Biomedical Engineering Reference
In-Depth Information
Table 6.2
Total cell fatty acid composition in 48 h
S. cerevisiae
cells in relation to different
incubation temper
atures (15, 20, 30, and 40°C) [
55
]
Strain
S. cerevisiae
BG7FI
S. cerevisiae
635
Temperature (°C)
Temperature (°C)
Fatty acid
a
15
20
30
40
15
20
30
40
C6:0
0.00
0.38
0.02
0.00
0.00
0.00
0.00
0.00
C8:0
0.00
0.46
0.21
0.06
0.00
0.16
0.00
0.33
C10:0
1.44
6.47
2.05
0.49
1.06
2.55
6.06
0.76
C10:1
0.00
0.54
0.00
0.00
0.00
0.27
0.00
0.00
C12:0
3.72
7.86
8.11
3.72
3.43
8.59
18.21
3.09
C12:1
0.11
0.61
0.93
0.16
0.24
0.57
0.76
0.37
C14:0
4.02
2.08
1.52
1.63
5.28
4.45
3.56
1.90
C14:1
0.81
0.76
0.62
0.23
1.78
1.57
1.25
0.20
C16:0
33.19
37.05
41.28
38.34
25.84
32.57
33.77
33.73
C16:1
33.62
26.13
25.06
30.46
37.26
28.85
19.47
30.67
C18:0
8.13
8.73
11.19
12.83
6.00
7.17
8.55
11.31
C18:1n9
12.41
8.29
7.82
9.67
17.17
12.50
7.03
15.34
C18:1n11
0.44
0.24
0.51
2.01
0.48
0.35
0.25
1.64
C18:2
2.12
0.39
0.68
0.42
1.47
0.41
1.09
0.64
Unsaturation
degree
b
0.51
0.37
0.36
0.43
0.59
0.45
0.31
0.49
C16:1/C16:0
1.01
0.70
0.61
0.79
1.44
0.88
0.58
0.91
C18:1/C18:0
1.58
0.98
0.74
0.91
2.94
1.79
0.85
1.50
Chain length
c
16.16
15.46
15.86
16.27
16.15
15.74
15.12
16.33
a
Expressed as a percentage of total fatty acids
b
D /mol = [1(mol%monoenes)/100 + 2(mol%dienes)/100 + 3(mol%trienes)]/100
c
S(PC)/100, where P is percentage of a fatty acid and C is its carbon atom number
on both sides of the plasma membrane causes the separation of the two monolayers
and the concurrent increased synthesis of C18 fatty acid residues, which helps in the
maintenance of membrane integrity [
52
] .
The decrease of the degree of fatty acid unsaturation along with the temperature
increase is widely documented. The incorporation of exogenous oleic acid has been
reported to increase the tolerance of yeasts to the lethal effect of temperatures
between 41°C and 47°C [
55
] . Table
6.2
shows the modulation of the membrane
fatty acid composition of two strains of
S. cerevisiae
in a temperature range from 15
to 40°C [
55
]. For both strains, the relationship between unsaturation level and tem-
perature showed two maximum values at 15 and 40°C. The latter corresponds to the
maximum fermentation temperature for these strains. These results suggest that the
role of the unsaturation level has to be considered not only in terms of the contribu-
tion to membrane fluidity when temperature decreases but also as a mechanism to
protect the cell membrane from damage generated by oxidative and thermal stresses
[
55,
56
]. It was postulated that an oxygen-consuming desaturase prevents the accu-
mulation of oxygen and reactive oxygen species such as H
2
O
2
in yeasts. During
sourdough fermentation, yeasts are exposed to H
2
O
2
[
57
]. It has been observed that
the co-inoculation of
S. cerevisiae
and
L. sanfranciscensis
into dough gives rise to
