Volatility of aroma compounds

Tandy, P., Courthaudon, J.-L., Dubois, C., and Voilley, A. Effect of interface in model food emulsions on the volatility of aroma compounds, / Agric. Food Chem., 44(2) 526-530, 1996. 

Polysaccharides, including starches and dextrins, have been shown to reduce the volatility of aroma compounds, such as limonene, isoamyl acetate, ethyl hexanoate and beta-ionones.237... 

Athes, V, Lillo, M.P.Y., Bernard, C., Perez-Correa, R., Souchon 1. (2004). Comparison of experimental methods for measuring infinite dilution volatilities of aroma compounds in water/ethanol mixtures J. Agric. Food Chem, 52, 2021-2027. 

The interactions between aroma compounds and macromolecules from yeast released during alcoholic fermentation (F) and autolysis (A) were studied by the headspace technique (11). The values of infinite dilution activity coefficients of volatile compounds were measured in a model wine with and without macromolecules at Ig/L (Table I). The volatility of ethyl decanoate stays constant in the presence of both extracts. For ethyl hexanoate and octanal, the F extract produces a significant (P< 0.01) decrease in the activity coefficient, by 12 and 8% respectively. Conversely F extract increases the volatility of isoamyl alcohol and ethyl octanoate by 6 and 19% respectively. The A extract increases the volatility of ethyl hexanoate by 6% and the volatility of ethyl octanoate by 15%. These results demonstrate the complex influence of macromolecules from yeast released during fermentation or autolysis on the volatility of aroma compounds. 

This study demonstrated the influence of natural colloids from wine (mannoproteins released from yeast) on the volatility of aroma compounds and therefore the possible role of these minor components of a wine matrix on sensory properties of wine. The physico-chemical interactions between aroma substances and exocellular yeast material depend on the nature of volatile compounds and of the macromolecules. 

Effect of Ethanol on Volatility of Aroma Compounds. The activity coefficients of volatile compounds obtained by headspace method are lower in the presence of ethanol at 126 ml/L than in water (Table V). The headspace responses of aroma compounds are reduced by one-half (11-18). The aroma compoimds are not very polar and are more soluble in ethanol than in water hence the activity coefficient decreases, as shown by other authors for alcoholic beverages (19). This effect of solubilisation can be explained by the presence of interactions between aroma compound, water and ethanol. 

The physico-chemical interactions between aroma compounds and other components depend on the nature of volatile compounds. The level of binding generally increased with the hydrophobic nature of the aroma. However interactions also depend on the nature of macromolecules such as yeast walls, mannoproteins, bentonite or smaller molecule such as ethanol. As a function of the nature of non-volatile component, the increase or decrease in the volatility of aroma compounds can influence largely the overall aroma of wine. 

The effect of ethanol on the volatility of aroma compounds is shown and it clearly appears that ethanol leads to a modification in macromolecule conformation such as protein, which changes the binding capacity of the macromolecule. 

Bianchi, F., Careri, M., and Musci, M. (2005). Volatile norisoprenoids as markers of botanical origin of Sardinian strawberry-tree (Arbutus unedo L.) honey Characterisation of aroma compounds by dynamic headspace extraction and gas chromatography-mass spectrometry. Food Chem. 89,527-532. 

The analysis of aroma compounds begins with the preparation of a concentrate containing the volatiles that smell like the starting material. However, as odorants are substances with a wide variety of functional groups, there is no ideal... 

Solvent extraction is an excellent choice for aroma-compound isolation from foods when applicable. Unfortunately, many foods contain some lipid material, which limits the use of this technique since the lipid components would be extracted along with the aroma compounds. Alcohol-containing foods also present a problem in that the choice solvents (e.g. dichloromethane and diethyl ether) would both extract alcohol from the product, so one obtains a dilute solution of recovered volatiles in ethanol. Ethanol is problematic since it has a high boiling point (relative to the isolated aroma compounds), and in concentration for analysis, a significant proportion of aroma compounds would be lost with the ethanol. As one would expect, the recovery of aroma compounds by solvent extraction is dependent upon the solvent being used, the extraction technique (batch or continuous), and the time and temperature of extraction. 

If one is considering the recovery of aroma compounds from waste gas streams, one should investigate the pollution-control literature. There are a large number of patents and scientific articles that deal with this issue. The techniques used are generally aimed at the removal of trace volatiles in air streams and are potentially suited to aroma recovery. The primary consideration is whether the techniques yield an isolate safe for human consumption. 

Besides the structural elucidation of glycosides, research is focused on the application of glycosidases to liberate the aroma-active aglycons from their bound forms. The development of a continuous process of enzymatic treatment (simultaneous enzyme catalysis extraction) [50] opened the doors for the industrial large-scale production of aroma compounds from their non-volatile conjugates. 

Volatiles (GC-FID) Alternate Protocol Quantification of Aroma Compounds by Isotope Dilution Gl.3.1... 

Aroma compounds are present in minute levels in foods, often at the ppb level ( ig/liter). In order to analyze compounds at these levels, isolation and concentration techniques are needed. However, isolation of aroma compounds from a food matrix, which contains proteins, fats, and carbohydrates, is not always simple. For foods without fat, solvent extraction (unit gu) can be used. In foods containing fat, simultaneous distillation extraction (SDE see Basic Protocol 1) provides an excellent option. Concentration of headspace gases onto volatile traps allows sampling of the headspace in order to obtain sufficient material for identification of more volatile compounds. A separate protocol (see Basic Protocol 2) shows how volatile traps can be used and then desorbed thermally directly onto a GC column. For both protocols, the subsequent separation by GC and identification by appropriate detectors is described in unitgu. 

The release of aroma compounds in the mouth during eating is primarily determined kinetically, rather than thermodynamically, because of the processes occurring when food is consumed. The model-mouth system was developed to study in vitro-like aroma release and considers the bolus volume, volume of the mouth, temperature, salivation, and mastication (van Ruth et al., 1994). Volatile compounds in the effluent of the model mouth are collected on porous polymers, such as Tenax TA. Alternatively, the effluent can be measured on-line by direct mass spectrometry techniques. The model mouth can be used to study the effects of food composition and structure on aroma release, as well as the influence of oral parameters related to eating behavior. 

Equilibrium concentrations describe the maximum possible concentration of each compound volatilized in the nosespace. Despite the fact that the process of eating takes place under dynamic conditions, many studies of volatilization of flavor compounds are conducted under closed equilibrium conditions. Theoretical equilibrium volatility is described by Raoulf s law and Henry s law for a description of these laws, refer to a basic thermodynamics text such as McMurry and Fay (1998). Raoult s law does not describe the volatility of flavors in eating systems because it is based upon the volatility of a compound in a pure state. In real systems, a flavor compound is present at a low concentration and does not interact with itself. Henry s law is followed for real solutions of nonelectrolytes at low concentrations, and is more applicable than Raoult s law because aroma compounds are almost always present at very dilute levels (i.e., ppm). Unfortunately, Henry s law does not account for interactions with the solvent, which is common with flavors in real systems. The absence of a predictive model for real flavor release necessitates the use of empirical measurements. 

The analysis of aroma compounds starts with the isolation of the volatile fraction from the food. Techniques used in the preparation of flavor extracts from foods have recently been reviewed [7-9], The most important task in the choice of the isolation procedure is to test whether the flavor of the extract is identical or at least similar to the flavor of the food itself. This has to be checked by a sensory evaluation of the food extract (e.g., after dilution with an appropriate medium like water or oil) before a time consuming chemical analysis is performed. 

Aging is important in mead production, particularly in relation to the development of aroma compounds, particularly ethyl acetate. Aging usually lasts between 1 and 10 years. Nevertheless, caution is required as ethyl acetate is sometimes considered an off-flavor, with a solvent-like odor (Mendes-Ferreira et al., 2010). Roldan et al. (2011) has observed that ethyl acetate content is related to the acetic acid content—meads with higher volatile acidity had higher ethyl acetate values. 

In Figure 3, as in Figure 2, samples isolated from oats with 7.4% and 8.3% lipid content were different with regard to chemical composition. Since the oil itself may play several roles, for example as generator of aroma compounds as well as solvent for other volatile compounds, it is of interest to follow the aroma pattern in the abovementioned samples. The amount of heterocycles decreased in most cases when the initial oat lipid content increased. Compounds such as pyrazine derivatives (methyl, 2,5-dimethyl, 2,6-dimethyl, 2-ethyl-5-methyl, trimethyl, 2,5-methyl-3-ethyl), furfural, 5-... 

Chilli or paprika is used for flavour, not heat, in some cuisines. Flavour is a complex sensation determined in the mouth. One of the most potent volatiles known to humans is found in chilli, the pyrazine 2-methoxy-3-isobutyl-pyrazine, the green bell pepper smell. Reports indicate that humans can detect this odour at two parts per trillion. Luning et al. (1994) reported the presence of more than 80 odour compounds in C. annuum. C.frutescenscv. Tabasco contained 125 compounds whose relative abundance changed with the season of harvest. The composition of aroma compounds of Tabasco differed significantly from that of the green... 

Silva et al. (2006) showed from sensory analysis that aromatic extracts obtained with a pentane/ether (1/1 v/v) solvent mixture, from cured vanilla beans, provided the flavour most representative of vanilla bean. They found clear differences between the numbers of aroma compounds identified in different organic aroma extracts 65 volatiles were identified in a pentane/diethyl ether extract by GC-MS analysis ether extraction gave 54 volatiles the pentane/dichlo-romethane solvent yielded only 41 volatiles. The volatile compounds identified included... 

Different studies have focused on the biosynthesis of aroma compounds during MLF and the concomitant organoleptic consequences (Laurent et al. 1994). Maicas et al. (1999) demonstrated that MLF noticeably changes major and minor volatile... 

Although there are many studies in the literature that have focused on the identification and quantification of wine aroma compounds, to understand fully wine aroma perception it is necessary to incorporate the study of the interactions between aroma components and non-volatile wine matrix macro-components. This phenomenon influences aroma volatility and solubility, and thus its release from wine. Aroma release ultimately influences aroma perception. Although some research has been devoted to the study of interactions of aroma compounds and non-volatile components of wine, the diversity and significant of these interactions have not been thoroughly considered. This chapter is devoted to a discussion of this topic. 

Partitioning of volatile substances between the liquid and gas phases is mainly governed by aroma compound volatility and solubility. These physicochemical properties are expected to be influenced by wine constituents present in the medium, for instance polysaccharides, polyphenols, proteins among others. Consideration of the physicochemical interactions that occur between aroma compounds and wine constituents is necessary to understand the perception of wine aroma during consumption. The binding that occurs at a molecular level reflects changes at a macroscopic level of the thermodynamic equilibrium, such as volatility and solubility, or changes in kinetic phenomena. Thus, thermodynamic and dynamic approaches can be used to study the behaviour of aroma compounds in simple (model) or complex (foods) media. 

Other methods to determine the interactions between aroma compounds and wine matrix components do not involve gas phase measurements. For example, the equilibrium dialysis method has been applied for determining interactions between yeast macromolecules and some wine aroma compounds (Lubbers et al. 1994a) and more recently to study the interaction of aroma compounds and catequins in aqueous solution (Jung and Ebeler 2003). While this method can be set up in different ways, a simple approach is to fill a dialysis cell (two chambers separated by a semiper-meable membrane) with an aromatized liquid. A non-volatile component of wine can be added to one chamber of the cell and then the system allowed to come to equilibrium. If the added non-volatile component binds the aroma compound, the other chamber will be depleted by this binding. Quantification of this change in concentration permits calculating the quantity that is bound to the added substrate. 

There are few studies reporting on the effect of ethanol on the release of aroma compounds using dynamic methodologies. In one study (dynamic headspace analysis and APCI-MS), Tsachaki et al. (2005) observed that in aqueous systems (no ethanol) there was a rapid decrease in MS signal intensity until the rate of replenishment equalled the rate of loss from headspace purging. However, above ethanolic solutions, there was a similar initial rapid decrease followed by a steady state loss at much higher levels (at 50-90%) of the initial relative intensity depending on the volatile compound (Fig. 8F.2). In contrast to the aroma release effects noted under... 

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