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Analysis of Alcoholic Beverages by Gas Chromatography

Fernando M. Lanças
M. de Moraes
Laboratorio de Cromatografia, Instituto de Quimica de SãoCarlos, Universidade de São Paulo, São Carlos/SP, Brazil

Introduction

Alcoholic beverages have been consumed by a significant range of worldwide population since the beginning of civilization until the present time. Therefore, there should be a great interest on consumption of beverages quality and, consequently, the usage of a suitable analytical technique to verify and control thisdesirable quality. Alcoholic beverages are classified, in a general way, in fermented beverages (such as beer, wine, sake, etc.) and distilled ones (vodka, whisky, aguardente, tequila, cognac, liquors, etc.). The main volatile substances present in most alcoholic beverages belongs to the following chemical classes: alcohols (including ethanol, methanol, isobutanol, 3-methyl butan-2-ol, etc.), esters(such as ethyl acetate, methyl acetate, ethyl isobutyrate, isoamyl acetate, etc.), aldehydes (propanal, isobutanal, acetal, furfural, etc.), acids (acetic acid, propionic acid, butyric acid, etc.) and ketones (acetone, diacetyl, etc.). Some of the substances are of greater concern than the others due to its relative quantities or to its flavored characteristic [1]. As an example, ethanol is the majorcompound in the group of alcohols being responsible for the formation of various other substances, such as acetaldehyde, resulting from ethanol oxidation, and it is the most abundant of the carbonylic compounds in distilled beverages. For the same reason, acetic acid is the major compound within its group, the carboxylic acids. Fusel alcohols (e.g., 1-propanol and 3-methyl butan- 2-ol) as well asethanol are also importantsubstances in the alcohols group contributing to the flavor of distilled beverages because their odor is very distinctive and characteristic. There is an enormous variety of substances in small concentrations belonging to the esters group. Even so, ethyl acetate corresponds to more than 50% of the esters within this group.
These compounds are responsible to importantcharacteristics as smell and taste, in which the large fraction of these substances originates from fermentation or during beverages storage [1]. Because gas chromatography (GC) is an analytical technique in which separation and identification of volatile compounds occurs, it might be considered the best technique for this kind of sample [2].

Analysis by Gas Chromatography

Analysis ofalcoholic beverages by gas chromatography have as their main objectives to investigate flavoring compounds and contaminants which might be intentional or occasional. Whereas the former ones (the flavors) are analyzed to control their favorable characteristics to the beverage, the adulterants have to be controlled due to their deleterious contribution. Adulteration includes the addition of certaincompounds to enhance a desirable flavor. Because these compounds are usually added as a racemic mixture, their presence can be verified using a suitable chiral column for enantiomer separation [3]. On the other hand, occasional contaminants are substances originating in small quantities during beverage production and might be carcinogenic. The main source might be raw materials like grape, sugar cane,...