THESE UNIQUE El Hassane Kéhien-Piho TOU - Nutridev

ARTICLE IN PRESS
E.H. Tou et al. / LWT 40 (2007) 1561–1569 1565
MG blend, the pH of the soaking water (supernatant)
decreased in a similar way from an initial value around 6.0
to a final value around 5.1 (Fig. 2A). As already mentioned
by Tou et al. (2006), this indicates that initial fermentation
occurs during the soaking step. Changes in sugar concentrations
(glucose, fructose, maltose and melibiose) in the
supernatant were investigated (Fig. 2B). The soaking step
was characterized by an initial increase in glucose and
fructose concentrations in the soaking medium due to
sugar diffusion out of the grains, followed by a decrease in
the concentrations of these sugars. At the end of soaking,
glucose and fructose concentrations reached a value
around 6.4 mmol/l. During the initial 12 h of soaking, the
pH
7
6
5
increase in glucose and fructose concentrations occurred
simultaneously with a decrease in pH (phase of slight
acidification). One possible explanation is that the rate at
which sugar diffuses out of the grains exceeds the rate of its
utilization by the microbial flora which is still in the initial
phase of growth. Changes in sugar concentrations in the
soaking water of MG blend were similar to those observed
during the soaking step in control (Tou et al., 2006).
Changes were also observed in the concentrations of the
main fermentation products (ethanol, lactate and acetate)
in the supernatant (Fig. 2C). Ethanol and lactic acid
concentrations increased significantly (Po0.001) during
soaking to reach final values of 76 and 67 mmol/l,
respectively. However, during the first 12 h, only ethanol
was formed. After 12 h of soaking, lactic and acetic acids
appeared and their concentrations increased simultaneously
with that of ethanol, indicating the beginning of
lactic acid fermentation (Fig. 2A). As was the case in the
soaking of millet in ben-saalga processing (Tou et al.,
2006), the soaking of the MG blend was dominated by
alcoholic fermentation.
B
mmol/l
4
3
14
12
10
8
6
4
2
3.1.2. Settling step
Changes in pH: A decrease in pH was observed during
fermentation in both processing methods (traditional and
CMI) (Fig. 3). Acidification profiles of pastes followed a
classical pattern similar to that of other fermented cerealbased
products (Kingamkono, Sjo¨gren, Svanberg, &
Kaijser, 1994).
In both processing methods, the pH decreased during
fermentation from an initial value around 6.5 to a final
value of around 4.0. Two phases of acidification were
distinguished: the first one occurred during the first 6 h
when the pH decreased from 6.5 to 4.7, followed by a
second phase of slower acidification (from 6 to 24 h), that
7
C
mmol/l
0
80
70
60
50
40
30
20
10
0
0 4 8 12 16
Soaking time (h)
Fig. 2. Changes in pH (A) (E: millet-groundnut and B: millet) and
concentrations of sugar; (B) (B: glucose, ’: fructose, n: melibiose and
m: maltose), ethanol, lactate and acetate; (C) (B: lactate, E: ethanol and
n: acetate) in the soaking water of millet–groundnut blend. Bars indicate
standard deviation.
pH
6
5
4
3
0 5 10 15 20 25
Fermentation time (h)
Fig. 3. Changes in pH during the fermentation step in MG-T and MG-
CMI processing methods (m: MG-T and B: MG-CMI). Bars indicate
standard deviation.