New NMKL-method: Total folate in food by LC-ESI-MS/MS. Quantification of 6 folate vitamers.
The standardized analytical method for folate in food has traditionally utilized quantification by a microbiological assay, a method that cannot distinguish between the different folate vitamers. This new NMKL method enables quantification of total folate based on quantification of six folate vitamers which contribute to the main folate activity. Besides providing the information about the content of the specific folate vitamers, the method includes fast extraction of folates from food that may be carried out within eight hours.
The essential part of the method is using a pure γ-glutamyl hydrolase, which enables efficient and fast break-down of the polyglutamates to monoglutamates. LC-ESI-MS/MS quantifies monoglutamates by use of 13C5-labelled internal standards.
A collaborative study was conducted in summer 2019 with participation of eight laboratories from seven European countries. The method has been successfully validated for total folate determination in strawberries, spinach, lentils, yogurt, liver and infant formula, providing acceptable Horwitz ratio values (0.60-1.94). The results are published in Food Chemistry (Ložnjak Švarc, P; Oveland, E; Strandler, HS; Kariluoto, S; Campos-Giménez, E; Ivarsen, E; Malaviole, I; Motta, C; Rychlik, M; Striegel, L; Jakobsen, J (2020): Collaborative study: Quantification of total folate in food using an efficient single-enzyme extaction combined with LC-MS/MS. Food Chemistry, 333, 127447).