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

Abstract

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.

Enhancing the Usability of Pea Protein Isolate in Food Applications through Modifying Its Structural and Sensory Properties via Deamidation by Glutaminase

“…The applicability of pea protein isolate (PPI) in aqueous-based products is, however, limited owing to its poor solubility, processability, flavor, and mouthfeel. Pea protein suspensions, especially those at high protein concentrations, have a gritty/chalky texture and a feeling of lumps stuck in the throat during swallowing, largely due to the aggregation of pea proteins via hydrophobic interactions, hydrogen bonding, as well as van der Waals attractive, electrostatic, and steric interactions. , …”

“…Deamidation leads to an increase in the number of negatively charged carboxyl groups, which causes a reduced isoelectric point (pI) and the exposure of hydrophobic regions, thereby improving the solubility, quality, stability, consumer acceptability, and other functional properties of proteins. − Appropriate extent of deamidation can improve protein’s functional properties such as protein solubility, foaming capacity, and emulsifying capacity, whereas excessive deamidation may destroy some protein properties and reduce protein utility. ,,− Compared to the physical and chemical methods for protein deamidation, enzymatic deamidation is preferable in the food industry due to its efficiency, safety, mild reaction conditions, high reaction speed, and substrate specificity . Glutaminase is a food-grade commercial enzyme that can specifically catalyze the deamidation of the glutamine and asparagine residues in proteins with relatively slight protein hydrolysis, as compared to other enzymes such as protease and transglutaminase. , A number of studies have demonstrated that the glutaminase-catalyzed deamidation could improve the solubility and other functional properties of food proteins with a higher degree of deamidation (DD). , But few studies have investigated the deamidation using glutaminase on the structural properties of pea proteins and sensory attributes of derived products.…”

Brown rice proteins as delivery system of phenolic and volatile compounds of raspberry juice

“…Hu et al . (2019) also reported that untreated rice proteins and glutaminase‐treated rice proteins differ in bands intensities. Characteristic amid bands include wavenumbers 1700–1600 cm −1 , 1550–1500 cm −1 , 1387 cm −1 , 1382 cm −1 and 1234 cm −1 corresponding to Amid I (C‐O stretching), Amid II (N‐H bending) and Amid III (C‐H and C‐N stretching and N‐H bending), respectively (Xiang et al., 2018).…”

Protein deamidation to produce processable ingredients and engineered colloids for emerging food applications

“…Deamidation under moderate conditions, for example, at pH 8 and 100°C for 30 min, can achieve proper solubility with minimal side reactions (Guan et al., 2017). Besides, rice protein powder products have an unpleasant taste with a strong sensation of grittiness and lumpiness, especially at high protein concentrations (Hu et al., 2019); modification by deamidation can overcome this. The limited deamidation of rice endosperm protein by glutaminase has been shown to improve protein suspensibility while reducing lumpiness and grittiness, and thus the overall palatability was enhanced (Hu et al., 2019).…”

“…Besides, rice protein powder products have an unpleasant taste with a strong sensation of grittiness and lumpiness, especially at high protein concentrations (Hu et al., 2019); modification by deamidation can overcome this. The limited deamidation of rice endosperm protein by glutaminase has been shown to improve protein suspensibility while reducing lumpiness and grittiness, and thus the overall palatability was enhanced (Hu et al., 2019). These new properties of deamidated rice protein suggest that deamidation is a potential approach for enhancing the usability of rice protein in the food industry.…”