Colorimetric Sensing of Putrescine and Cadaverine Using Ninhydrin as a Food Spoilage Detection Reagent

A simple colorimetric method is demonstrated for the quantitative detection of aliphatic biogenic amines, putrescine and cadaverine using ninhydrin. The protocol is based on the formation of a complex equivalent to that of Ruhemann's purple with a molar ratio of 1:2.5 between putrescine and ninhydrin which exhibited an absorption peak at 564 nm. The observation was theoretically verified using density functional theory (DFT). It is observed that the colorimetric detection protocol was rapid at 80 degrees C. Putrescine and cadaverine exhibited a similar colour on reaction with ninhydrin at pH 8.0, since the structure of both the biogenic amines is quite similar except for an addition of a methylene group, a distinguishable colour change was not observed. The analytical response was studied at 564 nm and 570 nm for putrescine and cadaverine respectively. Putrescine exhibited a linear range of 25-150 ppm, while cadaverine showed a non-linear range of 35-150 ppm. The detection limit for putrescine and cadaverine was observed to be 10 ppm and 40 ppm respectively. The specificity of the method was tested employing nine amino acids in comparison with that of aliphatic biogenic amines. Graphical