| With the improvement of people’s living standard, milk has become more and more important in people’s daily life. In recent years, since food safety incidents of domestic milk powders occurred frequently, consumers begin to lose confidence in domestic milk powder. With the advent of economic globalization, foreign milk powder gradually dominated the high-end milk powder market in China. How about the quality of the domestic milk powder? This is the meaning of the experiment. Vitamin is an important indicator of measuring quality of the powdered milk, so this paper takes domestic milk powder as material of this experiment, studied extraction, UPLC detection condition of vitamins of 10 kinds of domestic milk powders, and analyse the nutritional value of domestic milk powder. The purpose of this experiment is to develop a method to simultaneous determine water-and fat-soluble vitamins in milk powder. The method is simple, fast, few solvent, few sample, low cost, environmental protection, automation and reliable. The details are as follows:1. Firstly, the UPLC condition to detect 4 kinds of water-soluble vitamins standard was optimized in the experiment. Suitable chromatographic column, mobile phase, flow-rate, temperature and pH were chosen to establish a UPLC detection method for the target. The suitable UPLC condition were Acquity UPLC BEH (2.1 ×100 mm,1.7μm, Waters company) C18 column, a mobile phase of methanol-water (15:85, V/V),5 mM/L octanesulfonic acid,0.5% triethylamine, with 2.4% glacial acetic acid at pH 3.5, temperature 40℃, and a flow rate of 0.3 ml/min. Under the condition of optimized HPLC, 4 kinds of vitamin was separated well, the correlation coefficients were greater than 0.999. The limits of detection were 0.00008-0.00043 mg/L. In the experiment, solvent was optimized for suitable polarity and the minimum area of solvent peak. The sample preparation method was that the sample was extracted with 4% trichloroacetic acid, then was centrifuged and filtered. The extraction was transferred to a 25 ml volumetric flask and the volume was filled with 4% trichloroacetic acid. The acid extract was filtered through a 0.45 um filter prior to UPLC analysis. In the recovery experiment, a majority of domestic milk powders gave satisfactory recoveries (from 80 to 109.0%). The method was proven to repeat with RSDs lower than 2.54%.2. Secondly, this study of simultaneous determination of 7 kinds of water-and fat-soluble vitamins in milk powder by UPLC has explored on the basis of the study of determination of 4 kinds of water-soluble vitamins in milk powder by UPLC. Water-and fat-soluble vitamins were separated on Acquity UPLC BEH (2.1Τ100 mm,1.7 μm, Waters company) C18 column in a single run using linear gradient elution with a mobile phase consisting of 0.010 trifluoroacetic acid of pH 4.0 and methanol (HPLC-grade) at the flow rate 0.2 ml/min. Under the condition of optimized UPLC,7 kinds of water- and fat-soluble vitamins was separated well, the correlation coefficients were greater than 0.999. The limits of detection were 0.0018～0.0120 mg/L. In the experiment, solvent was optimized for suitable polarity and the minimum area of solvent peak. The sample preparation method was that the sample was extracted with solution consisted of 0.010% trifluoroacetic acid:methanol (50:50, V/V), then was centrifuged and filter. The extraction was transferred to a 25 ml volume tricflask and the volume was filled with solution consisted of 0.010% trifluoroacetic acid:methanol (50:50, V/V). The acid extract was filtered through a 0.45 μm filter prior to UPLC analysis. In the recovery experiment, a majority of domestic milk powders gave satisfactory recoveries (from 79.0 to 109.6%). The method was proven to repeate with RSDs lower than 2.59%.3. Finally, making use of the variety and content of vitamins of all kinds of domestic milk powders as index, is to study the quality of the domestic milk powder. The result shows that the content and variety of vitamins of MN and YL milk powders are superior to YX brand milk powder, and MN and YL milk powders pay more attention to add vitamins to meet the needs of different consumers. |
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