Peptic hydrolysis of gluten, glutenin and gliadin from wheat grain: Kinetics and characterisation of peptides

Abstract The kinetics of the hydrolysis of gluten, glutenin and gliadin by pepsin was studied by following the reaction of the hydrolysate with ninhydrin and by SDS‐gel electro‐phoresis. Glutenin was more rapidly hydrolysed than native molecules of gliadin and produced components of different size. The first stage of hydrolysis of gliadin resulted in the formation of fragments mainly in the range 25 000 and 10 000 daltons whereas polypeptides generated from glutenin had subunits of molecular weight (MW) in the range 65 000, 30 000 and 10 000. Further hydrolysis resulted in the formation of subunits of MW around 24 000 and 14 000 for glutenin and gliadin respectively. The final stage of hydrolysis produced a quantity of peptides of MW under 10 000 and a small quantity of free amino acids. No obvious differences in the molecular weights of the polypeptides released were found when the enzyme to gliadin ratio was varied. Components obtained from glutenin and gliadin were further characterised after gel filtration on Sephadex G50. Large polypeptides derived from both gliadin and glutenin contained large amounts of proline and glutamate. Surface hydrophobicity of derived components were different, and inferior to, those of the reduced glutenin and native gliadin. Reduction of disulphide bonds of digested polypeptides of glutenin showed the existence of peptides branched by interchain disulphide bonds. Peptic cleavage sites were probably located differently in glutenin and gliadin molecules.