THESE UNIQUE El Hassane Kéhien-Piho TOU - Nutridev

E.H. Tou et al. / International Journal of Food Microbiology 106 (2006) 52–60 59
more easily available to LAB through reduction in size during
grinding of the grains and also possibly by the autolysis of
yeasts or other biological factors. The soaking step can thus be
regarded as a fermentation process, which combines substrate
diffusion out of the grains and metabolic activity of the
microorganisms during which ethanol production relies mainly
on the fermentation of glucose, fructose and maltose. Sucrose,
which is the main disaccharide of the grains, was not detected
as a substrate in the soaking water, probably due to endogenous
invertase activity in the grain converting sucrose into glucose
and fructose and/or a perfect coupling between the diffusion
rate and consumption rate by microorganisms. This hypothesis
is currently being further investigated.
For the settling step, glucose and fructose appeared to be the
main substrates for lactic acid fermentation. However, a closer
examination of data brought to light an unbalanced situation,
since the production of around 10 mmol/l of ethanol and 30
mmol/l of lactic acid, i.e. a total of 40 mmol/l of fermentation
end-products, cannot be explained by an initial concentration of
8 and 3.6 mmol/l of glucose and fructose, respectively. From the
total concentration of the end-products it can be inferred that 20
mmol/l of ‘‘glucose equivalent’’ (considered as glucose and
fructose) would have been necessary, taking as hypothesis that 2
mol of fermentation end-product (i.e. ethanol or lactic acid) are
formed per mole of substrate, and that fructose is used as
substrate and not as an electron acceptor. Thus, such a balance
highlights a deficit in substrate for fermentation and suggests the
use of an additional carbon source, probably starch, which is
widely available in the pearl millet grain. This hypothesis is
consistent with the presence during the settling step of
amylolytic lactic acid bacteria, and suggests an active role
during fermentation. This is also consistent with other reports on
their presence at similar ratios in other traditional fermented
cereal pastes and dough (Diaz-Ruiz et al., 2003; Johansson et al.,
1995; Sanni et al., 2002) and with the ability of their a-amylase
to hydrolyse native starch (Rodriguez-Sanoja et al., 2000).
5. Conclusion
This study of the processing of pearl millet into ben-saalga
allowed a detailed flow diagram to be established and
fermentation steps to be characterized, providing a rational
basis for further investigations to ensure reproducible conditions
for the production of constant food quality. However, if
some information has been obtained on changes in nutritional
characteristics during processing, a more detailed study is
required to improve not only production conditions but also
gruel nutritional characteristics. Particular attention will have to
be paid to identifying methods to improve the energy and
nutrient density of traditional gruels.
Acknowledgements
This work was performed in the framework of the project
Cerefer (www.mpl.ird.fr/cerefer/) funded by the European
Commission, Contract No. ICA4-CT-2002-10047.
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