Functionality and characterization of kafirin-rich protein extracts from different whole and decorticated sorghum genotypes

• Sorghum decortication led to kafirin extracts with high purity and low fat content.
• Functional properties of kafirin extracts were different among sorghum genotypes.
• Kafirin solubility and emulsifying capacities were diminished due to hydrophobicity.
• Kafirin functional properties were not affected by sorghum decortication.
• Kafirins from decorticated sorghums had lower FTIR α-helical:β-sheet ratios.

The study of food-grade isolated kafirin proteins has increased recently due to the interest of their potential applications in gluten-free products. However, functionality of extracted proteins and fractions have been poorly characterized. In this investigation, kafirins were extracted from whole or decorticated sorghum genotypes (white-regular, white-waxy, red-regular and high-tannin) with 70% aqueous ethanol with metabisulfite. Chemical composition, color parameters, functionality and molecular characterization of kafirin extracts were determined. When kafirin extracts were obtained from decorticated sorghums, higher protein purities (81.5–93.3%), lower lipid contents (1.9–12.6%), better color parameters, and higher yields were obtained compared to counterparts extracted from whole caryopses. Functional properties of the extracted kafirins showed low water solubility, free amino nitrogen, and emulsifying activity, but adequate water holding and fat absorption capacities and in vitro protein digestibility. Differences in functionality were attributed to sorghum genotype. SDS-PAGE showed extraction of α1-, α2-, β-, and γ-kafirins with no contamination of other protein fractions. FTIR indicated a reduction in α-helix:β-sheet after extraction, especially in proteins obtained from decorticated sorghums. High correlations found from Pearson analysis could be used to optimize protein yield and the functionality (emulsifying activity and solubility) of the extracted proteins to be applied in gluten-free food systems.