Modification of rice protein with glutaminase for improved structural and sensory properties

Summary Rice protein is highly nutritive and hypoallergenic but certain physicochemical properties restrict its applications in beverages. This study aimed to tackle this issue by modifying rice endosperm protein with glutaminase via deamidation. Glutaminase treatment facilitated an increase in deamidation degree and mean particle size of rice protein and a continuing decrease in turbidity with time. Favourable changes induced in sensory properties included: improved suspendability (increased by 81.25%), lumpiness (decreased by 84.78%), grittiness (decreased by 72.34%) and overall taste liking (improved by 12.24%). Visual observations of rice protein dispersions and turbidity measurements further confirmed the improved suspendability in water. Fourier transform infrared spectroscopy analysis revealed that the action of glutaminase did not remarkably change the protein structure, but slightly reduced α‐helical conformation whilst increased β‐sheet and β‐turn structures. Glutaminase could be useful for deamidation modification of products with high content of glutamine residues (like rice protein), through inducing the breakdown of some intermolecular and intramolecular bonds including hydrophobic interactions and hydrogen bonding without serious cleavage of the peptide bonds, allowing protein rearrangements to more flexible or extended forms. As a result of protein unfolding with more hydrophobic clusters exposed, certain physicochemical properties of rice protein were improved.