Impact of proteins on pasting and cooking properties of waxy and non-waxy rice

Changes of RVA viscosity and texture properties of waxy rice (n=9) and non-waxy rice (n=10) were analyzed through protein removal or disulfide bond disruption. Protease or DTT had similar effects on the pasting behavior of the waxy rice, but affected differently that of non-waxy rice. For all waxy rice flour treated with DTT or protease, the peak, breakdown and consistency viscosity values all significantly decreased, and the viscosity curves barely rose from the baseline. Pre-incubation of flours with a protease increased RVA pasting temperatures, decreased viscosities along all the points of the curves and the slopes of the linear parts of the curves for all non-waxy cultivars. DTT decreased RVA pasting temperatures and peak viscosities of all non-waxy flour, but increased breakdown viscosities in six non-waxy rice cultivars. With DTT-added cooking water, the hardness of cooked waxy and non-waxy rice, as determined by Instron, generally decreased. With DTT-added cooking water, the adhesiveness of all cooked waxy rice significantly decreased, while it increased significantly or remained the same in all cooked non-waxy rice. The above results indicated that the protein agent of a network linked by disulfide bonds increased the RVA gelatinized paste rigidity, the hardness and adhesiveness of cooked rice of all waxy cultivars, while in non-waxy cultivars, both the network and the increase of the gelatinized paste concentrations resulting from protein hydration contributed to the enhancements of the RVA paste rigidity and the cooked rice hardness.