Sampling techniques for the determination of volatile components in grape juice, wine and alcoholic beverages

When considering the analysis of volatile organic compounds the first step, sample preparation, is probably underestimated when compared with the chromatographic separation or with the analyte identification by mass spectrometry. Wines and alcoholic beverages are very complex matrices. Volatile compounds present in these beverages belong to several different chemical families and some of them, which have real impact on aroma characterization, are present in very low amounts. In addition to this known complexity, the aroma profile is not static and changes from the outset of the technological process almost until beverage consumption. The composition and quantity of the detected compounds strongly depends on the extraction technique used to remove and isolate them from their matrix. An ideal sampling method, for all kinds of compounds and matrices, does not exist, and no single isolation technique produces an extract that replicates the original sample. This chapter discusses liquid-phase, solid-phase, and supercritical fluid extraction methods, together with headspace microextraction methodologies and newly developed microextraction methods. The choice of an ideal procedure depends on the objective of the study, the target compounds, the matrix, and the sensitivity of the analytical method. Advantages or disadvantages of each method are also discussed.