This standard applies to the determination of crude protein in fruit and vegetable products. GB/T 8856-1988 Method for determination of crude protein in fruit and vegetable products GB/T8856-1988 Standard download decompression password: www.bzxz.net
This standard applies to the determination of crude protein in fruit and vegetable products.

National Standard of the People's Republic of China
Method for determination of crude protein in fruit and vegetable productsUDC634.1/635
GB8856—88
This standard adopts the international standard ISO1871-1975 "General description of the determination of nitrogen content in agricultural foods by Kjeldahl method". Scope of application
This standard applies to the determination of crude protein in fruit and vegetable products. 2 Reference standards
GB5009.5—85 Method for determination of protein in food 3 Principle
Use sulfuric acid to digest organic matter in the presence of a catalyst to convert organic nitrogen into ammonia nitrogen. Alkaline distillation, and use boric acid solution to absorb ammonia. Titrate with hydrochloric acid standard solution. The result multiplied by the protein conversion factor of 6.25 is the crude protein content. 4 Reagents
All reagents are analytical grade and are prepared with distilled water without ammonia. 4.1 Copper sulfate.
4.2 Potassium sulfate.
4.3 Sulfuric acid.
4.42% boric acid solution (m/V).
4.5 Mixed indicator solution: 1 part of 0.1% methyl red ethanol solution and 5 parts of 0.1% bromocresol green ethanol solution are mixed before use. Or 2 parts of 0.1% methyl red ethanol solution and 1 part of 0.1% methylene blue ethanol solution are mixed before use. 4.640% sodium hydroxide solution (m/V).
4.70.05N hydrochloric acid standard solution.
5 Apparatus
Nitrogen determination distillation apparatus: as shown in the figure.
Approved by the Ministry of Commerce of the People's Republic of China on February 29, 1988 112
Implemented on July 1, 1988
6 Operating method
GB8856-88
Nitrogen determination distillation apparatus
1-500mL nitrogen determination bottle; 2-nitrogen determination distillation ball; 3-throttling clamp; 4-bucket; 5-condenser; 6-receiving bottle 6.1 Sample treatment: Weigh 0.5-2g solid sample or 2-8g semi-solid sample with an accuracy of 0.001g, or accurately pipette 5-15mL liquid sample (equivalent to approximately 20-40mg nitrogen) and transfer it into a dry 500mL nitrogen determination bottle, add 0.5g copper sulfate, 5g potassium sulfate and 20mL sulfuric acid, mix thoroughly, put a small funnel at the mouth of the bottle, and support the bottle at an angle of 45° on an asbestos net with small holes. Heat carefully until all the contents are carbonized and the foam disappears completely. Increase the fire and keep the liquid in the bottle slightly boiling until the liquid turns transparent blue-green. Continue heating for 30 minutes. Remove and cool. Carefully add 200mL of water and cool again. Add an appropriate amount of boiling aid (such as granular pumice). 6.2 Add 25mL of 2% boric acid solution and 5 drops of mixed indicator solution to the receiving bottle. Connect the distillation device and insert the outlet of the condenser under the surface of the boric acid solution. Loosen the throttle clamp, pour 70-80mL of 40% sodium hydroxide solution through the funnel, rotate the nitrogen determination bottle, mix the contents, pour in 100mL of water, clamp the throttle clamp, heat and distill until the ammonia is completely evaporated, and collect about 150mL of distillate (within 30 minutes). Remove the condenser from the liquid surface, distill for another 1 minute, and stop heating. Rinse the outside of the lower end of the condenser with a small amount of water. Remove the receiving bottle and titrate with 0.05N hydrochloric acid standard solution until gray or blue-purple is the end point. Perform a reagent blank test at the same time.
6.3 Calculation
Where: X
(V/-V,) XNX0. 014 ×F × 100m
The content of crude protein in the sample, %;
The volume of hydrochloric acid standard solution consumed by the sample, mL; The volume of hydrochloric acid standard solution consumed by the reagent blank, mL; The equivalent concentration of the hydrochloric acid standard solution;
The number of grams of nitrogen equivalent to 1mL of 1N hydrochloric acid standard solution; -The mass (or volume) of the sample, g (or mL); Protein conversion factor, 6.25.
6.4 Result
GB885688
If the repeatability requirements are met, take the arithmetic mean of the two determinations as the result. The result is accurate to 0.01% (m/m). 6.5 Repeatability
The relative error of the results of two simultaneous or consecutive determinations by the same analyst should not exceed 5%. Additional Notes: www.bzxz.net
This standard was proposed by the Bureau of Subsidiary Foodstuffs of the Ministry of Commerce of the People's Republic of China. This standard was drafted by the Food Testing Institute of the Ministry of Commerce. The main drafters of this standard were Rao Zeqing and Yang Cuiqiao. 114
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