Inhibition of aggregation of physically modified rice proteins by isoconcentration of l-Arg and l-Glu

Abstract

Unwelcome protein aggregation plays a negative role in food sensory properties. In this study, the aggregation tendency of a typical hydrophobic protein (rice proteins) was effectively inhibited by addition of equimolar l-arginine (l-Arg) and l-glutamine (l-Glu). Soluble rice proteins were prepared by freeze-milling treatment (FM-RPs), and their spontaneous aggregation during buffer storage was characterized. Studies from confocal laser scanning microscopy, atomic force microscopy and scanning electron microscopy indicated that spherical FM-RPs were disintegrated into irregular structures that then spontaneously reorganized into amorphous aggregates during storage. Kinetics studies manifested a sigmoidal growth of the aggregation. Examinations of amide I region of aggregates confirmed that FM-RPs were rich in antiparallel and intermolecular β-sheets, and the hydrophobic bonding of which gave rise to the formation of insoluble agglomerates. Importantly, simultaneous addition of equimolar l-Arg and l-Glu at an isoconcentration of 10 mM reduced the plateau aggregation of FM-RPs from 25.74 to 7.96%. Conformational measurements and ζ-potential studies demonstrated sheet-turn transformations of FM-RPs during aggregation, which lead to stabilization of proteins in solutions.

Keywords: Aggregation; Rice proteins; l-Arginine and l-glutamine.