2nd International Conference on Chemical, Biological, and Environmental Sciences (ICCBES’15) May 20-21, 2015 Dubai (UAE)
Comparative Study of the Effects of Sodium
Sulphate and Sodium Acetate on Some
Functional Properties of Some Melon Seed
Flours: Protein Solubility Profile and Water
Absorption Capacity
Ogundele, J. O. 1, 2

of food proteins, they include, Nitrogen Solubility Index
(NSI), Water Soluble Protein (WSP), Water Dispersible
Protein (WDP) and Protein Dispersible Index (PDI). Some
correlations have been found between functional
characteristics of proteins in various applications and the
nitrogen solubility index. Generally. In order to obtain
optimum functionality in foods where gelation, emulsification
and foaming properties are required, a highly soluble protein is
desirable (1). Protein functionality is dependent on
hydrophobic, electrostatic, and steric parameters of the
proteins, which are essential for defining the protein structure
(2). Water absorption capacity is important in the development
of ready to eat food cereal grains, since a high water
absorption capacity may assure product cohesiveness (3).
Some protein with high water absorption capacities when
added to products being formulated may imbibe a
disproportionate amount of water and dehydrate other
component in the food systems or vice-versa. Thus,
adjustments in water ratio may be necessary to obtain the
required viscosity e.g., when soy proteins are added to dough,
extra water must be added for proper development (1)
Sodium bisulfate is used as a food additive to leaven cake
mixes (make them rise) as well as being used in meat and
poultry processing and most recently in browning prevention
of fresh-cut produce. Sodium and sulphate ions are essential to
all living organisms and their intracellular and extracellular
(4): concentrations are actively regulated according to WHO
(5). Sulphates are used as additives (5). In the food industry
and the estimated average daily intake of sulphate in food in
the USA is 453 mg/person, based on data on food
consumption and reported usage of sulphates as additives.
Sodium acetate has a wide range of applications in many
industries. In pharmacology, it is used as either a diuretic or an
expectorant. It is also an important food additive to preserve
foods and enhance their flavors (6). Sodium acetate and acetic
acid solutions act as buffers to maintain relatively constant pH.
In the medical field, sodium acetate solutions treat patients
with high blood acid levels and/or low sodium levels (7).
This research work is therefor to determine the effect of
sodium sulphate and sodium acetate on the protein solubility
Abstract— Sulphates and sodium acetate are used in the food and
pharmaceutical industries as additives. The use of sodium sulphate
(Na2SO4) and sodium acetate (CH3OONa) in this capacity may affect
some functional properties of food. Therefore, the Protein solubility
(PS) of some melon seed flours were determined as a function of
Na2SO4 and CH3OONa ionic concentrations. The PS of the seeds are
least at 0.50 % Na2SO4 concentration and are highest at 2.00 to 10.00
% Na2SO4 concentration. The order of the highest protein solubility
(%) of the melon seeds with Na2SO4 is 84.24 (L. siceraria II) > 83.79
(C. colocynthis) > 66.88 (C. vulgaris) > 62.43 (L.siceraria III) >
34.64 (L. siceraria I). Generally, PS of these seed flours are relatively
lower in sodium acetate solutions than in sodium sulphate solutions
with the highest % protein solubility of 47.89% for Citrullus
colocynthis seed flour at 5.00 (g/g %) CH3OONa concentration.
Na2SO4 therefore favours the protein solubility of these melon seed
flours at different concentrations than CH3OONa. The water
absorption capacity (WAC) of the seed flours are generally highest at
0.50 % Na2SO4 and least at 10.00 % Na2SO4.
Keywords— Protein solubility, Water absorption capacity,
Sodium sulphate, Sodium acetate.
I. INTRODUCTION
A functional property is any non-nutritional property of a
food or food additive that affects its utilization. It denotes
those physico-chemical properties of food proteins that
determine their behaviour in food during processing, storage,
preparation and corruption. The protein nature and charge
density facilitate interaction with the other food present such
as water, ions, lipids carbohydrate, vitamins, colour and
flavour constituents depending upon the environmental pH,
ionic strength (salt concentration), and temperature during
preparation, processing and storage (1) .
Protein solubility is the percentage of total protein
(nitrogen in a sample) that is water dispersible based on
method used. Several terms are used to describe the solubility
1
Industrial Chemistry Department, Federal University Oye Ekiti, Ekiti
State, Nigeria.
2
Chemistry Department, Federal University of Technology, Akure, Ondo
State,
Nigeria.
e-mail:
[email protected]
or
:
[email protected].
http://dx.doi.org/10.17758/IAAST.A0515046
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2nd International Conference on Chemical, Biological, and Environmental Sciences (ICCBES’15) May 20-21, 2015 Dubai (UAE)
varieties of gourd seeds occur between 0.5 and 1.0 (g/ml %)
Na2SO4 concentration with values of (29.91, 17.68, 21.04,
26.32 and 20.06) % for Citrullus colocynthis, Citrullus
vulgaris, Lageneria siceraria I (AWG) and Lageneria
siceraria I (BBG) and Lageneria siceraria III (BGG)
respectively.
and water absorption capacity of some gourd melon seeds.
II. MATERIALS AND METHOD
Materials: The seeds of Citrullus colocynthis, Citrullus
vulgaris, Lageneria siceraria I (African wine kettle),
Lageneria siceraria II (Basketball gourd) and Lageneria
siceraria III (Bushel gourd) were bought from markets in Ilora
Oyo State, Nigeria. They were dehulled, oven dried and milled
into fine flour samples.
Protein solubility profile as a function of pH (PS):
Mixture of 5% flour/distilled water was homogenized and left
to solubilize at ambient temperature (35oC) for about 5
minutes. The pH of the mixture was adjusted to pH 2-11 with
0.1M HCl and 0.1 M NaOH and centrifuged at 3,500 r/min for
30 min (8). The supernatant was decanted and the soluble
protein determined using Kjeldahl’s method (AOAC, 1990).
The values were expressed as the percentage of the protein
content of each flour sample and plotted against pH.
Determination of water absorption capacity (WAC):
1.00g of flour sample was mixed with 10.00cm3 distilled water
and centrifuged for 30mins at 3,500r/min. The supernatant was
decanted into a 10.00cm3 graduated measuring cylinders. The
volume noted was used to determine the volume of water
absorbed by difference and was converted to gram using the
density of water to be 1.00 g/cm3 (10).
Effect of salts on functional properties of samples:
Na2SO4 and CH3OONa solutions of concentrations 0.50, 1.00,
2.00, 5.00 and 10.00 % (g/g) were made. These were used in
place of distilled water in the determination of the effects of
ionic strength on protein solubility and water absorption
capacity of the gourd seed flours, without adjusting the pH.
Statistical Analysis: One way analysis of variance
(ANOVA) and least significance difference (LSD) were
carried out on the replicate data generated using SPSS 18. The
results are expressed as mean ± standard deviation. Duncan
was also used to determine values that are significantly
different with p≤ 0.05 (Ogundele (11).
90
% Protein solubility
80
C.colocynthis
60
C.vulgaris
50
LS(AWG)
40
LS(BBG)
30
LS(BGG)
20
10
0
0
2
4
6
8
10
12
Sodium sulphate concentration (%)
Fig 1 Protein solubility profile of five varieties of gourd melon seeds
at different concentrations of sodium sulphate
Fig 2 Protein solubility profile of gourd seeds with sodium acetate
concentrations
The (%) protein solubility (PS) of the gourd seed flours with
CH3OONa concentrations in Figure 2 are relatively low
compared with PS of the samples with Na2SO4. The highest %
protein solubility are (47.89. 35.37, 29.47, 31.56 and 31.22) at
(5.00, 10.00, 2.00, 2.00 and 10.00) (g/ml %) CH 3OONa
concentration for Citrullus colocynthis, Citrullus vulgaris,
Lageneria siceraria I (AWG) and Lageneria siceraria II
(BBG) and Lageneria siceraria III (BGG) respectively.
Hence, Citrullu colocynthis has the highest and Lageneria
siceraria I (AWG) has the least % protein solubility among the
five samples with CH3OONa concentrations. These values are
similar to the the PS of mushroom samples results ranging
from 6.00 ± 2.00 to 45.00 ± 2.00% (14). The least % PS of
the melon seeds with CH3OONa concentrations are (23.92,
26.54, 21.05, 26.32 and 13.38) %. These low values may be
due to some hydrophobic groups produced as a result of the
weak dissociation of CH3OONa hence, CH3COONa may have
decreased the preferential binding effect of water to the gourd
melon seed flours.
Table 1 shows the water absorption capacity of the five
varieties of gourd seeds with different concentrations of
Na2SO4. The WAC of C. colocynthis ranges from 1.93±0.12
(at 0.50 % Na2SO4) to 0.07±0.13 (at 10.00 % Na 2SO4), for C.
III. RESULTS AND DISCUSSION
The protein solubility of the five varieties of gourd melon
seed flour samples with Na2SO4 concentration is relatively
high and follow similar patterns (Figure 1). Citrullus
colocynthis, Citrullus vulgaris, Lageneria siceraria II (BBG)
and Lageneria siceraria III (BGG) all have their highest
protein solubility (%) of 83.79, 66.88, 84.24 and 62.42 at
10.00 (g/ml %) Na2SO4 concentration respectively while
Lageneria siceraria I (AWG) has its highest protein solubility
of 36.64% at 2.00 g/ml % Na2SO4 concentration. The order of
the highest protein solubility (%) of the gourd seeds is 84.24
(L.siceraria II) > 83.79 (C.colocynthis) > 66.88 (C.vulgaris) >
62.43 (L.siceraria III) > 34.64(L. siceraria I). These results are
comparable with the protein solubility of between 65 and 82 %
obtained by Masood and Rizwana on legume protein isolates
(12). The solubility of a protein is usually affected by its
hydrophilicity or hydrophobic balance, depending on surface
active agents, can form and stabilize the amino acid
composition, particularly at the protein surface (13).
Generally, the least protein solubility (%) values of the five
http://dx.doi.org/10.17758/IAAST.A0515046
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2nd International Conference on Chemical, Biological, and Environmental Sciences (ICCBES’15) May 20-21, 2015 Dubai (UAE)
REFERENCES
vulgaris it ranges from 1.67±0.12 (at 0.50 % Na 2SO4) to
0.07±0.13 (at 2.00 % Na2SO4); for L.siceraria I, WAC ranges
from 1.97±0.12 (at 2.00 % Na2SO4) to 0.22±0.22 (at 10.00 %
Na2SO4); L. siceraria II WAC ranges from 2.17±0.12 (at 2.00
% Na2SO4) to 0.14±0.25 (at 10.00 % Na2SO4); L.siceraria III
2.86±0.45 to 0.00±0.0. The relatively high values of WAC
observed at 0.5% Na2SO4 concentration may be due to
electrostatic repulsion at low salt concentration and salting in
effect on the seed flours. When the seed flours are desired as
ingredient in food system especially as soup thickeners, salt
concentration of about 0.50% may be used. This is because
hydrated salt ions does not affect the hydration shell of the
charged groups on the protein (14).
Therefore, the increase in the water absorption capacity results
from water associated with the bound ions. Generally, all the
samples have the least WAC at 10.00 % Na2SO4.
C.
colocynthis and C. vulgaris both exhibit gradual decrease in
WAC with increasing % Na2SO4. Akintayo reported similarly,
a steady decrease in WAC with increasing salt concentration
of some beans (15). WAC is affected by anion, pH, amino acid
and surface charge. At high salt concentration, electrostatic
interactions are of importance as far as binding of water to
protein is concerned because competition of the protein ion for
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succinated derivatives of African yam-bean (Sphenostylis
sternocarpa that upon further increase in the ionic strength
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in the water absorption capacity (16). Fagbemi reported that
Na2SO4 encouraged higher WAC for full fat and defatted
bread fruit nut and fluted pumpkin probably because of the
high hydration capacity of Na2SO4 (1).
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[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
IV. CONCLUSION
[13]
There is appreciable effect of sodium sulphate solution on
the protein solubility of these five varieties of gourd melon
seed flours at different concentrations. The least protein
solubility occur at 0.50 % Na2SO4 and the highest occur
between 2.00 and 10.00 % Na2SO4. Protein solubility of these
seed flours with sodium sulphate solutions are higher than in
sodium acetate solutions. The water absorption capacity of the
melon seed flours are generally highest at 0.50% Na2SO4 and
reduces gradually with increasing salt concentration and
ventually became least at 10.00 % Na2SO4 concentration.
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TABLE I
EFFECT OF NA2SO4 ON WATER ABSORPTION CAPACITY OF FIVE VARIETIES OF GOURD SEEDS (G/G)
Concentration (g/g)
Sample
0.50
1.00
2.00
5.00
10.00
C.colocynthis
1.93±0.12b
1.80±0.35b
1.61±0.00b
1.59±0.12b
0.07±0.13a
C.vulgaris
L.siceraria I
1.67±0.12b
1.93±0.12c
1.53±0.12b
1.74±0.12c
1.42±0.22ab
1.97±0.12c
0.35±0.12a
1.32±0.12b
0.07±0.13a
0.22±0.22a
L.sicerariaII
1.73±0.12c
2.07±0.12c
2.17±0.12c
0.90±0.12b
0.14±0.25a
1.93±0.42b
1.87±0.24b
1.89±0.10b
2.86±0.45c
0.00±0.00a
L.sicerariaIII
Values with different superscripts on the same row are significant at (p≤ 0.05).
http://dx.doi.org/10.17758/IAAST.A0515046
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