Effect of mild-parboiling treatment on the structure, colour, pasting properties and rheology properties of germinated brown rice

The effects of mild-parboiling treatment (MPT) on the structure, colour, pasting and rheology properties of germinated brown rice (GBR) were investigated and compared with those of white rice (WR). The results showed that some fissures appeared on the surface-layer and cross-section of GBR, meanwhile, the region of cross-section near its surface became compacter and smoother after MPT. Incomplete gelatinization of GBR occurred during MPT, as evidenced by the decrease of relative crystallinity from 27.51% to16.87% and the transformation of crystalline structure from A-type into the mixture of A-type and Vh-type. The significantly (p < 0.05) darker colour and increased colour difference (ΔE) of GBR were observed after MPT. All pasting parameters of GBR, except breakdown, increased significantly (p < 0.05) to the values which were close to or even higer than those of WR after MPT. All flours of WR, GBR and mild-parboiled germinated brown rice (MP-GBR) exhibited gel-like viscoelastic, non-Newtonian shear-thinning, and thixotropic behaviors. Additionally, the storage/loss modulus (G′/G″), loss tangent (tan θ) steady shear viscosity (η) and hysteresis loop area of GBR increased and closed to or above those of WR while the shear stress (τ) of GBR decreased to the close level of WR after MPT.