The Rapid Detection of Sage Adulteration Using Fourier Transform Infra-Red (FTIR) Spectroscopy and Chemometrics

Background: Sage, a common term for the various species of the genus Salvia L., is an herb that is mainly used as a seasoning, or for medicinal purposes. Valuable herbs such as sage, are under constant threat from criminals dealing in economically motivated adulteration. Objective: In this study, the development of a rapid screening technique to detect adulteration in sage was developed using FTIR and chemometrics. Method: A range of sage samples were collected, along with possible known adulterants, olive leaves, myrtle leaves, sumac, hazelnut leaves, cistus and phlomis, strawberry tree leaves and sandalwood. The samples were analyzed on the Thermo Nicolet iS5 FTIR with iD7 attenuated total reflectance accessory and diamond crystal. Chemometric techniques were applied to convert this raw spectral data obtained from the instrument into qualitative models. The qualitative chemometric models for adulteration detection were obtained using principal component analysis and orthogonal partial least squares-discriminant analysis following preprocessing of the spectra. Results: The orthogonal partial least squares-discriminant analysis models had a measurement of fit of 0.978 and 0.952 and a measurement of prediction of 0.975 and 0.936 for binary and multiclass models, respectively. The receiver operating curves following external validation had an area under the curve of 1, indicating excellent method performance. Conclusions: The use of FTIR and chemometrics can potentially screen unknown sage samples for adulteration and can be used in the fight against fraud in the herb and spice industry.