Through-container, extremely low concentration detection of multiple chemical markers of counterfeit alcohol using a handheld SORS device

Abstract

Major food adulteration incidents occur with alarming frequency and are episodic, with the latest incident, involving the adulteration of meat from 21 producers in Brazil supplied to 60 other countries, reinforcing this view. Food fraud and counterfeiting involves all types of foods, feed, beverages, and packaging, with the potential for serious health, as well as significant economic and social impacts. In the spirit drinks sector, counterfeiters often 'recycle' used genuine packaging, or employ good quality simulants. To prove that suspect products are non-authentic ideally requires accurate, sensitive, analysis of the complex chemical composition while still in its packaging. This has yet to be achieved. Here, we have developed handheld spatially offset Raman spectroscopy (SORS) for the first time in a food or beverage product, and demonstrate the potential for rapid in situ through-container analysis; achieving unequivocal detection of multiple chemical markers known for their use in the adulteration and counterfeiting of Scotch whisky, and other spirit drinks. We demonstrate that it is possible to detect a total of 10 denaturants/additives in extremely low concentrations without any contact with the sample; discriminate between and within multiple well-known Scotch whisky brands, and detect methanol concentrations well below the maximum human tolerable level.

Figure 1

(a) Abridged dendrogram obtained by hierarchical cluster analysis of the PC-DFA scores of all the Raman spectral data collected using SORS; encoding used: gin (G), vodka (V) rum (R), 4 brands of whisky (W1-W4). MB-PCA super scores plots of the Raman spectral data collected using, (b) SORS with a Resolve instrument and, (c) TRS with a TRS100 instrument. Different symbols represent the different additives, and the abbreviations are shown in Table 1.

Figure 2

The zero measurement SORS spectra (a) of bottle glass from three commercial spirits drinks (b) vodka in clear glass bottle, gin in brown glass bottle, and Scotch whisky in green glass bottle. Resolve is a handheld SORS (through-barrier) device which takes two measurements, a zero and an offset. The difference between these is that the laser physically moves. The zero measurement can be thought of as traditional backscatter mode, with the Raman signal acquired being biased to the surface. So in the case of the glass bottles that we see here (b), it is generally just the fluorescence of the glass that is observed.

Figure 3

The PC-DFA scores plot (a), and MB-PCA super scores plot (b) of the Raman spectral data collected using SORS with a Resolve instrument through commercial glass bottles (Fig. 2b). Different symbols represent the different spirit types, and the colours indicate the level of methanol present in each of the samples.