Food Chemistry

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 toZehentbauerandGrosch, 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 theMaillardreaction,

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 concen-

trations of 2-acetyl-1-pyrroline and 2-acetyl-

tetrahydropyridine 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 com-

pounds are involved in the aroma of rye bread