Role of rice protein subunit ratios on functionality and end-product development

Justification: Rice, a major cereal crop, undergoes processing that results in a significant amount of by-products, including rice bran and broken kernels. This study examines protein quality and product development differences among brown rice, broken kernel, and rice bran, despite being derived from a single seed.

Objective: (i) Analyze differences in the content of protein subunits, including albumin, globulin, glutelin, and prolamin, from rice protein. (ii) Investigate differences in structural, functional, and nutritional properties for plant-based cheese development.

Methods: Protein was extracted from broken kernels (BK), rice bran (RB), and brown rice (BR) by using alkaline-acid extraction at pH 9.0 and precipitation at pH 3.5. Osborne extraction fractionated albumin, globulin, glutelin, and prolamin. Functional, structural, and nutritional characteristics were evaluated to assess protein quality. Plant-based cheese prototypes were formulated with 12% of BK, RB, and BR protein and analyzed for texture.

Results: The percent of albumin, globulin, glutelin, and prolamin fractions were found 8.80%, 7.04%, 74.78%, and 9.38% from BK; 40.96%, 11.11%, 38.14%, and 9.78% from RB; and 16.63%, 6.51%, 64.82%, and 12.05% from BR, respectively. BR and BK proteins exhibited higher solubility, 18% and 15%, respectively, than RB due to lower fiber-protein interaction. Surface hydrophobicity was lowest in BR (34.26) and highest in RB (43.18). BR had the highest emulsion activity (0.810) and stability (0.484), while RB excelled in foaming due to its high albumin content. FTIR analysis showed the strongest C=N stretching in RB (78) compared to BR (76) and BK (72), indicating greater hydrogen bonding and protein folding. BK protein showed the highest in-vitro digestibility (0.74 mg/ml) and free amino acid content (0.804 mg/ml). RB cheese exhibited lower hardness (3949.73 g) and gumminess (945.59), likely due to its balanced subunit profile.

Significance: The findings highlight the distinct properties of proteins, emphasizing their versatility in food applications.