Abstract:

11 rice cultivars with different amylose contents were chosen to determine the impact of protein on forming a viscosity curve when treated with reduced reagent dithiothreitol (DTT) to disrupt the protein disulphide bonds, and then to understand how protein affect the eating quality of cooked rice. DTT decreased RVA pasting temperatures and peak viscosities of flours with different degrees in all cultivars, while increased breakdown viscosities in 5 cultivars. DTT also changed the slopes of the linear parts of the curves for each variety. The addition of DTT to the cooking water decreased the hardness, while increased the adhesiveness of cooked rice. The disulfide bond-containing protein had a substantial impact on the pasting and cooking properties of rice. RVA measurements indicated that in addition to the disulphide bond network, protein hydration based increase of the gelatinized paste concentration contributed to the enhancements of the paste rigidity during cooking. The role of disulphide bonds in augmenting the breakdown viscosity values indicated that in the absence of the rigidity conferred by the disulfide-bound protein, swollen starch granules broke apart more easily when shear stress was high. From these observations, it was anticipated that disulfide bond-containing protein agency also played a role in the texture of cooked rice; this was confirmed by cooking rice in the presence of DTT. The agency of protein network increased hardness and decreased the stickiness of the cooked rice. Furthermore, the observation that the effects of DTT on high-amylose rice texture properties were slight suggested that, apart from an agency of protein network, a strengthening of an amylose barrier present in the rice endosperm seemed equally or more important.

Key words: Rice, Proteins, Disulphide bonds, Starch, RVA, Texture