title: Swelling of whey and egg white protein hydrogels with stranded and particulate microstructures.
abstract: Swelling of protein hydrogels in alkaline conditions strongly depends on the gel microstructure. Stranded transparent gels swell as predicted using a modified Flory-Rehner model with the net protein charge. Particulate opaque gels swell very differently, with a sudden increase at a narrow pH range. Its swelling is not controlled by the protein charge, but by the destruction of the non-covalent interactions. Comparable dissolution thresholds, one with pH and another with the degree of swelling, are observed in both types of microstructures. These conclusions are valid for both whey protein isolate (WPI) gels and egg white gels, suggesting that they are universal for all globular proteins that can form such microscructures. Differences are observed, however, from the prevalent chemical crosslinks in each protein system. Non-covalent interactions dominate WPI gels; when such interactions are destroyed at pH≥11.5 the gels swell extensively and eventually dissolve. In egg white gels, the higher degree of disulphide crosslinking allows extensive swelling when non-covalent interactions are destroyed, but dissolution only occurs at pH≥13 when covalent crosslinks are cleaved. The current study highlights that the microstructure of protein hydrogels, a unique particularity of protein systems compared to other synthetic hydrogels, defines swelling.
authors.affiliation: Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou City 215123, Jiangsu, PR China.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou City 215123, Jiangsu, PR China.
authors.forename: Lei
authors.initials: L
authors.lastname: Zhao
authors.affiliation: Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou City 215123, Jiangsu, PR China.
authors.forename: Xiao Dong
authors.initials: XD
authors.lastname: Chen
authors.affiliation: Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou City 215123, Jiangsu, PR China. Electronic address: ruben@suda.edu.cn.
authors.forename: Ruben
authors.initials: R
authors.lastname: Mercadé-Prieto
mesh_terms: D004527:Egg Proteins / Q000737:chemistry*; D020100:Hydrogels / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D014867:Water / Q000737:chemistry; D000067796:Whey / Q000737:chemistry*; D000067816:Whey Proteins / Q000737:chemistry*
chemical_list: D004527:Egg Proteins; D020100:Hydrogels; D000067816:Whey Proteins; D014867:Water
keywords: Microstructure; Protein hydrogel; Swelling