Gracia Patricia Blanch

Preconcentration of volatile components of foods: optimization of the steam distillation-solvent extraction at normal pressure

Abstract Optimization of the experimental conditions affecting the simultaneous steam distillation-solvent extraction of volatile components of foods was carried out by using the modified sequential simplex method. For this purpose, a new micro steam distillation-extraction device was constructed. The apparatus includes an enlarged surface condenser which contributes to preventing eventual losses of high-volatility components. Determination in the μg/l range of compounds having different polarities and volatilities are accomplished with high recoveries. The construction of the apparatus is such that the use of extraction solvents having densities either higher or lower than that of the solvent sample is feasible with only one configuration.

Enantioselective analysis of chiral polychlorinated biphenyls in sediment samples by multidimensional gas chromatography-electron-capture detection after steam distillation-solvent extraction and sulfur removal

Enantioselective analysis of the chiral polychlorinated biphenyls (PCBs) 95, 132 and 149 in river sediment samples was carried out by multidimensional gas chromatography with an achiral-chiral column combination and electron-capture detection. The investigations revealed the PCB congeners analysed to be present racemic within experimental error. A micro simultaneous steam distillation-solvent extraction device was used as extraction method. This technique proved to be a versatile tool for the extraction of organochlorine compounds from several matrices and was used for the extraction of PCBs from sediment samples. The removal of interfering elementary sulfur was carried out by the treatment with copper powder during the extraction.

Impact of postharvest methyl jasmonate treatment on the volatile composition and flavonol content of strawberries

BACKGROUND Although strawberry aroma is very complex, certain compounds have been described as main contributors, i.e. furanones, aldehydes, alcohols, sulfur compounds and particularly methyl and ethyl esters. In addition, strawberries possess potent antioxidant activity because of their high content of phenolic compounds. Among them, flavonols are highlighted as important antioxidant compounds in strawberry. The objective of this study was to assess the effect of methyl jasmonate (MJ) on the composition of the major contributors to aroma and on the content of certain flavonols in strawberry fruits. RESULTS The levels of all studied volatile compounds were significantly affected by MJ treatment, though the individual effect differed according to the specific compound considered. Most of them increased significantly (P < 0.05), except methyl butanoate, which always showed higher levels in untreated strawberries. In contrast to aroma compounds, the change in the concentration of flavonols (i.e. myricetin, quercetin and kaempferol) was not significant in MJ-treated strawberries. Considering the health-promoting activity of these compounds, further investigations on the experimental conditions related to the treatment are required to control flavonol bioformation by means of MJ. CONCLUSION The exogenous application of MJ vapour to strawberry enhances, in general, the production of the most relevant aroma-active compounds. On the contrary, MJ treatment does not appear to influence the levels of myricetin, quercetin and kaempferol. Thus postharvest MJ treatment is proposed as an approach to obtain improved strawberry fruits in terms of sensory quality and health-promoting properties.

Rapid extraction of wine aroma compounds using a new simultaneous distillation-solvent extraction device

The potential of the simultaneous distillation-solvent extraction (SDE) technique for the rapid enrichment of wine aroma compounds was investigated. Several aspects concerning the extraction and concentration of volatiles from aqueous-alcoholic samples were studied and three different modes of operation, namely SDE at normal pressure, SDE at reduced pressure and SDE involving the concentration of the dynamic headspace resulting from purging the sample with an inert gas, are considered. A new SDE apparatus previously designed in our laboratory, to allow the use of extraction solvents denser or lighter than the solvent sample with only one configuration, was employed.

(+)-methyl jasmonate-induced bioformation of myricetin, quercetin and kaempferol in red raspberries.

The effect of postharvest treatment with enantiomers of methyl jasmonate (MJ) in conjunction with ethanol on bioformation of myricetin, quercetin and kaempferol in red raspberry was studied. For comparison, postharvest treatment with the commercial stereoisomeric mixture of MJ in conjunction with ethanol was simultaneously accomplished. The levels obtained were contrasted with those determined in untreated (control) samples. Exogenous (+)-MJ induced an enhancement in the levels of myricetin, quercetin and, particularly, kaempferol whereas the exposition to (-)-MJ exhibited the opposite effect. Enzymatic assays were carried out in presence and absence of (-)-MJ and (+)-MJ to evaluate possible changes in the activity of the enzymes regulating the bioformation of flavonols in red raspberries as a consequence of the treatments. From the results of the assays both (-)-MJ and (+)-MJ inhibited the activity of flavanone 3β-hydroxylase (FHT) and flavonol synthase (FLS), which are directly involved in the formation of flavonols from (-/+)-naringenin. From these results, it is speculated that the activity of phenylalanine ammonia lyase (PAL) regulating the formation of (-/+)-naringenin from l-phenylalanine by (+)-MJ in conjunction with ethanol is promoted. Postharvest treatment of red raspberry with (+)-MJ in ethanol is proposed as a mean to increase flavonol content in red raspberries.

Determination of (E)-5-methylhept-2-en-4-one in deodorised hazelnut oil. Application to the detection of adulterated olive oils

The presence of (E)-5-methylhept-2-en-4-one (filbertone) in a hazelnut oil, deodorised in a laboratory system using nitrogen as stripping gas, is studied regarding its usefulness as a chiral marker for detecting adulterations of olive oil. The analytical method involves the use of both simultaneous distillation–solvent extraction as a sample concentration step and a chiral stationary phase in the subsequent gas chromatographic analysis. The procedure is simple, rapid, effective for detecting adulterations of olive oil with hazelnut oil and can reduce falsely negative results obtained if conventional parameters included in current regulations are exclusively considered when establishing purity in olive oils. © 2000 Society of Chemical Industry

Evaluation of pesticide residue contents in fruit juice by solid-phase microextraction and multidimensional gas chromatography coupled with mass spectrometry

A new method based on the use of SPME followed by the MDGC-MS analysis was developed to determine pesticides in fruit juice. Different pesticide mixture standards (i.e. Mix 101, 13 and 164) were initially analyzed to optimize the separation conditions. To evaluate the advantages of the two-dimensional system over monodimensional GC, a comparative study on relative standard deviations, detection limits and correlation coefficients was carried out. As a result, selective transfers of some pesticides from the first to the second dimension were at times essential to avoid overlapping. The selected separation conditions from the study with standards were applied to fruit juices spiked with some pesticide standards. The results found in this work prove that the employment of a multidimensional analysis technique permits to avoid false positives obtained frequently on monodimensional techniques as a consequence of interferences of the analytes with matrix components.

Enantioselective isolation of methyl jasmonate using permethyl-β-cyclodextrin HPLC

A method based on the use of HPLC for the enantioselective resolution of the four stereoisomers of methyl jasmonate (MJ) with no need for the previous formation of the diastereoisomers is developed. To that end, a Nucleodex-beta-PM column as well as an optimization process considering different flow rates and mobile phase compositions were required. As a result, 0.8 mL/min and 55:45 methanol/water composition were the conditions selected to carry out the separation of the stereoisomers. Isolation of pure (-)- and (+)-MJ was accomplished by collecting the HPLC fractions corresponding to their elution time. SPE was subsequently used to concentrate and change the solvent of the HPLC fractions collected. Chiral GC and polarimetry were additionally employed to evaluate the purity and optical rotation, respectively, of the enantiomers separated. The results found in this study are particularly relevant considering that MJ stereoisomers are not commercially available.

Solid phase microextraction as a methodology in the detection of irradiation markers in ground beef

The usefulness of solid phase microextraction (SPME) to detect the occurrence of the irradiation markers 2-dodecylcyclobutanone (2-DCB) and 1,3-bis(1,1-dimethylethyl)benzene in irradiated ground beef was evaluated. To that aim, beef samples were irradiated with different irradiation doses and subsequently examined together with non-irradiated beef samples used as control samples. The SPME conditions applied were selected as a result of performing an optimization process including different fibers (PDMS, DVB/CAR/PDMS, polyacrylate and PDMS/DVB), as well as extraction times (10, 25 and 40min) and temperatures (40 and 60°C). For comparison, 2-DCB and 1,3-bis(1,1-dimethylethyl)benzene were additionally identified in some of the samples by steam distillation-solvent extraction (SDE). Although this study is a preliminary work, from the results obtained SPME seemed to be a rapid and valuable technique to determine 2-DCB and 1,3-bis(1,1-dimethylethyl)benzene in ground beef subjected to irradiation, offering advantages over other methods reported in the literature. In addition, SPME allowed to confirm the validity of 2-DCB as an useful marker to distinguish non-irradiated from irradiated ground beef. On the contrary, the occurrence of 1,3-bis(1,1-dimethylethyl)benzene was however established in both types of samples by SPME and SDE.

Preconcentration of samples by steam distillation-solvent extraction at low temperature

Abstract Operation of a micro steam distillation—solvent extraction (SDE) device in two different modes, namely at reduced pressure and involving the concentration of the dynamic headspace resulting from purging the sample with an inert gas, was investigated. A notable advantage of the proposed micro SDE apparatus is that the use of extraction solvents denser or lighter than the sample solvent is feasible with only one configuration. The modified simplex method was used to improve the performance of the analytical procedure by optimization of several experimental conditions involved in the process.