DSpace at VNU: Effects of pH and salt concentration on functional properties of rambutan (Nephelium lappaceum L.) seed albumin concentrate

1212

International Journal of Food Science and Technology 2016, 51, 1212–1219

Original article
Effects of pH and salt concentration on functional properties
of rambutan (Nephelium lappaceum L.) seed albumin concentrate
Huynh Thanh Hai Vuong, Ngoc Minh Chau Tran, Thi Thu Tra Tran, Nu Minh Nguyet Ton &
Van Viet Man Le*
Department of Food Technology, Ho Chi Minh City University of Technology, 268 Ly Thuong Kiet street, District 10, Ho Chi Minh City,
Vietnam
(Received 1 December 2015; Accepted in revised form 10 February 2016)

Summary

Searching new protein sources is essential due to an increase in protein demand. In this study, rambutan
seed albumin concentrate (RSAC) with the protein content of 80.8% was isolated from defatted rambutan
seed meal. The effects of pH and sodium chloride concentration on solubility and functional properties of
RSAC were investigated. RSAC had minimum solubility at pH 4. Water absorption capacity at pH 7 and
oil absorption capacity of RSAC were 0.79 and 6.13 mL gÀ1, respectively. Both foaming and emulsifying
capacities achieved maximal levels at pH 12. In sodium chloride solution, foaming capacity and stability
achieved maximal levels at the concentration of 0.6 mol LÀ1, while the highest emulsifying capacity and
stability were noted at the concentration of 0.2 mol LÀ1. The least gelation concentration of RSAC was
100 g LÀ1 and this value decreased by five times as salt concentration in the protein solution was
0.6 mol LÀ1. RSAC was a potential functional ingredient in food processing.

Keywords

Albumin, functional properties, pH, rambutan seed, salt concentration.

Introduction

In food industry, proteins not only contribute to
nutritional value but also affect physico-chemical characteristics and sensorial properties of food (Yada,
2004). Plant proteins have attracted great attention
due to low cost and high productivity. According to
Osborne classification, plant proteins consisted of four
major fractions: water-soluble albumin, salt-soluble
globulin, alkaline-soluble glutelin and alcohol-soluble
prolamin. The ratio of protein fractions varied from
plant to plant. Increase in world population increases
the demand for protein. Although conventional plant
protein sources including soy, wheat, sorghum, lupin
and chickpeas have been widely and effectively used
for human consumption, searching new protein
sources is essential for protein demand in developing
countries (Day, 2013).
Rambutan (Nephelium lappaceum L.) is a popular
crop widely cultivated in tropical countries. Rambutan
fruits have been used in the production of juice, jam,
jelly, marmalade and canned fruit in syrup. The
percentage of seed varied from 4 to 9% fruit weight
*Correspondent: Fax: +84 8 38637504;
e-mail:

(Sirisompong et al., 2011). In some Asian countries,
rambutan seeds are edible after roasting, while in
others, the seeds are considered as a waste material
(Solıs-Fuentes et al., 2010). The oil and protein contents in rambutan seeds were 37.1–38.9% and 11.9–
14.1%, respectively (Augustin & Chua, 1988). Some
studies focused on rambutan seed oil, the physicochemical and thermal characteristics of which may

become interesting for specific applications in several
segments of the food industry (Solıs-Fuentes et al.,
2010; Sirisompong et al., 2011). After oil extraction,
protein is one of the valuable components in the
obtained residue and defatted rambutan seed meal
(DFRM) can be considered as a nonconventional
protein source. There have been so few studies on
rambutan seed proteins. According to Augustin &
Chua (1988), the amino acid profile of rambutan seed
proteins showed that the proteins were of good quality
for food use. Our preliminary study revealed that
albumin was the major protein fraction in rambutan
seeds (Data not shown). Albumin can be extracted by
water which is an inexpensive and eco-friendly solvent.
In addition, water did not modify native structure of
the extracted proteins as well as their functional
properties as compared with other solvents such as
salt solution, alkaline or alcohol (Yada, 2004). Many

doi:10.1111/ijfs.13087
© 2016 Institute of Food Science and Technology


Effects of pH and salt concentration H. T. H. Vuong et al.

studies reported functional properties and effects of
processing parameters on functional properties of
water-soluble proteins from different plant sources
including great northern bean (Sathe & Salunkhe,
1981), oat seed (Ma & Harwalkar, 1984), tepary bean

(Idouraine et al., 1991), wheat germ (T€
om€
osk€
ozi et al.,
1998), pea seed (Lu et al., 2000; Adebiyi & Aluko,
2011), African locust bean (Lawal et al., 2005), ginkgo
seed (Deng et al., 2011) and kidney bean (Mundi &
Aluko, 2012). These efforts were aimed at effective
application of unconventional protein sources to formulation of new food products. However, functional
properties of rambutan seed albumin concentrate
(RSAC) have never been reported.
In this study, RSAC was prepared from DRSM.
The effects of pH and salt concentration on solubility
and functional properties of the RSAC were investigated for the purpose of evaluating the potentiality of
this new protein source in food product formulation.
The investigated functional properties included water
and oil absorption capacity, emulsifying capacity,
emulsion stability, foaming capacity, foam stability
and gelation capacity.
Materials and methods

30 min and the supernatant was adjusted to pH 4.2
using HCl solution (0.1 mol LÀ1) for albumin precipitation. The solid phase was recovered by centrifugation at 5000 g, 20 °C for 30 min and re-dissolved in
de-ionised water. The procedure of albumin precipitation was repeated twice. Finally, the precipitate was
freeze-dried, ground and stored at À18 °C.
Proximate composition of albumin concentrate

Protein content was determined by Kjeldahl method
(Bradstreet, 1965). Total sugar and reducing sugar
contents were evaluated by spectrophotometric

method with phenol–sulphuric acid (DuBois et al.,
1956) and 3,5-dinitrosalicylic acid (Miller, 1959),
respectively. Polyphenol content was measured by
spectrophotometric method using Folin–Ciocalteu
reagent (Singleton & Rossi, 1965). The moisture, ash,
lipid and total acid contents were analysed using
AOAC official methods (Helrich, 1990). Surface
hydrophobicity of soluble proteins was measured by
fluorescence spectrometric method described by Kato
& Nakai (1980) using 8-anilino-1-naphthalene
sulphonate. Sulfhydryl group content was determined
according to the method described by Thannhauser
et al. (1987).

Materials

Seeds of rambutan (Nephelium lappaceum L.) fruits
were originated from a canned fruit processing plant
in Dong Nai, Vietnam. The seeds were ground, defatted with hexan at 40 °C for 36 h and stored at À18 °C
before use.
De-ionised water was used as extraction solvent. All
chemicals used in this study were of analytical grade
and purchased from Sigma-Aldrich (St. Louis, MO,
USA).
Preparation of rambutan seed albumin concentrate

For albumin extraction, 100 g defatted rambutan seed
meal and 1 L de-ionised water were mixed at 200 rpm,
30 °C for 2 h. The mixture was centrifuged at 1500 g,
20 °C for 30 min for solid removal. The extract was

dialysed against distilled water to remove salts and to
coagulate contaminating salt-soluble protein fraction
(globulin) using a membrane with molecular weight
cut-off of 6 KDa (Biovision, Milpitas, CA, USA). The
dialysis bag was placed in a beaker containing distilled
water. The outer phase was continuously stirred using
a magnetic stirrer. The dialysis was performed at the
ambient temperature. After 8 h, the dialysis bag was
removed and the liquid phase in the beaker was
replaced by distilled water. The dialysis was repeated
three times. Upon completion of dialysis, the content
of dialysis bag was centrifuged at 5000 g, 20 °C for

© 2016 Institute of Food Science and Technology

Protein solubility

Protein solubility was determined by the method of
Lawal et al. (2005). The protein sample (125 mg) was
dispersed in distilled water (25 mL), and the slurry
was adjusted to the desired pH (2–12) using HCl solution (0.5 mol LÀ1) or NaOH solution (0.5 mol LÀ1).
The slurry was mixed at 30 °C for 1 h with a magnetic
stirrer before centrifuging at 12 000 g for 20 min at
4 °C. Protein content in the supernatant was determined by Kjeldahl method. The nitrogen solubility
index (NSI) (%) was calculated as follows:
NSI ¼ Amount of nitrogen in the supernatant (g)=
Amount of nitrogen in the initial sample (g).
Effects of NaCl concentration (0–1 mol LÀ1) on
protein solubility were also investigated.
Water absorption capacity and oil absorption capacity

Water absorption capacity (WAC) and oil absorption
capacity (OAC) were measured by the method of
Lawal et al. (2005). The protein sample (1 g) was
mixed with distilled water (10 mL) or soybean oil
(10 mL) for 30 s. The samples were then kept at
30 Æ 1 °C for 30 min before centrifuging at 5000 g for
30 min. The volume of supernatant was noted in a
10-mL graduated cylinder. WAC and OAC were

International Journal of Food Science and Technology 2016

1213


1214

Effects of pH and salt concentration H. T. H. Vuong et al.

calculated as mL water or mL oil trapped by 1 g
protein sample. Effects of pH (2–12) and NaCl concentration (0–1 mol LÀ1) on WAC were studied.
Emulsifying capacity and emulsion stability

Emulsifying capacity (EC) and emulsion stability (ES)
were evaluated using the method suggested by Pearce
& Kinsella (1978).
The protein sample (500 mg) was dissolved in Britton-Robinson Universal buffer (100 mL). Then, 4 mL
the protein dispersion and 4 mL soybean oil were
mixed and homogenised at 2000 rpm for 1 min using
a Heidolph Diax 900 homogeniser (Heidolph Instruments GmbH & Co., Schwabach, Germany). At 0 and

10 min after the homogenization, 0.05 mL of the
obtained emulsion was pipetted from the bottom of
the tube and subsequently diluted into 10 mL of the
same buffer containing sodium dodecyl sulphate
(1 g LÀ1). Absorbance of the diluted sample was
recorded at 500 nm using a spectrophotometer.
The absorbance obtained at the initial time after
being homogenised was the EC. The ES was calculated
as follows:
ES ¼ ðA0 =DAÞ Â Dt
where A0 is the absorbance of the diluted emulsion
immediately after homogenization, and ΔA is the
reduction in absorbance at the interval time (Δt).
Effects of pH (2–12) and salt concentration
(0–1 mol LÀ1) on EC and ES of the RSAC were examined.
Foaming capacity and foam stability

Foaming capacity (FC) and foam stability (FS) were
evaluated by the method described by Deng et al.
(2011). The protein sample (2 g) was dispersed in distilled water (100 mL), and the mixture was adjusted to
the desired pH (2–12) or NaCl concentration (0–
1 mol LÀ1). The resulting blend was vigorously stirred
for 2 min by a Heidolph Diax 900 homogeniser (Heidolph Instruments GmbH & Co.). The blend was immediately transferred into a 100-mL graduated cylinder.
The volume was recorded before and after stirring. In
addition, foam volume change in the graduated cylinder
was also recorded at 120 min of storage. FC (%) and
FS (%) were calculated as follows:

Gelation capacity

Gelation capacity was evaluated by least gelation concentration (LGC) using the method described by
Lawal et al. (2005). Rambutan seed albumin concentrate was added to distilled water; the solid content of
sample suspensions was varied from 10 to 200 g LÀ1
with the increment of 10 g LÀ1. Each test tube contained 5 mL sample suspension. The suspension was
mixed on a vortex mixer for 5 min and heated in a
boiling water bath for 1 h. The mixture was cooled in
a water bath at 4 °C for 2 h after which the tube was
inverted. The lowest concentration at which the sample
did not fall down or slip from an inverted tube was
taken as the LGC.
Effects of pH were evaluated by adjusting pH of the
sample suspensions to various values (2–10) prior to
heating. Effects of salt concentration were investigated
by preparing sample suspensions in NaCl solution with
different concentrations (0–1 mol LÀ1).
Statistical treatment

All experiments were performed in triplicate. The
experimental results were expressed as means Æ standard deviations. Mean values were considered significantly different when P < 0.05. One-way analysis of
variance was performed using the software Statgraphics Centurion XV.
Results and discussion

Proximate composition of albumin concentrate

Table 1 shows that the protein level in the RSAC was
similar to that in the albumin concentrate from great
northern bean (81.70%) (Sathe & Salunkhe, 1981), pea
seed (86.26%) (Adebiyi & Aluko, 2011) and ginkgo
seed (87.70%) (Deng et al., 2011). Among the nonpr
otein compounds, reducing sugars may participate in

Maillard reactions while polyphenols may take part in
protein–polyphenol interactions. These reactions could
change both nutritional value and functional properties of proteins (Belitz et al., 2009). It can be noted
that the RSAC had higher total and free sulfhydryl
content as well as higher surface hydrophobicity than
the ginkgo seed albumin (Deng et al., 2011). According to Belitz et al. (2009), sulfhydryl content
could enhance gelation capacity, while surface

FC ¼ ½Volume after stirring -Volume before stirringŠ ðmLÞ=Volume before stirring ðmL Þ;
FS ¼ ½Volume after 120 min standing -Volume before stirringŠ ðmLÞ=
½Volume after stirring -Volume before stirringŠ ðmLÞ:

International Journal of Food Science and Technology 2016

© 2016 Institute of Food Science and Technology


Effects of pH and salt concentration H. T. H. Vuong et al.

Table 1 Proximate composition of rambutan seed albumin concentrate (n = 6)
Moisture (%)
Protein (%)
Lipid (%)
Total sugars (%)
Reducing sugars (%)
Ash (%)
Total acid (%)
Polyphenols (%)
Free SH content (lmol gÀ1)
Total SH content (lmol gÀ1)

Surface hydrophobicity (S0)

hydrophobicity could improve
foaming properties of proteins.

4.33
80.78
0.27
5.69
1.04
4.43
0.78
0.77
26.70
82.70
652.72

emulsifying

Æ
Æ
Æ
Æ
Æ
Æ
Æ
Æ
Æ
Æ
Æ

0.15
2.38
0.01
0.12
0.01
0.21
0.01
0.01
1.13
3.51
6.74

and

The effects of salt concentration on the NSI of the
RSAC are visualised on Fig. 1b. Increase in salt concentration from 0 to 1 mol LÀ1 gradually reduced the
NSI from 66.7% to 41.7%. It was reported that the
solubility of pumpkin seed albumin in NaCl solutions
(0.5 and 1.0 mol LÀ1) was also lower than that in deionised water. Salt ions could remove hydrate layers
around protein molecules and that led to a reduced
protein solubility (Rezig et al. (2016). However, these
results were different to the previous findings of Deng
et al. (2011) who reported that increase in salt concentration up to 0.5 mol LÀ1 improved the NSI of ginkgo
seed albumin due to salting-in effect. Difference in solubility of rambutan seed albumin and gingko seed
albumin in a salt solution was probably due to their
various conformational characteristics.

Protein solubility

Water absorption capacity

Solubility profile of a protein concentrate is a good
index of its functional properties and potential applications (Kinsella & Melachouris, 1976). The pH-solubility
profile of RSAC is visualised on Fig. 1a. The lowest
NSI (15.56%) was recorded at pH 4. Similar pH value
was also reported for minimum solubility of water-soluble proteins from tepary bean (Idouraine et al., 1991)
and pea seed (Adebiyi & Aluko, 2011). However, the
lowest solubility of African locust albumin (Lawal
et al., 2005) and kidney bean albumin (Mundi & Aluko,
2012) was observed at pH 5. Albumins from different
plant sources showed various pI values probably due to
difference in amino acid composition. In the isoelectric
region, low electrostatic repulsive forces enhanced the
formation of protein aggregates and reduced the protein
solubility (Mao & Hua, 2012). On the contrary, the NSI
of RSAC increased as the pH decreased from 4 to 2 or
increased from 4 to 7 since the electrostatic repulsive
forces between protein molecules increased protein–solvent interactions (Belitz et al., 2009). It can be noted
that the solubility of the RSAC was nearly unchanged
as the pH varied from 7 to 12.

Figure 2a presents that Water absorption capacity
(WAC) of RSAC decreased with the increase in pH
from 2 to 4 and then increased when the pH raised
from 4 to 9. The lowest WAC (0.69 mL gÀ1) was
observed at pH 4 which was near the pI value of the
rambutan seed albumin. Interaction between protein
molecules was enhanced in the isoelectric region and
that resulted in poor WAC (Deng et al., 2011). As the

pH was above 9, WAC of RSAC was reduced. Alkali
solution can break hydrogen, amide and disulphide
bonds in protein molecules (Fabian & Ju, 2011) and
that could change WAC as well as other functional
properties of proteins.
In distilled water, the WAC of RSAC was 0.79
mL gÀ1 which was higher than that of ginkgo seed albumin (0.41 mL gÀ1) (Deng et al., 2011). Nevertheless,
RSAC showed much lower WAC than great northern
bean albumin (3.18 mL gÀ1) (Sathe & Salunkhe, 1981),
oat seed albumin (2.4 mL gÀ1) (Ma & Harwalkar,
1984), African locust bean albumin (3 mL gÀ1) (Lawal
et al., 2005) and kidney bean albumin (3.4 mL gÀ1)
(Mundi & Aluko, 2012). Low WAC of protein was due

Figure 1 Effects of pH and NaCl concentration on solubility of rambutan seed albumin concentrate (Results were average of
three replicate Æ standard deviation).

© 2016 Institute of Food Science and Technology

(b) 80
Nitrogen soluble index (%)

Nitrogen soluble index (%)

(a) 80

60

40

20

60

40

20

0

0
2 3 4 5 6 7 8 9 10 11 12
pH value

0

0.2

0.4

0.6

0.8

1

NaCl concentration (mol L–1)

International Journal of Food Science and Technology 2016

1215


Effects of pH and salt concentration H. T. H. Vuong et al.

(b)
Water absorption capacity (mL g–1)

(a) 2
Water absorption capacity (mL g–1)

1216

1.5

1

0.5

0

2

1.5

1

0.5

0

2 3 4 5 6 7 8 9 10 11 12
pH value

0

0.2
0.4
0.6
0.8
1
NaCl concentration (mol L–1)

to its high solubility in distilled water (El-Adawy,
2000). Figure 2b demonstrates that increase in salt
concentration from 0 to 0.6 mol LÀ1 enhanced WAC
of RSAC while further increase in salt concentration
reduced the WAC. Similar observation was noted
for both ginkgo seed albumin (Deng et al., 2011)
and African locust bean albumin (Lawal et al.,
2005). At low salt concentration, hydrated salt ions
could link to charged groups on protein molecules;
increase in WAC was due to water molecules which
were bound to the salt ions. However, high salt concentration increased the interactions between water
molecules and salt ions; this led to dehydration of
the proteins and subsequent reduction in WAC
(Lawal et al., 2005). Proteins with high WAC could
contribute to the body and freshness of various viscous foods such as soups, dough, custards and
baked products (Kinsella & Melachouris, 1976).
Oil absorption capacity

The Oil absorption capacity (OAC) of RSAC was
6.13 mL gÀ1 which was much higher than that of great
northern bean albumin (3.29 mL gÀ1) (Sathe & Salunkhe, 1981), oat seed albumin (2.8 mL gÀ1) (Ma &
Harwalkar, 1984), African locust bean albumin
(3.4 mL gÀ1) (Lawal et al., 2005) and kidney bean
albumin (2.37 mL gÀ1) (Mundi & Aluko, 2012). The
OAC of RSAC (6.13 mL gÀ1) was lower than that of
ginkgo seed albumin (9.3 mL gÀ1) (Deng et al., 2011)
although the surface hydrophobicity of RSAC
(S0 = 652.7) was much higher than that of ginkgo seed
albumin (S0 = 23.5). Difference in OAC was probably
due to various conformational characteristics,
lipophilic groups, surface hydrophobicity (Kinsella &
Melachouris, 1976) and nonprotein compounds in the
protein concentrates (Yada, 2004). The OAC of
protein could affect its emulsifying as well as flavour
binding properties (Mundi & Aluko, 2012). Protein
concentrate with high oil absorption could be used in
the formulation of different products such as sausages,

International Journal of Food Science and Technology 2016

Figure 2 Effects of pH and NaCl concentration on water absorption capacity of
rambutan seed albumin concentrate (Results
were average of three replicate Æ standard
deviation).

cake batters, mayonnaise and salad dressings (Chandi
& Sogi, 2007).
Foaming properties

Figure 3a presents that FC of RSAC decreased with
the increase in pH from 2 to 4 while further increase in
pH improved FC. It was reported that FC was pH
dependent and protein solubility was a prerequisite for
good FC (Mundi & Aluko, 2012). Proteins with high
solubility could diffuse easily and rapidly to the air–water interface for air bubble encapsulation and that leads
to an improved FC (Belitz et al., 2009). The lowest FC
(55.2%) was observed at pH 4 which was the point of
least solubility of RSAC. In the isoelectric region, low
solubility of kidney bean albumin (Mundi & Aluko,
2012) also resulted in low FC. It was noteworthy that
the NSI of RSAC remained unchanged in the pH range
of 7–12. However, the FC of RSAC was improved with
the increase in pH from 7 to 12 and achieved maximum
of 232.8% at pH 12. It can be explained that as the pH
raised from 7 to 12, the net charge of RSAC augmented
and this phenomenon could weaken hydrophobic interactions and enhance protein flexibility for air bubble
encapsulation (Chau et al., 1997). In addition, pH 12
enhanced protein deformability (Fabian & Ju, 2011)
which could facilitate the formation of cohesive films
around air bubbles (Belitz et al., 2009).
Figure 3b shows that maximum FS was recorded at
pH 4. This observation agreed with the findings of
Lawal et al. (2005) who reported that at the isoelectric
point, protein film surrounding the air bubbles was
stabilised due to the lack of repulsive forces between
protein molecules and that generated an improved FS.
Nevertheless, our result contrasted with the data of
Deng et al. (2011) who stated that protein aggregation

at the isoelectric point resulted in reduced FS. It can
be noted that conformational characteristics of various
proteins at the isoelectric point were different. As a
result, protection of air bubbles by protein film in
foam system could be different.

© 2016 Institute of Food Science and Technology


Effects of pH and salt concentration H. T. H. Vuong et al.

(b) 100
Foaming stability (%)

Foaming capacity (%)

(a) 300

200

100

0

75

50

25

0
2 3 4 5 6 7 8 9 10 11 12
pH value

Figure 3 Effects of pH and NaCl concentration on foaming capacity and stability of
rambutan seed albumin concentrate (Results
were average of three replicate Æ standard
deviation).

(d)

Foaming stability (%)

Foaming capacity (%)

(c) 150

100

50

0
0

0.2

0.4

0.6

0.8

1

NaCl concentration (mol L–1)

The effects of salt concentration on foaming properties of RSAC are visualised on Fig. 3c,d. As the salt
concentration increased from 0 to 0.6 mol LÀ1, the FC
and FS increased by 79% and 25%, respectively. It
should be noted that increase in salt concentration from
0 to 0.6 mol LÀ1 decreased the NSI of the RSA by
31%. Low protein solubility negatively affected foaming
properties (Yada, 2004). However, our results showed
that the surface hydrophobicity of RSAC increased by
22% when the salt concentration augmented from 0 to
0.6 mol LÀ1. Proteins with high surface hydrophobicity
could be easily adsorbed at the air–water interface via
hydrophobic areas and generate cohesive film around
air bubbles; high surface hydrophobicity of proteins was
an important characteristic for foam formation and stabilization (Belitz et al., 2009).
When the salt concentration was higher than
0.6 mol LÀ1, both FC and FS of RSAC were reduced.
Deng et al. (2011) also noted a reduction in FC and
FS of ginkgo seed albumin as the salt concentration
was higher than 0.5 mol LÀ1. These authors explained
that high salt concentration promoted protein aggregation and that led to decreased foaming properties.
In distilled water, the FC and FS of RSAC were
comparable to those of ginkgo seed albumin (Deng
et al., 2011) and African locust bean albumin (Lawal
et al., 2005). Proteins with good foaming properties

would be used for foam stabilization in some foods

© 2016 Institute of Food Science and Technology

2 3 4 5 6 7 8 9 10 11 12
pH value
100

75

50

25

0
0

0.2 0.4 0.6 0.8
1
NaCl concentration (mol L–1)

such as baked goods, sweets and desserts (Kinsella &
Melachouris, 1976).
Emulsifying properties

The effects of pH on EC and ES of RSAC were
described as U-shaped curves (Fig. 4a,b). Similar
results were mentioned for African locust bean albumin (Lawal et al., 2005). Minimum EC and ES were
recorded in the isoelectric region (pH 4). Under strong
acidic (pH 2) or alkaline conditions (pH 12), the emulsifying properties were strongly improved. EC achieved

maximum at pH 12, while the highest ES was noted at
pH 2. Emulsifying properties of a protein depended on
its hydrophilic–lipophilic balance as well as net charge,
which were affected by pH value (Ragab et al., 2004).
Extreme acidic or alkaline pH may promote partial
denaturation of protein; this phenomenon could facilitate mutual cohesion between oil phase and protein
and result in stabilised protein film around dispersed
droplets in the emulsion (Lawal et al., 2005).
As the salt concentration increased from 0 to
0.2 mol LÀ1, the EC and ES of RSAC achieved
maximum while further increase in salt concentration
reduced both EC and ES (Fig. 4c,d). Low salt concentration may facilitate formation of charged layers
around oil droplets and that would result in mutual
repulsion between dispersed droplets in oil-in-water

International Journal of Food Science and Technology 2016

1217


Effects of pH and salt concentration H. T. H. Vuong et al.

(b) 40
Emulsion stability (min)

Emulsifying ability (Abs)

(a) 1
0.8
0.6

0.4
0.2
0

30

20

10

0
2 3 4 5 6 7 8 9 10 11 12
pH value

2 3 4 5 6 7 8 9 10 11 12
pH value

(d) 20
Emulsion stability (min)

(c) 0.5
Emulsifying ability (Abs)

1218

0.4
0.3
0.2
0.1

15

10

5

0

0
0

0.2

0.4

0.6

0.8

1

0

NaCl concentration (mol L–1)

0.2

0.4

0.6

0.8

NaCl concentration (mol L–1)

emulsion. As a consequence, protein emulsifying properties would be improved (Yuliana et al., 2014). In
addition, low salt concentration could promote formation of hydrate layers around interfacial material and
that would reduce interfacial energy and retard coalescence of the oil droplets in the emulsion (Lawal et al.,
2005). Nevertheless, high salt concentration reduced
the emulsifying properties due to salting-out effect
(Ragab et al., 2004). Proteins with good emulsifying
properties would be used in formulation of various
food emulsions (Yada, 2004).
Gelation capacity

Table 2 reveals that the LGC of RSAC in distilled
water (100 g LÀ1) was lower than that of great
northern bean albumin (180 g LÀ1) (Sathe & Salunkhe, 1981) and kidney bean albumin (160 g LÀ1)
(Mundi & Aluko, 2012). Gel formation from protein
solution depends on different interactions between protein molecules including hydrophobic and electrostatic

1

Figure 4 Effects of pH and NaCl concentration on emulsifying capacity and stability
of rambutan seed albumin concentrate
(Results were average of three replicate Æ
standard deviation).

interactions, hydrogen bonds and disulphide bonds
formed from the released thiol groups during protein

gelation (Belitz et al., 2009). It can be noted that the
total and free sulfhydryl contents in RSAC (Table 1)
were higher than those in kidney bean albumin (4.60
and 2.20 lmol gÀ1) and that could improve the gelation. Based on the LGC as index of gelation, it can be
predicted that RSAC was a potential gelating protein
ingredient in food industry.
The lowest LGC was noted for pH 4 at which the
protein solubility was minimum. Similar result was
reported for African locust bean albumin (Lawal
et al., 2005). In the isoelectric region, minimal electrostatic repulsion promoted the formation of the necessary intermolecular forces between the protein
molecules and resulted in better gelation. At pH 2 and
10, the LGC increased probably due to increased electrostatic repulsion between the protein molecules.
As the salt concentration varied from 0.4 to 0.6 mol
LÀ1, the LGC of RSAC significantly decreased. The
LGC in salt solution of 0.6 mol LÀ1 was 5 times lower

Table 2 Effects of pH and NaCl concentration on least gelation concentrations (LGC) of rambutan seed albumin concentrate (n = 3)
pH
LGC (g LÀ1)
NaCl concentration (mol LÀ1)
LGC (g LÀ1)

2

4

80 Æ 0
0.0
100 Æ 0

60 Æ 0
0.2
100 Æ 0

International Journal of Food Science and Technology 2016

6
60 Æ 0
0.4
40 Æ 0

7
100 Æ 0
0.6
20 Æ 0

8
100 Æ 0
0.8
100 Æ 0

10
100 Æ 0
1.0
100 Æ 0

© 2016 Institute of Food Science and Technology


Effects of pH and salt concentration H. T. H. Vuong et al.

than that in distilled water. That was due to moderate
increase in ionic strength which enhanced interaction
between charged macromolecules (Belitz et al., 2009).
Lawal et al. (2005) also concluded that the LGC of
African locust albumin in NaCl solution of 0.4 mol
LÀ1 was 33% lower than that in distilled water.
However, at high salt concentration, the LGC
augmented due to shielding effect on the protein molecules. This phenomenon enhanced salting-out and
reduced gelation capacity of the protein.
Conclusion

RSAC showed high surface hydrophobicity which
favoured its emulsifying and foaming properties.
Moreover, gelation capacity was one of the outstanding properties of RSAC due to high sulfhydryl content. The adjustment of pH or the addition of sodium
chloride improved various functional properties of the
protein. RSAC was a potential protein ingredient for
formulation of new food products.
Acknowledgment

This research is funded by Vietnam National University – Ho Chi Minh City (VNU-HCM) under grant
number B2014-20-08.
References
Adebiyi, A.P. & Aluko, R.E. (2011). Functional properties of protein fractions obtained from commercial yellow field pea (Pisum
sativum L.) seed protein isolate. Food Chemistry, 128, 902–908.
Augustin, M. & Chua, B. (1988). Composition of rambutan seeds.
Pertanika, 11, 211–215.
Belitz, H.D., Grosch, W. & Schieberle, P. (2009). Food Chemistry.
Berlin: Springer Berlin Heidelberg.
Bradstreet, R.B. (1965). The Kjeldahl Method for Organic Nitrogen.

USA: Academic Press Inc.
Chandi, G.K. & Sogi, D.S. (2007). Functional properties of rice bran
protein concentrates. Journal of Food Engineering, 79, 592–597.
Chau, C.F., Cheung, P.C.K. & Wong, Y.S. (1997). Functional properties of protein concentrates from three chinese indigenous legume
seeds. Journal of Agricultural and Food Chemistry, 45, 2500–2503.
Day, L. (2013). Proteins from land plants – Potential resources for
human nutrition and food security. Trends in Food Science & Technology, 32, 25–42.
Deng, Q., Wang, L., Wei, F. et al. (2011). Functional properties of
protein isolates, globulin and albumin extracted from Ginkgo
biloba seeds. Food Chemistry, 124, 1458–1465.
DuBois, M., Gilles, K.A., Hamilton, J.K., Rebers, P.A. & Smith, F.
(1956). Colorimetric method for determination of sugars and
related substances. Analytical Chemistry, 28, 350–356.
El-Adawy, T.A. (2000). Functional properties and nutritional quality
of acetylated and succinylated mung bean protein isolate. Food
Chemistry, 70, 83–91.
Fabian, C. & Ju, Y.-H. (2011). A review on rice bran protein: its
properties and extraction methods. Critical Reviews in Food Science
and Nutrition, 51, 816–827.
Helrich, K. (1990). Official Methods of Analysis of the AOAC, Volume 2. Arlington, TX: Association of Official Analytical Chemists
Inc.

© 2016 Institute of Food Science and Technology

Idouraine, A., Yensen, S.B. & Weber, C.W. (1991). Tepary bean flour,
albumin and globulin fractions functional properties compared with
soy protein isolate. Journal of Food Science, 56, 1316–1318.
Kato, A. & Nakai, S. (1980). Hydrophobicity determined by a fluorescence probe method and its correlation with surface properties
of proteins. BBA – Protein Structure, 624, 13–20.
Kinsella, J.E. & Melachouris, N. (1976). Functional properties of

proteins in foods: a survey. Critical Reviews in Food Science and
Nutrition, 7, 219–280.
Lawal, O.S., Adebowale, K.O., Ogunsanwo, B.M., Sosanwo, O.A. &
Bankole, S.A. (2005). On the functional properties of globulin and
albumin protein fractions and flours of African locust bean (Parkia
biglobossa). Food Chemistry, 92, 681–691.
Lu, B.-Y., Quillien, L. & Popineau, Y. (2000). Foaming and emulsifying properties of pea albumin fractions and partial characterisation of surface-active components. Journal of the Science of Food
and Agriculture, 80, 1964–1972.
Ma, C.Y. & Harwalkar, V.R. (1984). Chemical characterization and
functionality assessment of oat protein fractions. Journal of Agricultural and Food Chemistry, 32, 144–149.
Mao, X. & Hua, Y. (2012). Composition, structure and functional
properties of protein concentrates and isolates produced from walnut (Juglans regia L.). International Journal of Molecular Sciences,
13, 1561–1581.
Miller, G.L. (1959). Use of dinitrosalicylic acid reagent for determination of reducing sugar. Analytical Chemistry, 31, 426–428.
Mundi, S. & Aluko, R.E. (2012). Physicochemical and functional
properties of kidney bean albumin and globulin protein fractions.
Food Research International, 48, 299–306.
Pearce, K.N. & Kinsella, J.E. (1978). Emulsifying properties of proteins: evaluation of a turbidimetric technique. Journal of Agricultural and Food Chemistry, 26, 716–723.
Ragab, D.M., Babiker, E.E. & Eltinay, A.H. (2004). Fractionation,
solubility and functional properties of cowpea (Vigna unguiculata)
proteins as affected by pH and/or salt concentration. Food Chemistry, 84, 207–212.
Rezig, L., Riaublanc, A., Chouaibi, M., Gueguen, J. & Hamdi, S.
(2016). Functional properties of protein fractions obtained from
pumpkin (Cucurbita maxima) seed. International Journal of Food
Properties, 19, 172–186.
Sathe, S.K. & Salunkhe, D.K. (1981). Functional properties of the great
northern bean (Phaseolus vulgaris L.) proteins: emulsion, foaming, viscosity, and gelation properties. Journal of Food Science, 46, 71–81.
Singleton, V.L. & Rossi, J.A. (1965). Colorimetry of total phenolics
with phosphomolybdic-phosphotungstic acid reagents. American
Journal of Enology and Viticulture, 16, 144–158.

Sirisompong, W., Jirapakkul, W. & Klinkesorn, U. (2011). Response
surface optimization and characteristics of rambutan (Nephelium
lappaceum L.) kernel fat by hexane extraction. LWT-Food Science
and Technology, 44, 1946–1951.
Solıs-Fuentes, J.A., Camey-Ortız, G., Hernandez-Medel, M.d.R.,
Perez-Mendoza, F. & Duran-de-Baz
ua, C. (2010). Composition,
phase behavior and thermal stability of natural edible fat from
rambutan (Nephelium lappaceum L.) seed. Bioresource Technology,
101, 799–803.
Thannhauser, T.W., Konishi, Y. & Scheraga, H.A. (1987). Analysis
for disulfide bonds in peptides and proteins. Methods in Enzymology, 143, 115–119.
T€
om€
osk€
ozi, S., Lasztity, R., S€
ule, E., Gaugecz, J. & Varga, J.
(1998). Functional properties of native and modified wheat germ
protein isolates and fractions. Food/Nahrung, 42, 245–247.
Yada, R.Y. (2004). Proteins in Food Processing. Boca Raton, FL:
Woodhead Publishing.
Yuliana, M., Truong, C.T., Huynh, L.H., Ho, Q.P. & Ju, Y.-H.
(2014). Isolation and characterization of protein isolated from
defatted cashew nut shell: influence of pH and NaCl on solubility
and functional properties. LWT - Food Science and Technology, 55,
621–626.

International Journal of Food Science and Technology 2016

1219