The behaviour of foie gras during cooking

The protein matrix was analysed in situ on tissue cryo-sections (6 microns thick) of foie gras sampled before and after cooking. The morphology of the protein matrix was characterised by histology on stained sections. The molecular structure was analysed on free-labelled tissue sections by FT-IR microspectroscopy (SMIS line) and synchrotron deep UV fluorescence microspectroscopy (DISCO line).

Before cooking, the protein matrix exhibited a rather fine morphology (cf. Figure 1) and the lipid droplets were small. After cooking, the matrix had thickened due to thermal denaturation and aggregation of proteins and the lipid droplets were larger, suggesting the fusion of smaller droplets during cooking. These findings were more marked when the fat loss was greater during cooking.

FT-IR microspectroscopy has provided information on the molecular structure of the proteins whereas fluorescence micro-spectroscopy characterised endogenous fluorescence attributed to tyrosine, tryptophan and collagen, and gives information on the composition of the biological tissue. Statistical analysis of the spectra showed a significant change in the composition and molecular structure of the protein during cooking. Furthermore, spectral differences dependent on the degree of fat loss were observed, either before or after cooking. These effects, even though slight, are significant enough to consider before cooking foie gras that could melt during cooking and to use it for the preparation of processed products.

Finally, the scientists have linked several analytical techniques which show that despite the standardisation of production and processes, the biophysical characteristics of raw foie gras may vary and all foie gras does not respond identically to cooking. Thierry Astruc, an author of the study, confirms the contribution of the synchrotron, “The chemical imaging techniques and localised spectroscopy are used to characterise the biological material in situ with minimal changes related to sample preparation. The coupling to synchrotron radiation allows the continuum of wavelengths to be exploited and the selection of those that are most relevant to amplifying the spectral responses. The spatial resolution improved significantly and the expertise of the scientists, on their equipment and in the data processing, ensures reliable results.”

When proteins are less heat sensitive, the lipid retention is better, which indicates better quality of foie gras. Doubtless, the researchers have also been able to verify the nuances of taste between the different samples....