Simultaneous distillation extraction aroma compounds

Aroma compounds are present in minute levels in foods, often at the ppb level ( ig/liter). In order to analyze compounds at these levels, isolation and concentration techniques are needed. However, isolation of aroma compounds from a food matrix, which contains proteins, fats, and carbohydrates, is not always simple. For foods without fat, solvent extraction (unit gu) can be used. In foods containing fat, simultaneous distillation extraction (SDE see Basic Protocol 1) provides an excellent option. Concentration of headspace gases onto volatile traps allows sampling of the headspace in order to obtain sufficient material for identification of more volatile compounds. A separate protocol (see Basic Protocol 2) shows how volatile traps can be used and then desorbed thermally directly onto a GC column. For both protocols, the subsequent separation by GC and identification by appropriate detectors is described in unitgu. 

The flavor constituents of plain and roasted cashew nuts have not been previously reported in the literature. In the present study, aroma compounds have been isolated from plain, oven-roasted and oil-roasted cashew nuts by simultaneous distillation extraction and by steam distillation followed by selective extraction, after pH adjustment. Compound identification was carried out by GC and GC-MS analyses. Esters and lactones are present in plain cashews whereas roasted samples also contain pyrazines. 

The nature of flavor compounds creates challenges for analysis. Aroma compounds must be volatile. They are usually present at very low concentrations in foods. Despite the fact that hundreds of volatile compounds are often present in a food, only a few may be odor-active. Gas chromatography has been an invaluable tool for separation and subsequent identification of volatile compounds. Concentration of flavor chemicals is often necessary since the compounds are usually present at low levels. Some methods of sample preparation are described in this handbook, including solid-phase microextraction (see Chapters 16, 20-22, 30, and 31), sorptive stir bar extraction (Chapter 32), absorption on a porous polymer (Chapters 21, 22, and 27), super-critical CO2 extraction (Chapter 22), simultaneous steam distillation (Chapter 31), accelerated solvent extraction (Chapter 35), simultaneous distillation extraction (Chapters 21 and 31), and direct gas injection with cryofocusing (Chapter 20). Sampling conditions are considered in Chapters 20, 23, and 24, and comparisons of some chemical detector sensitivities are made in Chapters 18, 23, and 27-29. 

The simultaneous distillation-extraction (SDE) under atmospheric pressure (53) is not always the most appropriate technique, and its use should be carefully considered. This technique is an elegant and rapid extraction method resulting in an aroma extract that is ready to be injected into a GC system after concentration. However, heat-induced artefact formation, decomposition of labile compounds, and loss of very volatile compounds are serious drawbacks. Furthermore, only steam-distillable volatiles are extracted. Polar compounds, such as hydroxyfura-nones and phenols, are particularly poorly recovered. 

More recently, several aroma compounds were isolated from cupuacu pulp by vacuum distillation, solid-phase extraction, and simultaneous steam distil-lation-extarction and were analysed by GC, GC-MS, and GG-O [8]. The olfaction of the extracts obtained by solid-phase extraction indicated linalool, a-ter-pineol, 2-phenylethanol, myrcene, and limonene as contributors of the pleasant floral flavour. In this study, the esters ethyl 2-methylbutanoate, ethyl hexanoate, and butyl butanoate were involved in the typical fruity characteristics. 

Reaction of an aqueous solution of cystine with thiamin, glutamate, and ascorbic acid produces a complex mixture of compounds with an overall flavor resembling that of roasted meat. The reaction was carried out at 120 C for 0.5h at pH 5.0 in a closed system. The aroma compounds were isolated by means of the simultaneous steam distillation/solvent extraction method. The flavor concentrate was pre-separated by liquid chromatography on silica gel and subsequently analysed by GC and GC/MS. Unknown flavor components were... 

Simultaneous Steam Distillation/Extraction An elegant apparatus was described by Nickerson and Likens ( 5) for the simultaneous steam distillation and extraction (SDE) of volatile components. This device has become one of the mainstays in the flavor field. In this apparatus, both the aqueous sample and water-immiscible solvent are simultaneously distilled. The steam which contains the aroma chemicals and the organic solvent are condensed together, and the aroma compounds are transferred from the aqueous phase to the organic phase. Typical solvents used are diethyl ether, pentane or a mixture thereof normal extraction times are one to two hours. 

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