Samuel Lubbers

Effects of physico-chemical parameters of a model wine on the binding of γ-decalactone on bovine serum albumin

Abstract To understand the effect of temperature, pH and the composition of alcoholic beverages in flavour-protein interactions, the binding of γ-decalactone to bovine serum albumin (BSA) was investigated using the equilibrium dialysis method. Thermodynamic analysis revealed that the affinity of aroma compound for BSA is higher at 10 °C than at 20 and 30 °C, while the number of binding sites (n = 6–7) is not modified at the three temperatures. pH did not have any appreciable effect on flavour binding in the presence of ethanol, but it was observed that a decrease of 1.8 pH unit reduces binding by 40% in its absence. The presence of ethanol has no effect on the number of binding sites and on the standard free energy (ΔG °) of the interactions. On the other hand, the binding constant (k) was 4.8-fold higher in water than in model wine (pH 3.5, ionized compounds, 10% w/w ethanol); so, the affinity of volatile compound was clearly lower in the model wine than in water.

Retention/release equilibrium of aroma compounds in fat‐free dairy gels

BACKGROUND The replacement of fat by thickeners in fat-free yogurts leads to an important modification of aroma compound partitioning, with an impact on aroma perception. Investigation of retention/release equilibria allows a good understanding of aroma compound behaviour depending on food composition. RESULTS Vapour/liquid equilibria of ten aroma compounds (two esters, two ketones, three aldehydes and three alcohols) in several media were studied to investigate the influence of pectin addition to fat-free dairy gel on the retention/release equilibrium. The partition coefficient of each aroma compound was measured by headspace analysis at equilibrium in six media (pure water, low-methoxylated pectin gels and dairy gels with or without added pectin). The release of aroma compounds was similar in the aqueous media (pure water and pectin gels) on the one hand and in the dairy gels on the other hand. However, a trend to greater release occurred with the addition of pectin in both cases. Four aroma compounds were more retained in dairy gels than in water and pectin gels. No relationship appeared between retention and either the chemical function or hydrophobicity (logP values) for the entire set. However, several subsets showed a linear correlation between K and logP values. CONCLUSION These results suggest that other structural properties than hydrophobicity are probably involved, changing the retention/release behaviour of aroma compounds according to the matrix composition. In order to probe the interactions, further experiments with a larger set of aroma compounds followed by molecular modelling interpretation are needed.

Proposed alternative phase ratio variation method for the calculation of liquid-vapour partition coefficients of volatiles.

The phase ratio variation PRV method is a classical way to determine the partition coefficients of volatile compounds between their solution and vapour phases in a variety of circumstances. However, some results obtained by this method can be disappointing. A new PRV equation in which the initial liquid-phase solute concentration is replaced by the liquid-phase solute concentration at equilibrium is proposed. This proposed PRV equation is a second-order polynomial equation. To thoroughly examine the possible modes of calculation, noisy dummy data were generated using both the classical, first-order PRV model (PRV(1)) and the proposed, second-order model (PRV(2)). Thus, pseudo-data obtained from simulations were compared to published experimental data. We observed that the second-order model, PRV(2), produces a lower variability, allowing improved K precision. Moreover, the obtained K(PRV(2)) values are very close to those obtained by classical equilibrium headspace analysis (EHSA). The PRV(2) model we propose responds to the demand for a simple, reliable method and is a useful alternative for the calculation of liquid-vapour partition coefficients.

Water and temperature contribution to the structuration of starch matrices in the presence of flavour

The effect of modulating the gelatinisation extent by hydration (50/50 and 80/20 water to starch ratio) and temperature (65 or 85 °C) on various properties of wheat starch in presence of flavours has been studied. The hydrothermal treatments resulted in samples with different properties. The lowest residual flavour content was found in samples treated at the highest hydration and temperature (85 °C) while the other treatment conditions led to samples with similar residual flavour content. Ethyl hexanoate significantly increased the characteristic pasting viscosities compared to starch±2-hexanone; suggesting a greater structuration with ethyl hexanoate. Heating starch in excess water caused amylopectin melting, but promoted an incomplete granular swelling as revealed by RVA. This study suggested that lowering the hydration upon treatment could limit both crystal melting (with a residual crystalline content up to 38% in the most extreme conditions) and granular swelling but increased granule organisation like following annealing.

Improvement of Partition Coefficients Determination of Aroma Compounds in Food Matrices by the Phase Ratio Variation Method

The Phase Ratio Variation (PRV) method is a very valuable method commonly used for liquid/vapor partition coefficients data acquisition of aroma compounds. Nevertheless, there are some limitations to this method, especially for volatile compounds. A careful examination of the PRV equation leads us to propose the following expression: 1/C vap-real = ( n liq /n 0 ) × 1 /C vap-ideal = ( n liq /n 0 ) × ( 1 /KC 0 + ( 1 /C o ) β ) We performed an examination for two cases of K values (K1=0.001 and K2=0.05), highlighting that a careful choice of β range values is crucial in the reliability of the regression calculation 1/A versus β.