Cereal Chem 63:197-200   |  VIEW ARTICLE
Enzymes That Contribute to the Oxidation of L-Ascorbic Acid in Flour/Water Systems.

P. Cherdkiatgumchai and D. R. Grant. Copyright 1986 by the American Association of Cereal Chemists, Inc. 

The enzymes lipoxygenase (LOX), peroxidase (POD), and polyphenol oxidase (PPO) were investigated to determine wheater they contribute either directly or indirectly to the oxidation of L-ascorbic acid (AA) in wheat flour. Water extracts of untreated patent Canadian hard red spring wheat flour contained significant amounts of both LOX and POD but no ascorbate oxidase (AOX) activity. However, significant AOX activity was found in flour/water suspensions. When the flour residue from a water extraction was subsequently extracted with 75% saturated Na2SO4 solution, 60% of the AOX activity of the flour suspension was solubilized, but this extract showed neither LOX nor POD activity. The assay for PPO showed no activity in the patent flour, although activity was detected in a whole wheat flour. It was concluded that patent flour contains an enzyme capable of oxidizing AA that is distinctly different from LOX, POD, or PPO. Water extracts supplemented with both H2O2 and AA rapidly oxidized AA, indicating a POD species that utilized AA as an H-donor. Because of the negligible H2O2 content in flour, significant oxidation of AA by this enzyme appeared unlikely. Water extracts supplemented with AA and linoleic acid oxidized AA at one half the rate of a flour/water suspension without any added linoleic acid. The natural levels of free linoleic acid in flour are high enough that indirect oxidation of AA by LOX could account of approximately 30-50% of the total AA oxidation in dough.