Determination of nitrogen content in egg yolk lecithin by Kjeldahl nitrogen analyzer

1 Preface

Egg yolk lecithin is a mixture of phospholipids, mainly composed of phosphatidylcholine（PC）， Therefore, its physiological function is mainly based on the function of PC. The nitrogen (N) content of egg yolk lecithin should be between 1.75% and 1.95%. Egg yolk lecithin is highly sensitive to heat and easily hydrolyzed under acidic, alkaline, and esterase conditions. Prohibited for individuals with protein and egg yolk allergies. Used for emulsifiers, liposome membrane materials, food industry, etc^[1]According to most reports,PC can inhibit serum triglycerides and total cholesterol, while increasing high-density lipoprotein. This experiment refers to the determination of egg yolk lecithin using the 0704 nitrogen determination method specified in the 2020 edition of the Chinese Pharmacopoeia^[2].

2 Sample Information

Ingredients: egg yolk or egg powder，Sample Name:Egg yolk lecithin

3 Instruments and Reagents

3.1 instrument

SKD-1000 fully automatic Kjeldahl nitrogen analyzer, SKD-20S2 infrared quartz digestion furnace, analytical balance, etc

3.2 reagent

Sulfuric acid (analytical grade),20g/L boric acid solution, bromocresol green methyl red mixed indicator, 400g/L sodium hydroxide solution, copper sulfate potassium sulfate mixed catalyst, 0.1mol/L sulfuric acid standard titrant.

4 Experimental Method

4.1 sampling

取Add 5g of copper sulfate potassium sulfate mixed catalyst to a sample of about 0.1g (accurate to 0.1mg), and then add 10ml of concentrated sulfuric acid.

Blank with the same catalyst and concentrated sulfuric acid.

4.2 Pre digestion treatment

Place the digestion tube with added samples and reagents on the digestion furnace, cover the waste discharge device, and set the parameters of the infrared quartz digestion furnace as shown in the table As shown in Figure 1:

table1. Digestive furnace parameter settings

4.3 test

After digestion is complete, wait for the digestion tube to cool to room temperature before removing it for later use. Check whether the reagents of the nitrogen analyzer are sufficient, and at the same time, blank the instrument. After the instrument blank is stable, the digested sample can be tested on the machine. The parameter settings of the nitrogen analyzer are shown in the table As shown in Figure 2:

tableParameter settings for nitrogen analyzer 2

5 Results and Discussion

5.1 experimental results

Selected for the experimentEgg yolk phospholipidsThe sample was digested, distilled, and titrated, and the experimental results are shown in the tableAs shown in Figure 3:

table3 Experimental results

5.2 empirical conclusion

The egg yolk phospholipids tested this timenitrogenThe content is1.80395%The RSD value is0.3258%The test results are lower thanNational standard requirements for Kjeldahl nitrogen analyzerRSD≤0.5%The indication error is0.5853%, less than the national standard requirement of ≤ 1% for Kjeldahl nitrogen analyzer,Indicating that the egg yolk contains phospholipidsSample nitrogenQualified content^[3].

6 References

[1]Guan Zhiyu. Pharmaceutical excipients and packaging materials[J] China Medical Science and Technology Press, 2017 (01): 21.

[2]Chinese Pharmacopoeia（2020 version）General Rule 0704

[3]GBT 33862-2017 Fully (Semi) Automatic Kjeldahl Nitrogen Analyzer [S]