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Research Article
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Effect of Sprouting on Chemical Composition and Amino Acid Content of Sudanese Lentil Cultivars |
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Mashair A. Sulieman,
Mashair A. Sulieman,
Mohamed M. Eltayeb,
Elfadil E. Babiker,
Abdelmoneim I. Mustafa
and
Abullahi H. El Tinay
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ABSTRACT
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The aim of this research was to study the effect of sprouting on the
chemical composition, energy and amino acid content of lentil cultivars.
Three Sudanese lentil cultivars (Rubatab, Nadi and Selaim) were sprouted
for 3 and 6 days. The sprouted seeds were dried and milled. The Proximate
composition and amino acids content as affected by sprouting were determined.
During sprouting crude fat and fiber were increased, whereas Nitrogen
Free Extract (NFE) and food energy were decreased. Sprouting of the seeds
was observed to affect amino acid content and showed that it increases
partly or all essential and nonessential amino acids with slight variation
between cultivars. For Selaim cultivar, sprouting for 3 days increased
the proportion of all essential amino acids except methionine, further
increase in the period of sprouting to 6 days was observed to decrease
amino acid content, this was observed for histidine, lysine and arginine.
This result was also observed for Rubatab cultivar in which the content
of essential amino acids increased due to sprouting except methionine
and lysine. In Nadi cultivar sprouting for 3 days increased the essential
and nonessential amino acids. Generally, all lentil cultivars were low
in their content of sulfur amino acids (methionine and cystine).
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INTRODUCTION
Seed germination is a primary step to generate a new plant. During
germination, a series of active and complex biochemical and physiological
reactions is taking place, which result in extensive changes in composition
and/or morphology. Intensive investigations on compositional changes of
plant seed during germination are important because the necessity of understanding
the compositional changes and relevant functions from the view point of
plant science. When the seeds are destined for food use, an understanding
of the compositional changes resulting from germination in relation to
food quality is also important (Chioce et al., 1997).
In Egypt, it is common to germinate some legume seeds which are rich
in protein (20-50%) such as termes (Lupin termes), broad bean (Vicia
faba) and chickpea (Cicer arietinum), before direct eating,
cooking or used in salad dressing. Germination improves the nutritional
value of proteins which are hydrolyzed into easily assimilable polypeptide
and essential amino acids and inactivate trypsin inhibitors (Ahmed et
al., 1995).
Germination is regarded at present as one of the cheapest and most effective
procedures to increase the nutritional value of legumes, supposedly through
the breakdown of certain anti-nutritional factors such as phytates, proteases
inhibitors, lectins and a-glactosides (De la Cuardra et al., 1994).
Germination of legume seeds for human consumption has been a common practice
in the orient for centuries and appears to be a simple and effective processing
method for achieving desirable changes in nutritional quality. At present,
germinated legumes are becoming an increasing proportion of the total
consumption of food legumes in the world (Ghavidel and Prakash, 2007)
and they also used to produce flours of high nutritional value.
Germination causes important changes in the biochemical, nutritional
and sensory characteristics of legume seeds. Extensive breakdown of seed
storage compounds and synthesis of structural proteins and other cell
components takes place during this process. Fats and carbohydrates that
are often at surplus levels in western diets are broken down while dietary
fibre, which is mostly at a sub-optimal level, increases. Vitamins and
secondary compounds, many of which are considered beneficial as anti oxidants,
often are altered, dramatically during germination. Phytic acid and dietary
fibre both affects the uptake of micro-nutrient in the digestive tract
and thesecompounds are altered differently during the germination process.
Other anti-nutrient factors, such as the flatulence-producing α galactosidase,
trypsin and chymotrypsin inhibitors, which affect the digestion of proteins
are also reduced after germination (Frias et al., 1995; Vidal-Valverde
et al., 1994).
MATERIALS AND METHODS
A bulk of healthy and clean seeds of lentil (Lens culinaris Medic) cultivars
(Rubatab, Nadi and Selaim) used in this study was obtained from Elhudeeba Research
Station, Sudan. this study was conducted during the season 2006/2007. The bulk
of each cultivar was divided into three equal portions, the first portion was
reserved as a control (unsprouted seeds), the second portion was allowed to
sprout for 3 days and the third portion was allowed to sprout for 6 days. Prior
to sprouting, the seeds were soaked at room temperature in distilled water for
2 h. Sprouting was carried out in sterile petri-dishes lined with wet filter
paper for 3 and 6 days in a refrigerator (4°C). At the end of respective
sprouting period samples were dried at room temperature, ground to pass through
a 0.4 screen for subsequent chemical analysis. The control groups (unsprouted
seeds) were ground and kept at 4°C for further analysis. Sample of unsprouted
and sprouted seeds were analyzed for total nitrogen, ether extract, crude fiber
and ash (AOAC, 1980). Crude protein was calculated by multiplying the percent
nitrogen by the factor 6.25. Nitrogen Free Extract (NFE) was estimated by difference.
The energy content was determined by multiplying the percentages of crude protein,
crude fat and NFE by factors of 4, 9 and 4, respectively (Osborne and Voogt,
1978). Five hundred milligrams of the pulverized sample (0.5 mm) was acid hydrolyzed
(6 M HCl) for about 24 h in a closed bottle, then the hydrolyzed sample was
divided into two portions one of them was oxidized (hydrogen peroxide/formic
acid) for 24 h and then chilled, the other portion was left without oxidation,
then the pH was adjusted to 2.2 with NaOH. The volume was completed to 100 mL
with citrate buffer pH 2.2. Two milliliters were then filtered (membrane filter)
and used for analyzing amino acid by using analyzer/ion exchange chromatography.
All amino acids were detected at 570 nm, except proline which was detected using
a separate detector channel at 440 nm. RESULTS AND DISCUSSION
As shown in Table 1, there were remarkable changes
in proximate composition and food energy values of lentil due to sprouting.
Crude fat and crude fiber increased slightly for the three cultivars as
sprouting progressed. Ash content was slightly increased for Selaim cultivar
while for Rubatab and Nadi it slightly decreased. The protein content
of Nadi and Selaim cultivars slightly increased while that of Rubatab
it decreased with sprouting. The Nitrogen Free Extract (NFE) and food
energy for all cultivars decreased with the sprouting time. The slight
increment in fat content during sprouting compared to other constituents
for all cultivars may be due to the fact that fat contains about twice
the food energy values of protein and carbohydrate (Osborne and Voogt,
1978), the reduction in food energy value of the sprouted seeds might
be attributed to the very slow increment in fat content with increasing
sprouting period. Nielson and Liener (1984) and Shastry and John (1991)
attributed the reduction in NFE and protein to their utilization during
sprouting. Reduction of some storage nutrients of lentil seeds resulted
in a concomitant increase in other nutrients.Changes in nutrient and in
anti-nutrient factors occurring during sprouting depend on the type of
legume and on the sprouting conditions such as time, temperature and light
cycle (Frias et al., 1995). This clearly indicates potential for
optimization. Kuo et al. (2003) who also reported that the growth
conditions during the sprouting process can have important effects on
the composition of secondary metabolites of nutritional importance.
For Selaim cultivar sprouting produced high increase in all essential
amino acids except methionine which was 0.6 g kg-1 in raw sample
and thereafter it decreased to 0.4 g kg-1 after 6 days sprouting
(Table 2). Sprouting of the seeds for 3 days increased
amino acids content, but sprouting for longer time (6 days) decreased
some of them such as threonine, histidine, lysine and arginine. Dramatic
increase was seen for the essential amino acids valine, isoleucine, leucine,
phenyalanine for Selaim sprouted for 6 days. There was an increment in
aspartic acid and proline which were also detected by Kuo et al.
(2003) in sprouted lentil. In Rubatab cultivar the increment of most amino
acids such as threonine, valine, isoleucine, phenyalanine and histidine
was observed after 3 days sprouting. Tow of the essential amino acids
(methionine and lysine) of this cultivar decreased due to sprouting for
6 days.
For Nadi cultivar sprouting resulted in an increase in amino acids content
such as threonine, valine, methionine, isoleucine, leucine, phenyalanine,
lysine and arginine after 3 days sprouting; these were. There was a decrease
in some amino acids such as aspartic acid, tyrosine and glycine in this
cultivar due to sprouting; such a decrease was also observed by Kuo et
al. (2003) in sprouted lentil. The increment of amino acids during
sprouting may be attributed to the fact that seedlings are the site of high amino acid biosynthetic activity, resulting in high
content of free amino acid.
Table 1: |
Proximate composition (%) and energy value (kcal/100
g) of lentil cultivars as affected by sprouting |
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Table 2: |
Effect of sprouting on amino acid content (g kg-1
US) of lentil cultivars |
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Values are means of duplicate samples |
Also storage proteins can undergo proteolysis
and contribute to the increase of free amino acids.
CONCLUSION
Germination resulted in remarkable changes in proximate composition
and food energy values of lentil. Lentil was low in sulphur-containing
amino acids (methionine, cysteine), germination caused an improvement
in content of essential and nonessential amino acids.
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