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.     

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.     

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.     

Aromatic profile of aqueous banana essence and banana fruit by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O)

Gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O) were used to determine the aromatic composition and aroma active components of commercial banana essence and fresh banana fruit paste. Totals of 43 and 26 compounds were quantified in commercial banana essence and fresh banana fruit paste, respectively. Five new components in commercial banana essence were identified as methyl butyrate, 2,3-butanediol diacetate, 2-hydroxy-3-methylethylbutyrate, 1-methylbutyl isobutyrate, and ethyl 3-hydroxyhexanoate. A total of 42 components appear to contribute to the aromatic profile in banana. Isoamyl acetate, 2-pentanol acetate, 2-methyl-1-propanol, 3-methyl-1-butanol, 3-methylbutanal, acetal, isobutyl acetate, hexanal, ethyl butyrate, 2-heptanol, and butyl butyrate had high concentrations and were most detected by GC-O panelists in the commercial banana essence. Volatile components found only in fresh banana fruit paste that were detected by aroma panelists include E-2-hexenal, limonene, and eugenol.     

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.     

Behavior of flavor compounds in model food systems: a thermodynamic study

Physicochemical parameters, such as hydrophobicity, water solubility, and volatility, of four flavor compounds (ethyl acetate, ethyl butyrate, ethyl hexanoate, and 2-pentanone) were determined. The amount of flavor compounds released from different model matrices (mineral water, purified triolein, an oil-in-water emulsion, a carbohydrate matrix, and a complex matrix containing lipids and carbohydrates) into the gaseous phase was determined at thermodynamic equilibrium, at 37 degrees C, by static headspace gas chromatography. The degree of interaction between the flavor compounds and the matrix components was shown by measuring the percentage retention using the water matrix as the reference. The partition of flavor compounds was principally dependent on their hydrophobicity. Physicochemical interactions that occurred in the different media led to different degrees of flavor retention. An impact of fat on flavor retention was demonstrated when a water matrix and an oil-in-water matrix or carbohydrate and complex matrices were compared. A carbohydrate impact on flavor compound retention was also detected, which was evident even in the presence of lipids.     

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.     

Competitive binding of aroma compounds by beta-cyclodextrin.

Retention of six aroma compounds has been studied after dehydration of ternary mixtures of aroma water and beta-cyclodextrin. A maximal retention of a mole of aroma per mole of beta-cyclodextrin has been observed for five of the aroma compounds, whereas retention of benzyl alcohol can be twice as high. Retention of a mixture of aroma compounds has also been studied. It has been noted that when volatile compounds compete for the same binding sites on beta-cyclodextrin, ethyl hexanoate, 2-methylbutyric acid, and benzyl alcohol are, respectively, better retained than ethyl propionate, hexanoic acid, and hexanol. Preferential retention observed with esters can be simply explained by their difference of physicochemical properties, but for the acids and alcohols a study at the molecular scale has been necessary. The better retention of 2-methylbutyric acid can be explained by differences in the nature of interaction between the acids and their carrier. At least selectivity of retention noted for the alcohol could be due to a difference in the location of the guest and also a difference in the number of aroma molecules that can be bound per polysaccharide molecule.     

Verification of a mouth simulator by in vivo measurements

The volatile content of the effluent from the retronasal aroma simulator (RAS) was compared with that of human breath using mass spectroscopy (MS-Nose). The ratios of volatile compounds from the RAS were closely related to those from the panelists' breath with the correlation coefficients ranging from 0.97 to 0.99 from model food systems. A greater sensitivity using the RAS was achieved because higher concentrations of volatiles in the MS-Nose were produced from the RAS than from the breath. In analyzing the effects on volatility of RAS parameters including airflow rate, temperature, saliva ratio, and blending speed, airflow rate had the greatest effect. The correlation coefficients for the real food systems studied ranged from 0.83 to 0.99. The RAS gives a good approximation of time-averaged flavor release in the mouth as defined by breath-by-breath measurements.     

Characterization of odor-active compounds in guava wine

The volatile compounds of guava wine were isolated by continuous solvent extraction and analyzed by GC-FID and GC-MS. A total of 124 volatile constituents were detected, and 102 of them were positively identified. The composition of guava wine included 52 esters, 24 alcohols, 11 ketones, 7 acids, 6 aldehydes, 6 terpenes, 4 phenols and derivatives, 4 lactones, 4 sulfur-compounds, and 5 miscellaneous compounds. The aroma-active areas in the gas chromatogram were screened by application of the aroma extract dilution analysis and by odor activity values. Twelve odorants were considered as odor-active volatiles: (E)-β-damascenone, ethyl octanoate, ethyl 3-phenylpropanoate, ethyl hexanoate, 3-methylbutyl acetate, 2-methyltetrahydrothiophen-3-one, 2,5-dimethyl-4-methoxy-3(2H)-furanone, ethyl (E)-cinnamate, ethyl butanoate, (E)-cinnamyl acetate, 3-phenylpropyl acetate, and ethyl 2-methylpropanoate.     

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.     

Influence of wine structurally different polysaccharides on the volatility of aroma substances in a model system

The influence of native polysaccharides on wine organoleptic quality has not been yet clarified. Hence, the effect of purified fractions of arabinogalactan-proteins (AGPs), monomeric and dimeric rhamnogalacturonans II (mRG-II and dRG-II), and mannoproteins (MPs) on the volatility of various aroma substances was examined using the exponential dilution technique. The volatility of isoamyl acetate and ethyl hexanoate in a model wine system was not affected upon addition of wine polysaccharides in the range 5-20 g/L. At higher levels, the two esters were significantly retained in solution in the presence of the protein-rich polysaccharides MP0 and AGP0 and weakly salted out in the presence of the uronic acid-rich fractions AGP4, mRG-II, and dRG-II. In addition, the volatility increase caused by dRG-II on the esters was reversed when water was used as the solvent. 1-Hexanol exhibited retention in water with four fractions in the strength order AGP0 > dRG-II > mRG-II > AGP4 but was strongly salted out in the presence of fraction MP0. Furthermore, the diacetyl activity in water was overall not modified increasing only at high concentrations of AGP4. Reference polysaccharides dextrin and dextran were used for binding strength comparison.     

Changes in the volatile compounds and chemical and physical properties of Kuerle fragrant pear (Pyrus serotina Reld) during storage

Volatiles from stored Kuerle fragrant pears (Pyrus serotina Reld) were studied using high-resolution gas chromatography and the solid-phase microextraction (SPME) method of gas chromatography/mass spectrometry (GC/MS). The dominant components were hexanal, ethyl hexanoate, ethyl butanoate, ethyl acetate, hexyl acetate, ethanol, alpha-farnesene, butyl acetate, and ethyl (E,Z)-2,4-decadienoate. By using GC-olfactometry, it demonstrated that the volatile compounds from SPME were responsible for the aroma of the Kuerle fragrant pear. The levels of sugars, organic acids, and phenolic acids in Kuerle fragrant pears were investigated using high-performance liquid chromatography (HPLC). Fructose was the dominant sugar, followed by glucose and sucrose. With increasing storage time, sucrose levels decreased; however, changes in fructose and glucose levels were not remarkable. There was a slight decrease in flesh firmness during storage. The general soluble solids concentration (SSC) declined slightly after 5 months storage. Some aroma-related volatile components increased during storage, while others decreased, especially the esters. The organic acids and phenolic acids also changed. The flavor of the Kuerle fragrant pears was affected by the change of volatile compounds and changes in chemical and physical properties.     

Characterization of aroma compounds in apple cider using solvent-assisted flavor evaporation and headspace solid-phase microextraction

The aroma-active compounds in two apple ciders were identified using gas chromatography-olfactometry (GC-O) and GC-mass spectrometry (MS) techniques. The volatile compounds were extracted using solvent-assisted flavor evaporation (SAFE) and headspace solid-phase microextraction (HS-SPME). On the basis of odor intensity, the most important aroma compounds in the two apple cider samples were 2-phenylethanol, butanoic acid, octanoic acid, 2-methylbutanoic acid, 2-phenylethyl acetate, ethyl 2-methylbutanoate, ethyl butanoate, ethyl hexanoate, 4-ethylguaiacol, eugenol, and 4-vinylphenol. Sulfur-containing compounds, terpene derivatives, and lactones were also detected in ciders. Although most of the aroma compounds were common in both ciders, the aroma intensities were different. Comparison of extraction techniques showed that the SAFE technique had a higher recovery for acids and hydroxy-containing compounds, whereas the HS-SPME technique had a higher recovery for esters and highly volatile compounds.     

Relationships between volatile production, fruit quality, and sensory evaluation in Granny Smith apples stored in different controlled-atmosphere treatments by means of multivariate analysis.

Aroma compounds, quality parameters, and sensory evaluation of Granny Smith apples were analyzed after 3, 5, and 7 months of cold storage in three controlled-atmosphere (CA) treatments, in which oxygen and carbon dioxide were held at 1, 2, and 3%. During poststorage ripening, the apples were kept at 20 degrees C for 1, 5, and 10 days before analytical measurements were made. The highest volatile emission was obtained after 5 months of storage in all CA treatments, reaching its highest value when a low-oxygen CA (LO) was used. Ultralow-oxygen CA (ULO) showed the highest ability to maintain apple firmness. The correlation among analytical and sensory parameters suggests that ethyl 2-methylbutyrate, 1-butanol, pentyl acetate, and tert-butyl propionate are the aroma compounds with the highest influence in the sensorial score. Concerning CA treatments, LO and ULO appear to be very valuable technologies for maintaining the sensorial quality even after 7 months of storage.     

Effect of carbohydrate substrate on fermentation by kefir yeast supported on delignified cellulosic materials

The suitability of delignified cellulosic (DC) material supported kefir yeast to ferment raw materials that contain various single carbohydrates, for the production of potable alcohol and alcoholic drinks, is examined in this investigation. Results are reported of fermentations carried out with sucrose, fructose, and glucose in synthetic media. Repeated batch fermentations at various initial sugar concentrations of sucrose, fructose, and glucose were performed at 30 degrees C in the presence of the aforementioned biocatalyst. The results clearly show feasible yields in the range of 0.38-0.41 g/g, alcohol concentrations of 7.6-8.2% v/v, fermentation time of 90-115 h, and conversion of 92-96%. DC material supported kefir fermented 11-fold more rapidly than free cells and 9-fold more rapidly in comparison to kissiris supported kefir. The main volatile byproducts such as amyl alcohols (mixture of 2-methyl-1-butanol and 3-methyl-1-butanol), ethanal, and ethyl acetate were formed in all sugar fermentation products. The formation of 65-110 ppm of ethyl acetate is as high and even higher than that obtained with traditional wine yeasts. The increase of the initial concentration of sugar in the fermentation media resulted in an increase in contents of volatiles. The fine aroma that was obtained in the product of fructose could be attributed to the high percentage of ethyl acetate on total volatiles. The efficiency of DC material supported kefir was the same for the fermentations of individual sugars or a mixture of fructose, sucrose, and glucose. When whey with raisin extracts was fermented, lower yields were obtained but the aroma of the product was even better.     

五九香梨贮藏期间挥发性化合物和理化性状的变化(英)

利用高效液相色谱法测定贮藏期间五九香梨的糖和有机酸的组成及变化,采用固相微萃取方式（SPME）进行萃取,并结合气相色谱和质谱（GC/MS）分析检测梨果实中的挥发性香气成分。得出以下主要结论：果糖是五九香梨的主要糖类,其次是葡萄糖和蔗糖。随着贮藏期的延长,果糖先有增加的趋势,在贮藏的第三个月内,果糖含量处于最高,而蔗糖和葡萄糖减少趋势不明显。五九香梨果实中的主要有机酸是苹果酸和柠檬酸,整个贮藏期间,柠檬酸和酒石酸含量处于上升趋势,苹果酸和奎宁酸含量在第一、二月贮藏期间增加,而后开始下降;莽草酸含量在贮藏期第一到第三阶段上升,而后略下降;琥珀酸含量在第一到第二阶段变化不明显,接着有上升的趋势,在第三阶段含量达到最高,第四和第五阶段略低于第三阶段;乙酸含量变化不明显。梨果实的硬度略有下降,贮藏的前3个月,可溶性固形物含量有上升的趋势,随后开始缓慢下降。五九香梨的主要香气成分化合物有乙酸己酯 (49.35%),乙酸丁酯 (19.56%),己酸乙酯 (5.16%),丁酸乙酯 (4.92%),乙酸乙酯 (1.08%),(E,Z)-2,4-癸二烯酸乙酯 (0.84%)等。在整个贮藏期间,部分香气成分随着贮藏期的延长而略有增加,尤其是酯类化合物。结果显示：果实硬度、可溶性固形物、糖、有机酸和香气的组成与变化对五九香梨果实的品质都有一定的影响。     

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.