Wheat-Based Glues in Conservation and Cultural Heritage: (Dis)solving the Proteome of Flour and Starch Pastes and Their Adhering Properties

Plant-based adhesives, such as those made from wheat,
have been
prominently used for books and paper-based objects and are also used
as conservation adhesives. Starch paste originates from starch granules,
whereas flour paste encompasses the entire wheat endosperm proteome,
offering strong adhesive properties due to gluten proteins. From a
conservation perspective, understanding the precise nature of the
adhesive is vital as the longevity, resilience, and reaction to environmental
changes can differ substantially between starch- and flour-based pastes.
We devised a proteomics method to discern the protein content of these
pastes. Protocols involved extracting soluble proteins using 0.5 M
NaCl and 30 mM Tris-HCl solutions and then targeting insoluble proteins,
such as gliadins and glutenins, with a buffer containing 7 M urea,
2 M thiourea, 4% CHAPS, 40 mM Tris, and 75 mM DTT. Flour paste’s
proteome is diverse (1942 proteins across 759 groups), contrasting
with starch paste’s predominant starch-associated protein makeup
(218 proteins in 58 groups). Transformation into pastes reduces proteomes’
complexity. Testing on historical bookbindings confirmed the use of
flour-based glue, which is rich in gluten and serpins. High levels
of deamidation were detected, particularly for glutamine residues,
which can impact the solubility and stability of the glue over time.
The mass spectrometry proteomics data have been deposited to the ProteomeXchange,
Consortium (http://proteomecentral.proteomexchange.org) via the MassIVE
partner repository with the data set identifier MSV000093372 (ftp://[e-mail]).