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This standard replaces the contents involving the determination of total volatile basic nitrogen (TVBN) in GB/T 5009.44-2003 Method for analysis of hygienic standard of meat and meat products, GB/T 5009.45-2003 Method for analysis of hygienic standards of fish and other aquatic products and GB/T 5009.47-2003 Method for analysis of hygienic standard of egg and egg products, and replaces SC/T 3032-2001 Determination of the total volatile basic nitrogen in fishery products.
The following main changes have been made in this standard with respect to GB/T 5009.44-2003 are as follows:
——The title is revised as "National food safety standard - Determination of total volatile basic nitrogen in foods";
——The application scope of this standard is modified;
——The determination method of TVBN in preserved eggs (century eggs) in GB/T 5009.47-2003 Method for analysis of hygienic standard of egg and egg products is integrated into this standard;
——The automatic Kjeldahl method is added as Method II;
——The operation method of the microdiffusion method is improved.
National food safety standard - Determination of total volatile basic nitrogen in foods
1 Scope
This standard specifies the determinative method of total volatile basic nitrogen (TVBN) in foods.
This standard is applicable to the determination of TVBN in foods mainly made of meat, fresh (frozen) meat of animals, meat products and prepared meat products, animal aquatic products and seafood products and their prepared products, preserved egg products such as preserved eggs (century eggs) and salted eggs.
Method I Semimicro-kjeldahl determination
2 Principle
TVBN includes alkaline nitrogenous substances, such as ammonia and amines, produced by the decomposition of protein in animal food due to the action of enzymes and bacteria. Since its volatility, TVBN is evaporated in alkaline solution, absorbed by boric acid solution, and titrated with standard acid solution to calculate its content.
3 Reagents and materials
Unless otherwise specified, analytically-pure reagents and Class-III water (defined in GB/T 6682) are adopted for the purpose of this method.
3.1 Reagents
3.1.1 Magnesium oxide (MgO).
3.1.2 Boric acid (H3BO3).
3.1.3 Trichloroacetic acid (C2HCl3O2).
3.1.4 Hydrochloric acid (HCl) or sulfuric acid (H2SO4).
3.1.5 Methyl red indicator (C15H15N3O2)。
3.1.6 Bromocresol green indicator (C21H14Br4O5S) or methylene blue indicator (C16H18ClN3S·3H2O).
3.1.7 95% ethanol (C2H5OH).
3.1.8 Silicon oil defoamer.
3.2 Preparation of reagents
3.2.1 Magnesium oxide suspension (10g/L): weigh 10g of magnesium oxide, add 1,000mL of water and shake them into suspension.
3.2.2 Boric acid solution (20g/L): weigh 20g of boric acid, add water to dissolve it and then dilute to 1,000mL.
3.2.3 Trichloroacetic acid solution (20g/L): weigh 20g of trichloroacetic acid, add water to dissolve it and then dilute to 1,000mL.
3.2.4 Hydrochloric acid standard volumetric solution (0.1000mol/L) or sulfuric acid standard volumetric solution (0.1000mol/L): prepared in accordance with GB/T 601.
3.2.5 Hydrochloric acid standard volumetric solution (0.0100mol/L) or sulfuric acid standard volumetric solution (0.0100mol/L): prepared with hydrochloric acid standard volumetric solution (0.1000mol/L) or sulfuric acid standard volumetric solution (0.1000mol/L) before use.
3.2.6 Methyl red ethanol solution (1g/L): weigh 0.1g of methyl red, dissolve it in 95% ethanol and then dilute to 100mL with 95% ethanol.
3.2.7 Bromocresol green ethanol solution (1g/L): weigh 0.1g of bromocresol green, dissolve it in 95% ethanol and then dilute to 100mL with 95% ethanol.
3.2.8 Methylene blue ethanol solution (1g/L): weigh 0.1g of methylene blue and dissolve it in 95% ethanol and then dilute to 100mL with 95% ethanol.
3.2.9 Mixed indicator solution: mix 1 part of methyl red ethanol solution and 5 parts of bromocresol green ethanol solution for immediate use, or 2 parts of methyl red ethanol solution and 1 part of methylene blue ethanol solution for immediate use.
4 Apparatus
4.1 Balance: with a sensibility of 1mg.
4.2 Mixer.
4.3 Conical flask with stopper, 300mL.
4.4 Semimicro nitrogen determination device: as shown in Figure A.1.
4.5 Pipettes: 10.0mL, 25.0mL and 50.0mL.
4.6 Microburet: 10mL, with the minimum scale division of 0.01 mL.
5 Analysis procedures
5.1 Semimicro nitrogen determination device
Install the semimicro nitrogen determination device in accordance with Figure A.1. Clean and check the tightness of the device before use.
5.2 Specimen treatment
For fresh (frozen) meat, strip of skin, fat, bone and tendon and take lean meat; for fresh (frozen) seafood and aquatic products, strip of shell, skin, head, internal organs, bone and fishbone and take the edible parts; then grind and stir the specimen evenly respectively. For finished product: directly ground and evenly stir the specimen. Meat paste, meat powder, dried meat floss, fish flour, dried fish flour and liquid samples may be used directly. For preserve eggs in salt such as preserved eggs (century eggs) and salted eggs: have their eggshells and egg membranes removed, and then add water to make egg:water = 2:1, and then grind them by a mixer and evenly stir them into homogenate. Weight, to the nearest of 0.001g, 20g of specimen for fresh (frozen) samples, or 10g of specimen for dried products such as meat powder, dried meat floss, fish flour and dried fish flour; pipette 10.0mL or 25.0mL of liquid samples, place it in a conical flask with stopper, accurately add 100.0mL of water, shake the flask from time to time so that the specimen is evenly dispersed in the specimen solution, and filter it after dipping for 30min. Weight, to the nearest of 0.001g, 15g of egg homogenate for preserved eggs and salted eggs (in calculating the content, the mass of the specimen is the mass of egg homogenate multiplied by 2/3). Put it in a conical flask with stopper, accurately add 100.0mL of trichloroacetic acid solution, vigorously and fully shake it for 1min, and let it stand for 15min to make the protein precipitate and then filter it. The filtrate shall be used in time, and the filtrate that cannot be used in time shall be stored in the refrigerator at 0℃ ~ 4℃ for later use. The trichloroacetic acid solution may be used instead of water for special samples which are rich in protein colloid, sticky and difficult to filter. During distillation, 1 ~ 2 drops of silicon oil defoamer may be added to samples with more foam.
5.3 Determination
Add 10mL of boric acid solution and 5 drops of mixed indicator solution into the receiving flask, insert the lower end of the condenser tube below the liquid level, accurately pipette 10.0mL of filtrate, inject it into the reaction chamber via a test glass, wash the test glass with 10mL of water and make it flow into the reaction chamber, and then plug the rod-shaped glass stopper. Then inject 5mL of magnesium oxide suspension into the reaction chamber, immediately close the glass stopper, and add water to the test glass to prevent air leakage. Clamp the screw clamp and start distillation. After distillation for 5min, move the distillate receiving flask to make the liquid level leave the lower end of the condenser tube, and then distill for 1min. Then rinse the outside of the lower end of the condenser tube with a small amount of water, and remove the distillate receiving flask. Titrate with hydrochloric acid or sulfuric acid standard volumetric solution (0.0100mol/L) to the end point. Use the mixed indicator solution prepared by 1 part of methyl red ethanol solution and 5 parts of bromocresol green ethanol solution, and the end point color is purple-red. Use the mixed indicator solution prepared by 2 parts of methyl red ethanol solution and 1 part of methylene blue ethanol solution, and the end point color is blue-purple. Carry out the reagent blank test at the same time.
6 Expression of analysis results
The content of TVBN in the specimen shall be calculated using Formula (1):
Foreword I
1 Scope
2 Principle
3 Reagents and materials
4 Apparatus
5 Analysis procedures
6 Expression of analysis results
7 Precision
8 Reagents and materials
9 Apparatus
10 Analysis procedures
11 Expression of analysis results
12 Precision
13 Principle
14 Reagents and materials
15 Apparatus
16 Analysis procedures
17 Expression of analysis results
18 Precision
19 Detection limit
Annex A Diagram of semimicro nitrogen determination and distillation device
