The relationship between protein flexibility and emulsifying activity was investigated by disrupting disulfide bonds and/or noncovalent interactions of the protein. Oil-in-water emulsions using model proteins (apomyoglobin, beta-casein, alpha-casein, lysozyme, bovine serum albumin, kappa-casein, and beta-lactoglobulin) were made in the presence of chemical denaturants (dithiothreitol and/or urea). In most cases, the presence of denaturants enhanced emulsifying activity. The effect was protein-specific and depended on the relative importance of disulfide bonds and noncovalent interactions in stabilizing the native conformation of each protein. Implications for the design of novel protein emulsifiers are discussed.