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Effect of Malting and Fermentation on α-amylase
inhibitors and subsequent digestibility in Pearl Millet
OBILANA, A.O., MAREMA, T.R., MASHEGO, A., FAKUDE, S.Q.
Department of Food Technology, Cape Peninsula University of Technology,
P O Box 1906, Cape Town 7535
ABSTRACT
In this study, a combination of malting and
fermentation was used to reduce the alpha
amylase inhibitor levels in pearl millet and to
increase starch digestibility. The samples were
subjected to three different processing
treatments (malting, fermentation, malting /
fermentation), and compared to the raw
unprocessed grain. Malted samples were
prepared by steeping 500g of millet for 3h at
250C and germinating at 300C for 5d and dried
at 500C in a hot air vacuum drier. Fermented
samples were prepared by subjecting 500g of
millet to natural fermentation for 24h in
distilled water at 30oC, drained and dried at
500C in a hot air vacuum drier. The
malted/fermented samples were prepared by
first malting the grain, then subjecting the
malted grain to natural fermentation as
described above. Triplicate samples of raw,
malted, fermented, malted/ fermented millet
were assayed for alpha-amylase inhibitor and
starch digestibility. A significant (P<0.05)
difference was observed in the alpha amylase
inhibitor
content
values
for
the
malted/fermented samples (44.9%), malted
samples (47.7%), raw samples (54.3%) and
fermented samples (55.6%). This reduction
would seem to have contributed to the observed
increase in the digestibility of the samples, with
the fermented (38.0%), malted (40.2%) and
Malted/fermented (48.5%) samples been
significantly (P<0.05) higher than the raw
(22.1%) samples.
DATA ANALYSES
RESULTS AND DISCUSSION
RESULTS AND DISCUSSION –
Cont’d
The experiment was repeated 3 times. All
analyses were performed in triplicate (n=3).
Data obtained was then analysed by one way
analysis of variance followed by the least
significant difference test (LSD test). Mean
differences was evaluated at the 5%
significance level and correlations at the 1%
and 5% significance level. All statistical
analyses were carried out using the SPSS
Statistics program 2008 version 17.0.0.
Similar reduction in alpha-amylase
inhibitor content after germination of
great northern beans was reported by
Abdelrahaman et. al. (2005) in their
studies on pearl millet. A much lower
reduction in this study was obtained as
compared to other research work. Since
natural fermentation is this instance was
used, the high microbial load during the
first hours might have used up most of the
carbohydrates and further converted the
product into other matter thus resulting in
excess of enzymes without substrate to
break down.
Therefore the inhibitor content might
appear to be higher since the assay basis
the inhibitor amount on the product
produced. The slight reduction during
malting might be due to removal of shoot
after germination which may have
contained some simple carbohydrates in it
which could have resulted in a higher
reduction when considered. The overall
reduction of alpha-amylase inhibitor in
pearl millet resulted in the increase in
starch digestibility as indicated.
Figure 3. Alpha amylase inhibitor activity,
and starch digestibility of raw and
processed pearl millet.
A significant (p ≤ 0.05) increase in starch
digestibility between the different groups was
noted (fig. 3). This increase was based on the
amount of maltose produced after digestion as
compared between the groups. Fermented
millet and malted millet had an insignificant
increase in starch digestibility suggesting that
fermentation and malting has almost the same
effect on the digestibility of starch. Onyango
et. al. (2004) reported an increase in starch
digestibility during fermentation in there
study, which is in agreement with results
obtained in this study.
Although there was a corresponding
increase in starch digestibility with
decreasing α-amylase inhibitor activity,
these increases can not be solely
attributed to the decreasing inhibitor
activity, as other factors (eg. Fibre,
phenolic compounds etc.) present in pearl
millet that could be affecting starch
digestibility.
INTRODUCTION
Pearl millet (Pennisetum glaucum) is a lesser
known grain that can be utilized as food
especially in the arid and semi arid regions of
the world.
It grows under hot and dry
conditions, on infertile soils with low water
binding capacity. It is high in carbohydrates
and a source of proteins and essential amino
acids. Anti-nutritional constituents naturally
present in pearl millet such as alpha-amylase
inhibitors, limit the digestibility of and starch.
In recent times, however, some of these
“antinutrients” (fibre, polyphenols) have been
found to have functional / health benefits when
consumed and as such have become the focus of
numerous researches to determine their role in
human health.
Figure 1. Process flow diagram for the
preparation of millet samples.
OBJECTIVE
The aim of this study is to investigate the effect
of a combination of malting and fermentation
processing in reducing or destroying enzyme (αamylase) inhibitors in pearl millet, with a view
to increase its digestibility hence nutritional
value.
A reduction in alpha-amylase inhibitor content
in between the groups was obtained as
illustrated in fig 3 . Though the reduction was
insignificant, a slight decrease was obtained. A
trend between the treatments was observed. A
decrease in sequence from raw, malted and
fermented & malted was 54% - 47%- 44%.
However no decrease was observed for
fermented millet.
METHOD AND MATERIALS
There were four (4) samples prepared for
analyses in total. The process flow for the
preparation of samples are given in figure 1.
The starch digestibility and α- amylase
inhibitor assays were carried out according to
the methods of Oyongo et al., (2004) and Alonso
et al., (1998) respectively.
However a slightly lower increase in
digestibility was noted in this study. During
malting, a 17% - 40% increase in digestibility
was observed and from 17% - 38% for
fermented. A significantly (p ≤ 0.05) higher
increase in the malted & fermented millet was
obtained (17%-48%). These results are also in
agreement with those reported by Archana et
al., (2001). He reported an increase in
digestibility of pearl millet from 17% - 36%.
Due to the degradation of starch as indicated
by the decrease in starch content as the pearl
millet samples are processed, a higher
concentration of simple carbohydrate is
obtained which suggest that more starch is
digested. Thus processing of pearl millet by
fermentation and malting, with fermentation <
malting< malted & fermented increases it’s
starch digestibility.
Figure 2. Malted pearl millet
These results show that malting of pearl millet
has a reductive effect on alpha amylase
inhibitor content.
CONCLUSIONS
.
Combination of malting and fermentation
has shown potential in reduction of αamylase enzyme inhibitors in pearl millet.
With this in mind, it is possible to use
these relatively inexpensive processing
methods in rural areas where pearl millet
is used as a food source, to help increase
digestibility
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