Judging a book by its odour

Material degradomics borrows the informatics ethic from molecular biology and biochemistry and applies it to historical artefacts, in particular old books. Degradomics could allow conservators to profile the complete gamut of volatile organic compounds released by artefacts and so tailor their efforts to improving stability or halting damage.

One may not be able to tell a good book by its cover, but scientists can now reveal something about the condition of an old book or manuscript by its odour. Indeed, most bookworms would recognise the musty smell of an old book. However, writing in the journal Analytical Chemistry, Matija Strlic and colleagues in the University College London Centre for Sustainable Heritage, The Tate, in London, and the Faculty of Chemistry and Chemical Technology, at the University of Ljubljana, Slovenia, describe a new test that can measure the degree to which an old document or book has degraded by analysing the mixture of volatile organic compounds that produce that musty smell.

The non-destructive sniff test could help libraries and museums preserve a range of prized paper-based objects, some of which are degrading rapidly due to advancing age. The test could be especially important for conservation of materials that have not necessarily been stored in ideal conditions, providing useful information as to how best to save them from irreversible decline.

Strlic explains that an old book's musty odour is caused by hundreds of different VOCs released into the air from the paper, but the key to their success was the identification of 15 compounds that can be used as markers of degradation.
"The aroma of an old book is familiar to every user of a traditional library," the researchers say, "A combination of grassy notes with a tang of acids and a hint of vanilla over an underlying mustiness, this unmistakable smell is as much a part of the book as its contents."

The particular nose a book will have is due to a blend of compounds that result from the complex network of degradation pathways. It is partially dependent on the original composition of the object including paper substrate, applied media, binding, and glues, as well as the adhesion of growing moulds and other microscopic organisms.

This complicated mixture of volatile substances holds important clues to the paper's condition, the researchers add. Other industries have a keen interest in the taint and odour or paper and cardboard. The food and pharmaceuticals packaging industries, for instance, study the transfer of volatile compounds from such materials into product during shipping and storage. The recycling industry can also screen for VOCs to quantify the fraction of recycled pulp in board stock. Identification of volatiles is now an almost routine analytical challenge, the researchers say. In most of these cases, taking samples destructively so that analysis can be carried out is not really a serious issue. However, snipping a piece from a rare and precious paper artefact is a different story...

The new technique, given the catchy name of "material degradomics", analyses the volatiles emitted by the artefact non-invasively by headspace analysis and suggests pathways of their synthesis. The researchers used their degradomics approach to sniff 72 historical papers from the 19th and 20th centuries.

The historic paper sample collection was well-characterized for various properties, including degree of polymerization of the constituent cellulose, lignin content, gelatin content, pH, aluminium content, ash content, fibre composition, rosin content, and reducing group content.

Using supervised and unsupervised methods of multivariate data analysis, the team was able quantitatively correlate volatile degradation products with properties important for the preservation of historic paper. Many of these papers contain rosin (pine tar) and wood-derived fibre (lignin), which are the most rapidly degrading types of paper found in old books. They also identified fifteen major VOCs as candidates for markers to track the degradation processes in literary artefacts in addition to the well-known volatile paper degradation products, acetic acid and furfural. Most notable among these were lipid peroxidation products.

The team conclude that they have shown that volatile degradic footprinting is a key tool to advancing our understanding of the pathways leading to production of VOCs during paper degradation, the composition of papers can be deduced on the basis of volatile degradation products, and that VOCs, which generate the smell of books, provide information on paper condition and stability.