A COMPARISON OF DIFFERENT EXTRACTION METHODS FOR THE VOLATILE COMPONENTS OF GRAPE JUICE

Different isolation methods for the volatile components of Muscat grape juice are compared in terms of the accuracy and precision of the quantitative analysis and the sensitivity achievable with each analytical procedure. These methods include continuous liquid-liquid extraction (LLE), simultaneous distillation-extraction (SDE) with freon-11, dichloromethane and n-pentane as extracting solvents, as well as a dynamic headspace sampling procedure (HSA) using both a sweeping and an aeration approach. Analysis of the grape juice extracts are carried out by capillary gas chromatography (GC) using a programmable temperature vaporizer (PTV) for sample introduction (in LLE and SDE methods). The injector was also used for trace analysis of enriched gaseous samples collected from the headspace of the sample by intermediate trapping in a suitable absorbent. Different isolation techniques result in compositionally different isolates. The SDE procedure was found to be the method of choice for a reliable quantification of the sample using dichloromethane as solvent, whereas the aeration mode of operation of the dynamic headspace sampling results in a more favorable extraction of volatile components and can be used quite well for identification purposes.