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.     

Effect of fat nature and aroma compound hydrophobicity on flavor release from complex food emulsions

Complex food emulsions containing either hydrogenated palm kernel oil (vegetable fat) or anhydrous milk fat (animal fat) were flavored by using different aroma compounds. The fats differed by their fatty acid and triacylglycerol compositions and by their melting behavior, while the aroma compounds (ethyl butanoate, ethyl hexanoate, methyl hexanoate, mesifurane, linalool, diacetyl, cis-3-hexen-1-ol, and gamma-octalactone) differed by their hydrophobicity. Application of differential scanning calorimetry to fat samples in bulk and emulsified forms indicated differences in the ratio of solid-to-liquid between temperatures ranging from 10 to 35 degrees C. Solid-phase microextraction coupled with GC-MS analysis indicated that flavor release from food emulsions containing animal or vegetable fat differed depending on both the fat nature and flavor compound hydrophobicity. The release of diacetyl was higher for emulsions containing animal fat, whereas the release of esters was higher for emulsions containing vegetable fat. The release of cis-3-hexenol, linalool, gamma-octalactone, and mesifurane (2,5-dimethyl-4-methoxy-(2H)-furan-3-one) was very similar for the two fatty systems. The above results were discussed not only in terms of aroma compound hydrophobicity, but also in terms of structural properties of the emulsions as affected by the lipid source.     

Effect of emulsion properties on release of esters under static headspace, in vivo, and artificial throat conditions in relation to sensory intensity

The effects of oil content and droplet size distributions of dilute oil-in-water emulsions on release of four esters with different hydrophobicities were studied under in vivo, static headspace, and artificial throat conditions. The effect of oil content on orthonasal and retronasal perceived intensity of ethyl hexanoate was studied using a seven-person panel. With increasing oil content and with a higher hydrophobicity of the aroma compound, a stronger decrease in aroma release was found. This effect was stronger under static headspace conditions than under in vivo and artificial throat conditions, and the sensory intensity of ethyl hexanoate was perceived stronger orthonasally than retronasally. The lowest effective oil content was determined for all systems. Of the compounds tested, droplet size distribution only influenced the in vivo release of geranyl acetate. The artificial throat results correlated well with in vivo release, giving support to the assumption that a thin layer of liquid remaining in the throat after swallowing determines aroma release.     

Headspace solid-phase microextraction method for the study of the volatility of selected flavor compounds

Changes in the volatility of selected flavor compounds in the presence of nonvolatile food matrix components were studied using headspace solid-phase microextraction (HS-SPME) combined with GC-MS quantification. Time-dependent adsorption profiles to the SPME fiber and the partition coefficients between different phases were obtained for several individual volatiles, showing that HS-SPME analysis with a short sampling time can be used to determine the "true" headspace concentration at equilibrium between the headspace and a sample matrix. Equilibrium dialysis followed by HS-SPME/GC-MS was carried out to confirm the ability of HS-SPME extraction for monitoring the free volatile compounds in the presence of proteins. In particular, a short sampling time (1 min) avoided additional extraction of volatiles bound to the protein. Interactions between several selected flavor compounds and nonvolatile food matrix components [beta-lactoglobulin or (+)-catechin] were also studied by means of HS-SPME/GC-MS analysis. The volatility of ethyl hexanoate, heptanone, and hexanal was significantly decreased by the addition of beta-lactoglobulin compared to that of isoamyl acetate. Catechin decreased the volatility of ethyl hexanoate and hexanal by 10-20% and increased that of 2-heptanone by approximately 15%. This study indicates that HS-SPME can be a useful tool for the study of the interactions between volatile compounds and nonvolatile matrix components provided the kinetic and thermodynamic behavior of the volatiles in relation to the fiber chosen for the studies is carefully considered.     

Delayed volatile compound release properties of self-assembly structures in emulsions

Temporal release and retention of aroma compounds from structured emulsions (where unsaturated monoglycerides are added to the oil) and conventional oil-in-water emulsions were studied using in vitro dynamic headspace analysis by proton-transfer reaction mass spectrometry and static headspace analysis by gas chromatography-mass spectrometry. Under dynamic conditions, the structured emulsion exhibited delayed release compared to the oil-in-water emulsion containing the same lipid content of 5%. The time to maximum concentration T max of amphiphilic and lipophilic aroma compounds increased by a factor of 1.2 (for 3 E-hexenal) to 1.9 (for octanal). The aroma release profile of the 5% lipid structured emulsion was close to that obtained for the oil-in-water emulsion containing 10% lipid. Under static conditions, the 5% lipid structured emulsion retained more of the most lipophilic aroma compounds than its counterpart 5% oil-in-water nonstructured emulsion. The present study provides potential solutions for modulating aroma release profiles of reduced-fat foods by self-assembly structures.     

Comparison of nosespace,headspace, and sensory intensity ratings for the evaluation of flavor absorption by fat

The goal of this study was to better understand the correspondence between sensory perception and in-nose compound concentration. Five aroma compounds at three different concentrations increasing by factors of 4 were added to four matrixes (water, skim milk, 2.7% fat milk, and 3.8% fat milk). These were evaluated by nosespace analysis with detection by proton transfer reaction mass spectrometry (PTR-MS), using five panelists. These same panelists evaluated the perceived intensity of each compound in the matrixes at the three concentrations. PTR-MS quantification found that the percent released from an aqueous solution swallowed immediately was between 0.1 and 0.6%, depending on the compound. The nosespace and sensory results showed the expected effect of fat on release, where lipophilic compounds showed reductions in release as fat content increases. The effect is less than that observed in headspace studies. A general correlation between nosespace concentration and sensory intensity ratings was found. However, examples of perceptual masking were found where higher fat milks showed reductions in aroma compound intensity ratings, even if the nosespace concentrations were the same.     

Headspace solid phase microextraction and gas chromatography-olfactometry dilution analysis of young and aged Chinese "Yanghe Daqu" liquors

The aroma compounds of young and aged Chinese "Yanghe Daqu" liquor samples were extracted by solid phase microextraction (SPME) and analyzed by gas chromatography (GC)-olfactometry dilution analysis. The original liquor samples were diluted with deionized water to give a final alcohol content of 14% (v/v). The samples were stepwise diluted (1:1) with 14% (by volume) ethanol-water solution and then extracted by headspace SPME. The samples were preequilibrated at 50 degrees C for 15 min and extracted with stirring at the same temperature for 30 min prior to injection into GC. The aroma compounds were identified by both GC-MS and GC-olfactometry using DB-Wax and DB-5 columns. The results suggested that esters were the major contributors to Yanghe Daqu liquor aroma. Ethyl hexanoate, ethyl butanoate, and ethyl pentanoate had very high flavor dilution values in both young and aged liquors (FD > 8192). Methyl hexanoate, ethyl heptanoate, ethyl benzoate, and butyl hexanoate could also be very important because of their high flavor dilution values (FD > or = 256). Moreover, two acetals, 1,1-diethoxyethane and 1,1-diethoxy-3-methylbutane, also were shown high flavor dilution values in Yanghe Daqu liquors (FD > or = 256). Other aroma compounds having moderate flavor dilution values included acetaldehyde, 3-methylbutanol, and 2-pentanol (FD > or = 32). Comparing young and aged liquors, the aroma profiles were similar, but the aroma compounds in the aged sample had higher flavor dilution values than in the young ones.     

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.     

Retention of aroma compounds in starch matrices: competitions between aroma compounds toward amylose and amylopectin

The retention of three aroma compounds-isoamyl acetate, ethyl hexanoate, and linalool--from starch-containing model food matrices was measured by headspace analysis, under equilibrium conditions. We studied systems containing standard or waxy corn starch with one or two aroma compounds. The three studied aroma compounds interact differently: ethyl hexanoate and linalool form complexes with amylose, and isoamyl acetate cannot. However, in systems containing one aroma compound, we observed with both starches a significant retention of the three molecules. These results indicate that amylopectin could play a role in the retention of aroma. In systems containing two aroma compounds in a blend, the retentions measured for isoamyl acetate and for linalool were either equal to or less than those in systems where they were added alone. This phenomenon was attributed to competition between aroma compounds to bind with starch. The retention of aroma compounds blended in starch-based systems gave us additional information which confirmed that interactions occur not only with amylose but also with amylopectin.     

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.     

Headspace GC and sensory analysis characterization of the influence of different milk additives on the flavor release of coffee beverages

Previous investigations of coffee flavor have been confined to the analysis of the aroma substances. These investigations showed that about 30 volatile compounds were substantially responsible for the coffee flavor. The aim of this study was to investigate the influence of different milk additives and one coffee whitener on the release of flavor impact compounds from coffee beverages. For the investigation of these effects an external static headspace technique was developed. With this technique the most potent odorants of the coffee beverage were determined. Analyses were performed by gas chromatography/olfactometry, flame ionization detection, and mass spectrometric detection. In addition, sensory studies of the odor profiles were performed. Milk and vegetable products as additives for coffee beverages affected the release of aroma substances in the brew through their lipid, protein, and carbohydrate components. All beverages with an additive showed reduced, but typical, odor profiles for each additive.     

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.     

Influence of lipid fraction, emulsifier fraction, and mean particle diameter of oil-in-water emulsions on the release of 20 aroma compounds

The influence of compositional and structural properties of oil-in-water emulsions on aroma release was examined under mouth conditions. The lipid (0.40 and 0.65) and emulsifier fractions (0.007, 0.010, and 0.014) were varied, as well as the mean particle diameter of the dispersed phase (0.60, 0.73, 0.85, and 1.10 microm). Aroma compounds were isolated in a model mouth system and quantified by gas chromatography-mass spectrometry. Studies were carried out to separate effects on the thermodynamic and the kinetic components of aroma release using equilibrium headspace analysis to distinguish the thermodynamic component. The lipid phase of the emulsions was composed of sunflower oil and the emulsifier phase was Tween 20. The release of 20 aroma compounds was evaluated; the compounds included alcohols (1-propanol, 1-butanol, 3-methyl-1-butanol, 2-pentanol, 1-hexanol, and 2-nonanol), ketones (diacetyl, 2-butanone, 2-heptanone, 2-octanone, and 2-decanone), esters (ethyl acetate, propyl acetate, butyl acetate, and ethyl butyrate), aldehydes (hexanal, heptanal, and octanal), a terpene (alpha-pinene), and a sulfur compound (dimethyl sulfide). Decrease in lipid fraction and emulsifier fraction, as well as increase in particle diameter, increased aroma release under mouth conditions. Differences between groups of compounds and between compounds of homologous series with varying chain lengths were found. Changes in particle diameter had a considerable effect on the thermodynamic component of aroma release, whereas hardly any influence of the lipid fraction and emulsifier fraction was observed. Lipid fraction, emulsifier fraction, and particle diameter affected the kinetic component of aroma release, which could partially be attributed to changes in viscosity.     

Flavor release from salad dressings: sensory and physicochemical approaches in relation with the structure

The effect of process and formulation on sensory perception and flavor release was investigated on salad dressing models. Oil/vinegar emulsions (phi = 0.5, droplet size > 10 microm) with thickeners and a whey protein concentrate were prepared with different fat droplet sizes and different distributions of fat droplet size. The effect of the amount of emulsifier was also tested. Sensory profile analysis was performed by a trained panel and flavor release quantified by dynamic headspace analysis. When the droplet size is increased, the lemon smell and citrus aroma significantly increase, whereas the egg note, mustard, and butter aroma significantly decrease. The concentrations of alcohols and acids significantly increase when droplet size increases, whereas those of other compounds such as limonene or benzaldehyde significantly decrease. The dispersion of the droplet size has a small effect on flavor perception, and the effect of the increase of the amount of emulsifier is noticed only by instrumental analysis.     

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.     

Aroma volatility from aqueous sucrose solutions at low and subzero temperatures

The gas-liquid partition coefficients of ethyl acetate and ethyl hexanoate have been measured in water and aqueous sucrose solutions from 25 to -10 degrees C by dynamic headspace. Experiments were carried out on sucrose solutions at temperatures where no ice formation was possible. Results showed that when sucrose concentration increased, aroma volatility increased except for ethyl hexanoate and in the highest sucrose concentration solution (57.5%). A quasi-linear temperature decrease on aroma volatility was observed in sucrose solutions from 25 to around 4 and 0 degrees C. Then, from 0 to -10 degrees C, aroma volatility did not decrease: ethyl acetate volatility remained constant but that of ethyl hexanoate increased. Enthalpy of vaporization and activity coefficients of the aroma compounds were calculated.     

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.     

Headspace solid phase microextraction (SPME) analysis of flavor compounds in wines. Effect of the matrix volatile composition in the relative response factors in a wine model.

The application of headspace solid phase microextraction (SPME) for flavor analysis has been studied. Headspace SPME sampling was tested for nine common wine flavor compounds in 10% (v/v) aqueous ethanol: linalool, nerol, geraniol, 3-methyl-1-butanol, hexanol, 2-phenylethanol, ethyl hexanoate, ethyl octanoate, and ethyl decanoate. The chemical groups (monoterpenoids, aliphatic and aromatic alcohols, and esters) showed specific behavior in SPME analysis. SPME sampling parameters were optimized for these components. Relative response factors (RRFs), which establish the relationship between the concentration of the compound in the matrix liquid solution and the GC peak area, were estimated for all compounds. Log(10)(RRF) varied from 0 (3-methyl-1-butanol) to 3 (ethyl decanoate), according to their molecular weight. Quantification by SPME was shown to be highly dependent on the matrix composition; the compounds with higher RRF were the less affected. As a consequence, the data obtained with this methodology should be used taking into consideration these limitations, as shown in the analysis of four monovarietal Bairrada white wines (Arinto, Bical, Cerceal, and Maria Gomes).