: 500 mL capacity. Can be used with agitator (5.7). Mixing cup (four-leaf type), shape as shown in Figure 1, dimensions approximately as shown.
5.9 Timer: can display 0-60s and 0-60min. 5.10 Flat spoon: length about 210mm.
5.11 Electric centrifuge: with speed display, vertical load, sleeve suitable for centrifuge tube (5.12) and can rotate outward, tube bottom acceleration of 160gn, and when the centrifuge cover is closed, the temperature is maintained at 20-25℃. Note: The acceleration generated during centrifugation is equal to 1.12rn\×10°; r is the effective radius of horizontal rotation, mmtn is the speed, r/min. 5.12 Glass centrifuge tube, conical, size, scale, marking, matte pattern, etc. as shown in Figure 2, with rubber stopper. The scale number and the mark "ml (20℃)" should be permanent and the scale lines should be clear and clean. At 20℃, the maximum capacity error is as follows: at 0.1mL: ±0.05mL;
-—0.1~~1mL: ±0.1mL;
-—1～2mL: ±0.2mL;
- 2～~5mL:±0.3mL;
.5～10mL:±0.5mL;
-At 10mL:±1mL.
Note: For routine production control, centrifuge tubes of other shapes can be used, but the capacity error must meet the requirements listed above. If the result is controversial or needs to be confirmed, the centrifuge tube specified in 5.12 should be used. 5.13 Siphon or straw connected to a water pump: It can remove the upper layer of liquid in the centrifuge tube (5.12). The tube is made of glass and has an upward U-shaped tube, which is suitable for siphoning (see Figure 2).
5.14 Glass stirring rod: 250mm long and 3.5mm in diameter. 5.15 Magnifying glass: Read the sediment volume. 1) For some agitators, the impeller may rotate counterclockwise (see a)). These The blades of the blender should be tilted upward from left to right, so that the direction of movement of the liquid in the blender cup produces the same effect as a clockwise rotating impeller. In other respects, such as the fixing method of the shaft and the distance from the bottom of the cup, the requirements for counterclockwise rotating impellers are the same as those for clockwise rotating impellers. 341
Unit: mm
GB/T5413.29—1997
Horizontal distance between blades (at the maximum circumference) Slope
Blending cup (plan view)
Inner diameter 84
Blending cup
Stirring rod
Figure 1 Blending cup and stirring paddle
Outer diameter 497
6 Kneading steps
6.1 Sample preparation
Frosted surface
mL(20℃)
Outer diameter 29. 2~-30
GB/T 5413.29—1997
Unit: mm
Outer diameter 4
Soft plastic tube
Figure 2 Centrifuge tube and matching siphon
Before the determination, the laboratory sample should be kept at room temperature (20~25℃) for at least 48h so that the factors affecting the insolubility index will be consistent in each sample.
Then repeatedly shake and invert the sample container to mix the laboratory sample. If the container is too full, transfer the entire sample to a clean, dry, airtight, opaque large container and mix thoroughly as described above. For instant milk powder, mix carefully to prevent the sample particles from reducing. 6.2 Preparation of the mixing cup
According to the determination temperature of the insolubility index (24℃ or 50℃), adjust the temperature of the mixing cup (5.8) to 24.0℃±0.2℃ or 50.0℃±0.2℃ respectively. The method is to place the mixing cup in a water bath (5.1) for a period of time until the water level is close to the top of the cup. Note: In the following text, "24.0℃±0.2℃ or 50.0℃±0.2℃ is appropriate" refers to the use of this temperature. 6.3 Sample portion
Weigh the sample with a spoon (5.3) or on a weighing paper (5.3) to an accuracy of 0.01g. The sample amount is as follows: a) whole milk powder, part skimmed milk powder, whole fat sweetened milk powder, milk-based infant food and other milk powder products produced with whole milk powder and part skimmed milk powder as raw materials: 13.00g; b) skimmed milk powder and buttermilk powder: 10.00g; c) whey powder: 7.00g.
6.4 Determination
6.4.1 Take out the mixing cup from the water bath (see 6.2), quickly wipe off the water on the outside of the cup, and use a measuring tube (5.5) to add 100mL±0.5mL of water at 24℃±0.2℃ or 50.0℃±0.2℃ to the cup (see Note 6.2). 6.4.2 Add 3 drops of silicone defoamer (4.1) to the mixing cup, and then add the sample (6.3). If necessary, use a brush (5.6) to make all the sample fall onto the water surface.
GB/T5413.29--1997
6.4.3 Place the mixing cup on the stirrer (5.7) and fix it, turn on the stirrer switch, mix for 90s, and then turn off the switch. If the agitator is a non-synchronous motor with a speed regulator or speed indicator, adjust the impeller speed to 3600 r/min ± 100 r/min within the first 5 seconds and mix for 90 seconds.
6.4.4 Remove the mixing cup from the agitator (stay for a few seconds to allow the liquid on the blades to flow into the cup), and let the cup stand at room temperature (see 9.2) for more than 5 minutes, but not more than 15 minutes (see 9.3). 6.4.5 Add 3 drops of silicone defoamer to the mixture in the cup (see 9.5), mix the contents of the cup thoroughly with a flat spoon (5.10) for 10 seconds (do not overdo it), and then immediately pour the mixture into the centrifuge tube (5.12) to the 50mL scale, that is, the top liquid level coincides with the 50mL scale line. 6.4.6 Place the centrifuge tube in the centrifuge (to be placed symmetrically), rotate the centrifuge rapidly, and generate an acceleration of 160g at the bottom of the tube, and then rotate it at 20-25℃ for 5 minutes. 6.4.7 Take out the centrifuge tube and use a flat spoon (5.10) to remove and pour off the upper layer of fat in the tube. Hold the centrifuge tube vertically and use a siphon or pipette (5.13) to remove the upper layer of liquid. If it is a drum-dried product, suck it until the top liquid level coincides with the 15mL scale. If it is a spray-dried milk powder, it coincides with the 10mL scale. Be careful not to stir the insoluble matter. If the volume of the precipitate is obviously more than 15mL or 10mL, do not perform the lower operation, record the insolubility index as \15mL" or 10mL", and indicate the recovery temperature as described in Chapter 7. Otherwise, operate as described in 6.4.8.
6.4.8 Add 24℃ or 50℃ water (see note 6.2) to the centrifuge tube until the liquid level coincides with the 30mL mark. Stir the precipitate thoroughly with a stirring rod (5.14). Place the stirring rod against the tube wall and add water of the same temperature to flush the liquid on the stirring rod until the liquid level coincides with the 50mL mark.
6.4.9 Plug the centrifuge tube with a rubber stopper, slowly turn the centrifuge tube 5 times to thoroughly mix the contents, open the stopper (place the bottom of the stopper against the edge of the centrifuge tube to collect the liquid adhering to it), and then centrifuge at the specified speed and temperature for 5 minutes as described in 6.4.6. Note: It is recommended that the centrifuge tube be placed in the centrifuge so that the scale line of the centrifuge tube is neither facing up nor down during the centrifuge rotation, but is in the middle. This makes it easy to estimate the volume of the precipitate even if the top of the precipitate is tilted. 6.4.10 Remove the centrifuge tube, hold the centrifuge tube vertically, and read the volume of the precipitate with your eye level with the top of the precipitate using an appropriate background as a control 1. If the volume of the precipitate is less than 0.5 mL, read it to the nearest 0.05 mL. If the volume of the precipitate is greater than 0.5 mL, read it to the nearest 0.1 mL. If the top of the precipitate is tilted, estimate its volume. If the top of the precipitate is not level, place the centrifuge tube vertically for a few minutes. Usually the top of the precipitate will become flatter, making it easier to read. Record the temperature of the reconstitution water. 7 Expression of Analytical Results
The insolubility index of the sample is equal to the volume of the precipitate in milliliters recorded in 6.4.10. Report the temperature of the water used for reconstitution. For example:
0. 1mL(24'℃)
4.1mL(50'C)
8 Allowable difference
8.1 Repeatability
The difference between the results of two separate tests on the same sample made by the same analyst using the same instrument within a short time interval shall not exceed 0.138M, where M is the average of the two test results. 8.2 Reproducibility
The difference between the results of two separate tests on the same sample made by two analysts in different laboratories shall not exceed 0.328M, where M is the average of the two test results.
1) Observe the centrifuge tube against a light or dark background, and the top of the precipitate will be more eye-catching and easier to read. 344
9 Precautions
GB/T5413.29—1997
9.1 Once the experiment is started, it should be carried out continuously. No step should be interrupted. All regulations regarding temperature and time must be strictly observed. 9.2 Since the determination of the insolubility index may be affected by the ambient temperature, it is recommended that the test process be carried out in a laboratory with a temperature of 20 to 25°C.
9.3 A standing time of 5 to 15 minutes is allowed in this test (6.4.4), which has been shown to have no significant effect on the insolubility index. If the temperature of several mixing cups has been adjusted in advance (see 6.2) and the samples (6.3) are weighed at the same time within 10 minutes, these samples can be measured simultaneously as a batch. In this way, it can be found that the revised operation steps of 6.2 and 6.4.1 have certain advantages, that is, add 100mL ± 0.5mL of water (at an appropriate temperature) to the mixing cup placed in the water bath. When the water temperature in the cup stabilizes at the correct value, remove a mixing cup from the water bath and then follow the steps 6.4.1 to 6.4.4. Similarly, prepare other mixing cups in sequence, so that batches of samples can be centrifuged simultaneously. 9.4 The amount of each sample is equal to: When mixed, the total solid content of the sample in 100 mL of water (expressed as the mass fraction of the mixture) is approximately the total solid content of the original liquid.
9.5 Adding 3 drops of silicone defoamer (4.1) in 6.4.5 is not necessary for products that are unlikely to foam during mixing. However, in order to make the operating steps consistent for all samples, 3 drops of defoamer should be added. Method 2 Determination of solubility
10 Definition
Solubility
The total mass dissolved after a specified dissolution process per 100 grams of sample. 11 Instruments
Common laboratory instruments and:
11.1 Centrifuge tube: 50 mL, thick-walled, hard (see Figure 3). 11.2 Beaker: 50 mL.
11.3 Centrifuge.
11.4 Weighing III: Aluminum III or glass blood with a diameter of 50~~70 mm. $38
Figure 3 Solubility Gravimetric Method Centrifuge Tube
12 Operation Steps
GB/T 5413.29—1997
12.1 Weigh 5g of sample (accurate to 0.01g) in a 50mL beaker, dissolve the milk powder in a 50mL centrifuge tube with 38mL of 25~~30℃ water several times, and add a stopper.
12.2 Place the centrifuge tube in 30℃ water for 5min, take it out, and shake it for 3min. 12.3 Place it in a centrifuge and centrifuge it at an appropriate speed for 10min to precipitate the insoluble matter. Pour off the supernatant and wipe the tube wall with a cotton plug. 12.4 Add 38mL of 25~30℃ water, add a stopper, and shake it up and down to suspend the precipitate. 12.5 Centrifuge again for 10 minutes, pour off the supernatant, and carefully clean the tube wall with a cotton plug. 12.6 Rinse the precipitate with a small amount of water into a weighing dish of known mass, first evaporate the water in the blood in a boiling water bath, and then transfer it to a 100℃ oven to dry to constant weight (the difference in the last two masses should not exceed 2mg). 13 Expression of analysis results
Solubility in sample (g/100g) 100—mass of sample, g;
Where: m-
Weighed blood mass, g,
Weighed blood and insoluble mass after drying, g; -Sample moisture, g/100g.
Note: The amount of sugar added should be deducted when calculating the sweetened milk powder. Allowable difference
(m2 m,) × 100
(1 B) × m
The difference between the two measured values of the same sample shall not exceed 2% of the average value of the two measurements. 346
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