Fourier Transform Infrared Spectroscopy with Multivariate Analysis as a Novel Method for Characterizing Alcoholic Streng
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Fourier Transform Infrared Spectroscopy with Multivariate Analysis as a Novel Method for Characterizing Alcoholic Strength, Density, and Total Dry Extract in Spirits and Liqueurs Ulrich Arzberger & Dirk W. Lachenmeier
Received: 7 November 2007 / Accepted: 3 December 2007 / Published online: 29 December 2007 # Springer Science + Business Media, LLC 2007
Abstract Fourier transform infrared (FTIR) spectroscopy allows fast throughput screening of beverages (less than 2 min per sample). Using partial least squares (PLS) regression, it was demonstrated that relative density and alcohol content, which have previously been calibrated only for extract-free spirits, can also be determined in highly viscous liqueur samples. In addition, total dry extract (TDE) was successfully calibrated for the first time for both spirit and liqueur screening. An inter-laboratory validation showed that the standard errors of prediction, ranging between 0.0006 and 0.0078 (relative density), 0.23 and 0.74 % vol (alcoholic strength), and 0.55 and 7.53 g/l (TDE), were satisfactory for use of the FTIR-PLS method in the context of screening analysis in official food control of alcoholic beverages. Keywords Spirit Drinks . Liqueur . FTIR . Chemometrics . Multivariate Data Analysis . PLS . Total Dry Extract
Introduction In the context of quality control of alcoholic beverages, a range of different analytical methods had to be used in the past. For example, the alcoholic strength was usually determined by reference methods like distillation and pycnometry or by more advanced analytical instruments U. Arzberger Chemisches und Veterinäruntersuchungsamt (CVUA) Stuttgart, Schaflandstr. 3/2, 70736 Fellbach, Germany D. W. Lachenmeier (*) Chemisches und Veterinäruntersuchungsamt (CVUA) Karlsruhe, Weißenburger Str. 3, 78187 Karlsruhe, Germany e-mail: [email protected]
using steam distillation and oscillation-type densimetry (Lachenmeier et al. 2003, 2005a, 2006a). In addition, higher alcohols and other volatile compounds were determined using gas chromatography (Lachenmeier et al. 2006b; European Commission 2000). Therefore, by means of these traditional techniques, beverage analysis is time consuming and expensive. Increasing requirements and cost pressures nowadays force both government and commercial food testing laboratories to replace these traditional reference methods with faster and more economical systems. The most promising approach to overcome these problems is the use of multivariate data analysis with different analytical techniques (Arvanitoyannis et al. 1999). Such techniques were used, for example, to classify vinegar samples using near-infrared spectroscopy (Saiz-Abajo et al. 2004a, b). Fourier transform infrared (FTIR) spectroscopy in the mid-infrared range was introduced into wine analysis (Patz et al. 1999, 2004; Nieuwoudt et al. 2004; Gishen and Holdstock 2000; Kupina and Shrikhande 2003; Coimbra et al. 2002), as well as into the analysis of other alcoholic beverages like spirits and beer (Palma and Barroso 2002; Lachenmeier 2007). As
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