Multimodal Mass Spectrometry Imaging to study aged cognac barrels – MULTI-ANGEL-MSI

The chemical interactions between the oak wood of the barrels and brandies are of high interest for the best possible understanding of the evolution over time of the products which are put to age in the barrels, as well as the control and the optimization of their taste qualities. On the one side most of the compounds extracted from wood by the alcohols are known, as are the chemical mechanisms of their transformation over time. On the other side the chemical composition of the wood of the barrels as a function of time - ageing in air before production, and ageing in the cellar in contact with alcohol - is known only globally, but not on a micrometric scale along thickness of the “tight and porous wall” that are the staves. The residual state of the barrels, from the inside to the outside of a stave, after the alcohol has been stored for several years to several decades, which can be likened to some kind of slow alcoholic extraction, is not known. It is known that a few percent of the alcohol evaporate through the wood each year, which is known as the "Angel's share". In addition, outside the barrels, in and around the cellars, there is an opportunistic fungus, Baudoinia compniacensis, known to grow in the presence of alcohol, but never on the wood itself. This fungus causes the blackening of outside and inside cellar walls.
Knowledge at the micrometric scale of the chemical composition of Cognac barrel staves, as well as research into the mechanisms of alcoholic growth, and repulsion by the wood, of the aforementioned fungus are of major importance and will be of interest to the industrial ecosystem of Cognac production and its traditional know-how.
Mass spectrometry imaging consists in recording mass spectra at regular intervals on a surface, which can then be used to reconstruct ion density maps that are called mass spectrometry images. Several methods exist to produce ions from the surface, and among them two are particularly popular, time-of-flight secondary ion mass spectrometry (TOF-SIMS), and matrix assisted laser desorption-ionization (MALDI source). The first makes it possible to record images of organic and inorganic ions at a spatial resolution of less than one micron, and also allows depth profile analyzes. The second allows access to larger biomolecules and, if coupled with Fourier transform mass spectrometers, provides excellent mass resolution (R > 100,000) and mass accuracy (1-2 ppm) at a spatial resolution of a few microns. The project gathers forces from two labs, LAMS in France and UBT in Germany, who are experts in these two methods, and who have already reached the proof-of-concept of the advantages of combining these them through a multimodal approach, to which is added the expertise of a laboratory bringing specialists in microbiology and analysis of metabolite networks (ICSN, France).
The project will combine two chemical imaging approaches, TOF-SIMS and MALDI, with the establishment of a multimodal analytical method, in order to study the chemical changes of oak wood with Cognac alcohols during aging in oak barrels, and the molecules protecting them from the fungus Baudoinia compniacensis. Chemical images of wood cross-sections from fresh and aged oak, from aged oak barrels (up to 150 years old), and of fungus cultures with and without contact to oak, will be acquired by TOF-SIMS and MALDI mass spectrometry.
Ion images from the analysis of wood and fungus will be combined with LC-MSMS data of extracts analysed which is analysed by advanced metabolite network algorithms (‘molecular networks’). This comprehensive study of the chemistry of the "Angels' share" will help to better understand the immaterial cultural heritage of the traditional methods and know-how of international reputation of the French cooperage.