A bookworm beetle grub found inside a paperback book, showing some of the damage caused. Credit: Dominic Mason
A bookworm isn’t just a moniker voracious readers take pride in. There are actual bookworms—often larvae of various types of insects, including beetles, moths, cockroaches and more, that bore or chew through book bindings and pages in their search for food.
There are three common types of paste used in book binding. Wheat paste is the most common, dating as far back as Ancient Egypt. Even today, wheat starch paste is still used as an adhesive for repairs by book and paper conservators. Meanwhile, flour glues are made from the insides of wheat grains, which includes the gluten that’s so delicious to bookworms and destructive microorganisms. Starch glue, on the other hand, is made from the proteins that remain after most of that gluten is removed, making it less attractive to pests.
Still—despite their long history—little is known about the protein makeup of these adhesives. In a new study, scientists at George Mason University set out to change that by using mass spectrometry and proteomics to contribute insights on adhesiveness and how they degrade, providing critical information for book conservators.
As described in the paper published in ACS’ Journal of Proteome Research, the researchers first prepared the wheat paste glue and starch paste glue by dissolving it in ultrapure water. Then, they extracted proteins from these lab-made versions to create protein profiles—or proteomes. Finally, they used mass spectrometry data and bioinformatics software to identify the types and relative abundance of proteins in the samples.
The researchers detected the presence of 759 protein groups in the flour-based glue compared with 58 in the starch-based glue, highlighting the richer proteomic profile of the former. Additionally, according to the study results, the proteins in starch glue were particularly durable and flexible, making it a potentially better choice than flour glue for book repairs.
The team then used the protein profiles to analyze historic book binding samples from the National Library of Medicine (NLM) archives. They confirmed that the adhesives were flour-based—due to their gluten content—and even identified degraded gluten in the samples, indicating possible damage and a loss of stickiness. Examining book covers specifically, the study authors discovered that a chemical breakdown of leather and glue feed each other—leading to faster overall deterioration.
“This work provides information that could signal to a conservator the need for repair, potentially preventing a book from being damaged or destroyed,” say the study authors.
More broadly, the researchers say their results demonstrate the potential of protein analysis in guiding overall conservation efforts.
“Understanding the chemical changes of wheat-based adhesives is essential to adopting best practices for restoration and conservation purposes,” they conclude. “Further research on wheat pastes and other plant adhesives should consider the wide range of parameters, such as preparation recipes, additives, and aging, as well as the wide variety and composition of the raw material.”