Effect of heat-induced formation of rice bran protein fibrils on morphological structure and physicochemical properties in solutions and gels

Abstract

The effects of heat-induced rice bran protein (RBP) fibrils on structure and properties of solutions and gels in a complex system were investigated using transmission electron microscopy (TEM), atomic force microscopy (AFM), Congo red spectral analysis, and circular dichroism (CD). Planar and 3-dimensional images of RBP fibrils all revealed structural details. A Congo red spectral shift indicated fibril formation. Fibril secondary structural components exhibited differences at pH 2.0 and pH 7.0. The β-type was decreased with an increased pH. Rheological results exhibited shear thinning behavior for all solutions. Addition of fibrils to RBP solutions, which made the system complex, resulted in an order of magnitude increase in viscosity and shear stress. Adding fibrils to RBP solutions accelerated the kinetics of gel formation, resulting in an increase in gel strength. Scanning electron microscopy (SEM) images showed gel network structural differences with and without fibrils at different pH values.

Rheology and microstructure of binary mixed gel of rice bran protein–whey: effect of heating rate and whey addition

“…Indeed, by adding fibrils of RBP to WPC, a coral‐like structure may be produced, indicating that gels with fibrils tended to show syneresis. This result implies that gels with fibrils had lower water‐holding capacity …”

“…It appears that it was a mesh‐like geometric property of the gel network; however, the micrographs at the same magnification revealed that the dimensions of the mesh‐like structure decreased upon increasing the ratio from 1:1 to 1:10 (Figs (c)–(f)). However, an amorphous structure has been seen for fibrous aggregates of RBP, which is affected by the concentration and heating . On the contrary, other hydrocolloids such as gellan gels and mixed systems such as WPI– κ ‐carrageenan and basil seed gum– β ‐lactogolbulin showed similar structures .…”

Conditions Governing Food Protein Amyloid Fibril Formation—Part I: Egg and Cereal Proteins

“…This is probably due to its insolubility and difficult isolation (Fabian & Ju, ). Rice bran protein forms amyloid‐like fibrils during heating at 90 °C and pH 2.0 for 2 hr (Zhang & Huang, ; Zhang, Huang, & Wei, ). The mean contour length and particle size of these fibrils increase with heating time (up to 360 min) and protein concentration (2, 10, and 50 mg/mL).…”

“…The maximum ThT fluorescence intensity after 360 min heating is about 2.5 times that after 10 min heating (Zhang et al., ). Rice bran protein fibrils formed by heating (90 °C, 2 hr) at pH 2.0 are linear strands, while adjusting the pH to 7.0 induces fibril clustering (Zhang & Huang, ). Increasing the ionic strength (0 to 500 mM salt) promotes fibril assembly of rice bran globulin when heated at 90 °C and pH 2.0 for 2 hr.…”

“…Rice bran albumin AF formation is enhanced by seeding. Adding fibrils to rice bran protein solutions accelerates the rate of gel formation at 90 °C and pH 2.0 (Zhang & Huang, ; Zhang et al., ).…”