2000 Volume 6 Issue 1 Pages 40-43
The effects of polyphenol oxidase (PPO) activity in wheat flour on the formation of protein-bound 5-S-cysteinyl-3, 4-di-hydroxyphenylalanine (5-S-cysteinyldopa) in gluten have been studied. The wheat was milled on a test mill. PPO activity of fractionated flour was determined by measuring the O2 consumption of aqueous suspension after addition of catechol, dopa or tyrosine as substrate. PPO activity of whole wheat toward tyrosine was lower than that toward catechol or dopa. Glutens prepared with whole wheat or short bran contain higher levels of protein-bound 5-S-cysteinyldopa than those prepared with white flour. PPO activity in wheat flour was related with formation amounts of protein-bound 5-S-cysteinyldopa in gluten. Heat treatment of whole wheat flour inhibited the formation of protein-bound 5-S-cysteinyldopa in gluten. When crude enzyme extracts prepared from wheat bran were added to dough, formation amounts of protein-bound 5-S-cysteinyldopa markedly increased. By the addition of enzyme-inhibitor, formation of protein-bound 5-S-cysteinyldopa in gluten was markedly decreased. It is believed that dough prepared with flour containing a high level of PPO activity has a network of protein-bound 5-S-cysteinyldopa formed from tyrosine and cysteinyl residue of protein.
