2009_Book_FoodChemistry

736 15 Cereals and Cereal Products
Table 15.58. Concentrations of the odorants in the
headspace of baguettes as a function of storage at room
temperature a
Odorants
Concentration
(ng/l air)after
1h 2.5h 4h
Methylpropanal 830 536 400
2-Methylbutanal 320 230 170
3-Methylbutanal 150 85 68
2,3-Butandione 980 705 670
2-Acetyl-1-pyrroline 3.7 3.3 3.7
Hexanal 216 237 254
(E)-2-Nonenal 28 36 44
(E,E)-2,4-Decadienal 7.8 6.5 6.6
a To determine the concentration, the air above the
baguette was collected for 15 min.
Table 15.59. Decrease (%) in 2-acetyl-1-pyrroline in
the crust of white bread during storage
Time (h)
0 0
3 46
24 77
168 89
2-Acetyl-
1-pyrroline
Table 15.60. Influence of the fermentation time and
temperature on the concentrations of odorants in the
baguette crust a
Odorant
Concentration (µg/kg)
Baguette I
Baguette II
2-Acetyl-1-pyrroline 16 14
Methylpropanal 1733 4331
2-Methylbutanal 1147 1487
3-Methylbutanal 426 680
Methional 31 49
1-Octen-3-one 3.8 2.1
(E)-2-Nonenal 61.8 40.4
a Dough I was fermented for 2 h 40 min at 26 ◦ C,
dough II for 2 h at 22 ◦ C and then 18 h at 4 ◦ C.
and the resulting increase in the dough temperature
result in a decrease in the Strecker aldehydes
in the crust (Fig. 15.48).
15.4.3.3.2 White Bread Crumb
In dilution analyses, 3-methylbutanol, 2-phenylethanol,
methional, (E)-2-nonenal and (E,E)-
2,4-decadienal were identified as the most
important odorants in the baguette crumb. The
odorants which produce the intense aroma note
were detected in a comparison of two baguettes
which were baked with two differently composed
pre-fermented doughs. The crumb of baguette I
had a pleasant intense odor, but in II this note
was weak and a rancid aroma defect appeared.
Table 15.61 shows that the concentrations of
2-phenylethanol and 3-methylbutanol, which
have a flowery/intense and alcoholic odor, are
higher in I than in II. The higher concentration
of the sweaty 2-/3-methylbutyric acid in II
produces the rancid aroma defect. A low yeast
concentration in a liquid preliminary dough,
which is only 1.5% based on the finished
dough I compared with 4.6% in dough II, is the
prerequisite for an optimal formation of both
the alcohols shown in Fig. 15.49. The curves
show that the concentrations of the two aroma
substances reach a plateau after eight hours
under the selected conditions. Their precursors
phenylalanine and leucine, which originate in the
flour and are degraded by yeast via the Ehrlich
pathway to give the odorants (cf. Formula 15.8)
are converted after this time or the bioconversion
stops because important yeast nutrients are
increasingly lacking.
Table 15.61. Odorants of white bread crumb – comparison
of two kinds of bread subjected to different dough
making a
Compound
Concentration (mg/kg)
Bread I Bread II
2-Phenylethanol 11.8 2.87
3-Methylbutanol 18.1 9.7
2-/3-Methylbutyric acid 0.55 1.5
a Recipe (kg): flour (I: 4.15; II: 4.9), water (I: 2.27;
II: 2.825), salt (I, II: 0.11), yeast (I: 0.125; II: 0.325),
pre-ferment (I: 2.005 of A; II: 0.5 of B). Pre-ferment A:
a suspension of flour (1 kg), water (1 kg) and yeast (5 g)
was incubated for 15 h at 30 ◦ C. Pre-ferment B: dough
made of flour (250 g), water (175 g) and yeast (75 g)
was incubated as in A.