THERMALLY INDUCED GELATION OF THE 12s RAPESEED GLYCOPROTEIN

Abstract

ABSTRACT Scanning electron microscopy (SEM) and rheological characterization were used to study gelation of the 12s rapeseed glycoprotein. Dispersions at pH 4 readily self‐associated on heating with gelation at 4.5% protein concentration and measurable thickening at 1% protein. The SEM studies revealed a progression in three dimensional ordering and a decrease in pore size as pH was increased from 6 to 10. At pH 4, the gel was amorphous and readily reverted to a sol. Gel strength was affected by changes in pH and sodium chloride concentration, the strongest gels being formed at high pH and ionic strength. Aging the dispersion in the cold prior to thermally induced gelation increased apparent viscosity. Urea and dithiothreitol had little effect on gelation although 0.15M dithiothreitol gels were less elastic in nature, suggesting intermolecular disulfide bonding may have a role in matrix formation. Selective reduction alkylation prevented gelation but the content of e‐amino groups of lysine was unchanged indicating that modification of some other functional group essential for gelation had preferentially occurred. Gel formation in the rapeseed protein system is obviously a complex phenomenon which may involve covalent, ionic, disulfide, hydrophobic and hydrogen bonding. The presence of a high level of carbohydrate (12.9%) suggests the possibility of protein‐carbohydrate interaction during gel formation.