Evaluation of head and broken rice of long grain Indica rice cultivars: Evidence for the role of starch and protein composition to head rice recovery.

Brown rice of different long-grain Indica cultivars was polished to variable degree of milling (DoM) to see the difference in proteins and starches characteristics in head (HR) and broken rice (BR). Study revealed differential accumulation of starch, fat and proteins in both HR and BR. Extended DoM of brown rice resulted in a progressive decrease in HR yield and increase in BR yield. The extended DoM caused a decrease in protein and fat content in both HR and BR, whereas; an increase in peak viscosity and final viscosity was observed. On the contrary, the setback viscosity of HR and BR of different rice cultivars was influenced by cultivars and extended DoM. Milled rice from different cultivars milled to 6% DoM showed higher levels of 59 kDa, 54 kDa, 51 kDa, 32 kDa, 31 kDa, 30 kDa, 28 kDa, 24 kDa, 23 kDa, 15 kDa, 13 and 12 kDa PPs, while 28 kDa, 24 kDa, 23 kDa, 15 kDa, 13 kDa and 12 kDa PPs was the least or not observed in BR. The major quantitative changes were observed in 28 kDa, 24 kDa, and 23 kDa PPs. MALDI-ToF/MS analysis revealed the identity of 28 kDa PP as 60S ribosomal protein L10a and glutelin type-D 1 proteins. Whereas, the identity of 24 and 23 kDa PP, respectively was established as pathogenesis-related protein 1 (Oryza sativa Japonica Group) and Oryza sativa 1-Cys peroxiredoxin A. HR showed the presence of highly condensed packaged starch granules with smooth edges, which were tightly imbibed in the proteins matrix. However, the inter-cultivar differences in the starch structure and packaging were also observed. On the contrary, BR revealed lesser accumulation of starch particles with abnormal protein filling and several fissures and cracks in the starch granules of BR of different cultivars. A graphical abstract showing differences in head and broken rice of different long grain Indica rice cultivars. The differences in the protein profile and internal starch granule structure, imbibed in protein matrix, are visible from SDS-PAGE and field emission scanning electron microscopic analysis. Unlabelled Image • Head rice yield decreased with the extended degree of milling (DoM). • Extended DoM caused a decrease in protein content, fat content in both head rice (HR) and broken rice (BR). • Peak viscosity and final viscosity of HR and BR was increased with extended DoM. • MALDI-ToF/MS analysis revealed the absence or least accumulation of glutelin type-D 1 protein in BR. • Storage of 60S ribosomal protein L10a, pathogenesis-related protein 1 and 1-Cys peroxiredoxin A was varied in HR and BR of different cultivars. [ABSTRACT FROM AUTHOR]