The use of a plant enzyme for rapid and sensitive analysis of naturally-occurring folates in food by liquid chromatography-tandem mass spectrometry

Petra Ložnjak*, Carolina García-Salinas, Rocío Isabel Díaz de la Garza, Anette Bysted, Jette Jakobsen

*Corresponding author for this work

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Abstract

A rapid, sensitive and reproducible method for analysis of naturally-occurring folates and folic acid in food has been developed and validated. A single-enzyme extraction step, in which a pure recombinant enzyme of plant origin (Arabidopsis thaliana) was used, enabled fast and reproducible deglutamylation during folate extraction within the incubation time of 1 h. Six commonly occurring folate forms (tetrahydrofolate, 5,10-methenyltetrahydrofolate, 10-formylfolic acid, 5-formyltetrahydrofolate, folic acid and 5-methyltetrahydrofolate) were detected and quantified in 9 min using liquid chromatography-tandem mass spectrometry (LC–MS/MS). 13C5-labeled 5-formyltetrahydrofolate, 13C5-labeled folic acid and 13C5-labeled 5-methyltetrahydrofolate were used as internal standards for the quantification. The method is described by a calibration curve (R2>0.99 and trueness 85–115%), a limit of quantification at 0.1 μg/100 g, trueness at 80–120% in spiked samples and certified reference materials, and a precision <10%. However, the precision in quantification of tetrahydrofolate was not within the acceptable limits due to the lack of use of the corresponding internal standard. An interconversion study of unstable formyl forms was performed which showed that 50% of 5,10-methenyltetrahydrofolate is converted to 5-formyltetrahydrofolate during the analysis. The developed LC–MS/MS method is a candidate for a future standard method for folate analysis in food.
Original languageEnglish
JournalJournal of Chromatography A
Volume1594
Pages (from-to)34-44
ISSN0021-9673
DOIs
Publication statusPublished - 2019

Keywords

  • Extraction
  • Folates
  • Food
  • Interconversion
  • LC–MS/MS
  • Plant enzyme

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