Original articleEffects of pH and salt concentration on functional properties Huynh Thanh Hai Vuong, Ngoc Minh Chau Tran, Thi Thu Tra Tran, Nu Minh Nguyet Ton & Van Viet Man Le* Departme
Trang 1Original article
Effects of pH and salt concentration on functional properties
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)
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 g1, 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 L1, while the highest emulsifying capacity and stability were noted at the concentration of 0.2 mol L1 The least gelation concentration of RSAC was
100 g L1 and this value decreased by five times as salt concentration in the protein solution was 0.6 mol L1 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
char-acteristics 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
(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 con-tents 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 physico-chemical 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
*Correspondent: Fax: +84 8 38637504;
e-mail: lvvman@hcmut.edu.vn
Trang 2studies 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
for-mulation 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
investi-gated 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
Materials
Seeds of rambutan (Nephelium lappaceum L.) fruits
were originated from a canned fruit processing plant
in Dong Nai, Vietnam The seeds were ground,
defat-ted with hexan at 40 °C for 36 h and stored at 18 °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
30 min and the supernatant was adjusted to pH 4.2 using HCl solution (0.1 mol L1) for albumin precipi-tation The solid phase was recovered by centrifuga-tion at 5000 g, 20 °C for 30 min and re-dissolved in de-ionised water The procedure of albumin precipita-tion was repeated twice Finally, the precipitate was freeze-dried, ground and stored at18 °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)
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 solu-tion (0.5 mol L1) or NaOH solution (0.5 mol L1) 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 deter-mined by Kjeldahl method The nitrogen solubility index (NSI) (%) was calculated as follows:
NSI¼ Amount of nitrogen in the supernatant (g)=
Amount of nitrogen in the initial sample (g)
Effects of NaCl concentration (0–1 mol L1) 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 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
Trang 3calculated as mL water or mL oil trapped by 1 g
protein sample Effects of pH (2–12) and NaCl
concen-tration (0–1 mol L1) 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
Brit-ton-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
Instru-ments 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 L1) 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:
ES¼ ðA0=DAÞ 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 L1) on EC and ES of the RSAC were
exam-ined
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
dis-tilled water (100 mL), and the mixture was adjusted to
the desired pH (2–12) or NaCl concentration (0–
1 mol L1) The resulting blend was vigorously stirred
for 2 min by a Heidolph Diax 900 homogeniser
(Hei-dolph Instruments GmbH & Co.) The blend was
imme-diately 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 con-centration (LGC) using the method described by Lawal et al (2005) Rambutan seed albumin concen-trate was added to distilled water; the solid content of sample suspensions was varied from 10 to 200 g L1 with the increment of 10 g L1 Each test tube con-tained 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 L1)
Statistical treatment All experiments were performed in triplicate The experimental results were expressed as means stan-dard deviations Mean values were considered signifi-cantly different when P< 0.05 One-way analysis of variance was performed using the software Statgraph-ics 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 proper-ties 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) Accord-ing to Belitz et al (2009), sulfhydryl content could enhance gelation capacity, while surface
FC¼ ½Volume after stirring -Volume before stirring ðmLÞ=Volume before stirring ðmL Þ;
FS¼ ½Volume after 120 min standing -Volume before stirring ðmLÞ=
½Volume after stirring -Volume before stirring ðmLÞ:
Trang 4hydrophobicity could improve emulsifying and
foaming properties of proteins
Protein solubility
Solubility profile of a protein concentrate is a good
index of its functional properties and potential
applica-tions (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-solu-ble 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–sol-vent 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
The effects of salt concentration on the NSI of the RSAC are visualised on Fig 1b Increase in salt con-centration from 0 to 1 mol L1 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 L1) was also lower than that in de-ionised 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 concen-tration up to 0.5 mol L1 improved the NSI of ginkgo seed albumin due to salting-in effect Difference in sol-ubility of rambutan seed albumin and gingko seed albumin in a salt solution was probably due to their various conformational characteristics
Water absorption capacity 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 g1) 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 g1which was higher than that of ginkgo seed albu-min (0.41 mL g1) (Deng et al., 2011) Nevertheless, RSAC showed much lower WAC than great northern bean albumin (3.18 mL g1) (Sathe & Salunkhe, 1981), oat seed albumin (2.4 mL g1) (Ma & Harwalkar, 1984), African locust bean albumin (3 mL g1) (Lawal
et al., 2005) and kidney bean albumin (3.4 mL g1) (Mundi & Aluko, 2012) Low WAC of protein was due
Table 1 Proximate composition of rambutan seed albumin
concen-trate (n = 6)
Reducing sugars (%) 1.04 0.01
Free SH content ( lmol g 1 ) 26.70 1.13
Total SH content ( lmol g 1 ) 82.70 3.51
Surface hydrophobicity (S 0 ) 652.72 6.74
0 20 40 60 80
2 3 4 5 6 7 8 9 10 11 12
pH value
0 20 40 60 80
NaCl concentration (mol L –1 )
Figure 1 Effects of pH and NaCl
concen-tration on solubility of rambutan seed
albu-min concentrate (Results were average of
three replicate standard deviation).
Trang 5to its high solubility in distilled water (El-Adawy,
2000) Figure 2b demonstrates that increase in salt
concentration from 0 to 0.6 mol L1 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
con-centration 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
vis-cous 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 g1which was much higher than that of great
northern bean albumin (3.29 mL g1) (Sathe &
Salu-nkhe, 1981), oat seed albumin (2.8 mL g1) (Ma &
Harwalkar, 1984), African locust bean albumin
(3.4 mL g1) (Lawal et al., 2005) and kidney bean
albumin (2.37 mL g1) (Mundi & Aluko, 2012) The
OAC of RSAC (6.13 mL g1) was lower than that of
ginkgo seed albumin (9.3 mL g1) (Deng et al., 2011)
(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,
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–wa-ter inair–wa-terface 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 inter-actions 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
0
0.5
1
1.5
2
2 3 4 5 6 7 8 9 10 11 12
–1 )
pH value
(a)
0 0.5 1 1.5 2
–1 )
NaCl concentration (mol L –1 )
(b)
Figure 2 Effects of pH and NaCl concen-tration on water absorption capacity of rambutan seed albumin concentrate (Results were average of three replicate standard deviation).
Trang 6The effects of salt concentration on foaming
proper-ties of RSAC are visualised on Fig 3c,d As the salt
concentration increased from 0 to 0.6 mol L1, 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 L1 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 L1 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
sta-bilization (Belitz et al., 2009)
When the salt concentration was higher than
0.6 mol L1, 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 L1 These authors explained
that high salt concentration promoted protein
aggrega-tion 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
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 albu-min (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 emul-sifying 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 facili-tate 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 L1, the EC and ES of RSAC achieved maximum while further increase in salt concentration reduced both EC and ES (Fig 4c,d) Low salt concen-tration may facilitate formation of charged layers around oil droplets and that would result in mutual repulsion between dispersed droplets in oil-in-water
0 100 200 300
2 3 4 5 6 7 8 9 10 11 12
pH value
(a)
0 25 50 75 100
2 3 4 5 6 7 8 9 10 11 12
pH value
(b)
0 50 100 150
NaCl concentration (mol L –1 )
0 25 50 75 100
NaCl concentration (mol L –1 )
Figure 3 Effects of pH and NaCl
concen-tration on foaming capacity and stability of
rambutan seed albumin concentrate (Results
were average of three replicate standard
deviation).
Trang 7emulsion As a consequence, protein emulsifying
prop-erties would be improved (Yuliana et al., 2014) In
addition, low salt concentration could promote
forma-tion of hydrate layers around interfacial material and
that would reduce interfacial energy and retard
coales-cence 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 L1) was lower than that of great
northern bean albumin (180 g L1) (Sathe &
Salu-nkhe, 1981) and kidney bean albumin (160 g L1)
(Mundi & Aluko, 2012) Gel formation from protein
solution depends on different interactions between
pro-tein molecules including hydrophobic and electrostatic
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 g1) and that could improve the gela-tion 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 electro-static repulsion promoted the formation of the neces-sary intermolecular forces between the protein molecules and resulted in better gelation At pH 2 and
10, the LGC increased probably due to increased elec-trostatic repulsion between the protein molecules
As the salt concentration varied from 0.4 to 0.6 mol
L1, the LGC of RSAC significantly decreased The LGC in salt solution of 0.6 mol L1was 5 times lower
0
0.2
0.4
0.6
0.8
1
2 3 4 5 6 7 8 9 10 11 12
pH value
(a)
0 10 20 30 40
2 3 4 5 6 7 8 9 10 11 12
pH value
(b)
0
0.1
0.2
0.3
0.4
0.5
0 0.2 0.4 0.6 0.8 1
NaCl concentration (mol L –1 )
0 5 10 15 20
NaCl concentration (mol L –1 )
Figure 4 Effects of pH and NaCl concen-tration on emulsifying capacity and stability
of rambutan seed albumin concentrate (Results were average of three replicate standard deviation).
Table 2 Effects of pH and NaCl concentration on least gelation concentrations (LGC) of rambutan seed albumin concentrate (n = 3)
Trang 8than 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
L1 was 33% lower than that in distilled water
However, at high salt concentration, the LGC
augmented due to shielding effect on the protein
mole-cules 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
outstand-ing properties of RSAC due to high sulfhydryl
con-tent 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
Univer-sity – Ho Chi Minh City (VNU-HCM) under grant
number B2014-20-08
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