PROTEIN-PROTEIN INTERACTIONS IN THE EXTRUSION OF SOYA AT VARIOUS TEMPERATURES AND MOISTURE CONTENTS

Soya protein isolate extruded at various temperatures and moisture contents was solubilized before and after processing in buffers containing urea, sodium disulphite, 2-mercaptoethanol, sodium dodecyl sulphate, alone or in combination to elucidate stabilizing mechanisms for their three dimensional structure. The main mechanisms were disulphide linkages, hydrophobic and electrostatic interactions. All extrudates resisted retorting in water at 120-degrees-C but complete disruption occurred in media containing reducing agents plus sodium dodecyl sulphate. Little change in amino acid occurred in extrusion except for aspartic and glutamic acids, which decreased in extrusion at 140-degrees-C. Infrared spectra showed the presence of beta-sheet anti parallel structures. Peptide bonds were of negligible importance in extrusion texturization of soya protein. If formed they only contributed to an insoluble phase in the melt.