Commentary on method for detection of menaquinone-7 in dietary supplements

Szterk et al. (Food Chemistry 243 (2018) 403-409) have recently analyzed the content of menaquinone-7 (MK-7) in eight dietary supplements. The authors concluded that five out of eight were below the declared content. For all samples, the authors used tetrahydrofuran (THF) to extract MK-7 prior to analysis. Two of the tested products that were below the declared content were microencapsulated MK-7 which had a coating with limited solubility in THF. By dissolving the coating with water and ethanol prior to extraction with ethyl acetate, all MK-7 will be made accessible prior to analysis by HPLC. We have repeated the analysis of the two microencapsulated products that Szterk et al. claimed were below the declared content, and have shown they contain 102% and 105% of the label claim. Since Szterk et al. have used a solvent that does not dissolve the coating on microencapsulated MK-7, their conclusion is not justified and is thus misleading.