**2. Principal component analysis of spectral data applied in the evaluation of the authenticity of matured distilled beverages**

The production of distilled alcoholic beverages can be summarised into at least three steps: *i)* obtaining and processing the raw materials, *ii)* fermentation and distillation processes, and *iii)* maturation of the distillate to produce the final aged product (Reazin, 1981). During the obtaining and fermentation steps, no major changes in the chemical composition are observed. However, throughout the maturation process, distillate undergoes definite and intended changes in aromatic and taste characteristics.

These changes are caused by three major types of reactions continually occurring in the barrel: *1)* extraction of complex wood substances by liquid (*i.e.:* acids, phenols, aldehydes, furfural, among others), *2)* oxidation of the original organic substances and of the extracted wood material, and *3)* reaction between various organic substances present in the liquid to form new products (Baldwin et al., 1967; Cramptom & Tolman,1908; Liebman & Bernice, 1949; Rodriguez-Madera et al., 2003; Valaer & Frazier,1936). Because of these reactions occurring during the maturation process, the stimulation and odour of ethanol in the distillate are reduced, and consequently, its taste becomes suitable for alcoholic beverages (Nishimura & Matsuyama, 1989). It is known that the concentration of extracts from wood casks in matured beverages seriously depend on the casks conditions (Nose et al., 2004). Even if their aging periods are the same, the use of different casks for the maturation process, strongly conditions the concentration of these extracts. (Philip, 1989; Puech, 1981; Reazin, 1981). Diverse studies on the maturation of distillates like whiskey, have demonstrated that colour, acids, esters, furfural, solids and tannins increase during the aging process. Except for esters, the greatest rate of change in the concentration of these compounds occurs during the first year (Reazin, 1981). For this reason, the extracts of wood and the chemically produced compounds during the aging process confer some optical properties that can be used to evaluate the authenticity and quality of the distillate in terms of its maturation process (Gaigalas et al., 2001; Walker, 1987).

The detection of economic fraud due to product substitution and adulteration, as well as health risk, requires an accurate quality control. This control includes the determination of changes in the process parameters, adulterations in any ingredient or in the whole product, and assessment that flavours attain well defined standards. Many of these quality control issues have traditionally been assessed by experts, who were able to determine the quality by observing their colour, texture, taste, aroma, etc. However, the acquisition of these skills requires years of experience, and besides that, the analysis may be subjective. Therefore, the use of more objective tools to evaluate maturation becomes essential. Nevertheless, it is difficult to find direct sensors for quality parameters. For this reason, it is necessary to determine indirect parameters that, taken individually, may weakly correlate to the properties of interest, but as a whole give a more representative picture of these properties. In this regard, different chromatographic techniques provide reliable and precise information about the presence of volatile compounds and the concentration of others (*i.e.:*  ethanol, methanol, superior alcohols or heavy metals, etc.), thus proving the quality and authenticity of distilled alcoholic beverages (Aguilar-Cisneros, et al., 2002; Bauer-Christoph et al., 2003; Ragazzo et al.,2001; Savchuk et al., 2001; Pekka et al., 1999; Vallejo-Cordoba et al., 2004). In spite of that, chromatographic techniques, generally destroy the sample under study and also require equipment installed under specific protocols and installations 24 Principal Component Analysis

**2. Principal component analysis of spectral data applied in the evaluation of** 

The production of distilled alcoholic beverages can be summarised into at least three steps: *i)* obtaining and processing the raw materials, *ii)* fermentation and distillation processes, and *iii)* maturation of the distillate to produce the final aged product (Reazin, 1981). During the obtaining and fermentation steps, no major changes in the chemical composition are observed. However, throughout the maturation process, distillate undergoes definite and

These changes are caused by three major types of reactions continually occurring in the barrel: *1)* extraction of complex wood substances by liquid (*i.e.:* acids, phenols, aldehydes, furfural, among others), *2)* oxidation of the original organic substances and of the extracted wood material, and *3)* reaction between various organic substances present in the liquid to form new products (Baldwin et al., 1967; Cramptom & Tolman,1908; Liebman & Bernice, 1949; Rodriguez-Madera et al., 2003; Valaer & Frazier,1936). Because of these reactions occurring during the maturation process, the stimulation and odour of ethanol in the distillate are reduced, and consequently, its taste becomes suitable for alcoholic beverages (Nishimura & Matsuyama, 1989). It is known that the concentration of extracts from wood casks in matured beverages seriously depend on the casks conditions (Nose et al., 2004). Even if their aging periods are the same, the use of different casks for the maturation process, strongly conditions the concentration of these extracts. (Philip, 1989; Puech, 1981; Reazin, 1981). Diverse studies on the maturation of distillates like whiskey, have demonstrated that colour, acids, esters, furfural, solids and tannins increase during the aging process. Except for esters, the greatest rate of change in the concentration of these compounds occurs during the first year (Reazin, 1981). For this reason, the extracts of wood and the chemically produced compounds during the aging process confer some optical properties that can be used to evaluate the authenticity and quality of the distillate in terms

The detection of economic fraud due to product substitution and adulteration, as well as health risk, requires an accurate quality control. This control includes the determination of changes in the process parameters, adulterations in any ingredient or in the whole product, and assessment that flavours attain well defined standards. Many of these quality control issues have traditionally been assessed by experts, who were able to determine the quality by observing their colour, texture, taste, aroma, etc. However, the acquisition of these skills requires years of experience, and besides that, the analysis may be subjective. Therefore, the use of more objective tools to evaluate maturation becomes essential. Nevertheless, it is difficult to find direct sensors for quality parameters. For this reason, it is necessary to determine indirect parameters that, taken individually, may weakly correlate to the properties of interest, but as a whole give a more representative picture of these properties. In this regard, different chromatographic techniques provide reliable and precise information about the presence of volatile compounds and the concentration of others (*i.e.:*  ethanol, methanol, superior alcohols or heavy metals, etc.), thus proving the quality and authenticity of distilled alcoholic beverages (Aguilar-Cisneros, et al., 2002; Bauer-Christoph et al., 2003; Ragazzo et al.,2001; Savchuk et al., 2001; Pekka et al., 1999; Vallejo-Cordoba et al., 2004). In spite of that, chromatographic techniques, generally destroy the sample under study and also require equipment installed under specific protocols and installations

**the authenticity of matured distilled beverages** 

intended changes in aromatic and taste characteristics.

of its maturation process (Gaigalas et al., 2001; Walker, 1987).

(Abbott & Andrews, 1970). On the other hand, the use of spectroscopic techniques such as infrared (NIR and FTIR), Raman, ultraviolet/visible together with multivariate methods, has already been used for the quantification of the different components of distilled beverages (*i.e.:* ethanol, methanol, sugar, among others). This approach allows the evaluation of quality and authenticity of these alcoholic products in a non-invasive, easy, fast, portable and reliable way (Dobrinas et al., 2009; Nagarajan et al., 2006). However, up to our knowledge, none of these reports has been focused on the evaluation of the quality and authenticity of distilled beverages in terms of their maturation process.

Mezcal is a Mexican distilled alcoholic beverage produced from agave plants from certain regions in Mexico (NOM-070-SCFI-1994), holding origin denomination. As many other similar matured distilled beverages, mezcal can be adulterated in the flavour and appearance (colour), these adulterations aiming to imitate the sensorial and visual characteristics of the authentic matured beverage (Wiley, 1919). Considering that the maturation process in distillate beverages has a strong impact on their taste and price, adulteration of mezcal beverage pursuit obtaining the product in less time. However, the product is of lower quality. In our group, a methodology based in the use of UV-absorption and fluorescence spectroscopy has been proposed for the evaluation of the authenticity of matured distilled beverages, and focused in mezcal. We took advantage of the absorbance/emission properties of woods extracts and molecules added to the distilled during maturation in the wood casks. In this context, principal component analysis method appears as a suitable option to analyse spectral data aiming to elucidate chemical information, thus allowing discrimination of authentic matured beverages from those nonmatured or artificially matured.

In this section, we present the PCA results obtained from the investigation of two sets of spectroscopic data (UV absorption and fluorescence spectra), collected from authentic mezcal samples at different stages of the maturation: *white or young* (non-maturated), *rested* (matured 2 months in wood casks), and *aged* (1 year in wood casks). Samples belonging to false matured mezcals (artificially matured) are labelled as: *abocado* (white or young mezcal artificially coloured and flavoured) and *distilled* (coloured white mezcal). These samples were included with the aim of discriminating authentic matured mezcals from those artificially matured. The discussion is focused on the influence of the pre-treatments of spectra on the scores and loadings values. The criteria used for the scores and loadings interpretation are also discussed.
