GB 5413.38-2016 PDF in English
GB 5413.38-2016 (GB5413.38-2016) PDF English
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National Food Safety Standard -- Determination of freezing point in raw milk in food
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| GB 5413.38-2010 | English | 239 |
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National food safety standard -- Determination of freezing point in raw milk
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Standards related to (historical): GB 5413.38-2016
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GB 5413.38-2016: PDF in English GB 5413.38-2016
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
National Food Safety Standard -
Determination of Freezing Point in Raw Milk in Food
ISSUED ON. AUGUST 31, 2016
IMPLEMENTED ON. MARCH 1, 2017
Issued by. National Health and Family Planning Commission of the
People’s Republic of China
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Principle ... 4
3 Reagents and Materials ... 4
4 Instruments and Equipment ... 5
5 Analytical Procedures ... 7
6 Expression of Analysis Results ... 9
7 Precision ... 9
8 Others ... 10
National Food Safety Standard -
Determination of Freezing Point in Raw Milk in Food
1 Scope
This Standard specifies the method of determining freezing point in raw milk with
thermistor freezing point meter.
This Standard is applicable to the determination of freezing point in raw milk.
2 Principle
Cool down raw milk sample to an appropriate temperature; when the test sample cools
down to -3 °C, instantaneously release heat to crystalize the sample. Wait till the
sample temperature reaches a balanced state, and temperature rise ≤ 0.5 m °C within
20 s, the instant temperature shall be considered as the freezing point of the sample.
3 Reagents and Materials
Unless otherwise indicated, the reagents adopted under this method are of analytical
purity or above. The water is second-grade water as specified in GB/T 6682.
3.1 Reagents
3.1.1 Ethylene glycol (C2H6O2).
3.1.2 Sodium chloride (NaCl).
3.2 Preparation of Reagents
3.2.1 Sodium chloride (NaCl). grind sodium chloride, then, place it in a drying oven;
start drying at 130 °C ± 2 °C for over 24 h. Cool it down in the dryer to room temperature.
3.2.2 Coolant. measure-take 330 mL of ethylene glycol (3.1.1) and place it in 1,000 mL
volumetric flask; add water to the constant volume and shake it well; its volume fraction
is 33%.
3.3 Sodium Chloride Standard Solution
3.3.1 Standard solution A. weigh-take 6.731 g of sodium chloride (3.2.1), then, dissolve
it in 1,000 g ± 0.1 g of water. Divide standard solution and store it in polyethylene plastic
of corresponding instrument. During normal stirring, metal stirring rod shall not touch
glass sensor or sample tube wall.
c) Crystallization device
When the test sample reaches -3.0 °C, initiate the mechanical vibration device for
crystallization. During crystallization, increase the amplitude of the metal stirring rod
within 1 s ~ 2 s, and touch the tube wall of the sample.
4.3 Drying oven. temperature can be controlled at 130 °C ± 2 °C.
4.4 Sample tube. borosilicate glass, length. 50.5 mm ± 0.2 mm, external diameter.
16.0 mm ± 0.2 mm, internal diameter. 13.7 mm ± 0.3 mm.
4.5 Weighing bottle.
4.6 Volumetric bottle. 1,000 mL, comply with Grade-A requirements in GB/T 12806-
2011.
4.7 Dryer. with silicone hygrometer inside.
4.8 Pipette. 1 mL ~ 5 mL.
4.9 Polyethylene bottle. capacity. ≤ 250 mL.
5 Analytical Procedures
5.1 Sample Preparation
Test sample shall be preserved in the refrigerator at 0 °C ~ 6 °C; complete the
determination within 48 h. Before determination, the sample shall be placed till it
reaches the room temperature. The temperature of the test sample shall be maintained
consistent with the temperature of sodium chloride standard solution during the
determination.
5.2 Instrument Pre-cooling
Initiate thermistor freezing point meter (4.2), wait till the sensor probe of thermistor
freezing point meter rises, then, open the cold trap cover; add corresponding volume
of coolant (3.2.2) as prescribed by the manufacturer; close the cover, initiate pre-
cooling of the freezing point meter. After 30 min of pre-cooling, start to determine the
freezing point.
5.3 Calibration
5.3.1 Principle
Before calibration, prepare sodium chloride standard solution (with different freezing
in turn; in initiated cold trap, insert a sample tube that contains calibration solution C.
When repeatedly measured value is at calibration value (-600 m °C ± 2 m °C),
complete the calibration.
5.3.3 Quality control calibration
Before each determination, quality control calibration shall be adopted. In successive
determination of milk sample, quality control calibration shall be conducted at least
every hour on the freezing point meter. If the difference between the arithmetic mean
value of two measurements and sodium chloride standard solution (-512 m °C) is > 2
m °C, re-conduct instrument calibration (5.3.2).
5.4 Sample Determination
5.4.1 Slightly shake the test sample (5.1), avoid the inlet of air, which will generate
bubbles. Transfer-take 2.5 mL of sample to a dry and clean sample tube; place the
sample tube in the measuring hole of previously calibrated thermistor freezing point
meter (4.2). Initiate the freezing point meter and cool down the sample. When the
temperature reaches -3.0 °C ± 0.1 °C, the sample starts to freeze; when the
temperature reaches a balance (temperature rise ≤ 0.5 m °C within 20 s), the freezing
point meter stops measurement, and the sensor probe rises. The displayed
temperature is the freezing point of the sample. After determination is completed,
guarantee that the probe and metal stirring rod are clean and dry.
5.4.2 If the sample starts to freeze before the temperature reaches -3.0 °C ± 0.1 °C,
re-take a sample for determination (5.4.1). If the sample still freezes too early, heat up
the remaining sample at 40 °C ± 2 °C for 5 min to melt crystallized fat, then, repeat the
steps of sample determination (5.4.1).
5.4.3 After the determination is completed, remove the sample tube; use water to rinse
the temperature sensor and metal stirring rod, then, wipe them clean.
5.4.4 Record the determined freezing point of the sample.
6 Expression of Analysis Results
Take the average value (unit. m °C) of two determination results as the measured
freezing point of raw milk sample; the result shall retain three significant figures.
7 Precision
The absolute difference between the two independent determination results obtained
under repeatability conditions shall not exceed 4 m °C.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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