Effect of high-speed shearing treatment on dehulled walnut proteins

Abstract

Abstract To understand more clearly about true characteristics of walnut protein, dehulled walnut kernels were used to prepare proteins, thus influences of polyphenols on proteins were minimized. Based on solubility, glutelin was found to be the predominant walnut protein (67.64% of total walnut proteins), meanwhile albumin and globulin accounted for 32.29%. SDS-PAGE and two-dimensional electrophoresis results showed that polypeptide profiles for albumin, globulin and glutelin exhibited significant differences. Walnut protein contained major polypeptides of MWs 30–35\u202fkDa (pI 5.5–7.5) and 17–22\u202fkDa (pI 9.0–10.0), along with minor polypeptides of MWs 50–73\u202fkDa (pI 6.0–7.5) and 11–13\u202fkDa (pI about 6.3). Disulfide bonds-linked polypeptides in walnut protein were determined with diagonal electrophoresis, and intermolecular disulfide bonds among polypeptides with MWs 30–34\u202fkDa and 17–22\u202fkDa were dominant. Further analysis by MALDI-TOF/TOF-MS showed that main components of walnut proteins were vicilin and legumin-like proteins. Through high-speed shearing (15,000\u202frpm) treatment at 60\u202f°C for 5\u202fmin, walnut protein solubility were greatly increased from 24.33% to 62.81% at pH 8.0 and from 50.93% to 76.65% at pH 9.0. High-speed shearing treatment, especially at basic pH, could be a better way to improve protein solubility, with decreased particle sizes and more globulin and glutelin solubilized.