GB 5009.6-2025 National food safety standard -Determination of fat in foods
1 Scope
This standard specifies the method for determination of fat in foods.
Method II in this standard Acid hydrolysis method is applicable to the determination of fat in foods (excluding milk and dairy products).
Method III in this standard Alkaline hydrolysis is applicable to the determination of fat in milk and dairy products, foods for special dietary uses and protein drinks.
Method IV in this standard Gerber method is applicable to the determination of fat in raw milk, sterilized milk and pasteurized milk.
First method Soxhlet extraction
2 Principle
After the sample is directly extracted with anhydrous ether or petroleum ether, the solvent is evaporated and dried to obtain the content of free fat.
3 Reagents and materials
Unless otherwise specified, only analytically pure reagents and Grade 3 water specified in GB/T 6682 are used for the purpose of this method.
3.1 Reagents
3.1.1 Anhydrous ether (C4H10O)
3.1.2 Petroleum ether (CnH2n+2), with a boiling range of 30℃~60℃
3.2 Materials
3.2.1 Quartz sand
3.2.2 Degreasing cotton
4 Apparatus and equipment
4.1 Homogenizer
4.2 Tissue crusher or grinder
4.3 Soxhlet extractor
4.4 Thermostat water bath
4.5 Analytical balance: with sensibility of 0.001g and 0.0001g respectively
4.6 Electric thermostaticdrying oven
4.7 Dryer Containing effective desiccant, e.g. silica gel
4.8 Filter paper
4.9 Evaporating dish
5 Analysis steps
5.1 Preparation of samples
Even liquid samples without particles are directly shaken for later use; liquid samples with particles or non-even liquid samples and semi-solid samples are evenly mixed with a homogenizer for later use; solid samples are crushed and mixed with a tissue pulverizer or grinder for later use; frozen beverage can be properly heated and melted, and fully stirred while it is hot for later use. The prepared samples shall be determined as soon as possible.
Note: Oil samples shall be dried at 105℃±2℃ for 1 h, then crushed, and passed through a screen with the aperture of 0.425mm.
5.2 Sample treatment
5.2.1 Solid samples: Weigh 2g~5g (accurate to 0.001 g) of even samples, and transfer them into a filter paper tube.
5.2.2 Liquid or semi-solid samples: weigh 5 g~ 10 g (accurate to 0.001g) of even samples, put them in an evaporating dish, add about 20g of quartz sand, evaporate it in a boiling water bath, dry it in an electric thermostaticdrying oven at 100℃ ±5℃ for 30min, take them out, grind them, and move them all into a filter paper tube. The evaporating dish and the glass rod with samples adhered to it are wiped with absorbent cotton stained with ether, and put the cotton into the filter paper tube.
5.3 Extraction
Put the filter paper cylinder into the extraction cylinder of Soxhlet extractor, connect it with a receiving bottle (accurate to 0.0001 g) that has been dried to constant weight, add anhydrous ether or petroleum ether from the upper end of the condenser tube of the extractor to two-thirds of the internal volume of the bottle, and heat it in a water bath at 50℃~60℃ to continuously reflux the anhydrous ether or petroleum ether for extraction (6 times /h~ 8 times /h), and generally extract for 6 h~ 10h. At the end of the extraction, take a drop of the extraction solution with a frosted glass rod, and no oil spots on the frosted glass rod indicate that the extraction is completed.
5.4 Weighing
Remove the receiving bottle, recover anhydrous ether or petroleum ether, evaporate it in a water bath at 60℃ when the solvent in the receiving bottle remains 1 mL~2 mL, then dry it at 100℃ ±5℃ for 1 h, then put it in a dryer to cool it to room temperature and weigh it (accurate to 0.0001g). Repeat the above operations until the weight is constant (until the difference between the two weighing is less than 2 mg), and take the smallest weight.
6 Expression of analysis results
