Interactions with aroma compound

Mannoproteins are complex hydrocolloids released from yeast cell walls during autolysis (Goncalves et al., 2002 Charpentier et al., 2004). According to Feuillat (2003), mannoproteins are important to wine quality as these contribute to protein and tartrate stability, interact with aroma compounds, decrease the astringency and bitterness of tannins, and increase the body of wine. For instance, Dupin et al. (2000) reported that mannoproteins prevent protein haze formation. Using a model wine. Lubbers et al. (1994) noted that yeast cell walls bound volatile aroma compounds, especially those more hydrophobic, and could potentially change the sensory characteristics of wines through losses of these aromas. 

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. 

Other than studies on the role of proteins released by yeast during autolysis (mannoproteins) on wine aroma, little work has been reported on interactions of other proteins with aroma compounds. One study investigating such interactions was published by Druaux et al. (1995). They used synthetic wines and bovine serum albumin (BSA) as a model protein. This protein was found to bind 5-decalactone and there was greater binding when in water than in a model wine environment (pH 3.5 and 10% ethanol). To our knowledge this is the only study focused on elucidating the effect of proteins (others than mannoproteins) on the aroma release in wine or model wine. 

The interaction between aroma compounds and other wine micro-organisms (e.g. lactic acid bacteria) or with metabolites produced during malolactic fermentation has been studied to a limited extent. Interactions between polysaccharides produced by the most common wine lactic bacteria (Oenoccocus oeni) during malolactic fermentation have been shown to be responsible for the reduced volatility of some aroma compounds in wines (Boido et al. 2002). The possibility of direct interactions between the surface of the bacteria cells and aroma compounds should also be considered since this type of interaction has been found for other food lactic bacteria (Ly et al. 2008). 

This paper reviews the interactions between aroma compounds and other components of a wine matrix colloids, fining agents and ethanol. Studies are carried out with model systems and instrumental methods to investigate flavor-matrix interactions. 

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. 

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. 

There is very little published on the interaction of either taste or aroma components with minor components in foods. Earlier in this chapter (Section 6.3.2), some discussion was presented on the interaction of high potency sweeteners with aroma. There is substantial interest in this particular interaction since the industry would like to know why diet products do not taste like the full sugar versions and vice versa. There are few other flavonfood interactions that have such a strong economic link to support this type of research activity. One other area that has received some attention is the interaction of melanoidins with aroma compounds in roasted coffee. This is again driven by economic considerations. A brief discussion of this interaction and pH effects follows. 

The unwanted interactions of aroma compounds with dairy products can be minimized when the mechanisms involved are known and the flavor and production process are adapted accordingly. 

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. 

Meat aroma is not the result of one chemical constituent but the sum of the sensory effects of many of these volatiles. Over 90% of the volume of volatile constituents from freshly roasted beef is from lipid, but approximately 40 percent of the volatiles from the aqueous fraction are thought to be heterocyclic compounds, many resulting from Maillard reaction products or their interactions with other ingredients. 

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. 

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. 

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