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Técnicas analíticas aplicadas a la determinación de compuestos aromáticos en alimentos vegetales
Abstract
El estudio del aroma de un alimento resulta relativamentedifícil, dada la gran complejidad y a la pocainformación que existe sobre este tema comparado con otros de la química de alimentos. La razón fundamental de esto es que los compuestos volátiles responsables del aroma se caracterizan por presentar una gran complejidad y variedad de estructuras químicas y por
encontrarse en muy pequeña concentración. En este artículo se realiza una revisión actualizada de las distintas
técnicas de extracción de volátiles: des ti !ación, extracción con solventes (continua y discontinua), extracción con tluidos supercríticos. extracción-destilación y técnicas de espacio de cabeza (estático y dinámico), seguido de análisis de la fracción volátil por cromatografía de gases (tipo de columna y naturaleza del relleno, gas portador y tipo de detector utilizado)
y su aplicabilidad a alimentos vegetales.
The study of flavour in food is difficult due to these compounds have received relatively little attention regarding with other food components. This review aims to present the curren! state of the different analytical techniques applied to the extraction of volatile compounds: distillation, solvent extraction (continous and discontinous), steam distillation-solvent extraction,
extraction with supercritical fluids, headspace methods (static and dynamic), followed by gas chromatographic
analysis of the volatile fraction (type of column, carrier gas. type of detector). A great number of references
about volatile analysis in food vegetables is given.
... Sampling and sample preparation (extraction, preconcentration, fractionation and isolation) are the steps that normally require the most time during the analytical procedure (Kataoka, Lord, & Pawliszyn, 2000;Maslamani, Manandhar, Geremia, & Logue, 2016). Sample preparation is a critical step, since a large amount of analyte can be lost and lead to significant errors (Andrade-Eiroa, Canle, Leroy-Cancellieri, & Cerdà, 2016a; Rodríguez-Bernaldo de Quirós, González-Castro, López-Hernández, & Simal-Lozano, 1996). Therefore, it is not an exaggeration to say that a good choice of the sample preparation procedure influences the analysis reliability and precision. ...
... Sample preparation techniques are based on different physicochemical properties of the analytes, such as their volatility, solubility in different organic phases, and their ability to be absorbed on a particular material. According to these properties, some extraction techniques can be classified as (Castro-Mejías et al., 2008;Rodríguez-Bernaldo de Quirós et al., 1996;Serrano de la Hoz, 2014): ...
The grape and wine aroma is one of the most determining factors of quality, therefore the study of their volatile composition is a very important topic in vitiviniculture. The range of concentrations in which many of these compounds are found is quite low, in concentrations of ng/L; due to this, a sample preparation stage is necessary before doing the chromatographic analysis of the volatile compounds. In this review, the main analytical techniques used for the extraction of volatile compounds in grapes and wines are studied. The techniques presented are liquid-liquid extraction (LLE), solid phase extraction (SPE), solid phase microextraction (SPME), stir bar sorptive extraction (SBSE), and thin film solid phase microextraction (TF-SPME). For each of these techniques, a description was made, and the different characteristics were numbered, as well as their main advantages and disadvantages. Furthermore, from the second technique, a comparison is made with the previous techniques, explaining the reasons why new techniques have emerged. Throughout the review it is possible to see the different techniques that have been emerging in the past years as an improvement of the classical techniques.
The vapour from whole Navel oranges was examined by using headspace techniques followed by capillary gas chromatography and gas chromatography–mass spectrometry with the aim of distinguishing good, damaged and diseased fruit by chemical means. Low concentrations of limonene were detected in the headspace of undamaged fruit, but mechanical damage caused considerable increases in the concentration of limonene and volatile terpene peel-oil constituents. Diseased oranges affected by common Penicillium infections produced different headspace profiles, containing relatively high concentrations of acetaldehyde, simple alcohols and esters. The method was reproducible (relative standard deviation 1–2%) and 23 potential compounds of interest could be separated in a single run by using a column containing a thick film of polar stationary phase.
Aroma concentrate separated from an aqueous solution of Haze honey by adsorptive column chromatography had a stronger aroma intensity than that separated by a combination of a preliminary extraction with acetone and separation of volatile compounds from acetone extract by steam distillation extraction. A total of 130 compounds were identified, including 27 alcohols, 19 aldehydes, 9 ketones, 12 esters, 8 acids, 35 hydrocarbons, 10 furanoids or pyranoids, and 10 miscellaneous compounds. The sensory importance of the volatile compounds was investigated by sniffing the fractions separated by preparative gas chromatography. As a result, benzeneacetaldehyde, linalool, phenethyl alcohol, p-cresol, p-anisaldehyde, methyl-p-anisaldehydes, trimethoxybenzene, 5-hydroxy-2-methyl-4H-pyran-4-one, and lilac aldehydes seemed to contribute to Haze honey aroma. Keywords: Aroma compounds; flavor components; honey; column concentration
Voltile flavor compounds in sesame seed oil were investigated. Commercially processed sesame seed oil was steam distilled under reduced pressure, and volatiles from the distillate were separated by an adsorptive column method. Among 171 individual peaks detected, 134 peaks were definitely or tentatively identified by analysis of mass spectra and modified Kovats indices. To elucidate the compounds directly contributing to the characteristic flavor, the odor concentrate was fractionated by silica gel thin-layer chromatography and preparative gas chromatography. As a result, 1-(5-methyl-2-furanyl)-1-propanone, 3-formylthiophene, 2-propyl-4-methylthiazole, 2-ethyl-4-methyl-1H-pyrrole, 2-ethyl-6-methylpyrazine, 2-ethyl-5-methylpyrazine, 4,5-dimethylisothiazole, 4,5-dimethylthiazole, 2,6-diethylpyrazine, 2-ethyl-2,5-dimethylpyrazine, 1-(2-pyridinyl)ethanone, and 1-(1-methyl-1H-pyrrol-2-yl)ethanone were considered to be principal contributors of sesame seed oil flavor. Keywords: Volatiles; flavor compounds; sesame seed oil
The analysis of volatile compounds, and particularly of certain hydrocarbons, e.g. pentane, and some aldehydes, e.g. hexanal, has been used to estimate the degree of oxidation of vegetable oil. We have tested a dynamic headspace technique without heating the sample during the purge time of the analysis. Some tests have been performed after heating the sample at 180°C for a specified time before the analysis, to compare the results of analysis with and without heating. The best results were obtained at room temperature.
Steam distillation (SD), simultaneous distillation-solvent extraction (SDE), and supercritical (CO2) extraction (SFE) were used to isolate volatile secondary metabolites from fresh, totally mature flowers of Colombian ylang-ylang (Cananga odorata). The various extracts were analyzed by capillary chromatography (DB-1, DBWAX, 60 m columns) using FID, NPD or MSD (EI, 70 eV). Kováts indexes, mass spectra, or standard substances were employed for compound identification. 51, 70, and 73 compounds at concentrations above 100 ppb were detected in the SD, SDE, and SFE extracts, respectively. The main constituents of these extracts were linalool (20.7, 28.0, and 16.5%), germacrene-D (10.1, 3.1, and 20.3%) benzyl benzoate (14.1, 2.9, and 3.9%), benzyl acetate (9.6, 17.0, and 6.2%), caryophyllene (3.1, 2.9, and 3.9%), and p-methylanisole (6.8, 6.1, and 2.7%). 85% of the composition of SDE extracts was represented by oxygenated compounds. Heavy hydrocarbons (Cn >20) and fatty acids were found only in the SFE extracts, which also had a higher content of nitrogenated compounds (phenylacetonitrile, 4-methylbenzaldoxime, indole, 2-phenyl-nitroethane, and methyl anthranilate) and sesquiterpenes (43% vs 19.5% in SD and 8.1% in SDE) and 1.5 – 2 times lower concentration of monoterpenes and light oxygenated compounds than the SD (49.7%) and SDE (64.5%) extracts.
Three types of tobacco products have been analysed for their volatile components which constitute the aroma of the product. Automatic thermal desorption gas chromatography-mass spectrometry (GC-MS) and direct headspace sampling gas chromatography-atomic emission detection (GC-AED) have been used. One product was found to contain three unusual volatile components which were not present in the other two. By combining information from both mass spectrometric and atomic emission detection (AED), elemental composition and partial molecular structures were obtained. Final identification was achieved by comparing, both chromatographically and spectroscopically, with an authentic sample. The three components were isomers of dipropyleneglycol methyl ether and were present in the product in the same ratio as in the authentic sample. Direct headspace sampling offered several advantages over the thermal desorption approach.
Static headspace sampling combined with gas chromatography using open-tubular (capillary) columns for the characterization
of the flavour of raw vegetables and some vegetable products is described. In order to avoid alteration of the composition
of the volatiles, the sample was thermostated for a short time only. Although equilibrium between vapour and sample was not
established the reproducibility of such conditions is demonstrated. Typical chromatograms are given; the most characteristic
compounds present were identified by mass spectrometry.
The aroma of wine consists of 600 to 800 aroma compounds from which especially those, typical for the variety, are already present in the grapes. The aroma extracts — received by extraction with trichlorofluoromethane — are separated by gas chromatography. There are significant varietal differences between the aromagrams (“fingerprint pattern”). Thus the amount of some flavour compounds (“key substances”) shows typical dependence on the variety. Especially monoterpene compounds play an important role in the differentiation of wine varieties.
The German white wines can be differentiated into three groups only by quantitative determination of 12 monoterpenes (“terpene profile”). These groups are: “Riesling type”, “Muscat type” and “Silvaner-Weißburgunder type”. Such “terpene profiles” are also useful for the separation of real Riesling wines from others called Riesling (e.g. Welschriesling, Kap Riesling, Emerald Riesling) but not produced from grapes of the variety Riesling. Including further components and by means of statistical methods as for example linear discriminant analysis even the different varieties within the mentioned groups (for instance the “Riesling”-group: Riesling, Kerner, Ehrenfelser, Bacchus, Müller-Thurgau) can be separated from each other.
To identify compounds causing “off-flavours” the sniffing technique is the method of choice. The off-flavour is pinpointed during gas chromatography separation of the complex aroma mixture by effluent sniffing. Once allocated, the chemical nature of the off-flavours is elucidated by spectroscopic methods. Substances contributing to the green pepper taint, the strawberry note, mousiness, corkiness etc. in wine could be found in this way.
A sensitive and rapid method for the determination of benzene, toluene, ethylbenzene and the xylenes (BTX) in ambient and exhaled air is described. After sampling of 1-4 l of ambient or exhaled air on graphitized charcoal tubes, the analytes were thermally desorbed by a microwave device coupled to a gas chromatograph interfaced to a mass spectrometer (GC-MS). The detection limits for benzene, toluene, ethylbenzene m- + p-xylene and o-xylene were 1.6, 3.0, 0.2, 1.4 and 0.4 μg/m3, respectively, when 1 l of air is sampled. In five smoking households a mean benzene concentration of 13.4 (range: 4.2–18.1) μg/m3 was measured. In five homes without smokers, the average concentration of benzene was 8.8 (5.5–12.8) μg/m3. The mean benzene concentrations in the exhalates were 50.2 (19.1–98.0) and 3.9 (0.5–8.8) μg/m3 for ten smokers and ten non-smokers, respectively. The method was found to be suitable for the determination of environmental BTX exposure in field studies.
Flavour release from three rehydrated vegetables: French beans, red bell peppers, and leeks, was studied directly in the mouth of 12 assessors (oral vapour) and in three mouth model systems; purge-and-trap, and dynamic headspace with and without mastication. Volatile compounds were analysed by gas chromatography and mass spectrometry, which resulted in 30, 52 and 42 identified compounds in French beans, bell, peppers, and leeks, respectively. Propanal, 2-methylpropanal, 2- and 3-methylbutanal, pentanal, hexanal, 2-pentenal, trans-2-hexenal, 2-heptenal, 2-butanone, and 6-methyl-5-hepten-2-one were present in each of them. Flavour release from the three vegetables in model system ‘dynamic headspace and mastication’ did not differ significantly from release in the mouth. Peak areas of volatiles released in the mouth had larger coefficients of variance than the ones released in the model system. Although assessors released volatile compounds with different efficiencies, they showed a statistically consistent efficiency in flavour release across the vegetables.