Degradation of C-hordein by metal-catalysed oxidation

Abstract

C-hordein is a monomeric prolamin protein in barley. The unusual primary structure of C-hordein has highly repetitive sequences and forms a secondary structure of beta-turns. C-hordein structure is similar to that of collagen protein, whose degradation by metal-catalysed oxidation has been intensively studied. No information exists on the metal catalysed oxidation of C-hordein, however. In this study, copper-catalysed hydrogen peroxide induced oxidation of C-hordein caused substantial degradation and formed some insoluble compounds. The use of a gliadin standard in R5 ELISA determinations causes an overestimation of hordeins in a sample. A C-hordein standard was therefore directly used as a standard, thus allowing the C-hordein to be analysed as its oxidised prolamin product. After 48 h of oxidation, the prolamin concentration of oxidised C-hordein decreased to 20% of its original amount for competitive ELISA, and to 3% for sandwich ELISA methods. Carbonyl groups were formed during the oxidation. Backbone fragmentation and side-chain modification suggested structural changes of R5 epitopes in C-hordein. Oxidation is an alternative to enzymatic hydrolysis when degrading and modifying C-hordein.

Keywords: Barley; Gluten-free; Prolamin; Proline; Protein oxidation.