Determination Of Organic Selenium And Total Selenium Contents In Selenium-enriched Food By Ultrasound Extraction-microwave Assisted Digestion-atomic Fluorescence Spectrometry

Background&Objective:Selenium?Se?is one of the essential trace elements in human and animals.Selenium is an important component of glutathione peroxidase?GSH-Px?,the strongest antioxidant enzyme in human body.Selenium deficiency can cause a decrease in GSH-Px activity,which leads to a weakened ability of tissue cells to resist oxidative damage,directly affecting cell division,reproduction,inheritance and growth,thereby interfering with the synthesis and metabolism of nucleic acids,proteins,polysaccharides and enzymes.Epidemiological studies have shown that selenium is associated with more than 40 diseases such as Keshan disease,cancer,cardiovascular disease,cataract,diabetes and AIDS.The human body cannot synthesize selenium by itself,and can only rely on the food contained selenium.Selenium comes from soil and grains,meat and seafood.It is generally believed that the low level of selenium in the soil is the main cause of selenium deficiency in human body.There is no specific drug for clinical treatment.Nutritionists suggest that supplementing selenium-containing foods through daily diet can maximize the damage caused by selenium deficiency. Selenium-containing health food is the best selenium supplement food.There are many kinds of selenium-containing health foods currently on the market,but there are also large differences in toxicity and biological activity due to their different valences and forms.The valence state of selenium in inorganic selenium is mainly in the form of tetravalent and hexavalent,such as Na₂SeO₃,CaSeO₃,Na₂SeO₄.Since inorganic selenium exists in an oxidized state,it can be reduced to selenide after passive absorption,and gradually converted into soluble selenomethionine selenium.The valence state of selenium in organic selenium is usually in the form of negative divalent,ie,selenocyst.The reduced form of lysine and selenomethionine can be absorbed by the active form of the intestine.Therefore,compared with inorganic selenium,inorganic selenium has the defects of weak biological activity,strong toxicity,low absorption rate and large environmental pollution.At present,China National Health and Family Planning Commission and the United Nations Food and Drug Administration issued in April 2017 and implemented in October 2017,"GB 5009.93-2017 national food safety standards for the determination of selenium in food"only detects the total selenium in food,that is,detecting organic selenium and inorganic selenium in food,intentionally or unintentionally confusing the function of organic selenium and inorganic selenium infood.Seriously misled consumers.How to identify and evaluate the quality and safety of health foods has become a focus of food quality evaluation.To provide a scientific theoretical basis for the research on the high availability and biosafety of human selenium sources,it is necessary and urgent to explore a method for detecting organic selenium in foods.Methods:According to the characteristics of the fluorescence of the characteristic wavelength emitted by the selenium atom from the reduction of hexavalent selenium to tetravalent,the atomic fluorescence spectrophotometer was used to establish the method of atomic fluorescence spectrometry?AFS?for the determination of selenium in 15batches selenium-rich health food.Explore the sample pretreatment method and the atomic fluorescence chromatographic system conditions to determine the best treatment method and detection method.Results:15 batches selenium-rich health food samples were extracted by 2 kinds of organic solvents,toluene and cyclohexane.The organic selenium content of 2 methods had no differences?P>0.05?,and cyclohexane was selected as the extraction organic solvent.15 batches selenium-rich health food samples were extracted by classical separatory funnel extraction method and ultrasonic extraction method.Compared with the classical separatory funnel extraction method,the content of organic selenium extracted by ultrasonic was higher?P>0.05?.Ultrasonic extraction of cyclohexane was selected as the extraction method.15 samples were digested by wet digestion and microwave digestion,respectively.Compared with the wet digestion,the organic selenium and the total selenium content in the microwave digestion method were higher?P<0.05?.When the concentration of NaBH₄ was 20 g/L,the fluorescence intensity of selenium reached the peak.When the volume fraction of HCl was between 5%and 15%,the fluorescence value tended to the highest level and stable.The volume fraction of 5%HCl was used as the carrier fluid.The standard curve of selenium is Y=159.14X+27.5,the linear range is 0¹20g/L,the correlation coefficient is 0.999,and the detection limit is 0.008?g/L.The precision relative standard deviation?RSD?of the selenium standard solution was 2.09%,the stability test RSD was 2.96%,the repeatability test RSD was1.59%,the sample recovery was 95.1%-106.2%,and the RSD was 3.19%.Atomic fluorescence spectrometry conditions:lamp current:100 mA,negative high voltage:340V,atomization temperature:800?,quartz furnace height:8 mm,carrier gas argon flow:500 ml/min,shielding gas argon flow?1000 ml/min,current carrying:5%HCl,reducing agent NaBH₄:15.0 g/L.Determination of organic selenium and total selenium in 15 batches of selenium-enriched health foods.The content of organic selenium ranged from 13.80 mg/kg to 4.85 mg/kg,and the total selenium content ranged from 5.42 mg/kg to 6.86 mg/kg,the percentage of organic selenium in total selenium ranged from 59.61%to 73.79%.Conclusion:The determination of organic selenium and total selenium in selenium-rich health food by hexane-ultrasonic extraction-microwave digestion-atomic fluorescence spectrometry has the advantages of low toxicity,good reproducibility,sensitivity and simplicity,and is suitable for determination of organic selenium and total selenium in selenium-enriched foods.