A simple paper-strip colorimetric method utilizing dehydrogenase enzymes for analysis of food components

Abstract

In this study, we present a simple chromatographic paper-based colorimetric assay for the analysis of selected food compounds. The biochemical principle utilises enzymes from the dehydrogenase family coupled with diaphorase in the presence of a tetrazolium dye, MTT, and NAD⁺. The colored reaction product that developed on the surface of the chromatography paper could either be qualitatively analysed by the naked eye, that is, it could be used for screening analysis, or it could be recorded by using a smartphone camera and evaluated in freeware ImageJ in order to obtain data for quantitative analysis. The general concept was demonstrated and optimised using (L)-glutamate dehydrogenase and the versatility of the proposed method was illustrated by using other enzymes from the dehydrogenase family. The linear range for (L)-glutamate was found to be 0.5–5.0 mmol L⁻¹ using the digital image method. The limit of detection found by the naked eye was 0.05 mmol L⁻¹ and 0.028 mmol L⁻¹ by digital imaging. The paper assay stored in a freezer provided a reproducible response for at least 6 weeks. This research presents the successful modification of an MTT-cell viability test principle and its use in the fabrication of an inexpensive, easy to prepare, simple to use, portable and rapid-responding paper-based assay.