The present disclosure relates to, inter alia, a green technology for crosslinking protein molecules for various uses, where the protein molecules can be contained in protein fibers such as, but not limited to, human hair, animal fibers, and mixtures thereof. In one aspect, the present disclosure relates to a crosslinking agent comprising an oxidized sugar having at least two aldehyde groups. In another aspect, the present disclosure relates to a method of crosslinking protein fibers. This method involves providing the aforementioned crosslinking agent and 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, thereby yielding a population of crosslinked protein fibers.