Impact of the homogenization process on the structure and antioxidant properties of chitosan-lignin composite films.

This work investigated the impact of two homogenization treatments, High Shear (HS) and High Pressure (HP), on the structure and antioxidant activity of chitosan-lignin bio-composite films. Laser light scattering analysis revealed that smaller lignin particles were obtained after HP processing, around 0.6µm, compared to HS treatment, between 2.5 and 5µm. Moreover, these particles were more homogeneously distributed in the chitosan film matrix after HP process, while some aggregates remained after HS treatment, as highlighted by two-photon microscopy. The surface hydrophobicity of the composite films, as measured by water contact angle, increased after the two homogenization treatments. Finally, the antioxidant activity of the composite films was determined using the DPPH· assay. No significant difference in the radical scavenging activity was noticeable, neither after HS nor HP processing. However, a migration of lignin residues from the film to the extraction medium was noticed, particularly for HP process.

About the Role of the Bottleneck/Cork Interface on Oxygen Transfer.

The transfer of oxygen through a corked bottleneck was investigated using a manometric technique. First, the effect of cork compression on oxygen transfer was evaluated without considering the glass/cork interface. No significant effect of cork compression (at 23% strain, corresponding to the compression level of cork in a bottleneck for still wines) was noticeable on the effective diffusion coefficient of oxygen. The mean value of the effective diffusion coefficient is equal to 10(-8) m(2) s(-1), with a statistical distribution ranging from 10(-10) to 10(-7) m(2) s(-1), which is of the same order of magnitude as for the non-compressed cork. Then, oxygen transfer through cork compressed in a glass bottleneck was determined to assess the effect of the glass/cork interface. In the particular case of a gradient-imposed diffusion of oxygen through our model corked bottleneck system (dry cork without surface treatment; 200 and ∼0 hPa of oxygen on both sides of the sample), the mean effective diffusion coefficient is of 5 × 10(-7) m(2) s(-1), thus revealing the possible importance of the role of the glass/stopper interface in the oxygen transfer.

Diffusion of oxygen through cork stopper: is it a Knudsen or a Fickian mechanism?

The aim of this work is to identify which law governs oxygen transfer through cork: Knudsen or Fickian mechanism. This is important to better understand wine oxidation during post-bottling aging. Oxygen transfer through cork wafers is measured at 298 K using a manometric permeation technique. Depending on the mechanism, we can extract the transport coefficients. Increasing the initial pressure of oxygen from 50 to 800 hPa leads to a change in the values of the transport coefficients. This implies that oxygen transport through cork does not obey the Knudsen law. From these results, we conclude that the limiting step of oxygen transport through cork occurs in the cell wall following Fickian law. From the diffusion dependence's coefficients with pressure, we also extract by applying transition state theory an apparent activation volume of 45 ± 4 nm(3). This high value indicates that oxygen molecules also diffuse from one site to another by passing through a gas phase.