Near infrared spectroscopy coupled to MCR-ALS for the identification and quantification of saffron adulterants: Application to complex mixtures

Abstract

The adulteration of saffron, due to its high market value, is an old and common practice. Hence, there is a high demand for rapid, easy-to-go, environmentally friendly and low-cost techniques able to perform the simultaneous identification and quantification of saffron adulterants. In this sense, the goal of this work was to use near infrared (NIR) spectroscopy coupled to multivariate curve resolution – alternating least-squares (MCR-ALS) for the identification and quantification of four common adulterants (onion, calendula, pomegranate and turmeric). A total of 38 samples containing all these adulterants were prepared. Several spectral regions and pre-processing techniques were tested in the calibration models to find the best combination. The application of MCR-ALS allowed the identification of the adulterants present in the samples through the comparison between the spectral profiles recovered by MCR-ALS and the respective spectra of pure adulterants. Additionally, the quantification of the adulterants was also successfully achieved in these complex samples with relative percentage errors in concentration predictions (RE) of around 10%, except for onion. Overall, the results obtained in this work demonstrate the suitability of NIR spectroscopy coupled to MCR-ALS analysis to identify and quantify adulterants in a very complex mixture and at low levels. To the best of our knowledge, it was the first time that NIR spectroscopy and MCR-ALS were coupled to simultaneously identify and quantify four adulterants in saffron samples.