Characterizing the structural and surface properties of proteins isolated before and after enzymatic demulsification of the aqueous extract emulsion of peanut seeds

Abstract

We isolated and characterized various proteins (adsorbed and unadsorbed) from the aqueous extract emulsion of peanut seeds. The peanut emulsion was further subjected to a freeze-thaw treatment or enzymatic hydrolysis by the alkaline endopeptidase Mifong®2709. The proteins in the residual cream layer and the aqueous phase, obtained from the freeze-thaw treatment as well as the cream layer peptides and aqueous phase peptides obtained at various periods of hydrolysis (namely 5, 10, 30, and 60 min), were isolated and analyzed for structural (molecular weight, disulfide bond content, and surface hydrophobicity) and surface (dynamic interfacial tension, emulsifying activity, and stability indices) properties. The peanut proteins adsorbed at the oil-water interface showed superior emulsification properties and unique structural characteristics consisting of large molecular weight proteins and small molecular weight oleosins, and also possessed a higher disulfide bond content and greater surface hydrophobicity. The proteins in the residual cream layer derived from the freeze-thaw treatment had a higher disulfide bond content, surface hydrophobicity, and emulsification indices than the proteins in the aqueous phase. In contrast, following the hydrolysis of the emulsion, the resulting cream layer peptides and the aqueous phase peptides exhibited a significantly lower disulfide bond content, weaker surface hydrophobicity and lower emulsification indices than the intact proteins. These protein structural changes following hydrolysis contributed to the destabilization of the peanut emulsions. We also observed a positive correlation for the disulfide bond content and the surface hydrophobicity with the emulsifying activity index (EAI), R2 = 0.963 and 0.982, respectively as well as the emulsion stability index (ESI), R2 = 0.920 and 0.906, respectively.