Enzyme-catalyzed acylation improves gel properties of rapeseed protein isolate.

Background: Although rapeseed protein isolate (RPI) possessed some good functional properties, the use of RPI as an ingredient in the food industry is restricted mainly due to its inferior gelation. The purpose of this study was to improve the heat-induced gel properties of RPI using double processes of acylation and additional transglutaminase catalysis.

Results: Scanning electron microscopy showed that the gel formed by native RPI exhibited randomly aggregated particulate network structures whereas transglutaminase (TG)-assisted RPI gels significantly improved gelation properties. More importantly, the combined modifications of RPI using TG-assisted acylation can form a gel with unique percolating and small porous structure. Furthermore, TG-catalyzed 5% acylated RPI gel (100 U g , protein basis) exhibited excellent gel properties in terms of gel strength, thermal stability, surface roughness and apparent viscosity compared to non-treated or single modification of RPI gel as determined by texture analyzer, atomic force microscopy and rheometer. Mechanistically, Fourier-transform infrared spectra and gel dissociation test revealed that TG-catalyzed acylation extensively unfolded the hydrophobic and sulfhydryl residues of RPI, in turn, reinforced re-assembly of protein molecules via hydrophobic interactions and disulfide bonds during gel formation.

Conclusion: Combined processes of acylation and additional TG catalysis improved the thermal gelation properties by altering inter- and intra-protein structures. Such sequential processes will provide a promising approach to improve the protein gelation that could be potentially applied in the food industry. © 2020 Society of Chemical Industry.