Some standard content:
ICS67.040
National Standard of the People's Republic of China
GB/T5009.3—2003
Replaces GB/T5009.3--1985
Determination of moisture in foods
Determination of moisture in foodsIssued on August 11, 2003
Ministry of Health of the People's Republic of China
Standardization Administration of the People's Republic of China
Implementation on January 1, 2004
GB/T5009.3—2003
This standard replaces GB/T5009.3—1985 "Determination of moisture in foods". Compared with GB/T5009.3-1985, this standard has been modified as follows: the Chinese name of the standard has been modified and changed to "Determination of Water Content in Foods"; the structure of the original standard has been modified in accordance with GB/T20001.4-2001 "Standard Preparation Rules Part 4: Chemical Analysis Methods".
This standard is proposed and managed by the Ministry of Health of the People's Republic of China. This standard is drafted by the Food Hygiene Supervision and Inspection Institute of the Ministry of Health. This standard was first issued in 1985 and this is the first revision. 26
1 Scope
Determination of Water Content in Foods
This standard specifies the method for determining water content in foods. GB/T5009.3-2003
The direct drying method in this standard is applicable to the determination of water content in foods such as cereals and their products, aquatic products, bean products, dairy products, meat products and stewed food products. The vacuum drying method is applicable to the determination of water content in easily decomposed foods such as sugar, candy and monosodium glutamate. The distillation method is suitable for the determination of moisture in foods containing more volatile substances, such as oils, spices, etc. Method 1 Direct Drying Method
2 Principle
The moisture in food generally refers to the total amount of substances lost when directly dried at around 100°C. The direct drying method is suitable for foods that do not contain or contain very little other volatile substances at 95°C~105°C. 3 Reagents
3.16mol/L hydrochloric acid: measure 100mL hydrochloric acid and dilute to 200mL with water. 3.26mol/L sodium hydroxide solution: weigh 24g sodium hydroxide, dissolve in water and dilute to 100mL. 3.3 Sea sand: Take sea sand or river sand washed with water to remove mud, first boil it with 6mol/L hydrochloric acid for 0.5h, wash it with water until it is neutral, then boil it with 6mol/L sodium hydroxide solution for 0.5h, wash it with water until it is neutral, and dry it at 105°C for use. 4 Instruments
4.1 Flat fan-shaped aluminum or glass weighing bottle: inner diameter 60mm~70mm, height less than 35mm. 4.2 Electric constant temperature drying oven.
5 Analysis steps
5.1 For solid samples, take a clean aluminum or glass flat weighing bottle, place it in a 95℃~105℃ drying oven, with the bottle cap tilted on the bottle side, heat for 0.5h~1.0h, take it out and cover it, cool it in a dryer for 0.5h, weigh it, and repeat drying to constant weight. Weigh 2.00g~10.00g of chopped or ground sample, put it in this weighing bottle, the sample thickness is about 5mm. Cover it, weigh it accurately, place it in a 95℃~105℃ drying oven, with the bottle cap tilted on the bottle side, dry it for 2h4h, cover it, take it out, cool it in a dryer for 0.5h, and weigh it. Then put it in a 95℃~105℃ drying oven to dry for about 1 hour, take it out, put it in a desiccator to cool for 0.5 hour, and then weigh it. When the difference between the two weights does not exceed 2 mg, it is constant.
5.2 Semi-solid or liquid sample: Take a clean evaporating dish, add 10.0g sea sand and a small glass rod, put it in a 95℃~105℃ drying oven, dry it for 0.5h~1.0h, take it out, put it in a desiccator to cool for 0.5h, weigh it, and repeat the drying until constant weight. Then accurately weigh 5g~10g of the sample, put it in the evaporating blood, stir it with a small glass rod, put it in a boiling water bath to evaporate it, and stir it at any time, wipe off the water drops on the bottom of the dish, put it in a 95℃~105℃ drying oven to dry for 4 hours, cover it, take it out, put it in a desiccator to cool for 0.5h, and weigh it. The following is in accordance with 5.1 from "then put it in a 95℃~105℃ drying oven to dry for about 1 hour". 6 Result calculation
The moisture content in the sample is calculated according to formula (1). 27
GB/T5009.3—2003
Wherein:
X—moisture content in the sample;
The mass of the weighing bottle (or evaporating blood plus sea sand, glass rod) and the sample, in grams (g); The mass of the weighing bottle (or evaporating blood plus sea sand, glass rod) and the sample after drying, in grams (g); The mass of the weighing bottle (or evaporating blood plus sea sand, glass rod), in grams (g). The calculation result is rounded to three significant figures.
7 Precision
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 5% of the arithmetic mean. Second method: vacuum drying method
8 Principle
The moisture content in food refers to the total amount of substances lost under certain temperature and reduced pressure, and is applicable to foods that are easily decomposed, such as sugar and monosodium glutamate.
9 Instruments
Vacuum drying oven. Other instruments are the same as 4.1.
10 Analysis steps
10.1 Sample preparation: Powder and crystal samples are weighed directly; hard candies are crushed in a mortar; soft candies are chopped with a blade, mixed and set aside. 10.2 Determination: Take a weighing bottle with constant weight and accurately weigh about 2g~10g of sample, put it into a vacuum drying oven, connect the drying oven to a water pump, pump out the air in the drying oven to the required pressure (generally 40kPa~53kPa), and heat it to the required temperature of 60℃±5℃ at the same time. Close the piston on the water pump or vacuum pump, stop pumping, keep a certain temperature and pressure in the drying oven, open the piston after 4h, let the air slowly pass into the drying oven through the drying device, and open it again after the pressure returns to normal. Take out the weighing bottle, put it in the dryer for 0.5h, weigh it, and repeat the above operation until constant weight.
11 Calculation of results
Same as Chapter 6.
Calculation results shall be retained to three significant figures.
12 Precision
The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. Method 3 Distillation method
13 Principle
The water in the food is distilled together with toluene or xylene, and the distillate is collected in the receiving tube, and the content is calculated based on the volume. It is suitable for foods containing more other volatile substances, such as oils, spices, etc. 14 Reagents
Toluene or xylene: Take toluene or xylene, saturate it with water first, separate the water layer, distill it, and collect the distillate for use. 28
15 InstrumentwwW.bzxz.Net
GB/T5009.3—2003
Moisture analyzer: as shown in Figure 1 (with adjustable electric furnace). The capacity of the moisture receiving tube is 5mL, the minimum scale value is 0.1mL, and the capacity error is less than 0.1mL.
—250mL conical flask;
2—- Moisture receiving tube, with scale
3—Condenser.
Figure 1 Moisture analyzer
16 Analysis steps
Accurately weigh an appropriate amount of sample (estimated to contain 2mL~5mL of water), put it into a 250mL conical flask, add 75mL of toluene (or xylene) from the newly steamed stuffing, connect the condenser and the moisture receiving tube, inject toluene from the top of the condenser, and fill the moisture receiving tube. Heat and distill slowly, so that two drops of distillate are obtained per second. After most of the water is evaporated, accelerate the distillation to about 4 drops per second. When all the water is evaporated and the volume of water in the receiving tube no longer increases, add toluene from the top of the condenser to rinse. If there are water droplets on the wall of the condenser tube, you can wipe them off with a copper wire with a small rubber head, and then distill for a while until there are no water droplets on the upper part of the receiving tube and the wall of the condenser tube. The horizontal surface of the receiving tube remains unchanged for 10 minutes as the distillation end point, and the volume of the water layer in the receiving tube is read. 17 Result calculation
The water content in the sample is calculated according to formula (2). X
Where:
The water content in the sample, in milligrams per hundred grams (mL/100g) (or the mass calculated according to the density of water at 20℃ 0.99820g/mL);
The volume of water in the receiving tube, in milligrams (mL); The mass of the sample, in grams (g).
The calculation result is rounded to three significant figures.
18 Precision
The absolute difference between two independent measurement results obtained under repeatability conditions shall not exceed 10% of the arithmetic mean. 29
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.