Origins of the difference between food folate analysis results obtained by LC–MS/MS and microbiological assays

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• 作者：Christiane Ringling ; Michael Rychlik
• 关键词：Liquid chromatography–tandem mass spectrometry ; Food folate ; Stable isotope dilution assay ; Microbiological assay ; Oxidation product of 5 ; methyltetrahydrofolate ; MeFox
• 刊名：Analytical and Bioanalytical Chemistry
• 出版年：2017
• 出版时间：March 2017
• 年：2017
• 卷：409
• 期：7
• 页码：1815-1825
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Analytical Chemistry; Biochemistry, general; Laboratory Medicine; Characterization and Evaluation of Materials; Food Science; Monitoring/Environmental Analysis;
• 出版者：Springer Berlin Heidelberg
• ISSN：1618-2650
• 卷排序：409

文摘

To investigate the often reported disagreement in food folate quantitation between the microbiological assay and high-performance liquid chromatography methods, different foods were analyzed both by a microbiological assay and by a liquid chromatography–tandem mass spectrometry (LC–MS/MS) method. For the LC–MS/MS analysis we emphasize the need for complete deconjugation of polyglutamic folate forms. Moreover, our results revealed no need for an additional enzyme treatment except in the deconjugation step. To check the efficiency of deconjugation without additional sample preparations, the amount of diglutamates was quantified and samples were screened for additional polyglutamates. A thorough investigation of a substance with a polyglutamate chain deconjugated like the folates revealed that it was an oxidation product of 5-methyltetrahydrofolate, a pyrazino-s-triazine called MeFox in previous reports. The latter is not microbiologically active and, therefore, does not contribute to the amount of total folates. But we found it is commonly present in foods, especially in those low in ascorbic acid. The microbiological assay showed different responses to the single vitamers. Therefore, it was necessary to perform calibration with the folate that had the highest portion in the folate distribution. The investigations showed that both methods can provide similar results when they both include a deconjugation step. This is particularly important for LC–MS/MS but probably also for the microbiological assay. Additionally, consideration of the folate distribution was found to be crucial for the accurate calibration of the microbiological assay.