Disclosed is a method of crosslinking protein fibers, including wool fibers, by (i) providing a crosslinking agent including an oxidized sugar mixture having a plurality of different oxidized sugars of different molecular lengths and having at least two aldehyde groups (e.g., oxidized soy flour sugars); and (ii) infiltrating a plurality of non-crosslinked protein fibers with the crosslinking agent under conditions effective to cause protein molecules contained in the non-crosslinked protein fibers to become crosslinked. This method yields a population of crosslinked protein fibers, where the protein molecules of the non-crosslinked protein fibers include amine groups that react with the aldehyde groups of the oxidized sugars to achieve the crosslinking of the protein molecules to yield the crosslinked protein fibers.