Rice is one of the staple foods that people eat every day. Its protein content is about 7%~9%. The protein content in rice directly affects the hardness of rice. The higher the protein content, the stronger the hardness of rice and the close relationship between protein and human health. The detection of protein content in food can be measured and analyzed using a nitrogen analyzer. Rice can also be used. This article describes in detail the steps for determining the protein content and the calculation of the results using a nitrogen analyzer.
Weighed m g of rice sample (about 0.65g), placed in a dry 250mL nitrogen fixed bottle, added 0.2g copper sulfate, 6g potassium sulfate and 20mL concentrated sulfuric acid, from the first method of GB/T5009.5-2003, test The sample was completely digested and transferred into a 100 mL volumetric flask, and made up to volume with distilled water. Pipette 50 mL of the sample treatment solution into a fixed nitrogen distillation apparatus, add 50 mL of sodium hydroxide solution (400 g/L), and boric acid solution (20 g/L) 50 mL. As an absorbing liquid, 3 drops of methyl red-methylene blue indicator solution were added, distilled, and titrated with c(1/2H2SO4)=0.04526 mol/L sulfuric acid standard titration solution, and a blank test was carried out, and corrected in the results.
Calculation formula: X=(V1-V2)×c×0.0140m×V50/V100×100(1)
Where: X—the amount of protein in the sample (in terms of nitrogen), unit: g/100g
V1—The volume of the standard titration solution of sulfuric acid consumed by the sample, unit: mL
V2—reagent blank consumption volume of sulfuric acid standard titration solution, unit: mL
C—the concentration of the standard titration solution of sulfuric acid, unit: mol/LV50—removed the volume of the sample digestive solution with a 50 mL pipette, unit: mL
V100—The volume of the digestive solution of a sample fixed to volume with a 100 mL volumetric flask, unit: mL
M—mass of the sample, unit: g0.0140~1.0mL sulfuric acid [c(1/2H2SO4)=1.000mol/L] The mass of the equivalent titration solution of the nitrogen, unit: g