Solid-phase microextraction method development for headspace analysis of volatile flavor compounds

Solid-phase microextraction (SPME) fibers were evaluated for their ability to adsorb volatile flavor compounds under various conditions with coffee and aqueous flavored solutions. Experiments comparing different fibers showed that poly(dimethylsiloxane)/divinylbenzene had the highest overall sensitivity. Carboxen/poly(dimethylsiloxane) was the most sensitive to small molecules and acids. As the concentrations of compounds increased, the quantitative linear range was exceeded as shown by competition effects with 2-isobutyl-3-methoxypyrazine at concentrations above 1 ppm. A method based on a short-time sampling of the headspace (1 min) was shown to better represent the equilibrium headspace concentration. Analysis of coffee brew with a 1-min headspace adsorption time was verified to be within the linear range for most compounds and thus appropriate for relative headspace quantification. Absolute quantification of volatiles, using isotope dilution assays (IDA), is not subject to biases caused by excess compound concentrations or complex matrices. The degradation of coffee aroma volatiles during storage was followed by relative headspace measurements and absolute quantifications. Both methods gave similar values for 3-methylbutanal, 4-ethylguaiacol, and 2,3-pentanedione. Acetic acid, however, gave higher values during storage upon relative headspace measurements due to concurrent pH decreases that were not seen with IDA.     

Optimization of solid phase microextraction analysis for the headspace volatile compounds of parmesan cheese

Optimum conditions of solid phase microextraction (SPME) analysis of the headspace volatile compounds of Parmesan cheese in airtightly sealed 100-mL bottles were developed. The coefficient of variation of SPME analysis on the headspace volatile compounds of Parmesan cheese was 2%. The reproducibility of SPME was improved by a combination of sampling at -10 degrees C, controlling the sample temperature, and uniform magnetic stirring of samples during equilibrium and isolation steps. The sensitivity of SPME increased by 125% in total peak areas by a combination of 40 min of sonication and 25% (w/v) sodium phosphate solution, compared with that of samples containing deionized water only (P < 0.05). The addition of salt solution or sonication treatment in samples increased the headspace volatile compounds of cheese quantitatively without producing any new volatile compounds.     

Influence of lambda-carrageenan on the release of systematic series of volatile flavor compounds from viscous food model systems

The effect of lambda-carrageenan addition level (0.1, 0.25, 0.4, and 0.5% w/w) and viscosity on the release of systematic series of aroma compounds (aldehydes, esters, ketones, and alcohols) was studied in thickened viscous solutions containing lambda-carrageenan and 10 wt % of sucrose. Air-liquid partition coefficients K (37 degrees C) of a total of 43 aroma compounds were determined in pure water and in the lambda-carrageenan solutions by static headspace gas chromatography. Mass transfer of the aroma compounds in water and in the thickened lambda-carrageenan solutions which had a wide viscosity range was assessed by dynamic headspace gas chromatography. K (37 degrees C) increased as the carbon chain increased within each homologous series. Esters exhibited the highest volatility, followed by aldehydes, ketones, and alcohols. Under equilibrium, no overall effect of lambda-carrageenan was found, except with the most hydrophobic compounds. Analysis of flavor release under nonequilibrium conditions revealed a suppressing effect of lambda-carrageenan on the release rates of aroma compounds, and the extent of decrease in release rates was dependent on the physicochemical characteristics of the aroma compounds, with the largest effect for the most volatile compounds. However, none of the effects was of a magnitude similar to the obtained changes in the macroscopic viscosity, and the suppressing effects are therefore attributable to the thickener and not the physical properties of the increasingly viscous systems.     

Phosphorus release from vivianite and hydroxyapatite by organic and inorganic compounds

Based on recent mining rates and the exhaustion of global phosphorus(P)reserves,there is a need to mobilize P already stored in soils,and its recovery from secondary resources such as Ca-and Fe-phosphates is important.The Ca-phosphate hydroxyapatite forms a good fertilizer source,while vivianite is formed in waterlogged soils and sediments.During sludge treatment,the formation of vivianite has been identified,being mainly Fe-phosphate.Long-term P release from both hydroxyapatite and vivianite was studied using different inorganic(CaCl2 and CaSO4)and organic(citric and humic acid)reagents during batch experiments.Reagents CaCl2 and CaSO4 represent the soil solution,while citric and humic acids as organic constituents affect P availability in the rhizosphere and during the process of humification.Additionally,the flow-through reactor(FTR)technique with an infinite sink was used to study the long-term P release kinetics.The cumulative P release was higher by organic acids than by inorganic compounds.The cumulative P release rates were higher in the FTR with CaCl2 as compared to the batch technique.The infinite sink application caused a continuously high concentration gradient between the solid and liquid phases,leading to higher desorption rates as compared to the batch technique.The predominant amount of the total P released over time was available for a short term.While inorganic anion exchange occurred at easily available binding sites,organic acids affected the more heavily available binding sites,which could be embedded within the mineral structure.The results showed that organic compounds,especially citric acid,play a superior role as compared to the inorganic constituents of the soil solution during the recovery of already stored P from the tertiary phosphates vivianite and hydroxyapatite.     

Use of fiber interface direct mass spectrometry for the determination of volatile flavor release from model food systems.

Described in this paper is a fiber interface direct headspace mass spectrometric system for the real-time measurement of flavor release. The system was optimized for the detection of the garlic aroma volatile, diallyl disulfide, from water. Parameters investigated included interface temperature, flow rate through the fiber, flow rate through the sample vessel, and sample stir rate. The delay time for detection of sample after introduction into the sample vessel was determined as 43 s. The system proved to be reliable and robust with no loss in sensitivity or contamination of the mass spectrometer over a 6 month period. The technique was applied to a homologous series of aliphatic alcohols from C(2) to C(7). Results showed that as polarity decreased with increasing chain length the release of volatile into the headspace was faster and gave a higher maximum intensity. Release of the garlic aroma volatile from different commercial mayonnaise products clearly showed a decrease in the release of diallyl disulfide as fat content increased. These results demonstrate the potential of using this technique as a tool for understanding the complex interactions that occur between flavor compounds and the bulk food matrix.     

Evolution of volatile sulfur compounds from soils treated with sulfur-containing organic materials

Release of volatile S compounds from soils treated with S-containing organic materials was studied by sensitive gas chromatographic techniques. Methyl mercaptan, dimethyl sulfide, dimethyl disulfide, carbonyl sulfide and carbon disulfide were identified as gaseous products of decomposition of animal manures, sewage sludges and plant materials in soils under aerobic or waterlogged conditions. No release of hydrogen sulfide was detected. Most of the S volatilized from soils treated with sludges was in the form of dimethyl sulfide and dimethyl disulfide. whereas most of the S volatilized from soils treated with manures and plant materials was in the form of methyl mercaptan and dimethyl sulfide. More S compounds were released, and more S was volatilized, by decomposition of manures, sludges or plant materials in soils under waterlogged conditions than by decomposition under aerobic conditions. When calculated as a percentage of the S added as organic material, the average amount of S volatilized under aerobic or waterlogged conditions was < 0.2% < 0.5% and < 3.4% for the sludges, manures and plant materials, respectively. The five volatile S compounds produced by decomposition of manures, sludges and plant materials in soils under aerobic and waterlogged conditions also were produced by decomposition of plant proteins (zein, gluten and gliadin). It is concluded that the volatile S compounds released by decomposition of the above organic materials in soils are largely, if not entirely, produced by microbial degradation of methionine and cystine in these materials.     

Determination of trace volatile organic compounds in fish tissues by gas chromatography

Several volatile organic compounds associated with petroleum fuels (mainly alkylated benzenes) were extracted from spiked fish tissue samples with a stream of air, trapped on charcoal, eluted with a solvent, and analyzed by gas chromatography. These volatile compounds are among the most water-soluble components of crude oils and petroleum products, and they have been associated with tainting in fish tissues. Recoveries for these compounds were about 90% when spiked directly either onto traps or into fish tissues although naphthalene desorbed poorly from the charcoal; recoveries of this compound were about 50%. Relative standard deviations (RSD) for most recoveries of spiked samples were in the 2-10% range based on 6 samples analyzed in duplicate. However, when live fish were contaminated experimentally by adding the aromatic compounds to the aquarium water, the RSDs were higher (10-30%).     

Interactions of soluble peptides and proteins from skeletal muscle on the release of volatile compounds

The ability of skeletal dipeptides (carnosine and anserine) and a sarcoplasmic protein (myoglobin) to interact with key flavor compounds (hexanal, octanal, methional, 2-pentanone, 2-methylbutanal, and 3-methylbutanal) has been studied using the solid phase microextraction (SPME) technique. Conditions for SPME analysis (fiber coating, sampling time, and linearity of detection) were optimized. The effect of pH on the binding was also investigated. Thermodynamic models were applied to evaluate the binding parameters n (number of binding sites), K (affinity constant), and DeltaG (Gibb's free energy) to all of the flavor compounds studied, and they showed an absence of cooperative effect. Carnosine was the peptide with the highest affinity for all of the volatile compounds except 2-pentanone. Its interaction with hexanal and methional was significantly affected by pH. Anserine showed a lower level of interactions with hexanal, methional, 2-methylbutanal, and 3-methylbutanal, whereas myoglobin interacted with only hexanal and 2-methylbutanal. Differences in aroma retention can thus result in different sensory perceptions of muscle foods.     

Optimization of multiple headspace solid-phase microextraction for the quantification of volatile compounds in dry fermented sausages

Multiple headspace solid-phase microextraction (HS-SPME) is a stepwise method that eliminates the influence of the matrix sample on the quantitative analysis of solid samples. The process was optimized for the analysis of volatile compounds in dry fermented sausages by gas chromatography and mass spectrometry. Different amounts of fermented sausages and different vial volumes were studied to obtain the theoretical exponential decay of the peak area of the four successive extractions in order to calculate the total area in the sausage. The highest number of volatile compounds analyzed by multiple HS-SPME in dry fermented sausages was obtained in a 10 mL headspace vial with 0.07 g of sample in the presence of water, 0.75 mg butylated hydroxytoluene, and 0.5 g sodium chloride. Finally, the method was characterized in terms of linearity and detection limits and applied to analyze the volatile compounds present in fermented sausages manufactured with either nitrate or nitrite.     

Dynamic interactions of natural organic matter and organic compounds

Purpose

This article reviews our current understanding about how organic chemicals and water interact dynamically with, and therefore coevolve with, soil and sediment natural organic matter (NOM). NOM can be regarded as a polymer-like phase that responds to the input of organic compounds in ways analogous to synthetic polymers.

Methods

Sorption selectivity of organic compounds is shown to result in part from the three-dimensional microstructure of NOM related to its glassy character. Sorption to NOM conforms to polymer theory by exhibiting isotherm shape and irreversible behaviors characteristic of the glassy organic physical state. The glassy state is a metastable state characterized by the presence of excess free volume (holes).

Results

In polymers and NOM, incoming molecules preferentially occupy holes due to the absence of a cavitation penalty. Incoming molecules can enlarge existing holes and create new holes that do not relax completely when the molecules leave. The physical changes in NOM induced by sorption result in hysteresis in the isotherm that persists indefinitely at ambient temperature.

Conclusions

Sorption selectivity and hysteresis have important implications for the fate and bioavailability of contaminants.     

Effect of some fat replacers on the release of volatile aroma compounds from low-fat meat products

The effect of fat content and carbohydrate fat-replacers on the release of volatile odor compounds from beefburger, salami, and frankfurter has been investigated. The reduction in fat content in any of the three meat products studied resulted in a tendency toward an increase in the quantities of volatiles released in the headspace. Tapioca starch and maltodextrin appear to delay the release of certain classes of compounds selectively; for instance, tapioca starch appears to slow the release of some Maillard products while maltodextrin has a similar effect on terpenes. In contrast, oat fiber decreases the release of most of the compounds analyzed. Thus, the addition of carbohydrate fat-replacers to low-fat meat products could assist the flavor qualities of low-fat meat products by slowing down the release of odor compounds.     

Use of electronic nose technology to measure soil microbial activity through biogenic volatile organic compounds and gases release

Gas and volatile organic compounds (VOCs) release in soil is known to be linked to microbial activity and can differently affect the life of organisms in soil. Electronic noses (E-noses) are sensing devices composed of sensor arrays able to measure and monitor gases and VOCs in air. This is the first report on the use of such a sensing device to measure specifically microbial activity in soil. In the present study, γ-irradiated sterilised soil was inoculated with Pseudomonas fluorescens. To be sure for a rapid microbial growth and activity, two pulses of nutrient solution with organic and inorganic C, N, P and S sources were added to soil and the resulting microcosms were incubated for 23 d. During the incubation, respiration and enzyme activities of acid phosphatase, β-glucosidase, fluorescein diacetate hydrolase and protease, were measured, and microbial growth as global biomass of vital cells based on substrate-induced respiration (SIR-C_mic) and enumeration of viable and culturable cells by means of dilution plate counts (CFU) were also monitored. Concurrently, VOCs and/or gas evolution in the headspace of the soil microcosms were measured through the E-nose, upon their adsorption on quartz crystal microbalances (QCMs) comprising the sensory device. The E-nose typically generated an odorant image (olfactory fingerprint) representative of the analysed samples (soils) and resulting from the concurrent perception of all or most of the analytes in headspace, as it commonly happens when several selective but not specific sensors are used together (array). The basic hypothesis of this study was that different soil ecosystems expressing distinct microbial metabolic activities, tested through respiration and enzyme activities, might generate different olfactory fingerprints in headspace. Furthermore, the possibility to detect several substances at the same time, released from the soil ecosystems, possibly deriving from both abiotic and biotic (microbial metabolism) processes provides an “odorant image” representative of the whole ecosystem under study. The E-nose here used succeeded in discriminating between inoculated and non-inoculated ecosystems and in distinguishing different metabolic and growth phases of the inoculated bacteria during incubation. Specifically, E-nose responses were proved highly and significantly correlated with all hydrolytic activities linked to the mobilisation of nutrients from soil organic matter and their cycling, with CO₂ fluxes (respiration and presumed heterotrophic fixation) and with P. fluorescens population dynamics during exponential, stationary and starvation phases measured by SIR-C_mic and CFUs. Interestingly, the E-nose successfully detected soil microbial activity stimulated by nutrient supply, even though none of the catalytic activities tested directly produced VOCs and/or gases. The E-nose technology was then proved able to supply a real holistic image of microbial activity in the entire gnotobiotic and axenic soil ecosystems.     

Gas chromatographic quantification of major volatile compounds and polyols in wine by direct injection

Methanol, propanol, isobutanol, isoamyl alcohol, 2-phenylethanol, acetaldehyde, 1,1-diethoxyethane, acetoin, ethyl acetate, ethyl lactate, and ethyl succinate and the polyols 2,3-butanediol (levo and meso forms) and glycerol were quantified by direct injection of wine samples. Linear responses over the usual concentration ranges for these compounds and r2 values from 0.9932 to 0.9998 were obtained. The confidence limits for the mean values ranged from 2.34% for diethyl succinate to 8.52% for 1,1-diethoxyethane, both at a probability level of 0.05. Relative errors ranged from 8 to 10% for the polyols and 1,1-diethoxyethane and were all less than 5% for alcohols and acetaldehyde. The proposed method is useful with a view to identifying relationships between alcoholic fermentation byproducts and controlling biological or chemical aging in wines.     

Fast screening method for volatile compounds of oak wood used for aging wines by headspace SPME-GC-MS (SIM)

A headspace solid-phase microextraction (HS-SPME) method is proposed for analyzing the main volatile components from a sensory standpoint (furfural, oak lactones, eugenol, vanillin, and syringaldehyde) present in nontoasted and toasted oak wood of different origins. To maximize the yield of compounds extracted from wood chips and to obtain a good precision of the method, the most important variables affecting HS-SPME have been studied. The best results were obtained when the sample was heated at 70 degrees C and the headspace extracted for 40 min with a DVB/CAR/PDMS fiber, which gave the overall best recovery. The values for the repeatability ranged from 6.4 to 7.8%, and those for the reproducibility from 5.4 to 8.7%. The precision of the results obtained makes the proposed technique appropriate for its use in characterizing oak wood samples of different origins and in the selection of the most suitable oak wood to age wines and spirits, on the basis of the chemical composition of the wood samples.     

Use of an autosampler for dynamic headspace extraction of volatile compounds from grains and effect of added water on the extraction.

An autosampler attached to a purge and trap instrument was used to aid routine analyses of grain samples for volatile compounds associated with off-odors. Trapped volatiles were transferred to a gas chromatograph/mass spectrometer instrument for separation and detection. Dynamic extraction of volatiles from approximately 18 g of whole grain at 80 degrees C was accomplished by purging helium through a sample vial with a Teflon-lined septum on each end. The autosampler automatically added internal standard to the sample before purging began, which required the addition of 1 mL of water for complete transfer of the standard to the sample. The added water enhanced extraction of 1-octen-3-ol, 1-octen-3-one, and some other compounds from soybeans but not from starchy grains such as corn and wheat. Addition of a free radical scavenger, such as citric acid, greatly diminished the recovery of 1-octen-3-ol and 1-octen-3-one from soybeans.     

Monitoring toasting intensity of barrels by chromatographic analysis of volatile compounds from toasted oak wood.

Toasting changes both the quantity and the quality of the extractable substances in the oak wood of barrels used for the aging of fine wines and spirits. Mastery and repeatability of toasting are vital in the production of quality barrels to be used for the aging of wines and spirits. In this study, we show that it is possible for a given cooperage to differentiate barrel toasting levels by analyzing a certain number of volatile and semivolatile compounds resulting from the thermal degradation of oak. Toasted wood components, which can be extracted by the wines or spirits during the aging process, are normally analyzed after the wood has soaked in standard alcoholic solutions and can be used to control the intensity of the wood toasting. The results of the comparative analysis presented in this work show that headspace analysis with a microextractive method using a stationary polydimethylsiloxane type phase is a promising technique for analyzing toasted oak wood from barrels. It is easier to use than the traditional maceration and extraction method and provides similar information.     

Release kinetics of volatile organic compounds from roasted and ground coffee: online measurements by PTR-MS and mathematical modeling

The present work shows the possibilities and limitations in modeling release kinetics of volatile organic compounds (VOCs) from roasted and ground coffee by applying physical and empirical models such as the diffusion and Weibull models. The release kinetics of VOCs were measured online by proton transfer reaction-mass spectrometry (PTR-MS). Compounds were identified by GC-MS, and the contribution of the individual compounds to different mass fragments was elucidated by GC/PTR-MS. Coffee samples roasted to different roasting degrees and ground to different particle sizes were studied under dry and wet stripping conditions. To investigate the accuracy of modeling the VOC release kinetics recorded using PTR-MS, online kinetics were compared with kinetics reconstituted from purge and trap samplings. Results showed that uncertainties in ion intensities due to the presence of isobaric species may prevent the development of a robust mathematical model. Of the 20 identified compounds, 5 were affected to a lower extent as their contribution to specific m/z intensity varied by <15% over the stripping time. The kinetics of these compounds were fitted using physical and statistical models, respectively, the diffusion and Weibull models, which helped to identify the underlying release mechanisms. For dry stripping, the diffusion model allowed a good representation of the release kinetics, whereas for wet stripping conditions, release patterns were very complex and almost specific for each compound analyzed. In the case of prewetted coffee, varying particle size (approximately 400-1200 microm) had no significant effect on the VOC release rate, whereas for dry coffee, the release was faster for smaller particles. The absence of particle size effect in wet coffee was attributed to the increase of opened porosity and compound diffusivity by solubilization and matrix relaxation. To conclude, the accurate modeling of VOC release kinetics from coffee allowed small variations in compound release to be discriminated. Furthermore, it evidenced the different aroma compositions that may be obtained depending on the time when VOCs are recovered.     

中试规模猪粪堆肥挥发性有机物排放特征

为监测堆肥过程挥发性有机物(volatile organic compounds,VOCs)排放情况,该文开展了猪粪堆肥现场试验,采用苏玛罐采样,气相色谱-质谱法分析了猪粪好氧堆肥过程中VOCs浓度。结果表明:猪粪好氧堆肥过程中可以检测出的VOCs有81种,包括烷烃类34种,芳香烃类21种,卤烃类19种,胺类1种,含硫化合物3种,氟利昂类3种;其中检出率高且浓度远远超过其嗅阈值的VOCs包括三甲胺、二甲基硫、二甲基二硫和二甲基三硫,VOCs排放主要发生在堆肥的前2周。该研究将为控制猪粪堆肥过程中VOCs气体排放提供科学数据支持。     

Optimizing headspace temperature and time sampling for identification of volatile compounds in ground roasted Arabica coffee

Equilibration time and temperature were the factors studied to choose the best conditions for analyzing volatiles in roasted ground Arabica coffee by a static headspace sampling extraction method. Three temperatures of equilibration were studied: 60, 80, and 90 degrees C. A larger quantity of volatile compounds was extracted at 90 degrees C than at 80 or 60 degrees C, although the same qualitative profile was found for each. The extraction of the volatile compounds was studied at seven different equilibration times: 30, 45, 60, 80, 100, 120, and 150 min. The best time of equilibration for headspace analysis of roasted ground Arabica coffee should be selected depending on the chemical class or compound studied. One hundred and twenty-two volatile compounds were identified, including 26 furans, 20 ketones, 20 pyrazines, 9 alcohols, 9 aldehydes, 8 esters, 6 pyrroles, 6 thiophenes, 4 sulfur compounds, 3 benzenic compounds, 2 phenolic compounds, 2 pyridines, 2 thiazoles, 1 oxazole, 1 lactone, 1 alkane, 1 alkene, and 1 acid.