Ascorbic acid (AA) is used as bread improver, as its addition to dough caus
es an increase in loaf volume and an improvement in crumb structure. To exp
lain these effects we review the stereospecificity of the improver action a
nd the properties of ascorbate oxidase and glutathione dehydrogenase and th
e occurrence of low molecular thiols in flour and their concentration chang
es during dough mixing in the presence and absence of AA. On rile basis of
thr results the improver action of AA is explained by a reaction sequence l
eading to a rapid removal of endogenous GSH, which otherwise would cause do
ugh weakening by sulphhydryl/disulphide interchange reactions with gluten p
roteins. To rest this hypothesis the binding sites of endogenous GSH in glu
ten proteins have been determined by the addition of S-35-labelled GSH as a
tracer to flour before dough mixing. The distribution of radioactivity in
the gliadin and glutenin fractions of gluten obtained from dough indicates
that the major portion of GSH is bound to glutenins. The isolation and sequ
ence analysis of radioactive cystine peptides from an enzymatic digest of g
lutenins demonstrates that GSH is almost exclusively linked to those cystei
ne residues of LMW subunits that hale been proposed to form intermolecular
disulphide bonds. (C) 1999 Academic Press.