Foods are complex multi-component systems which are composed of volatile and non-volatile substances. The flavour profile of a food is an important criterion for the selection of our foodstuffs.
The main objective of this study was the clarification of the complex relationships of the flavour release as a function of the composition of the food matrix at molecular level. Therefore the influence of matrix effects onto the partition coefficients, odour activity values and sensory properties of selected flavour compounds, in model and in real food systems were investigated. Different matrices were selected to measure their influence onto the partition coefficients of odorants: water, water-ethanol- mixtures, matrices containing lipids and more complex samples, such as mixtures of water, oil, proteins and polysaccharides. The studies included a series of lactones, esters and alcohols (γ-octalactone, γ-nonalactone, γ- decalactone, δ-octalactone, δ-nonalactone, δ-decalactone, ethyl hexanoate and ethyl octanoate, 3-methyl-1-butanol and 2-phenylethanol).
The vapour pressures and partition coefficients were determined using static headspace gas chromatography (HS-GC) techniques. The influence of the model systems on the adsorptions of the odorants at the gas-tight syringes were taken into account. The results obtained, showed that the vapour pressures of the flavour compounds are decreasing with the increasing of the molecular weight of the compounds. The comparison of water/air partition coefficients (logPW/A) with miglyol/air partition coefficients of selected odorants (logPM/A) showed that for miglyol system, the logPM/A are higher than the logPW/A for all flavour compounds studied. The measurement of the partition coefficients of selected aroma compounds in water-oil matrices (emulsions) revealed that the fat content of emulsions influence significantly the partition coefficients of odorants. The highest partition coefficients were obtained in emulsions where the portion between water/miglyol/emulsifier was: 47.5 + 47.5 + 5, w/w/w.
In the present study the flavour release of different aroma compounds (ethyl hexanoate and S- (-)-limonene) in carbohydrate-water solutions was examined. The static headspace method allows the measurement of the released odour components that interact with β -cyclodextrin. The HS-GC analysis of β -cyclodextrin-water/odorant mixtures showed a reduction of the odorant in presence of the carbohydrate.
The influence of the various matrices on the human biological response of odorants was investigated by an olfactometer (e.g. determination of the threshold values of odorants in air and in the presence of ethanol) and the headspace odour activity values (HOAV’s) were calculated. The results showed that the threshold values in air in absence of ethanol were lower than the values in presence of ethanol, which means the presence of ethanol in the matrix increase the threshold value of the odorant.
The studies also included the influence of wine matrix onto the partition coefficients of important wine flavour compounds. The quantification of the aroma compounds in white wine samples was achieved by isotope dilution analyses and standard addition method. Odorants in the headspace above wines were analysed by HS-GC techniques and the partition coefficients (wine/air) calculated. The results pointed out that the presence of ethanol in wine matrix does not influence the partition coefficients of selected aroma compounds. The highest partition coefficients in wines were found for the two alcohols: 2-phenylethanol and 3- methyl-1-butanol.
Concerning COST Action 921 custard samples were investigated as real foodstuff and the aroma compounds were quantified in the matrix and in the headspace above the food. The research data indicated that the partition coefficients custard/air are located between the partition coefficients water/air and partition coefficients miglyol/air, but closer to the miglyol/air values. Furthermore the mass transfer rates of selected odorants were investigated in custard- and milk powder/water samples. The values of the mass transfer rate were found higher in milk powder/water systems than in custard model. Nevertheless the results indicated that the viscosity of the matrix did not significantly influence the values of mass transfer rate of selected flavour compounds.
Molecular Modelling methods have been used for the prediction of solvation free energies of the flavour compounds studied in different model solutions, e.g. water and water-oil systems. The results showed that the predicted values (Mopac 97) for γ-decalactone, γ-nonalactone and 2-phenylethanol in water are in good agreement with experimentally solvation free energies.