Differential Maillard Sensitivity Of Exoproteins Favors Keratin Recovery During Sludge Biopolymer Extraction

Abstract Proteins are an abundant extracellular polymeric substance (EPS) of activated sludge from wastewater. Hot alkalinization is implemented industrially to recover the EPS from sludge. We sought to assess the feasibility of protein recovery from alkali EPS. We detected a low abundance of bacterial proteins in the EPS. Human keratin was highly abundant and could also be recovered. Keratin was observed as a dominant and integral component of the activated sludge flocs, and it was thus not an extraction artifact. Alkali extraction promoted Maillard reaction between proteins and sugars and removed recoverable peptide signatures. Subsequent chemical modification, along with denaturation, impaired protein binding to ion exchange resins, making bacterial proteins inaccessible to isolation. Keratin has high resistance to Maillard reaction under extraction conditions and thus persists in the EPS. While Maillard modifies bacterial proteins, the resultant product, and possibly even keratin itself, are valuable recoverable byproducts from activated sludge. Synopsis The different sensitivities of proteins to Maillard reaction determines which proteins dominate alkaline extracellular polymeric substance (EPS) extract from activated sludge, with keratin dominating in alkaline EPS and an integral activated sludge component.