THESE UNIQUE El Hassane Kéhien-Piho TOU - Nutridev

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ARTICLE IN PRESS
E.H. Tou et al. / LWT 40 (2007) 1561–1569
A
mmol/L
B
mmol/L
14
12
10
8
6
4
2
0
140
120
100
80
60
40
20
0
C
mmol/l
D
80
70
60
50
40
30
20
10
0
0 4 8 12 16 20 24 0 4 8 12 16 20 24
mmol/L
80
70
60
50
40
30
20
10
0
Fermentation time (h)
Fermentation time (h)
Fig. 4. Changes in sugar concentrations (J: glucose, ’: fructose, n: melibiose and m: maltose) in MG-T (A) and MG-CMI (B), and in ethanol, lactate
and acetate concentrations (B: lactate, E: ethanol and n: acetate) in MG-T (C) and MG-CMI (D) in supernatant of pastes during the fermentation step.
Bars indicate standard deviation.
resulted in a slight decrease in pH from 4.7 to about 4.0.
The combined effects of the decrease in pH to under 4.5
with the production of antimicrobial compounds by LAB
(lactic acid and possibly bacteriocins) and the final cooking
step when the temperature reaches boiling point, ensure
conditions that prevent contamination by food-borne
pathogens (Nout et al., 1989; Kingamkono et al., 1994;
Nout & Motarjemi, 1997; Lei & Jakobsen, 2004).
Changes in mono- and di-saccharide, ethanol, lactic and
acetic acid concentrations during the fermentation step:
Analyses of sugars in the pastes during fermentation
revealed the presence of maltose, glucose, fructose and
melibiose (Fig. 4A and B). Changes in ethanol, lactate and
acetate, identified as the main fermentation products in the
pastes, were also monitored during fermentation in both
processing methods (Fig. 4C and D).
Glucose and fructose were the major sugars in MG-T
samples and their concentrations decreased due to their
consumption by bacteria during fermentation (Fig. 4A).
Maltose concentration was very low in MG-T pastes
(below 2 mmol/l). Conversely, the initial maltose concentration
in MG-CMI samples was not only significantly
(Po0.05) higher than its final concentration in the MG-T
samples but itself increased significantly (Po0.05) during
fermentation to reach a final value of 93.2 mmol/l (Fig. 4A
and B). This increase in maltose concentration is due to the
action of barley malt amylase on pre-gelatinized millet
starch. Despite probable consumption of maltose due to
micro-organism activities, maltose accumulated in the
MG-CMI pastes during fermentation as production
exceeded consumption (Fig. 4B). It should be noted that
the high final maltose concentration associated with a low
final pH may present a risk of post-contamination by
spoilage yeasts, with possible product alteration if storage
conditions are not appropriate.
Lactic acid was the major product formed during
fermentation with final concentrations of 53 and
71 mmol/l after 24 h of fermentation in MG-T and MG-
CMI, respectively (Fig. 4C and D). Thus, the fermentation
steps in both processing methods, as in the control, were
characterized by lactic acid fermentation. However, in
MG-CMI samples, the final lactic acid concentration was
significantly (Po0.05) higher than in MG-T samples,
which was itself higher than in the control (35.4 mmol/l).
These results are consistent with the higher concentrations
of fermentation substrates (maltose and glucose) in the
MG-CMI pastes. Apart from the step of backslop
inoculation, which accelerates the initiation of fermentation,
the CMI processing method is very close to that of
togwa (Kitabatake et al., 2003). These authors also
reported an increase in substrate (glucose) and fermentation
products (lactic acid) during settling.
Although the lactic acid content of the three types
of gruels, ben-saalga, MG-T and MG-CMI gruels was
different, their pH values, respectively, 3.8870.2, 3.8070.1
and 3.9070.1, were very close. Given that concentrations
of maltose and fermentation products—such as lactic
acid—increased considerably, this may have consequences