The detection and determination of adulterants in turmeric using fourier-transform infrared (FTIR) spectroscopy coupled to chemometric analysis and micro-FTIR imaging

Like many herbs and spices, turmeric is at risk of fraud due to its high commercial value and soaring consumer demand. Turmeric powder in particular is prone to adulteration; therefore, fast and robust screening methods are required to detect this fraud. In the present study, both Fourier transform infrared (FTIR) coupled with chemometric analysis and micro-FTIR imaging have been successfully used to correctly identify authentic and spiked samples of turmeric. In terms of performance, 100% of typical turmeric in the validation set were predicted correctly. In relation to correct classification of the spiked samples, 98.75% were classified correctly as atypical, against the 2-class and multiclass models. For the micro-FTIR imaging method, selectivity was 0.94 for authentic samples and ranged from 0.6 to 1 for spiked turmeric samples. A survey of commercial turmeric samples was undertaken and the results from the FTIR analysis revealed that 20% of the samples were atypical. Twenty survey samples, both typical and atypical, were sent to an independent lab as part of a comparative study and the results demonstrated a good correlation between the two spectroscopic methods, with 80% of the samples returning the same result in both methods. The results demonstrate that spectroscopic methods can be successfully used to identify adulterated turmeric powder. Additionally, the results from the survey highlight the fraud problem in turmeric and demonstrate the need for reliable, rapid and robust screening methods to tackle this problem.