Time-of-Flight Secondary Ion Mass Spectrometry Coupled with Unsupervised Methods for Advanced Saffron Authenticity Screening

Abstract

Saffron, renowned for its aroma and flavor, is susceptible to adulteration due to its high value and demand. Current detection methods, including ISO standards, often fail to identify specific adulterants such as safflower or turmeric up to 20% (w/w). Therefore, the quest continues for robust screening methods using advanced techniques to tackle this persistent challenge of safeguarding saffron quality and authenticity. Advanced techniques such as time-of-flight secondary ion mass spectrometry (TOF-SIMS), with its molecular specificity and high sensitivity, offer promising solutions. Samples of pure saffron and saffron adulterated with safflower and turmeric at three inclusion levels (5%, 10%, and 20%) were analyzed without prior treatment. Spectral analysis revealed distinct signatures for pure saffron, safflower, and turmeric. Through principal component analysis (PCA), TOF-SIMS effectively discriminated between pure saffron and saffron adulterated with turmeric and safflower at different inclusion levels. The variation between the groups is attributed to the characteristic peaks of safflower and the amino group peaks and mineral peaks of saffron. Additionally, a study was conducted to demonstrate that semi-quantification of the level of safflower inclusion can be achieved from the normalized values of its characteristic peaks in the saffron matrix.

Keywords: PCA; TOF-SIMS; adulteration; authenticity; mass spectrometry; multivariate analysis; safflower; saffron; spices; turmeric.

Figure 1

Positive TOF-SIMS spectra of pure saffron (red), safflower (green), and turmeric (blue) are shown in regions (a) 20–240 m/z and (b) 240–940 m/z with individual intensity scales. For visual clarity, the regions above 120 u.m.a and above 700 u.m.a are multiplied by 10 consecutively. The chemical structures of the crocin1 molecule, as well as the curcumin molecule and the putative fragmentations, are presented in the red and blue spectra, respectively.

Figure 2

PC1 (93%) vs. PC2 (5%) score plot of pure saffron (green) and saffron adulterated with 20% safflower (blue) and 20% turmeric (red). The colored ellipses around the points define the 95% confidence limit for each sample group.

Figure 3

Loading plots of (a) PC1 and (b) PC2 score plots for TOF-SIMS spectra of pure saffron and saffron adulterated with 20% safflower and 20% turmeric.

Figure 4

PC1 vs. PC2 score plot of pure saffron (green), saffron adulterated with safflower (blue), and with turmeric (red). The ellipses around the points define the 95% confidence limit for each sample group.

Figure 5

Variation in the characteristic peaks of safflower in the adulterated saffron samples at 5% (Saf 95:5 Saffl), 10%(Saf 90:10 Saffl), and 20%(Saf 80:20 Saffl) and in pure safflower (Saffl 100) presented (a) by overlaying their normalized mass spectra and (b) comparing the variation in the 4 major peaks’ intensities with safflower % in the samples.