Non-targeted spatially offset Raman spectroscopy-based vanguard analytical method to authenticate spirits: White Tequilas as a case study

Abstract

Adulteration and counterfeiting are ongoing problems for alcoholic drinks, including beers, wines, and spirits. To fight against them, official analytical methods need to be complemented with faster, trustworthy, non-invasive and in-situ ones, which have been named as vanguard methods, to increase the efficiency in the detection probability of truly adulterated alcoholic drinks. The analytical methodology proposed here synergistically combines a novel measurement analytical technique (spatially offset Raman spectroscopy, SORS) with chemometrics methods, i.e., principal component analysis (PCA), soft independent modeling of class analogies (SIMCA), partial least squares regression-discriminant analysis (PLS-DA), support vectors machine, (SVM) and quantitative partial least squares regression (PLSR). The applicability of the proposal is tested with Tequila to (i) differentiate among 100 % agave and mixed white packaged Tequilas, and (ii) to predict the alcoholic content. SORS spectra of 51 samples were obtained in the 300–2000 cm−1 range, from which classification and regression models were developed. The best classification performances were obtained with PLS-DA and SVM with 100 % sensitivity, specificity and overall classification rate. PLSR exposed a better trend of the samples than PCA in the exploratory analysis; and yielded predictive models capable of foreseeing alcoholic contents with average errors lower than 4 %. These results demonstrate the potential of this fast, in-situ analytical approach to be used as a vanguard analytical method to screen adulterated or counterfeited Tequilas and to assess the conformity of the alcoholic stated in the label.