ABSTRACT
Off-flavors in foods may originate from environmental pollutants, the growth of microorganisms, oxidation of lipids, or endogenous enzymatic decomposition in the foods. The chromatographic analysis of flavors and off-flavors in foods usually requires that the samples first be processed to remove as many interfering compounds as possible. For analysis of foods by gas chromatography (GC), sample preparation may include mincing, homogenation, centrifugation, distillation, simple solvent extraction, supercritical fluid extraction, pressurized-fluid extraction, microwave-assisted extraction, Soxhlet extraction, or methylation. For high-performance liquid chromatography of amines in fish, cheese, sausage and olive oil or aldehydes in fruit juice, sample preparation may include solvent extraction and derivatization. Headspace GC analysis of orange juice, fish, dehydrated potatoes, and milk requires almost no sample preparation. Purge-and-trap GC analysis of dairy products, seafoods, and garlic may require heating, microwave-mediated distillation, purging the sample with inert gases and trapping the analytes with Tenax or C18, thermal desorption, cryofocusing, or elution with ethyl acetate. Solid-phase microextraction GC analysis of spices, milk and fish can involve microwave-mediated distillation, and usually requires adsorption on poly(dimethyl)siloxane or electrodeposition on fibers followed by thermal desorption. For short-path thermal desorption GC analysis of spices, herbs, coffee, peanuts, candy, mushrooms, beverages, olive oil, honey, and milk, samples are placed in a glass-lined stainless steel thermal desorption tube, which is purged with helium and then heated gradually to desorb the volatiles for analysis. Few of the methods that are available for analysis of food flavors and off-flavors can be described simultaneously as cheap, easy and good.
Subject(s)
Flavoring Agents/analysis , Food AnalysisABSTRACT
Most surfactants employed for extraction purposes contain strongly absorbing chromophores, and therefore cannot be used with the ultraviolet-visible HPLC detector because of the high background created. Alkyltrimethylammonium surfactants, which do not have strongly absorbing chromophores, have shown promise as an extractant compatible with HPLC-ultraviolet-visible detection. In our extraction procedure, alkyltrimethylammonium surfactants are added to a sample containing organic analytes in distilled water. Sodium chloride is next added, then the entire sample is shaken. Before centrifugation, 1-octanol is added to aid in the two phase formation of surfactant-rich and aqueous phases. In this paper, we present the results of our studies on the extraction behavior of an alkyltrimethylammonium surfactant technique using various organic compounds as test probes. Specifically studied are the extraction behavior of organic bases, isomers of varying polarity and a zwitterionic species that has different charges at various pH values. Results from multiple extractions to obtain quantitative recovery of analytes is also presented. The composition of each phase is elucidated through the interpretation of data obtained from thermogravimetric and carbon, hydrogen and nitrogen (CHN) instrumentation.
Subject(s)
Quaternary Ammonium Compounds/chemistry , Surface-Active Agents/chemistry , Chromatography, High Pressure Liquid , Spectrophotometry, Ultraviolet , Water/chemistryABSTRACT
Described is a rapid microwave-mediated steam distillation device for determining two predominant off-flavor compounds, geosmin and methylisoborneol, in catfish tissue. A microwave on-time of 10 min is needed to efficiently remove these off-flavor compounds from the sample matrix and trap them on a solid phase adsorbent. A minimal amount of organic solvent is used to elute the trapped compounds. The extract is then analyzed by gas chromatography with ion trap detection in the selective ion storage mode. Detection limits in the sub-parts-per-billion range are obtained with this method.
