Formation of Protein-Bound 3,4-Dihydroxyphenylalanine and 5-S-Cysteinyl-3,4-dihydroxyphenylalanine as New Cross-Linkers in Gluten

The formation of protein-bound 5- S -cysteinyl-3,4-dihydroxyphenylalanine (5- S -cysteinyldopa) and 3,4-dihydroxyphenylalanine (dopa) as new cross-linkers in gluten was investigated. Gas-phase acid hydrolysis of gluten was carried out in the presence of 5% phenol. For identification of dopa and 5- S -cysteinyldopa, alumina extraction of catechols in the hydrolysates was performed. The presence of dopa and 5- S -cysteinyldopa in the hydrolysates of gluten was determined using HPLC equipped with an electrochemical detector. When mushroom tyrosinase, which has an oxidant-like effect on the physical properties of dough, was added to dough, the amount of protein-bound 5- S -cysteinyldopa increased. It is concluded that the oxidizing effect of tyrosinase is due to the formation of protein-bound 5- S -cysteinyldopa and dopa as cross-linkers of gluten.