Difference analysis of the structure and functional properties among coix seed prolamin fractions (α‐, β‐, and γ‐coixin)

The differences in proteins in structural characteristics are reported to affect their physicochemical and functional properties. In this study, three types of prolamins (γ-, α-, and β-coixin) derived from coix seed separately distributed among fractions 1-3 extracts. They were studied respecting molecular weight, amino acid composition, secondary structure, microstructure, surface hydrophobicity, solubility, water holding capacity, and oil holding capacity. Results showed that the molecular weights of those three fractions were between 10 and 40 kDa. The secondary structure of those fractions was almost the same, mainly based on β-sheet and irregular structure. The microstructure of α- and γ-coixin presented an irregular shape, whereas β-coixin presented a regular spherical shape. Those three fractions exhibited species of abundant essential amino acids with the same amino acid composition but different contents. The β-coixin fraction had the highest content of hydrophobic amino acids (238.39 mg/g) followed by the α-coixin fraction (235.05 mg/g), whereas the γ-coixin fraction had the lowest content (33.27 mg/g). The γ-coixin fraction has the maximum surface hydrophobicity, whereas the β-coixin fraction has the highest solubility. In addition, the good amphiphilicity of β-coixin fraction made it possible to be used as a surfactant. The excellent functional properties of the β-coixin fraction presented in this research would widen the applications of coix seed prolamins. PRACTICAL APPLICATION: The molecular weights of those three fractions were between 10 and 40 kDa. The secondary structure was almost the same, mainly based on β-sheet and irregular structure. Those three fractions exhibited species of abundant essential amino acids with the same amino acid composition but different contents. The WHC and OHC of β-coixin were the best, indicating its potential as a surfactant and forming stable lotion.