Influence of the food matrix structure on the retention of aroma compounds

The retention of the aroma compounds in a multicomponent medium like the food matrix is influenced by their affinity with the protein when lipid is present at a low level (0.5%). The effect of the structure of the media is also studied by using two media with the same composition; one was emusified, and the other was not. Among the studied aroma compounds, 2-nonanone and isoamyl acetate present opposite behaviors: the volatility of isoamyl acetate is not affected by the change of the medium structure whereas that of 2-nonanone increases. The decrease of retention of 2-nonanone in an emulsified system would be due to a modification of the fixation site for this compound on the protein or to a competition between the lipid and the aroma compound while the protein is adsorbed at the lipid-water interface.     

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.     

Influence of physicochemical interactions between amylose and aroma compounds on the retention of aroma in food-like matrices

In food matrices, where starch is often used as a gelling or texturing agent, the occurrence of amylose-aroma complexes and their effect on the release of aroma compounds are difficult to determine. Indeed, thick or gelled systems are known to reduce the diffusion rate of flavor molecules, resulting in an increase of retention. Moreover, interactions between aroma compounds and matrix components might increase the retention of aroma compounds. The complexing behavior of three aroma compounds with amylose was studied by DSC and X-ray diffraction to determine the relative importance of these two factors. Their interaction properties were different: two of them formed complexes, and the third did not. These aroma compounds were added in food matrices containing different starches that induced different textures. Their retention was studied by static headspace analysis. The retention of aroma compounds appeared to depend on the amylose/amylopectin ratio of starch, both from the formation of complexes and by a viscosity effect.     

Antioxidant properties of aroma compounds isolated from soybeans and mung beans

Aroma compounds contained in the extracts of soybean and mung bean that possess antioxidant activity were identified by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). The major aroma constituents of soybeans were 1-octen-3-ol (13.699 ppm), maltol (1.662 ppm), phenylethyl alcohol (1.474 ppm), hexanol (1.430 ppm), and gamma-butyrolactone (1.370 ppm). The major aroma constituents of mung beans were hexanol (3.234 ppm), benzyl alcohol (2.060 ppm), gamma-butyrolactone (1.857 ppm), 2-methyl-2-propenal (1. 633 ppm), and pentanol (1.363 ppm). The major aroma chemicals of soybeans and mung beans were examined for antioxidative activities in two different assays. Eugenol, maltol, benzyl alcohol, and 1-octen-3-ol showed potent antioxidative activities in two different assays. Eugenol, maltol, benzyl alcohol, and 1-octen-3-ol inhibited the oxidation of hexanal by 100%, 93%, 84%, and 32%, respectively, for a period of 40 days at the 500 microg/mL level. Eugenol, maltol, benzyl alcohol, and 1-octen-3-ol inhibited malonaldehyde (MA) formation from cod liver oil by 91%, 78%, 78%, and 78%, respectively, at the 160 microg/mL level. The antioxidative activity of eugenol was comparable to that of the natural antioxidant alpha-tocopherol (vitamin E).     

Retronasal transport of aroma compounds

A comparison was made between the amounts of volatiles in the headspace above a solution and the breath volatile content (exhaled from the nose or mouth) after consumption of the same solution. The amounts of volatiles in the breath were lower than those in the headspace, with breath exhaled via the mouth containing, on average, 8-fold more volatiles than breath exhaled via the nose. Dilution of the sample by saliva in-mouth did not appear to be a major factor affecting volatile delivery. Instead, the rate of in vivo equilibration (mass transfer) appeared to be the most significant factor, principally affecting volatile delivery from the solution to the gas phase. Thereafter, gas-phase dilution of the volatile as it passed through the upper airway resulted in a further decrease in volatile concentration. The final factor affecting the volatile concentration exhaled from the nose was absorption of volatiles to the nasal epithelia, which was greatest for those compounds with the lowest air/water partition coefficients.     

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.     

In vivo aroma release of milk gels of different hardnesses: inter-individual differences and their consequences on aroma perception

The effect of textural modifications of solid milk gels on in vivo aroma release and aroma perception was investigated with a panel of 14 subjects. Great inter-individual differences were observed on aroma-release data, and the consequences of these differences on aroma perception were studied. From a hierarchical cluster analysis performed with several parameters extracted from release curves, the subjects were gathered into two groups, and a specific aroma-release profile was identified for each one. Then, by using a sensory profile, we showed that the intensity of the aroma perception was dependent on the release profile presented by the panelist. Second, we observed that, during the chewing phase, the aroma was perceived as more intense for the firmer gel and for panelists for whom the aroma release begins during the chewing of the product.     

Comparison of key aroma compounds in cooked brown rice varieties based on aroma extract dilution analyses

The aroma compounds present in cooked brown rice of the three varieties Improved Malagkit Sungsong (IMS), Basmati 370 (B 370), and Khaskhani (KK), and of the variety Indica (German supermarket sample), were identified on the basis of aroma extract dilution analyses (AEDA). A total of 41 odor-active compounds were identified, of which eleven are reported for the first time as rice constituents. 2-Amino acetophenone (medicinal, phenolic), which was up to now unknown in rice aroma, exhibited the highest flavor dilution (FD) factor among the 30 to 39 odor-active compounds detected in all four varieties. 2-Acetyl-1-pyrroline, exhibiting an intense popcorn-like aroma-note, was confirmed as a further key aroma constituent in IMS, B 370, and KK, but was not important in Indica. Differences in the FD factors between the varieties were found for the previously unknown rice aroma compound 3-hydroxy-4,5-dimethyl-2(5H)-furanone (Sotolon; seasoning-like), which was higher in B 370 than in IMS and KK. In IMS, a yet unknown, spicy smelling component with a very high FD factor could be detected, which contributed with lower FD factors to the overall aromas of B 370 and KK, and was not present in Indica. The latter variety, which was available on the German market, differed most in its overall aroma from the three Asian brown rices.     

Approaches to wine aroma: release of aroma compounds from reactions between cysteine and carbonyl compounds in wine

Under conditions close to those of wine, that is, low pH, aqueous medium, and low temperatures, this work examines the role of carbonyl (acetoin and acetol) and dicarbonyl (glyoxal, methylglyoxal, diacetyl, and pentane-2,3-dione) compounds associated with cysteine in the formation of odorous products. In particular, thiazole, 4-methylthiazole, 2-acetylthiazole, and trimethyloxazole and two sulfur and oxygenated heterocyclic compounds, 2-furanmethanethiol and thiophene-2-thiol, are examined. For thiophene-2-thiol, the reactional mechanism is proposed. Attempts were made to detect these compounds in wines from various origins. Certain molecules were identified for the first time in wine.     

Influence of strawberry yogurt composition on aroma release

The primary objective of this study was to determine how yogurt ingredients affect aroma release in the mouth during eating. A model strawberry flavor consisting of ethyl butanoate, ethyl 3-methylbutanoate, (Z)-hex-3-enol, 2-methylbutanoic acid, 5-hexylhydro-2(3H)-furanone, and 3-methyl-3-phenylglycidic acid ethyl ester was added to unflavored, unsweetened yogurt that had different added sweeteners and hydrocolloids. In all, 12 yogurt formulations were examined to determine the effects of gelatin, modified food starch, pectin, sucrose, high-fructose corn syrup, and aspartame on aroma release. Aroma release was monitored by breath-by-breath analysis (proton-transfer reaction-mass spectrometry) during eating of the test yogurts. Results showed aroma release of the ethyl butanoate, (Z)-hex-3-enol, and ethyl 3-methylbutanoate to be suppressed by sweeteners, with 55 DE high-fructose corn syrup having the greatest effect. Addition of thickening agents had no significant effect on the aroma release profiles of the compounds under study.     

Potent aroma compounds of two red wine vinegars

Gas chromatography olfactometry (GCO) was used to determine key aroma compounds of two red wine vinegars. Sensory analysis was performed to choose the best neutralization agent of acetic acid (NaOH or MgO) and to test representativeness of four extracts obtained by different methods (dichloromethane extraction, XAD-2, mixture of XAD-2 and XAD-7, and Extrelut resins extraction). Neutralization with NaOH followed by dichloromethane extraction was selected to extract volatile compounds of vinegars. Key odorant compounds were determined by GCO based on detection frequency with 13 people. In the two red wine vinegars, 13 odors were perceived by at least 70% of the panelists, and 8 compounds among the 13 were identified: acetic acid, 3-methylbutyric acid, 2-phenyl-1-ethanol, 2, 3-butanedione, butyric acid, 2-methylbutyric acid, mixture of 2- and 3-methyl-1-butanol, and two newly identified compounds in vinegar, 3-hydroxy-2-pentanone and 3-(methylthio)-1-propanal. Quantification of all the volatile compounds was performed by GC-FID, and 10 other compounds were identified for the first time in wine vinegar.     

Influence of ingredients on the self-diffusion of aroma compounds in a model fruit preparation: an nuclear magnetic resonance-diffusion-ordered spectroscopy investigation

Diffusion-ordered spectroscopy (DOSY)-pulsed field gradient (PGF) nuclear magnetic resonance (NMR) spectroscopy was used to measure self-diffusion coefficients of aroma molecules in model fruit preparations. The impact of the sucrose content on aroma diffusion was specifically investigated, and the relationship with viscosity, water activity, and dry matter parameters was evidenced. DOSY-PGF NMR spectroscopy was found to be a relevant and accurate technique to follow self-diffusion of aroma compounds at low concentrations in a complex food matrix and to obtain information on diffusion of the sucrose and of the water molecules. We showed that aroma self-diffusion was strongly decreased in fruit preparation because of the high sucrose content, which induces the formation of a network through hydrogen bonds with water. Self-diffusion coefficients were determined for aroma molecules of different natures, and values are related to the physicochemical properties of the molecule.     

Influence of eggs on the aroma composition of a sponge cake and on the aroma release in model studies on flavored sponge cakes

The use of solvent-assisted flavor evaporation extraction (SAFE) and purge and trap in Tenax allowed the identification of more than 100 volatile compounds in a sponge cake (SC-e). Gas chromatography-olfactometry (GC-O) of the SAFE extracts of crumb and crust were achieved in order to determine the most potent odorants of SC-e. The change in the traditional dough formulation of SC-e in which eggs were substituted by baking powder (SC-b) as the leavening agent produced important changes in some key aroma compounds. The release curves of some aroma compounds-some of them generated during baking and others added in the dough-were followed by cumulative headspace analysis. In the flavored SC-b, the aroma release curves showed a plateau after 15 min of purge, while the release increased proportionally with the purge time in the flavored SC-e. In general, except for some of the aroma compounds with the highest log P values, the rate of release of most of the added and generated aroma compounds was significantly influenced by the changes in the cake formulation. The higher rates of release found for the aroma compounds in SC-b could contribute to explain its rapid exhaustion of aroma compounds in the purge and trap experiments and might lead to poorer sensorial characteristics of this cake during storage.     

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.     

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.     

Elucidation of the emulsification properties of sugar beet pectin

A protocol has been developed to fractionate sugar beet pectin using hydrophobic affinity chromatography. Three samples eluted from the column using 4 M NaCl as solvent (fractions 1A, 1B, and 1C), two fractions eluted using 2 M NaCl (fractions 2A and 2B), and one fraction eluted using water (fraction 3). The fractions were shown to be very polydisperse, and differences between the GPC refractive index and UV absorbance (214 nm) elution profiles demonstrated chemical heterogeneity. They were found to contain significantly different proportions of protein (1A, 2.79%; 1B, 0.97%; 1C, 0.77%; 2A, 1.41%; 2B, 5.09%; and 3, 5.89%) and ferulic acid (approximately 1A, 0.5%; 1B, 0.5%; 1C, 0.9%; 2B, 1.5%; and 3, 2%). The weight-average molecular mass, M(w), of the fractions also varied (1A, 153 kDa; 1B, 155 kDa; 1C, 306 kDa; 2A, 562 kDa; 2B, 470 kDa; 3, 282 kDa). Three fractions, that is, 1A, 1B, and 3, produced orange oil emulsions with a relatively small droplet size that were stable over a period of weeks. The other three fractions (1C, 2A, and 2B with higher M(w) values) produced emulsions with an initially larger droplet size, and the droplet size increased considerably over time. The increased droplet size may be influenced by the viscosity of the aqueous continuous phase. There was no simple relationship between protein or ferulic acid content and emulsification ability. For example, fraction 1B, which contained the lowest proportion of both protein and ferulic acid, produced stable emulsions of similar droplet size to fraction 3, which contained the largest proportion of protein and ferulic acid. The role of protein in the emulsification process was investigated by measuring the amount of protein in the aqueous phase before and after emulsification. It was clearly demonstrated that proteinaceous material adsorbed at the oil-water interface. It is evident that the emulsification properties of sugar beet pectin are influenced by the accessibility of the protein and ferulic acid groups to the surface of the oil droplets, the proportion of ester groups, and the molecular mass distribution of the fractions.     

Biosynthesis of strawberry aroma compounds through amino acid metabolism

The fate of amino acids in relation to aroma biogenesis was studied in strawberries using the in vitro growth approach. This fruit presented differences in the level of metabolization for different amino acids. Incubations of strawberries with L-isoleucine gave rise to an increase of fourteen compounds in this fruit aroma, either not detected previously or constituents of strawberry aroma. However, L-valine incubations did not provide a significant change in this fruit aroma. Strawberry feeding with L-isoleucine resulted in a 7-fold increase in the sum of 2-methylbutanoate esters, and a double production of 2-methylbutyl esters compared to those of control fruits. Around 94% of the ester increase corresponded to 2-methylbutanoates, with ethyl 2-methylbutanoate being the most representative compound (92%). On the other hand, among the 2-methylbutyl esters, comprising around 6% of total aroma volatiles increase, 2-methylbutyl acetate was the major compound (95%) arising from L-isoleucine strawberry feeding. The role of enzymatic activities within the amino acid metabolic pathway in strawberry fruits is discussed.     

Odor-active compounds of Iberian hams with different aroma characteristics

The odor-active compounds of different commercial types of Iberian hams (Montanera and Pienso) were researched by gas chromatography-olfactometry based on a detection frequency method. The hams (long- and short-Montanera and Pienso Iberian hams) showed different sensory profiles, differences being significant for Montanera ham typical odor, aroma intensity and persistence, and cured and moldy aroma. Significant differences were also found for some odorants. The largest differences appeared in 2-acetyl-1-pyrroline, hexanal, (Z)-3-hexenal, ethyl 2-methylbutyrate, (E)-2-hexenal, 1-octen-3-one, 1-octen-3-ol, 2-propionyl-1-pyrroline, octanal, and an unknown odorant. Sensory characteristics and olfactometric profiles were significantly different between Montanera and Pienso hams. Significant differences also appeared between long- and short-Montanera hams, which shows great variability in this commercial type. Otherwise, the largest scores for moldy aroma in long-Montanera hams matched with the largest detection frequency of 1-octen-3-one and 1-octen-3-ol in this group.     

Modeling the partition of volatile aroma compounds from a cloud emulsion

Parameters determining the partitioning behavior of volatile compounds between a cloud emulsion and the gas phase were measured under static equilibrium headspace conditions, using volatiles (e.g., ethyl hexanoate, cymene, and octanol) representing different volatilities and different degrees of hydrophobicity. The significant factors were the molecular characteristics of the volatile and the concentration of the oil phase. The nature of the lipid (C8 and C12 triglycerides), particle size, and emulsifier type (modified starch and gum arabic) did not significantly alter volatile partitioning. An empirical model based on the partition behavior and physicochemical parameters of 67 volatile compounds was produced. This predicted the partition of volatiles (R(2) = 0.83) in cloud emulsions as a function of lipid content. The significant terms (P < 0.05) in the empirical model were Log P, Log solubility, the dipole vector, and the oil fraction.     

A hairy root culture of melon produces aroma compounds

Musk melon is the favorite fruit with a high market value in Japan, and the fragrance is one of the major factors determining the fruit quality of melon. In this study, mutant melon hairy roots which had been induced by means of the T-DNA insertion mutagenesis were found to produce volatile compounds with the fruity fragrance of mature melon. The volatile compounds were extracted and identified by GLC-mass spectrometry. Some essential oils such as (Z)-3-hexenol, (E)-2-hexenal, 1-nonanol, and (Z)-6-nonenol were stably synthesized by these hairy roots despite the increased number of subcultures. The productivity of these compounds by the best hairy root line was shown to be considerably higher than naturally ripened melon fruits.