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Research Article
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Biochemical Characteristics of Sorghum (Sorghum bicolor L. Moench) Flour Supplemented with Cluster Bean (Cyamopsis tetragonolaba L.): Influence of Fermentation and/or Cooking
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Hayat Z. Elbashir,
AbdelMoniem ,
I. Mustafa,
Abdullahi H. El-Tinay
and
Elfadil E. Babiker
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ABSTRACT
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The aim of the present study is to investigate the effect
of cluster bean supplementation followed by fermentation and cooking on
biochemical characteristics of sorghum cultivars flour. Two Sudanese sorghum
cultivars (Dabar and WadAhmed) were supplemented with cluster bean. The
flour of the two cultivars and supplements were fermented for different
periods of time and then cooked. The proximate composition of the cultivars
flour and cluster bean showed that the protein was found to be 8.36, 9.76
and 44.65% for Dabar, WadAhmed and cluster bean, respectively. Fermentation
of the cultivars flour for different periods of time significantly (p<=0.05)
changed the titratable acidity, non protein nitrogen, crude protein and
the dry matter for both cultivars. The protein digestibility of the cultivars
flour and supplements was significantly (p<=0.05) increased with fermentation
time even after cooking. The protein fractions contents of the flour before
and after cooking and that of the supplements were fluctuating for both
cultivars. Lysine content of the cultivars flour was significantly (p<=0.05)
increased with fermentation time even after supplementation. However,
other amino acids contents were fluctuating with fermentation time before
and after supplementation for both cultivars.
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How
to cite this article:
Hayat Z. Elbashir, AbdelMoniem , I. Mustafa, Abdullahi H. El-Tinay and Elfadil E. Babiker, 2008. Biochemical Characteristics of Sorghum (Sorghum bicolor L. Moench) Flour Supplemented with Cluster Bean (Cyamopsis tetragonolaba L.): Influence of Fermentation and/or Cooking. Journal of Biological Sciences, 8: 722-729. DOI: 10.3923/jbs.2008.722.729 URL: https://scialert.net/abstract/?doi=jbs.2008.722.729
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INTRODUCTION
Malnutrition and under nutrition are prevalent in
several parts of the developing countries in the world. The reasons behind
this situation include high population density, poor socioeconomic status
for the people, inadequate sanitary and health facilities and non-availability
of enough quantity and quality of foods (FAO, 1997). Although these factors
are closely interrelated, major food sources, dietary habits and the processing
methods used in the preparation of food significantly influence the nutritional
status of the populations. Animal foods, although excellent in nutritional
quality, are not available in enough quantity to these populations mainly
due to their higher costs and certain religious traditions and customs.
Hence, greater emphasis has been placed throughout the world on increasing
the production of plant foods, improving their nutritional quality and
developing simple and economical methods for their storage and processing.
Cereals, legumes and oil seeds form a major bulk of dietary proteins,
calories, vitamins and minerals to the developing nations (Steller, 1993).
With increasing dependence upon cereal grains to provide both energy and
protein requirements for man living in the developing countries, the need
for raising the overall nutritional status of cereal grains has become
increasingly important and much effort has been made to improve the amount
and quality of cereal proteins. Many methods employed to improve the nutritional
quality and organoleptic properties of cereal-based foods include genetic
improvement, amino acid fortification, supplementation or complementation
with protein rich sources such as grain legumes and defatted oil seed
meals (Ibrahim et al., 2005). In recent years large and concentrated
efforts have been directed to enhance the nutritional quality of almost
all agriculturally significant cereal grains and in particular aimed at
attaining the most favorable levels in the essential amino acids in cereal
proteins such as sorghum and millet. Sorghum like other cereals is known
to be deficient in lysine which creates amino acid imbalance and subsequent
growth retardation. Therefore, various means have been proposed to improve
the nutritional quality of dishes prepared from sorghum; these include
germination and fermentation to increase the available lysine level (Ibrahim
et al., 2005). According to FAO (1997) sorghum (Sorghum bicolor
(L.) moench) is considered as one of the most important food
crops in the world, following wheat, rice, maize and barely. It represents
an important source of calories and protein to the vast majority of the
population as well as for poultry and livestock. Sorghum was consumed
by Sudanese as fermented Kisra (unleavened bread) and Asida or thick porridge
(Dewit and Kessel, 1996). Sorghum can be supplemented with other ingredients,
such as legumes to improve its nutritional value particularly the protein
(Ibrahim et al., 2005). Cluster bean or cluster bean (Cyamopsis
tetrgonoloba) belongs to family Fabaceae is bushy, drought tolerant,
nitrogen fixing and protein rich summer legume. Cluster bean has acquired
an economic and industrial importance after the discovery of the gummy
substance (galactomannan) in the seed endosperm, which is used in food
and industrial products. The present study was carried out to investigate
the effect of cluster bean supplementation followed by fermentation and
cooking on biochemical characteristics of sorghum cultivars flour.
MATERIALS AND METHODS
Two sorghum cultivars Wad Ahmed and Dabar were obtained
from the Agricultural Research Station, Wad Medani, Sudan. Cluster bean
seeds were obtained from Cluster Bean Notational Company (Khartoum). The
study was conducted during the season 2005/2006.
The grains of both cultivars were cleaned manually to
remove husks, damaged grains and other extraneous materials. The cleaned
grains of each cultivar were milled into fine flour with a hammer mill
(Gibbons Electric, Essex, UK) to pass through a 0.4 mm mesh size screen.
The flour of the cultivars was supplemented with cluster bean flour in
the ratio of 1:2.1, 1:2.4 for Dabar and Wad Ahmed, respectively, to raise
the protein content of each cultivar to 19.86 and 19.82%, respectively.
The cultivars flour with or without cluster bean was fermented according
to El-Tinay et al. (1979) method with a minor modification. About
200 ml distilled water was added to the flour and mixed well with a glass
rod. The slurry was allowed to ferment naturally at room temperature ((28 ± 3 ° C).
Samples were withdrawn at different periods of time (0, 8, 24 and 36 h).
The pH was measured during fermentation using pH meter (PUSL Munchen 2,
KARL-KOLB, Germany). Thereafter, the samples were dried in a Gallenkamp
oven (BS model OV-160; Manchester, UK) at 50 ° C for 24 h. The dried
samples were milled into fine flour with a hammer mill (Gibbons Electric,
Essex, UK) to pass through a 0.4 mm mesh size screen. The fermented flour
with or without cluster bean was cooked in a water bath for 20 min. The
viscous mass was spread in petri dishes and dried using Gallenkamp oven
(BS model OV-160; Manchester, UK) at 50 ° C for 24 h. The dry flakes
were milled into fine flour with a hammer mill (Gibbons Electric, Essex,
UK) to pass through a 0.4 mm mesh size screen and kept for further analysis.
The dry matter and crude protein (Nx6.25) were determined
according to AOAC (1984).
Total titratable acidity was determined according to
AOAC (1984) method. About 10 g of material were weighed into 250 mL beaker
and added to 150 mL of distilled water and mixed well. The mixture was
filtered through Whatman No. 1 filter paper. The filtrate was then titrated
against 0.1 N NaOH using 0.30 mL phenolphthalein indicator. Titratable
acidity was expressed as lactic acid using the following equation:
0.009 = g lactic acid equivalent to 0.1 N sodium hydroxide.
Non-protein nitrogen was determined according to the
method of Gheyasuddin (1970) using 5.0 g of the sample suspended in 2
mL H2SO4 diluted in 150 mL distilled
water in a 200 mL volumetric flask.
The in vitro protein digestibility was carried
out using pepsin alone according to the method of Maliwal (1983) as described
by Monjula and John (1991) with a minor modification.
The proteins from the defatted flours of the samples
were fractionated according to the technique of Osborne as described by
Abd El-Aal et al. (1986) using distilled water, 1 M NaCl, 70% ethanol
and 0.2% NaOH solutions for albumins, globulins, prolamins and glutelins,
respectively. The nitrogen content of each fraction was determined using
the micro-Kjeldahl procedure (AOAC, 1984). The residue left after extraction
was also analyzed for nitrogen content. Each fraction was expressed as
a percent of the total nitrogen.
The amino acid composition of the samples was determined
using an amino acid analyzer Sykam System 7130 (Widner and Eggum, 1966)
after hydrolyzing the samples with 6 N HCl at 110 ° C for 24 h. The
sulphur-containing amino acids were oxidized using performic acid before
the acid hydrolysis. The contents of different amino acids recovered were
presented as g/100 g.
Three samples for each parameter were prepared, each
sample was analyzed in triplicate and the values were then averaged. Data
were assessed by Analysis of Variance (ANOVA) as described by Snedecor
and Cochran (1987) and by Duncan`s (1955) multiple range test with probability
p<=0.05.
RESULTS AND DISCUSSION
Table 1 shows changes in pH, Titratable
Acidity (TA), Crude Protein (CP), Non-Protein Nitrogen (NPN)
Table 1: |
Changes in pH and percent Titratable Acidity (TA), Crude Protein,
(CP) Non-Protein Nitrogen (NPN) and Dry Matter (DM) during natural
fermentation of sorghum cultivars |
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Values are means ± SD. Means not sharing a common
superscript letter(s) in a column are significantly different at p<=0.05 |
Table 2: |
Changes in protein digestibility (%) of sorghum cultivars (Dabar
and WadAhmed) supplemented with cluster bean during fermentation and
cooking |
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Values are means ± SD. Means not sharing a common
superscript letter(s) in a column are significantly different at p<=0.05 |
and Dry Matter (DM) during fermentation of sorghum cultivars
flour. Fermentation of sorghum cultivars flour remarkably decreased the
pH of the media with time. Fermentation up to 36 h significantly (p<=0.05)
reduced the pH to 4.1 and 3.9 for Dabar and Wad Ahmed cultivars, respectively.
Simultaneously with drop in pH there was a gradual increase in the TA
for the two cultivars. Chavan and Kadam (1989) stated that during fermentation,
pH decreases with a concomitant increase in acidity as lactic acid accumulates
due to microbial activity. According to El Hidai (1978) natural fermentation
of sorghum is mainly due to lactic acid by Lactobacillus sp., yeast
and acetic acid fermentations during the later stages of fermentation.
During fermentation TA significantly (p<=0.05) increased from 0.17 to
1.25% and from 0.19 to 1.42% for Dabar and Wad Ahmed, respectively. These
results are in agreement with many researchers (El-Tinay et al.,
1985; Hamad and Field, 1997; Yousif and El-Tinay, 2001). The protein
content of unfermented flour of Dabar cultivar was 9.34% while that of
WadAhmed cultivar was 10.20%. The protein content increased significantly
(p<=0.05) from 9.34% to 12.20% and from 10.20% to 11.50% at the end of
fermentation period for Dabar and Wad Ahmed cultivars, respectively. The
results obtained agree with previous studies conducted by Yousif and El
Tinay (2001) and Ibrahim et al. (2005) for sorghums. The observed
increase in the protein content of treated samples was probably due to
loss in dry matter content through depletion of carbohydrates (Ahmed et
al., 1991). They elucidated that it thus may be an apparent and not
real increase. However, cells of the fermented micro-organisms could have
contributed to the protein content. Therefore, they suggested that fermentation
of sorghum results in an observable increase in crude protein content.
For Dabar cultivar NPN increased from 0.10% at zero time
to 0.30% at the end of fermentation time while for Wad Ahmed cultivar
it was increased from 0.04% at zero time to 0.18% at the end of fermentation
period. An increase in NPN was reported by El-Tinay et al. (1979).
The gradual decrease in dry matter towards the end of fermentation for
both cultivars is mainly due to the utilization of part of the meal nutrients
by the fermenting organisms; hence the two cultivars showed a gradual
loss in dry matter of about 4.4 and 5.7% for Dabar and Wad Ahmed cultivars,
respectively after 36 h of fermentation.
Changes in in vitro Protein Digestibility (IVPD)
as affected by supplementation, fermentation and cooking are shown in
Table 2. After supplementation of the cultivars flour
with cluster bean, the protein content significantly increased to 20.02%
for both cultivars. Further increment was observed when the supplemented
flour was fermented for different periods of time. Fermentation after
supplementation of the two cultivars flour caused additional increase
in total protein content to 22.93 and 20.79% for Dabar and Wad Ahmed cultivars,
respectively. Au and Field (1981) indicated that the protein is the more
limiting nutrient in most human diets than carbohydrates. Therefore, any
process that appears to increase its content even at the expense of carbohydrates
may be advantageous nutritionally.
Values of pepsin in vitro protein digestibility
of naturally fermented dough of Dabar cultivar increased significantly
(p<=0.05) from 10.32% at zero time to 17.4% for 24 h dough. Thereafter
it decreased and reached a value of 14.95% at the end of fermentation
period (36 h). For Wad Ahmed cultivar the IVPD increased significantly
(p<=0.05) from 9.28% at zero time to 14.68% at the end of fermentation
period (36 h). The current findings agreed
Table 3: |
Effect of fermentation, supplementation and cooking on protein fractions
(%) of Dabar cultivar |
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Values are means ± SD. Means not sharing a common
superscript letter(s) in a column are significantly different at p<=0.05 |
with the previous study carried by Chavan (1988) who
stated that the IVPD of sorghum increased markedly after fermentation
for 24 h and also that carried by Yousif and El-Tinay (2001) who indicated
that the IVPD of sorghum increased from zero time up to 28 h of fermentation.
Fermented sorghum products such as Kisra i.e., fermented Sudanese unleavened
bread, Abrey i.e., a fermented Sudanese flakes (Axtell et al.,
1981) and Nasha i.e., a fermented Sudanese baby food (Graham et al.,
1986) showed an improvement in protein digestibility over that of unfermented
cooked flours. Changes in IVPD of the two cultivars as a result of cluster
bean supplementation followed by fermentation are shown in Table
2. The results obtained showed a marked increase (p<=0.05) in IVPD
with maximum values obtained when the supplements were fermented for 36
h for both cultivars. Ibrahim et al. (2005) reported that the IVPD
of Dabar and Wad Ahmed cultivars improved significantly (p<=0.05) during
fermentation and even after supplementation with whey protein.
Cooking of unfermented sorghum flour with or without
cluster bean reduced the IVPD of both cultivars. However, during fermentation
the IVPD increased with time for both supplemented flour for both cultivars
even after cooking. It seems likely that supplementation followed by fermentation
alleviated the effect of cooking on protein digestibility. The IVPD of
Dabar supplemented with cluster bean after cooking was found to be 14.24%
at zero time and it was significantly (p<=0.05) increased at the end of
fermentation period to 17.07% and that of Wad Ahmed supplemented with
cluster bean after cooking scored 13.31% at zero time and it slightly
increased after 36 h of fermentation to 13.41%. Cooking significantly
(p<=0.05) reduced the IVPD of the supplemented samples from 18.7 to 14.2%
and from 17.1 to 13.3% for Dabar and Wad Ahmed, respectively. However,
values obtained after supplementation still higher than those obtained
before supplementation.
It was concluded that the IVPD of the cultivars and their
supplements were reduced for all levels of treatments after cooking. This
opposing correlation between cooking and IVPD was reported by many researchers
(Rom and Shull, 1992; Oria et al., 1995; Hamaker et al.,
1994). They suggested that on cooking more disulphide cross linked protein
oligomers and polymers are formed. During cooking enzymatically resistant
protein polymers are formed through bonding of the β and γ-kafirins
and possibly other proteins which are located on the outside of the protein
bodies. They concluded that the disulphide cross linked proteins thus
formed would then prevent access to and restrict digestion of the more
digestible and centrally located γ-kafirin within the protein body.
To alleviate the effect of cooking, Arbab and El-Tinay (1997) suggested
that sorghum should be cooked with reducing agents to improve the protein
digestibility.
Table 3 shows variation in protein
solubility fractions of cooked and uncooked flour of Dabar cultivar after
fermentation and/or supplementation. The albumin+globulin fraction was
13.33% at zero time and 12.99% at the end of fermentation period. It increased
significantly (p<=0.05) during the first 8 h of fermentation (18.30%)
but started to decrease gradually up to the end of fermentation process.
Cooking of the fermented dough significantly (p<=0.05) reduced globulin+albumin
fraction. Supplementation of the flour with cluster bean greatly increased
the level of globulin+albumin fraction. However, cooking of the supplemented
dough reduced the level of globulin+albumin fraction but still significantly
(p<=0.05) greater than the values before supplementation during all fermentation
periods. This study showed an improvement in globulin and albumin fractions
for both cultivars. As reported by Wu and Wall (1980) the globulin+albumin
fraction is characterized by higher levels of lysine, therefore, the nutritional
value of sorghum could be modified as a result of fermentation. El-Khalifa
and El-Tinay (1994) fractionated fermented sorghum proteins using the
classical Mendle-Osborne procedure and they reported that fermentation
of sorghum flour for 14 h acquired slight increase in albumin+globulins
fraction. Similar observation was noticed by Yousif and El-Tinay (2001).
The prolamin (Kafirin) was found to be a major fraction
with value of 28.56% before fermentation and 28.93% at the end of fermentation
period. The amount of prolamin was fluctuated with fermentation time.
Cooking of the fermented dough significantly (p<=0.05) reduced the amount
of prolamin. Supplementation before and after cooking significantly (p<=0.05)
reduced the amount of prolamin (Table 3). The G1-glutelin
(Cross liked-kafirin) was 25.38% at zero time and increased significantly
(p<=0.05) at the end of fermentation period (36.60%). Fermentation of
cooked flour significantly (p<=0.05) increased the amount of the fraction
with a maximum value of 35.33% obtained after 24 h fermentation. Supplementation
of the flour with cluster bean significantly (p<=0.05) decreased G1-glutelin
fraction. However, fermentation of the supplemented flour increased the
fraction content but to a level less than that of untreated flour. The
G2-glutelin (glutelin-like) was 3.26% at zero time thereafter
it increased gradually with the fermentation time and had a significant
increment (p<=0.05) after 24 h of fermentation. Cooking of the fermented
flour slightly decreased the content of G2-glutelin. Supplementation
and fermentation of the flour significantly (p<=0.05) increased the amount
of the fraction with higher increment obtained after the mixture was fermented
for 24 h (25.66%). Cooking of the supplemented and fermented flour significantly
(p<=0.05) decreased G2-glutelin fraction but still above the
level of untreated flour. The G3-glutelin (true-glutelin) was
24.49% at zero time and reached 20.99% at the end of fermentation period.
Supplementation had no great effect on the level of the
fraction. However, cooking of the supplements significantly (p<=0.05)
increased G3-glutelin fraction. Cooking of the fermented dough
before and after supplementation significantly (p<=0.05) increased the
insoluble protein content. The current result agreed with the findings
carried out by Fageer et al. (2004) and El-Khalifa et al.
(1999). Hamaker et al. (1986) stated that on cooking, the kafirin
proteins tend to become less soluble as a result of disulphide cross linking.
Cooking significantly (p<=0.05) increased the G1-glutelin (cross
linked-kafirin) while G2-glutelin (glutelin-like) slightly
decreased. G3-glutelin (true-glutelin) significantly (p<=0.05)
increased. Hamaker et al. (1986) reported that on cooking, the
alcohol soluble proteins are converted to higher molecular weight fractions,
namely G3 and non extractable fraction. A range of 97.30 to
103.08% was the protein recovered for all treatments. The changes in protein
fractions as a result of supplementation and fermentation agrees with
the previous results reported by Ibrahim et al. (2005) when they
supplemented sorghum cultivars with whey protein.
Table 4 shows variation in protein
solubility fractions of the flour of WadAhmed cultivar after fermentation
and/or supplementation. The results obtained for WadAhmed regarding the
classification of proteins into different fractions are similar to those
obtained for Dabar cultivar.
Table 5 shows the amino acid content
of fermented Dabar cultivar flour before and after supplementation. The
essential amino acids; threonine, methionine, tyrosine, histidine, arginine
and lysine were increased after 24 h of fermentation, while valine, cystine
and isoleucine were slightly increased at the initial 8 h of fermentation
and thereafter decreased towards the end of fermentation. Leucine and
phenylalanine fluctuating throughout the fermentation period reaching
a maximum value after 24 h of fermentation.
The amino acid content of Wad Ahmed cultivar (Table
6) indicated a progressive increase in threonine, leucine, phenylalanine,
histidine and lysine at the end of fermentation while sulphur-containing
amino acids (cystine and methionine) and arginine increased after 24 h
of fermentation. Valine and isoleucine were fluctuating throughout the
fermentation process. Tyrosine was highly increased at the initial 8 h
and then decreased towards the end of fermentation. The amino acid content
of Dabar (Table 5) and Wad Ahmed cultivars (Table
6) supplemented with cluster bean were greatly improved particularly,
threonine, histidine, arginine, the aromatic amino acids (phenylalanine
and tyrosine). Lysine which is the limiting amino acid in cereals was
highly increased from 0.19 and 0.2 g/100 g protein to 3.94 g/100 g and
3.97 g/100 g for supplemented Dabar and Wad Ahmed, respectively after
36 h of fermentation. Although there was a remarkable increase in lysine
content but is still slightly below the required value specified by FAO/WHO
(1990).
Table 4: |
Effect of fermentation, supplementation and cooking on protein
fractions (%) of WadAhmed cultivar |
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Values are means ± SD. Means not sharing a common
superscript letter(s) in a column are significantly different at p<=0.05 |
Table 5: |
Amino acid content (g/100 g protein) of Dabar cultivar flour with
or without supplementation during fermentation |
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Values are means of duplicate determinations |
Table 6: |
Amino acid content (m/100 g protein) of WadAhmed cultivar flour
with or without supplementation during fermentation |
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Values are means of duplicate determinations |
In conclusion, sulphur-containing amino acids (cystine
and methionine) decreased upon supple- mentation with cluster bean this
mainly because the amino acid profile of the legume protein isolates is
characterized by high lysine content and low sulphur-containing amino
acids (Pusztia et al., 1979). Moreover, the content of valine,
isoleucine, leucine were noticeably diminished.
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