Effect of ethanol, temperature, and gas flow rate on volatile release from aqueous solutions under dynamic headspace dilution conditions

On the basis of a mechanistic model, the overall and liquid mass transfer coefficients of aroma compounds were estimated during aroma release when an inert gas diluted the static headspace over simple ethanol/water solutions (ethanol concentration = 120 mL x L(-1)). Studied for a range of 17 compounds, they were both increased in the ethanol/water solution compared to the water solution, showing a better mass transfer due to the presence of ethanol, additively to partition coefficient variation. Thermal imaging results showed differences in convection of the two systems (water and ethanol/water) arguing for ethanol convection enhancement inside the liquid. The effect of ethanol in the solution on mass transfer coefficients at different temperatures was minor. On the contrary, at different headspace dilution rates, the effect of ethanol in the solution helped to maintain the volatile headspace concentration close to equilibrium concentration, when the headspace was replenished 1-3 times per minute.     

Model studies on the release of aroma compounds from structured and nonstructured oil systems using proton-transfer reaction mass spectrometry

Relative retention, volatility, and temporal release of volatile compounds taken from aldehyde, ester, and alcohol chemical classes were studied at 70 degrees C in model systems using equilibrium static headspace analysis and real time dynamic headspace analysis. These systems were medium-chain triglycerides (MCT), sunflower oil, and two structured systems, i.e., water-in-oil emulsion and L2 phase (water-in-oil microemulsion). Hydrophilic domains of the emulsion type media retained specifically the hydrophilic compounds and alcohols. Four kinetic parameters characterizing the concentration- and time-dependent releases were extracted from the aroma release curves. Most of the kinetic parameter values were higher in structured systems than in oils particularly when using MCT. The oil nature was found to better control the dynamic release profiles than the system structures. The release parameters were well-related (i) to the volatile hydrophobicity as a function of the oil used and (ii) to the retention data in the specific case of the L2 phase due to a specific release behavior of alcohols.     

Dynamic headspace analysis of the release of volatile organic compounds from ethanolic systems by direct APCI-MS

Static equilibrium headspace was diluted with a stream of nitrogen to study the stability of the volatile headspace concentration. The headspace dilution profile of 18 volatile compounds above aqueous and ethanolic solutions was measured in real time using atmospheric pressure chemical ionization-mass spectrometry. Under dynamic conditions the volatiles headspace concentration above water solutions decreased readily upon dilution. The presence of ethanol helped to maintain the volatile headspace concentration when the ethanol solution concentration was above 50 mL/L. This effect was such that under dynamic conditions the absolute volatile concentration above an ethanolic solution was higher than that above an aqueous solution, contrary to results observed in equilibrium studies. The ratio of the headspace concentration of volatiles above ethanolic 120 mL/L and water solutions was correlated to their air/water partition coefficient.     

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.     

Effect of xanthan on flavor release from thickened viscous food model systems

The influence of xanthan concentration (0, 0.02, 0.1, 0.4, and 0.8% w/w) and bulk viscosity on the release of 20 aroma compounds of different chemical classes (5 aldehydes, 4 esters, 5 ketones, 3 alcohols, and 3 terpenes) was evaluated in xanthan-thickened food model systems having different viscosities. Interactions between flavor compounds and xanthan were assessed by measuring air-liquid partition coefficients, K, of aroma compounds in pure water and in the xanthan solutions by static headspace gas chromatography. Mass transfer of aroma compounds was estimated by dynamic headspace gas chromatography. Notably, limonene and some of the esters and aldehydes exhibited decreased K values in the presence of xanthan, indicating that the release of these volatile aroma compounds was reduced due to interaction with the xanthan matrix. The degree of interaction depended on the physicochemical characteristics of the aroma compounds. A similar tendency was observed at nonequilibrium with the decreases in release rates being most pronounced for limonene, followed by the esters and aldehydes, with no effect for ketones and an apparent "salting out" effect for alcohols. The reduction in flavor release by xanthan was thus dependent on the physicochemical properties of the aroma compounds and was apparently a result of the aroma-xanthan interactions and not influenced by the viscosity of the system itself.     

Effect of salivary components on volatile partitioning from solutions

Partition of fourteen volatile compounds, representing the diverse physicochemical properties of aroma compounds, was measured by static equilibrium headspace in solutions containing the components of artificial saliva, either singly or in mixtures. Comparison of a bovine salivary mucin and pig gastric mucin showed no significant difference in partition behavior of the volatiles, so gastric mucin was used. Mucin viscosity changed with pH, but binding of volatile compounds did not show a marked dependence on pH. All combinations of the salivary components were tested for their effect on partition. Three types of behavior were noted. Partition of some compounds was unaffected by mucin, and with other compounds mucin decreased partition, whereas another group showed a decrease with mucin that was affected by the presence of salivary salts and sugar. When volatiles or sugar were added to a mucin solution, the final headspace concentration depended on the order of addition, indicating some competition for binding. These solute-mucin effects are discussed in relation to mucin structure and behavior in solution.     

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.     

Flavor release and rheology behavior of strawberry fatfree stirred yogurt during storage

The influence of storage on the aroma release in headspace and rheological properties in strawberry-flavored fatfree stirred yogurts was determined. Three periods of storage at 10 degrees C were chosen for analysis: 7, 14, and 28 days. The headspace composition was assessed in a flask in static mode. The SPME fiber was carefully chosen, and results are presented in detail (choice and degradation). The flow properties of the final product were measured in order to follow n (flow behavior index) and K (consistency index), and the apparent viscosity was determined (eta in Pa.s). The quantity of flavors in the headspace of products at the 28 days of aging was significantly weaker for methyl 2-methyl butanoate, ethyl hexanoate, and hexyl acetate. The decrease was half of that in comparison with the seventh day. It was supposed that modification in rheological parameters can partly explain these results. Indeed, the apparent viscosity of the products significantly increased during the three times of storage. The composition of the flavored yogurt, proteins, exopolysaccharides, and fruit preparation, seemed to have a great impact on the release of aroma compounds. The aroma compound amount in the headspace decreased when the matrix changed from water to yogurt. With the fruit preparation, the headspace amounts for esters were significantly lower than in water alone, respectively, 23, 27, 29, and 17% less for methyl 2-methylbutanoate, ethyl hexanoate, hexyl acetate, and benzyl acetate. In flavored yogurt, the amount of aroma compounds in the headspace decreased again in comparison with the result obtained with the fruit preparation. Ethyl hexanoate and hexyl acetate presented the higher decreases of 48 and 53%, respectively.     

Analysis of volatile compounds released during the grinding of roasted coffee beans using solid-phase microextraction

A dynamic solid-phase microextraction (SPME) method to sample fresh headspace volatile compounds released during the grinding of roasted coffee beans was described and the analytical results using gas chromatography/mass spectrometry (GC/MS) and GC/olfactometry (GC/O) were compared to those of the conventional static SPME sampling methods using ground coffee. Volatile compounds released during the grinding of roasted coffee beans (150 g) were obtained by exposing the SPME fiber (poly(dimethylsiloxane)/divinylbenzene, PDMS/ DVB) for 8 min to nitrogen gas (600 mL/min) discharged from a glass vessel in which the electronic coffee grinder was enclosed. Identification and characterization of volatile compounds thus obtained were achieved by GC/MS and GC/O. Peak areas of 47 typical coffee volatile compounds, separated on total ion chromatogram (TIC), obtained by the dynamic SPME method, showed coefficients of variation less than 5% (n = 3) and the gas chromatographic profile of volatile compounds thus obtained was similar to that of the solvent extract of ground coffee, except for highly volatile compounds such as 4-hydroxy-2,5-dimethyl-3(2H)-furanone and 4-ethenyl-2-methoxyphenol. Also, SPME dilution analysis of volatile compounds released during the grinding of roasted coffee beans showed linear plots of peak area versus exposed fiber length (R (2) > 0.89). Compared with those of the headspace volatile compounds of ground coffee using GC/MS and GC/O, the volatile compounds generated during the grinding of roasted coffee beans were rich in nutty- and smoke-roast aromas.     

Partition and release of 21 aroma compounds during storage of a pectin gel system

The increasing popularity of low-fat products increases the need for a better understanding of how flavor release is affected by partial substitution of fat with hydrocolloids. Partitioning and release of aroma compounds from four pectin gels with different compositions were studied with static headspace and with a model mouth. Air/product partition coefficients determine the potential extent of aroma release, and mass transfer determines the rate at which aroma compounds are released to the vapor phase. This study showed that the gel network had large effects on the partition of aroma compounds between the gel and vapor phase. The specific properties of the aroma compounds were also of importance for the air/gel partition. Storage of the four gels showed that one of the weaker gels was influencing the concentration of aroma compounds in the headspace, probably caused by formation of a denser network over time.     

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.     

Comparison of different methods: static and dynamic headspace and solid-phase microextraction for the measurement of interactions between milk proteins and flavor compounds with an application to emulsions

Interactions between 10 aroma compounds from different chemical classes and 5 mixtures of milk proteins have been studied using static or dynamic headspace gas chromatography and solid-phase microextraction (SPME). Static headspace analysis allows the quantification of the release of only the most abundant compounds. Dynamic headspace analysis does not allow the discrimination of flavor release from the different protein mixtures, probably due to a displacement of headspace equilibrium. By SPME analysis and quantification by GC-MS (SIM mode) all of the volatiles were quantified. This method was optimized to better discriminate aroma release from the different milk protein mixtures and then from oil/water emulsions made with these proteins. The highest difference between the release in different proteins was observed for ethyl hexanoate, which has a great affinity for beta-lactoglobulin. Ethyl hexanoate is thus less released from models and emulsions containing this protein.     

Flavor release from iota-carrageenan matrices: a kinetic approach

Release of aroma compounds in selected iota-carrageenan systems was studied by static headspace analysis. By varying the sodium chloride content, different rheological behaviors were obtained ranging from solution to gel. From the release curves, mass transfer (h(D)) and partition coefficients (K(ga)) of ethyl butanoate, ethyl hexanoate, and linalool were extracted using a mathematical model based on the penetration theory. This model, previously developed for flavor release from stirred solutions, was found to fit well the data obtained from structured systems (nonstirred conditions) at the beginning and at the end of the release curves: this allowed the determination of h(D) and K(ga). Matrix effects appeared to be dependent on the chemical class of the compounds. For the alcohol, the main effect on both equilibrium partitioning and mass transfer across the interface was ascribed to a salting effect. In the opposite, for esters, iota-carrageenan addition induced an increase of aroma retention and also a slower transfer across the interface. The respective effects of an increasing viscosity of the medium and of the formation of a tridimensionnal network are discussed.     

Volatile release from an emulsion: headspace and in-mouth studies

The headspace concentrations of three esters above solutions containing emulsified lipids were more resistant to dilution by a stream of gas than those above water alone. The effect was greatest for ethyl octanoate, and least for ethyl butyrate, with ethyl hexanoate showing intermediate behavior. This correlated with their solubility in the lipid fraction of the emulsion. Headspace analysis (comparing the emulsion with water) underestimated the release of the esters during consumption. The ratios observed between water and emulsion systems were different for the maximum breath concentration compared with headspace analysis. The emulsion appears to have acted as a reservoir for volatile release, counteracting the effects of sample dilution by saliva.     

Volatile composition of sunflower oil-in-water emulsions during initial lipid oxidation: influence of pH.

The formation of odor active compounds resulting from initial lipid oxidation in sunflower oil-in-water emulsions was examined during storage at 60 degrees C. The emulsions differed in initial pH, that is, pH 3 and 6. The volatile compounds were isolated under mouth conditions and were analyzed by gas chromatography/sniffing port analysis. The lipid oxidation rate was followed by the formation of conjugated hydroperoxide dienes and headspace hexanal. The initial pH affected the lipid oxidation rate in the emulsions: the formation of conjugated diene hydroperoxides and the hexanal concentration in the static headspace were increased at pH 6. Pentanal, hexanal, 3-pentanol, and 1-octen-3-one showed odor activity in the emulsions after 6 days of storage, for both pH 3 and 6. Larger amounts of odor active compounds were released from the pH 6 emulsion with extended storage. It was shown that this increased release at pH 6 was not due to increased volatility because an increase in pH diminished the static headspace concentrations of added compounds in emulsions.     

Volatile release from aqueous solutions under dynamic headspace dilution conditions.

Static equilibrium was established between the gas phase (headspace) and an unstirred aqueous phase in a sealed vessel. The headspace was then diluted with air to mimic the situation when a container of food is opened and the volatiles are diluted by the surrounding air. Because this first volatile signal can influence overall flavor perception, the parameters controlling volatile release under these conditions are of interest. A mechanistic model was developed and validated experimentally. Release of compounds depended on the air-water partition coefficient (K(aw)) and the mass transport in both phases. For compounds with K(aw) values <10(-)(3), K(aw) was the factor determining release rate. When K(aw) was >10(-)(3), mass transport in the gas phase became significant and the Reynolds number played a role. Because release from packaged foods occurs at low Reynolds numbers, whereas most experiments are conducted at medium to high Reynolds numbers, the experimentally defined profile may not reflect the real situation.     

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.     

Experimental and modeling studies showing the effect of lipid type and level on flavor release from milk-based liquid emulsions

The purpose of this work was to study two key parameters of the lipid phase that influence flavor release-lipid level and lipid type-and to relate the results to a mass balance partition coefficient-based mathematical model. Release of 10 volatile compounds from milk-based emulsions at 10, 25, and 50 degrees C was monitored by 1-min headspace sampling with a solid-phase microextraction fiber, followed by GC-MS analysis. As compared to the observations for milk fat, changing to a lipophilic lipid (medium-chain triglycerides, MCT) and adding a monoglyceride-based surfactant did not influence the volatiles release. However, increasing the solid fat content was found to increase the release. At 25 degrees C, and even more so at 10 degrees C, concurrent with an increase in their solid fat content, hydrogenated palm fat emulsions showed increased flavor release over that observed for emulsions made with coconut oil, coconut oil with surfactant, milk fat, and MCT. However, at 50 degrees C, when hydrogenated palm fat emulsions had zero solid fat content, there was no difference in flavor release from that observed for milk fat emulsions. Varying milk fat at nine levels between 0 and 4.5% showed a systematic dependence of the release on the lipid level, dependent on compound lipophilicity. Close correlations were found between the experimental and model predictions with lipid level and percent liquid lipid as variables.     

Effect of copper on the volatility of aroma compounds in a model mouth system

Copper is thought to influence aroma perception by affecting volatility of aroma compounds in the mouth through interaction with salivary components, especially proteins. Our objective was to identify the effect of copper on the volatility of aroma compounds and the role of copper-protein interaction in volatile chemistry in the mouth. Copper (2.5 mg/L) and four aroma compounds (hexanal, butyl acetate, 2-heptanone, and ethyl hexanoate, 0.5 microL/L each) were added to model systems containing water, electrolytes, and artificial saliva at different pH levels. Headspace concentration of each volatile was measured using SPME-GC analysis. Copper in the model systems increased headspace concentration of volatiles at pH 6.5, but no change in volatility was observed at pH 7.0. At pH 7.5, the presence of copper in the artificial saliva system containing mucin and alpha-amylase decreased headspace volatile concentration, whereas histatin did not cause any changes in volatility. Effect of copper on volatiles at pH 6.5 may be due to increased solubility of copper at lower pH. Salivary proteins seem to interact with copper at pH 7.5. The interaction may change configuration of binding sites for aroma compounds in mucin.     

Inverse gas chromatographic evaluation of the influence of soy protein on the binding of selected butter flavor compounds in a wheat soda cracker system

Binding of selected volatile butter flavor compounds to wheat vs soy-containing crackers was studied by inverse gas chromatography (IGC), sensory evaluation, and equilibrium sorption measurements. IGC data showed greater binding of gamma-butyrolactone and butyric acid to both types of crackers than either diacetyl or hexanal, possibly due to the involvement of stronger binding forces such as hydrogen bonding and even ionic forces in the case of butyric acid. The presence of soy proteins did not affect binding of diacetyl and hexanal but increased binding of strongly interacting compounds gamma-butyrolactone and especially butyric acid, probably through enhanced matrix polarity. In agreement with the IGC data, sensory evaluation results showed that the headspace aroma intensities were similar between the two diacetyl-flavored crackers, while they significantly differed between the butyric acid-flavored crackers. In addition, equilibrium sorption measurement data showed that binding of butyric acid was higher in the soy-containing cracker, but sorption of diacetyl to the two crackers did not significantly differ.