Aroma compound interactions

Fig. 3.1 Three factors influence flavour perception. The first includes all aspects that are related solely to the food, such as the aroma-active compounds present and interactions between the food matrix and aroma compounds. The second comprises all aspects related to the in-mouth situation. This makes the person eating the food an integral part of the system being analysed, and takes account of interactions between food and consumer. Finally, psychosocial and cognitive effects modulate aroma perception...

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. 

Pozo-Bayon, M. A. and Reineccius, G. (2009). Interactions between wine matrix macrocomponents and aroma compounds. In "Wine Chemistry and Biochemistry", (M. C. Polo and M. V. Moreno-Arribas, Eds), pp. 417- 35. Springer Life Sciences Publisher, New York. 

Heterocyclic aroma compounds found in meat primarily arise from interactions between mono- and dicarbonyl compounds, H2S and ammonia. The carbonyl compounds are derived from the Maillard reaction, including Strecker degradation of amino acids, oxidation of lipids and aldolization reactions. H2S is produced by thermal degradation of sulfur amino acids and ammonia by amino acid pyrolysis. 

Heterocyclic compounds are dominant among the aroma compounds produced in the Maillard reaction, and sulfur-containing heterocyclics have been shown to be particularly important in meat-like flavors. In a recent review, MacLeod (6) listed 78 compounds which have been reported in the literature as possessing meaty aromas seven are aliphatic sulfur compounds, the other 71 are heterocyclic of which 65 contain sulfur. The Strecker degradation of cysteine by dicarbonyls is an extremely important route for the formation of many heterocyclic sulfur compounds hydrogen sulfide and mercaptoacetaldehyde are formed by the decarboxylation and deamination of cysteine and provide reactive intermediates for interaction with other Maillard products. 

However, the formation of volatile aroma compounds from the interaction of Maillard intermediates with lipid-derived compounds has received little attention. 

Aroma compounds originate from biosynthetic pathways inside an animal, a botanical body, and other life-forms as well as enzymes and thus frequently carry chiral components within the molecule. Determination of such enantiomeric properties can, in many cases, be accomplished using a GC column with a chiral stationary phase (CSP) application.75-79 These columns, usually called chiral GC column, will provide diastereometric interaction that could lead to resolution of enantiomers. Commercially available chiral GC columns predominantly utilize cyclodextrin derivatives as CSPs. Chiral columns consisting of multiple cyclodextrin derivatives intending synergic effect in resolution property80 are also successful in the market. In practice, these columns are mainly operated as secondary columns in MDGC technique. 

Chalier, R, Angot, B., DelteU, D., Doco, T., Gunata, Z. (2007). Interaction between aroma compounds and whole mannoprotein isolated from Saccharomyces cerevisiae strains. Eood Chem., 100, 22-30. 

Finally, some of the most powerful wine aroma compounds take part in reversible interactions which evolve during wine aging and that can be reversed, at least in part, when the wine takes contact with air. These aspects have not yet been studied in depth, but it is well known that carbonyls form reversible associations with sulfur dioxide and that mercaptans take part in complex redox equilibria. These molecules involved in interactions or in redox equilibria are the most likely cause of the aromatic changes noted during the aging of wine or after the bottle is opened. 

Interactions Between Wine Matrix Macro-Components and Aroma Compounds... 

F.1.2 Methods to Measure Interactions Between Aroma Compounds and Wine... 

F.2 Interactions Between Aroma Compounds and Specific Wine Matrix Components. 421... 

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. 

The methods employed to measure the interactions that occur between aroma compounds and other food or beverage constituents are frequently based on measuring changes in the vapour-liquid equilibrium when different macromolecules are present in the media. The determination of the gas-liquid partitioning with and without a food macromolecule is widely employed. 

Some static headspace methods do not require an external calibration and are based on measurements performed at thermodynamic equilibrium between liquid and gas phase. In the phase ratio variation method (PRV) described by Ettre and Collaborators (1993), the partition coefficient calculation is based on the fact that the headspace concentration changes as a function of the phase volume ratio (gas and liquid phases), while the partition coefficient remains constant. This method has been recently applied to study the interactions between aroma compounds and macromolecules in different food systems (Savary et al. 2006, 2007) but so far not to the wine. 

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. 

The above-mentioned methods can be used to demonstrate the existence of molecular interactions between aroma compounds and other wine macromolecules nevertheless, they do not provide any insight into the nature of this interaction. Determining the nature of an interaction typically involves the use of spectroscopic methods unfortunately, this methodology has not been extensively applied to studying wine flavour interactions. 

Early studies carried out by King and Solms (1982) documented interactions between phenolic compounds and aroma compounds in water systems. They suggested that hydrophobic interactions between aroma compounds and phenolic compounds increased solubility of aroma compounds thereby decreasing the activity coefficient of the aroma compounds. 

Using exponential dilution analysis and an NMR technique, Dufour and Bayonove (1999) confirmed the existence of weak interactions between catequins and aroma compounds in model wine systems and they also agreed that mutual hydrophobicity was the driving force for this interaction. They also showed a different type of interaction depending on the type of polyphenols (catequin or tannin), and on the nature of the aroma compound. 

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