2009_Book_FoodChemistry

15.4 Baked Products 737
Fig. 15.48. Influence of the kneading intensity on the dough temperature and on the concentrations of 2- and
3-methylbutanal in the baguette crust. 2-Methylbutanal (•–•), 3-methylbutanal (◦–◦). Abscissa: kneading time (s)
and dough temperature T ( ◦ C) (according to Zehentbauer and Grosch, 1998)
(15.8)
The crumb contains the precursors of the
roasty odorants 2-acetyl-1-pyrroline and 2-
acetyltetrahydropyridine (cf. 5.3.1.6), but the
temperature in the baking process is sufficient to
form these substances only in the crust. If white
bread is toasted, the two odorants are formed with
increasing browning of the toast (Fig. 15.50),
whereby 2-acetyl-1-pyrroline increases much
more. Of the odorants from the Maillard reaction,
4-hydroxy-2,5-dimethyl-3(2H)-furanone also
appears with a high aroma value. In the case
of fiber-enriched toast bread 2-/3-methylbutyric
acid is a critical odorant. The addition of oat
bran is preferable to wheat bran because it yields
less 2-/3-methylbutyric acid and, consequently,
a rancid/sweaty aroma defect is avoided.
Important precursors of 2-acetyl-1-pyrroline are
ornithine and 2-oxopropanal (cf. 5.3.1.7), mainly
originate from yeast metabolism. The concentrations
of 2-acetyl-1-pyrroline and 2-acetyltetrahydropyridine
in the crumb are less than
those in the crust by a factor of about 30.
The reason being that only in the crust area is
the temperature high enough to release aroma
substances or their precursors from yeast.
15.4.3.3.3 Rye Bread Crust
Dilution analyses show that the following compounds
are involved in the aroma of rye bread