introduction
As one of the three major energy-enhancing nutrients of the human body, fat has many important physiological effects on the human body. More than 90% of fats and oils are fatty acids, and fatty acids are divided into saturated fatty acids, monounsaturated fatty acids and polyunsaturated fatty acids. The n-6 and n-3 fatty acids contained in polyunsaturated fatty acids are essential fatty acids that cannot be synthesized by the human body and must be obtained from food.
In addition to the influence of congenital factors and early education, the development of physique, intelligence and behavior of infants is also closely related to the nutritional status of the day after tomorrow. The results of Japanese nutrition expert Iino's research show that more than 80% of children's brain development depends on nutrition. Among the many nutrients, the close relationship between fatty acids and intellectual development is recognized by the academic community. Associate Professor of the Department of Nutrition and Food Safety, College of Food Science, China Agricultural University, said: "When paying attention to the reasonable intake of dietary fat, you must consider the combination of various fatty acids. The appropriate proportion of fatty acid intake can reduce obesity, The risk of cardiovascular disease and the development of the brain and vision of the fetus, infants and young children." Therefore, the composition of fatty acids in infant foods has attracted people's attention. The Ministry of Health issued the national food safety standard "GB 5413.27-2010" in 2010. Determination of fatty acids in infant foods and dairy products [1] , specifies the method for the determination of fatty acids. This method is based on the first method in the standard method for the determination of fatty acids in infant foods and dairy products by gas chromatography.
Experimental part
Main equipment and reagents
Instruments: Gas Chromatograph, Trace 1310, ThermoFisher, USA. Reagents: Sodium carbonate solution, accurately weigh 6 g of anhydrous sodium carbonate, dissolve in water and dilute to 100 mL; toluene, chromatographically pure; acetyl chloride methanol solution: Measure 40 mL of methanol in 100 mL dry beaker, accurately absorb 5.0 mL of acetyl chloride was slowly added dropwise, continuously stirred, cooled and transferred to a 50 mL dry volumetric flask; fatty acid methyl ester mixed standard solution, 100 mg/L.
Gas chromatographic conditions: column TR-FAME, 100m, 0.25mm, 0.20μm (P/N: 260M238P, S/N: 0036515); the column temperature was programmed to be as follows: 60 ° C (for 1 min); 20 ° C / min To 160 ° C, hold for 2 min, 4 ° C / min to 240 ° C (for 15 min). The carrier gas was high purity nitrogen (purity 99.999%); the flow rate was 1.0 mL/min. The inlet is an SSL inlet, temperature: 260 ° C, injection mode split, split ratio, 10:1. Detector temperature: 280 ° C, hydrogen 35 mL / min, air 350 mL / min, tail gas nitrogen 40 mL / min.
Sample preparation method
Weigh 0.5 g of the sample to be tested in a 15 mL dry screw glass tube, add 5.0 mL of toluene, add 6.0 mL of 10% acetyl chloride methanol solution, tighten the screw cap, shake and mix, and place in a water bath at 80 ° C ± 1 ° C. h, shake out once every 20 minutes, take out after cooling in water bath and cool to room temperature. Transfer the reacted sample solution to a 50 mL centrifuge tube, clean the glass tube three times with 3.0 mL sodium carbonate solution, combine the sodium carbonate solution into a 50 mL centrifuge tube, mix and centrifuge at 5000 rpm for about 5 min. The supernatant was taken as a test solution and measured by a gas chromatograph.
Sample determination
In the above-mentioned derivatized sample, the concentration range of the analyte is wide, and the sample is directly injected, diluted 10 times, and 100 times, and then separately injected, and each component is quantified by a sample suitable for the dilution factor. Detected with a new generation of Trace 1310 gas chromatograph from Thermo Scientific with an FID detector. The fatty acid methyl ester derived from the sample can be qualitatively analyzed by retention time, and the peak area is quantified by external standard method.
Results and discussion
Chromatogram and linear range of standard samples
The chromatogram of the 37 fatty acid methyl esters in the standard sample is shown in Figure 1. 37 The World leader in serving science The retention time and name of fatty acid methyl esters are listed in Table 1 using standard samples to prepare total concentrations of 20 μg/mL, 40 μg/mL, 100 μg/mL, 200 μg/mL, respectively. 400 μg/ml series standard working solution, inject 1 μL, and then perform GC-FID measurement according to the above-mentioned measurement method. The concentration of the standard substance is plotted on the abscissa, and the peak area of ​​each standard substance is plotted on the ordinate. The curves, the linear correlation coefficients of the various fatty acid methyl esters are listed in Table 1. The detection limits were calculated at 3 times the signal-to-noise ratio and the results are shown in Table 1.
Actual sample determination
The fatty acid content of five samples of soybean powder, soy milk powder, milk powder I, rice flour and milk powder II was determined by the method. The spectrum of the determination is shown in Fig. 2. The results of each test are shown in Table 2.
C22: 6 ns is docosahexaenoic acid (DHA), C20:5 is Eicosa Pentaenoic acid (EPA), and C20: 4n6 is Arachidonic acid (ARA). Studies have shown that DHA is good for the baby's brain and eyes. The content of DHA in optic nerve cells and retinal tissues is as high as 40%-47%. If DHA is absent in food, the content of DHA in retinal tissue can be decreased, resulting in decreased vision. These three fatty acids are added to most infant formulas, and studies have shown that these three fatty acids play a key role in infant intelligence and vision development. The results of this study indicate that the content of these three fatty acids in infant formula is significantly higher than other foods. ,
in conclusion
Fatty acid in infant foods is produced by methyl acetyl chloride methanol methyl esterification method, extracted with toluene and then determined by gas chromatography. The method is simple in operation and good in reproducibility. 37 kinds of fatty acid methyl esters are well separated by using a 100m special column for fatty acid methyl ester analysis. Thermo Fisher Scientific's Trace1300 Series Gas Chromatograph is used for the determination of fatty acid methyl esters in infant foods with high sensitivity and accurate results.
references
[1] GB 5413.27-2010 Determination of fatty acids in infant foods and dairy products
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