Authentication of saffron (Crocus sativus L.) using 1H nuclear magnetic resonance (NMR) spectroscopy

Abstract

Saffron, the dried stigmata of the plant Crocus sativus L., is a spice used for colouring and flavouring food. It is considered to be the most expensive spice, which can be explained by the laborious way the stigmata have to be harvested. There is a considerable profit to be made by adulterating saffron, e.g. by mixing it with other saffron plant materials such as flower petals and styles or other colouring plants such as safflower or turmeric. Another way of adulteration is to use artificial colours to falsify deteriorated natural material or complete imitation using coloured paper. Fifteen saffron samples (mostly from internet trade) were analysed using 1H nuclear magnetic resonance (NMR) spectroscopy for the saffron-specific colouring agents. Thirteen samples were found by NMR to consist of natural saffron material (as validated by microscopic analysis), but one sample was additionally (and illegally) coloured with tartrazine (E102). Two samples were complete frauds (coloured paper), and 8 samples had to be objected because of offences against mandatory food labelling requirements. NMR has been proven to be of higher versatility and specificity to detect saffron adulteration compared to traditionally applied techniques such as UV/VIS spectrophotometry or thin-layer chromatography. The nontargeted spectral “fingerprinting approach” is specifically advantageous to detect food fraud with previously unexpected substances. Due to the high quota of non-compliance, the importance to check saffron spices for authenticity must be stressed.