Physical, functional, and cooking properties along with storage study of bioprocessed pigmented red and black rice

This study investigates the quality characteristics of pigmented brown rice from red and black varieties obtained through bioprocessing via germination and subsequent hydrothermal treatment (steaming). The objective was to evaluate how these processes affect the milling, physical, functional, cooking, sensory, and storage properties of the rice. Bioprocessing resulted in a 30–33% reduction in milling yield in both and a 45% decrease in the hardness of red rice grains, with no significant changes in other physical properties. The insoluble amylose content increased by 21% in bioprocessed red rice and by 25–27% in bioprocessed and steam-treated in both. Functional properties related to alkali spreading and sedimentation values remained unchanged in both, but water absorption capacity increased by 13.7% in bioprocessed red rice and by 25% and 18% in bioprocessed and steam-treated red and black rice, respectively. Pasting properties, such as gelatinization temperature (GT), increased, while peak viscosity was reduced by 80% in red and ~ 15 times in black and cold paste viscosity by 54% in red and ~ 14 times in black variety. On the other hand, subsequent hydrothermal treatment showed increase in PV and other properties but remained lower than the control in red, whereas in black, it increased and reached control values. Solid loss increased by 26% in bioprocessed red rice, while cooking time was reduced by 11% in both bioprocessed rice and by 22% in both steam-treated rice. Sensory evaluation showed that bioprocessed rice had a softer texture, lower firmness, higher stickiness, and lower overall acceptability. However, subsequent hydrothermal treatment resulted in improvements in grain integrity, firmness, and overall acceptability. Texture analysis revealed an 82% reduction in hardness and a 20% increase in elasticity for red rice, while the black variety showed a 305% increase in gumminess and a 240% increase in adhesiveness. During storage, the bioprocessed and treated rice samples maintained good quality characteristics, with moisture levels within safe limits, free fatty acids below 0.04%, and peroxide values within acceptable limits. In conclusion, bioprocessed and hydrothermally treated red and black rice exhibited quality characteristics suitable for use as whole grain rice, with notable improvements in various quality attributes.