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The Content, Antioxidant Activity, and Structural Characteristics of Sodium Alginate Extracting from Sargassum polycystum Grew in Vietnam: Effect of Various Extraction Conditions

Authors:

Abstract

Introduction: Alginate is a biopolymer commonly in brown algae, high content, diversity in structure and bioactivity. They are applied to other fields such as food, functional food, pharmaceuticals, and heavy industry and extracted from Sargassum, Laminarin, Tubinaria and Sargassum polycystum species commonly grow in the world than another genus. The content, the antioxidant activity, and the physical chemistry properties of alginate extracting from the species did not exhibit in the previous studies. Methods: The study focused on the impact of various extraction conditions (temperature (40 to 90,oC), time (01 to 06, hours), the solvent-to-material ratio (10/1 to 40/1, v/w), solvent pH (8, 9, 10), and numbers of extraction (1, 2, and 3 times) on alginate content and its antioxidant activity, also evaluated sugar compositions, average molecular, viscosity, and 13C-NMR spectrum characteristics of alginate. Results: The results showed that the suitable condition for the extraction of alginate was for 4 hours at 60oC with the ratio of Na2CO3 (pH 9)-to-material (40/1, v/w) and one number of extraction. The highest alginate content was 176.22 mg uronic acid equivalent/g DW, corresponding to antioxidant activity (188.54 mg ascorbic acid equivalent/g DW). Alginate possessed the intrinsic viscosity (271.86, ƞ) and the average molecular weight (78.6, kD). Different sugar compositions of antioxidant alginate were fructose, fucose, mannose, galactose, rhamnose, mannose, and glucose. The 13C-NMR spectrum of antioxidant alginate exhibited chemical shifts of C sites of D-mannuronic (M) and L-guluronic (G), corresponded to C1, C2, C6, and C2, C3, C4, C5, C6, respectively. Conclusion: Alginate is non-toxic, therefore, antioxidant alginate extracting from brown algae Sargassum polycystum grown in Vietnam is a potential in functional food and pharmaceuticals.
_____________________________________________________________________________________________________
*Corresponding author: E-mail: cuong_mails@yahoo.com.vn;
Journal of Pharmaceutical Research International
33(41A): 197-206, 2021; Article no.JPRI.72634
ISSN: 2456-9119
(Past name: British Journal of Pharmaceutical Research, Past ISSN: 2231-2919,
NLM ID: 101631759)
The Content, Antioxidant Activity, and Structural
Characteristics of Sodium Alginate Extracting from
Sargassum polycystum Grew in Vietnam: Effect of
Various Extraction Conditions
Nguyen Dinh Thuat
1,2
, Vu Ngoc Boi
3
, Nguyen Xuan Hoan
4
,
Dang Thi Thanh Tuyen
3
, Do Thuy Kieu
3
, Nguyen Kim Nguyen
3,5
,
Nguyen Ngoc Bao Huy
1,2
, Pham the Trinh
6
, Pham Thanh Thuan
7
and Dang Xuan Cuong
1,2,4*
1
Nha Trang Institute of Technology Application and Research, VAST, 650000 Khanh Hoa, Vietnam.
2
Graduate University of Science and Technology, VAST, 100000 Ha Noi, Vietnam.
3
Faculty of Food Science, Nha Trang University, 650000 Khanh Hoa, Vietnam.
4
Ho Chi Minh City University of Food Industry, 700000 Ho Chi Minh, Vietnam.
5
Tuy Hoa city medical center, 56100 Tuy Hoa, Vietnam.
6
Department of Science and Technology, 63000 Dak Lak, Dak Lak, Vietnam.
7
General Surgery Department, Ninh Thuan Provincial General Hospital, 59000 Ninh Thuan, Vietnam.
Authors’ contributions
This work was carried out in collaboration among all authors. All authors read and approved the final
manuscript.
Article Information
DOI: 10.9734/JPRI/2021/v33i41A32318
Editor(s):
(1)
Dr. Barkat Ali Khan, Gomal University, Pakistan.
Reviewers:
(1)
Salama K. Ibrahim, Bayero University Kano, Nigeria.
(2)
Ratan Sadhukhan, University of Arkansas for Medical Sciences, USA.
Complete Peer review History:
https://www.sdiarticle4.com/review-history/72634
Received 06 June 2021
Accepted 10 August 2021
Published 17 August 2021
ABSTRACT
Introduction:
Alginate is a biopolymer commonly in brown algae, high content, diversity in
structure and bioactivity. They are applied to other fields such as food, functional food,
pharmaceuticals, and heavy industry and extracted from Sargassum, Laminarin, Tubinaria and
Sargassum polycystum species commonly grow in the world than another genus. The content, the
antioxidant activity, and the physical chemistry properties of alginate extracting from the species did
not exhibit in the previous studies.
Original Research Article
Thuat et al.; JPRI, 33(41A): 197-206, 2021; Article no.JPRI.72634
198
Methods:
The study focused on the impact of various extraction conditions (temperature (40 to
90,
o
C), time (01 to 06, hours), the solvent-to-material ratio (10/1 to 40/1, v/w), solvent pH (8, 9, 10),
and numbers of extraction (1, 2, and 3 times) on alginate content and its antioxidant activity, also
evaluated sugar compositions, average molecular, viscosity, and
13
C-NMR spectrum characteristics
of alginate.
Results: The results showed that the suitable condition for the extraction of alginate was for 4
hours at 60
o
C with the ratio of Na
2
CO
3
(pH 9)-to-material (40/1, v/w) and one number of extraction.
The highest alginate content was 176.22 mg uronic acid equivalent/g DW, corresponding to
antioxidant activity (188.54 mg ascorbic acid equivalent/g DW). Alginate possessed the intrinsic
viscosity (271.86, ƞ) and the average molecular weight (78.6, kD). Different sugar compositions of
antioxidant alginate were fructose, fucose, mannose, galactose, rhamnose, mannose, and glucose.
The
13
C-NMR spectrum of antioxidant alginate exhibited chemical shifts of C sites of D-mannuronic
(M) and L-guluronic (G), corresponded to C
1
, C
2
, C
6
, and C
2
, C
3
, C
4
, C
5
, C
6
, respectively.
Conclusion: Alginate is non-toxic, therefore, antioxidant alginate extracting from brown algae
Sargassum polycystum grown in Vietnam is a potential in functional food and pharmaceuticals.
Keywords: Alginate; antioxidant; extraction; Sargassum polycystum; structure.
1. INTRODUCTION
Alginate is a polysaccharide commonly in brown
algae with basic units such as D-mannuronic (M)
and L-guluronic (G) that contained various single
sugars [1]. Alginate content was up to 52 (%,
DW) that depended on the genus, species, and
environmental conditions [2,3]. Alginate of
different brown algae species possesses various
bioactivities, described by the previous notices
[4]. The difference depends on the M
w
, viscosity,
and SO
2
-4
numbers of the group in their
molecular structure [5,6]. Different bioactivities of
alginate were known as antioxidant [7],
antibacterial [8], antibiotics [9], diabetes,
adiposity [5], and stomach protection [10,11].
Numerous studies showed that alginate occurs in
other fields, for example, textiles, food industry,
agrifoods (slow-release fertilizer),
pharmaceuticals (drug release, encapsulation,
stomach-treated support, and cell
immobilization), paper, and medical supplies,
among others [12], cosmetics [13], functional
food [14]. Therefore, alginate is usually found,
extracted, purified, and evaluated on its
bioactivities.
Nowadays, there are many methods of alginate
extraction, for example, the assistance of
enzymes, microwave, and ultrasound,
pressurized liquid extraction [5], maceration [7].
Different extracting methods caused the
difference in alginate content, bioactivities,
structure characteristics, M
w
, and viscosity [6].
The notices on the impact of various extraction
conditions according to the maceration such as
solvent pH, time, temperature, the solvent-to-
material ratio, and numbers of extraction on
alginate content, also the correlation between
alginate content and its antioxidant activity, M
w
,
viscosity, and structural characteristics of
alginate extracting from brown algae Sargassum
polycystum grown in South-Centre of Vietnam
did not find. While the species commonly
distribute in the world with high reserves and
contains numerous bioactive substances.
Therefore, the current study focused on the over
problems for the orientation of alginate
application into functional food and
pharmaceuticals.
2. MATERIALS AND METHODS
2.1 Sample Preparation
Brown algae Sargassum polycystum grown in
the South-Center of Vietnam was selected,
cleaned, and stored under 10
o
C for transferring
to the laboratory. The elimination of the salts and
the impurities of the seaweed was performed
continuously by using fresh water and then dried
until 19±1 % of humidity in the laboratory. After
drying, the seaweed grinding was to the powder
that stored under 10
o
C for further studies.
2.2 Experience Design
2.2.1 Effect of extracting temperature
The soaking of brown algae powder was for 04
hours with the Na
2
CO
3
(pH 10)-to-powder of 40/1
(v/w) at the temperature (40, 50, 60, 70, 80, and
90
o
C) and then filtered for the filtrate collection
servicing the survey of the extraction
temperature.
Thuat et al.; JPRI, 33(41A): 197-206, 2021; Article no.JPRI.72634
199
2.2.2 Effect of extracting time
For the survey of the extraction time, the keeping
of brown algae powder was in Na
2
CO
3
solution
(pH 10) at 50
o
C with the solvent-to-material ratio
of 40/1 (v/w) for 01, 02, 03, 04, 05, and 06 hours,
respectively.
2.2.3 Effect of solvent pH
Brown algae powder added with the ratio solvent
(pH of 8, 9, and 10)-to-material (40/1, v/w) and
kept at 50
o
C for 04 hours, respectively, and
filtered for the solvent pH survey.
2.2.4 Effect of the solvent-to-material ratio
For the collection of the solvent-to-material ratio,
the soak of brown algae powder in Na
2
CO
3
solution was with the ratio Na
2
CO
3
(pH 9)-to-
material (10/1, 20/1, 30/1 and 40/1, v/w) at 50
o
C
for 04 hours, respectively, and filtered for the
filtrate.
2.2.5 Effect of the number of the extraction
For the survey of the extractions number, brown
algae powder was macerated in Na
2
CO
3
(pH 9)
solution with the ratio solvent-to-material (40/1,
v/w) at 50
o
C for 04 hours and repeated
triplication and filtered for the filtrate. The
analysis of alginate content and antioxidant
activity for all filtrates in various extraction
conditions. Alginate extracted in a suitable
condition was continuously purified for the
evaluation of the structural characteristics.
2.3 Purification of Antioxidant Alginate
The conversion of antioxidant alginate to
antioxidant calcium alginate was by using 10%
CaCl
2
solution (the CaCl
2
-to-alginate ratio of
2.0/1.0). Then, filtering and washing the
precipitate with clean water was five times. The
colour elimination of antioxidant calcium alginate
was effectuated continuously by using 20-30 mL
chlorine (1 % chlorine solution/100 g antioxidant
calcium alginate) for 30 minutes and then the
movement of the chlorine out the residue with
fresh water. The residue was soaked in a
solution (pH 2.0) for the formation of antioxidant
alginic acid. Finally, the preparation of
antioxidant purified sodium alginate was by using
the maceration of antioxidant alginic acid in
Na
2
CO
3
solution with the Na
2
CO
3
-to-alginic acid
ratio of 0.35/1 (w/w). Finally, the precipitation of
antioxidant sodium alginate and the cleaning of
them was with 96% ethanol. Antioxidant purified
alginate was cool dried and evaluated for M
w
,
viscosity, sugar compositions and structural
characteristics.
2.4 Quantification of Alginate Content
200 mL alkaline extract in section 2.2 added
538.5 mL of 96 % ethanol to reach 70 % ethanol
in the mixture. After which the mixture is filtered
and the residue was collected and dried until a
constant weight was achieved. One mL of
residue solution (01 mg/ 01 mL) was mixed 01
mL of 0.8 M sodium hydroxide and vortexed.
After 5 minutes, the mixture was neutralized by
adding 120 mL of 2.25M citric acid and then
added to 40 mL of DMMB reagent
(Dimethylmethylene Blue Assay). The mixture
was continuously vortexed and kept at room
temperature for 45 minutes. Alginate content and
the non-precipitating alginate ratio in ethanol
were calculated based on the mixture
absorbance at the wavelength of 520 and 650
nm and the 520:650 nm ratio [15].
2.5 Determination of Antioxidant Activity
The antioxidant activity of alginate was
determined based on the description of Dang et
al. (2020) [7]. The method is the reaction
between alginate and Mo
6+
ion for forming Mo
5+
in the acid environment. The absorbance
measurement was at the wavelength of 655 nm
with the standard of ascorbic acid.
2.6 Determination of Viscosity and
Average Molecular Weight
The intrinsic viscosity parameter of sodium
alginate was determined based on the machine
Viscometers - AMETEK Brookfield and used for
calculating the average molecular weight of
sodium alginate.
2.7 Determination of Sugar Composition
of Alginate
Sugar composition of antioxidant alginate was
measured using the GC - FID method on
Agilent's 6890 N gas chromatograph (USA).
Chromatography conditions: Agilent's 6890 N
gas chromatograph (USA) included automatic
sample injector, injection chamber, column
furnace, flame ionization detector (FID), and HP5
MS column (30 m x 0.25 m, x 0.25 m). Injection
chamber temperature 280
o
C, line split ratio of
Thuat et al.; JPRI, 33(41A): 197-206, 2021; Article no.JPRI.72634
200
50/1, program temperature column at 100
o
C,
increase to 325
o
C at a rate of 20
o
C/min, keep
the heat for 10 minutes. The probe temperature
was at 300
o
C. Carrier gas speed was 01 mL/min.
Derivation process: The hydrolysis of the sample
(m, g) was in 1.5 M HCl, makeup to 10 mL for
reacting with acetic anhydride and finally injected
into the GC system.
2.8 Determination of Structure
Characteristics
NMR spectra were recorded on Bruker AVANCE
Neo 600 MHz instrument at 70ºC, using D
2
O
solvent with 01 % CD
3
COOD and DSS as an
internal standard with water reduction
measurement technique.
2.9 Data Analysis
Data was expressed under the average ±
standard deviation (Mean ± SD) and removing
unnormal values using the Duncan method. The
analysis of statistics, ANOVA, and regression
was using MS. Excel 2010.
3. RESULTS AND DISCUSSION
3.1 Effect of Various Extraction
Conditions
3.1.1 Effect of extraction time
The extraction time affected alginate content and
their antioxidants (p<0.05). Alginate content
increased from 96.75 to 109.87 mg uronic acid
equivalent/g DW as the extraction time increase
from 01 to 02 hours. Alginate content
continuously increased and got the highest value
of 162.17 mg uronic acid equivalent/g DW at 04
extraction hours when the extraction time
increased from 02 to 04 hours. Alginate content
changed according to the non-linear model of
level 2 and decreased as the extraction time was
more than 04 hours (decreased to 150.88 mg
uronic acid equivalent/g DW). At the extraction
time of 6 hours, the antioxidant activity got the
highest value of 192.71 mg ascorbic acid
equivalent/g DW (Fig. 1). Antioxidant activity
increased the linear model as the extraction time
increase from 01 to 06 hours. Antioxidant activity
corresponded to 174.28 ascorbic acid
equivalent/g DW as alginate content of 162.17
mg uronic acid equivalent/g DW. The lowest
alginate content was 96.75 mg uronic acid
equivalent/g DW, their antioxidant activity
corresponded to 118.62 mg ascorbic acid
equivalent/g DW. Alginate content and its
antioxidant activity was a strong correlation
(R
2
=0.9534) and interacted according to the non-
linear equation (y = -0.0227x
2
+ 6.8502x
333.16). Generally, the longer the extraction
time, the higher the efficiency of the compounds.
However, the effect of extraction time on alginate
content and their antioxidants depends on the
material characteristics (size, moisture content,
growth time, harvest method). Long extraction
time will consume more energy and other costs.
In the current study, the extraction time of more
than 04 hours caused the full destruction of
brown algae structure and forming the paste
mixture that was difficult during the filtering
process. The extraction time of alginate
depended on the genus, species such as
Sargassum sp. (2.5 hours) [16], Macrocystis
pyrifera (120 minutes) [17], Sargassum
mangarevense, Turbinaria ornata (4 hours),
Sargassum wightii (12 hours) [2].
3.1.2 Effect of the extraction temperature
The extraction temperature affected alginate
content and antioxidant activity (p<0.05). The
current study was suitable for the notice of Tores
et al. (2007) on the impact of temperature on the
extraction yield of alginate [18]. When the
temperature increased from 40 to 50
o
C, alginate
content strongly changed from 132.17 to 162.17
mg uronic acid equivalent/g DW and
continuously increased at 60
o
C (164.22 mg
uronic acid equivalent/g DW) (Fig. 2). Alginate
content decreased from 164.22 down 151.08 mg
uronic acid equivalent/g DW as the extraction
temperature increase to 90
o
C. Alginate content
changed according to the level 2–model with the
maximum peak at 50
o
C. The difference in
alginate content as extracting at 50 and 60
o
C
was not significant (p<0.05). The thing was also
suitable for the description of Gholamipoor et al.
(2013) on the extraction temperature of alginate
from Sargassum angustifolium [19]. As the
extraction at 50
o
C, antioxidant activity
corresponded to 174.28 mg ascorbic acid
equivalent/g DW, while the extraction at 90
o
C,
antioxidant activity decreased to 130.24 mg
ascorbic acid equivalent/g DW. Alginate content
got 164.22 mg uronic acid equivalent/g DW,
corresponded to the antioxidant activity of 177.48
mg ascorbic acid equivalent/g DW. As alginate
content of 160.05 uronic acid equivalent/g DW,
the antioxidant activity got 170.03 mg ascorbic
acid equivalent/g DW. Alginate content
correlated to antioxidant activity according to the
non-
linear model of level 2 (y = 0.1166x
33.681x
+ 2568.4) with strong adjusted R
(79.28
%). Under the impact of time and
temperature, alginate still played an important
role in exhibiting antioxidant activity.
3.1.3 Effect of solvent pH
Solvent pH impacted alginate content and
antioxidant activity of
various extracts from brown
algae Sargassum polycystum (p
<0.05). Alginate
content strongly increased to 169.75 mg uronic
acid equivale
nt/g DW, corresponded to 111.55
as pH increase from 8 to 9.
Alg
inate content decreased by 4.47
solvent pH increased over 9 (pH 10). At pH
solvent of 9, antioxidant activity was 1.15 and
1.02 times, compared to pH 8 and 10,
respectively (Fig. 3). The current study was
suitable for the notices of Hernández
al. (1999) on alginate cont
ent that depended on
the concentration of an alkaline solution (exhibit
via pH index) at the extraction step [20]. The
alkaline extraction process converts the alginic
acid from its insoluble form to the soluble sodium
alginate form and diffuses out of the
The concentration of Na
+
is a decisive factor in
the conversion of alginic acid to alginate.
Therefore, the alginic acid has not fully converted
to sodium alginate form as the low pH, and then
alginic acid still exists in the seaweed residue in
the form of insoluble, not diffused to the outside.
With higher pH, the concentration of Na
increases, the reaction process takes place
Fig. 1.
Alginate content and antioxidant activity for different extraction time
Thuat et al.; JPRI, 33(41A): 197-206, 2021
; Article no.
201
linear model of level 2 (y = 0.1166x
2
+ 2568.4) with strong adjusted R
2
%). Under the impact of time and
temperature, alginate still played an important
role in exhibiting antioxidant activity.
Solvent pH impacted alginate content and
various extracts from brown
<0.05). Alginate
content strongly increased to 169.75 mg uronic
nt/g DW, corresponded to 111.55
%
inate content decreased by 4.47
% when
solvent pH increased over 9 (pH 10). At pH
solvent of 9, antioxidant activity was 1.15 and
1.02 times, compared to pH 8 and 10,
respectively (Fig. 3). The current study was
suitable for the notices of Hernández
-carmona et
ent that depended on
the concentration of an alkaline solution (exhibit
via pH index) at the extraction step [20]. The
alkaline extraction process converts the alginic
acid from its insoluble form to the soluble sodium
alginate form and diffuses out of the
solution.
is a decisive factor in
the conversion of alginic acid to alginate.
Therefore, the alginic acid has not fully converted
to sodium alginate form as the low pH, and then
alginic acid still exists in the seaweed residue in
the form of insoluble, not diffused to the outside.
With higher pH, the concentration of Na
+
increases, the reaction process takes place
better, the alginic acid content in the seaweed
turns to more and more soluble alginate and
diffuses out of the solutio
n at the time. Alginate
was cleavage that caused the tends of the
alginate content as solvent pH continuously
increase [21].
3.1.4 Effect of the solvent-to-
material ratio
The increase of alginate content and antioxidant
activity and the filter
processing was comfortable
when the Na
2
CO
3
solution-to
-
increased. Alginate content as the extraction with
the solution-to-
material ratio (20/1, v
89.8, 93.23, and 118.13
%, compared to the ratio
of solvent-to-
material (40/1, 30/1, and
The antioxidant activity got the highest value as
the extraction with 40/1 (v/w) and the lowest
value with 10/1 (v/w) (143.68 mg ascorbic acid
equivalent/g DW. Alginate content was 176.22
mg uronic acid equivalent/g DW, its antioxidant
activity
corresponded to 188.54 mg ascorbic acid
equivalent/g DW (Fig. 4). As alginate content of
152.28 mg uronic acid equivalent/g DW,
antioxidant activity only was 169.73 mg ascorbic
acid equivalent/g DW. ANOVA analysis showed
that the change of the solution-
to
impacted alginate content and its antioxidant
activity (p
<0.05). The variation of antioxidant
alginate content under the impact of the solvent
ratio did not appear in the previous
studies
that mainly focused on temperature,
extraction
time [17], and the Na
concentration [16].
Alginate content and antioxidant activity for different extraction time
; Article no.
JPRI.72634
better, the alginic acid content in the seaweed
turns to more and more soluble alginate and
n at the time. Alginate
was cleavage that caused the tends of the
alginate content as solvent pH continuously
material ratio
The increase of alginate content and antioxidant
processing was comfortable
-
material ratio
increased. Alginate content as the extraction with
material ratio (20/1, v
/w) was
%, compared to the ratio
material (40/1, 30/1, and
10/1, v/w).
The antioxidant activity got the highest value as
the extraction with 40/1 (v/w) and the lowest
value with 10/1 (v/w) (143.68 mg ascorbic acid
equivalent/g DW. Alginate content was 176.22
mg uronic acid equivalent/g DW, its antioxidant
corresponded to 188.54 mg ascorbic acid
equivalent/g DW (Fig. 4). As alginate content of
152.28 mg uronic acid equivalent/g DW,
antioxidant activity only was 169.73 mg ascorbic
acid equivalent/g DW. ANOVA analysis showed
to
-material ratio
impacted alginate content and its antioxidant
<0.05). The variation of antioxidant
alginate content under the impact of the solvent
ratio did not appear in the previous
that mainly focused on temperature,
time [17], and the Na
2
CO
3
Alginate content and antioxidant activity for different extraction time
s
Fig. 2.
Alginate content and antioxidant activity at different extraction temperatures
Fig. 3.
Alginate content and antioxidant activity at different solvent pH
Fig. 4.
Alginate content and antioxidant activity at different the solvent
Thuat et al.; JPRI, 33(41A): 197-206, 2021
; Article no.
202
Alginate content and antioxidant activity at different extraction temperatures
Alginate content and antioxidant activity at different solvent pH
Alginate content and antioxidant activity at different the solvent
-to-
materia ratio
; Article no.
JPRI.72634
Alginate content and antioxidant activity at different extraction temperatures
Alginate content and antioxidant activity at different solvent pH
materia ratio
Fig. 5.
Alginate content and antioxidant activity at different numbers of extraction
Fig. 6. Sugar composition of alginate extracting from brown algae
Fucose spectrum; b) Xylose spectrum; c) Rhamnose, manose, glucose, galactose, and
Table 1. Chemical shifts of standard alginate via
C1
103.23
102.22
Fig. 7.
13
C NMR spectrum of alginate extracting from brown algae
Thuat et al.; JPRI, 33(41A): 197-206, 2021
; Article no.
203
Alginate content and antioxidant activity at different numbers of extraction
Fig. 6. Sugar composition of alginate extracting from brown algae Sargassum polycystum:
Fucose spectrum; b) Xylose spectrum; c) Rhamnose, manose, glucose, galactose, and
fructose spectrum
Table 1. Chemical shifts of standard alginate via
13
C NMR spectrum
C2
C3
C4
C5
103.23
72.64 74.01 80.62 78.72
102.22
67.81 71.79 82.56 69.95
C NMR spectrum of alginate extracting from brown algae Sargassum polycystum
; Article no.
JPRI.72634
Alginate content and antioxidant activity at different numbers of extraction
Sargassum polycystum:
a)
Fucose spectrum; b) Xylose spectrum; c) Rhamnose, manose, glucose, galactose, and
C6
177.46
177.65
Sargassum polycystum
Thuat et al.; JPRI, 33(41A): 197-206, 2021; Article no.JPRI.72634
204
3.1.5 Effect of the numbers of the extraction
The alginate content of the extract was the
inverse ratio to the number of extraction. Alginate
content got the highest value (176.22 mg uronic
acid equivalent/g DW) for the 1
st
extraction.
Alginate content for the 2
nd
and 3
rd
extraction
corresponded to 33.33 and 13.14 %, compared
to the 1
st
extraction. Therefore, the extraction
yield of alginate for the 1
st
extraction got 68.27
%. For the 1
st
extraction, the antioxidant activity
got the highest value and corresponded to 2.179
and 1.28 times, compared to the 3
rd
and 2
nd
extraction. For the 2
nd
extraction, antioxidant
activity was the average level, corresponding to
147.21 mg ascorbic acid equivalent/g DW,
compared to the 1
st
and 3
rd
extraction (Fig. 5).
Alginate content, antioxidant activity, and the
yield of alginate extraction in the current study
were higher than the notice of Yudiati et al.
(2018) [22]. Under the same extraction
conditions, in the first extraction, the alginic acid
content in the seaweed changed to highly soluble
alginate and diffused out of the solution, so the
obtained alginate content would be high. The
destruction of the seaweed structure and the
alginate cleavage occur more strongly in the
following extractions, leading to a decrease in the
obtained alginate with an increasing number of
extraction times.
3.2 Physico-chemistry Characteristics of
Antioxidant Alginate
Intrinsic viscosity (ƞ) and M
w
(kD) of antioxidant
alginate corresponded to 271.86 and 78.6,
respectively. The thing exhibited that alginate
extracting from brown algae Sargassum
polycystum possessed a molecular weight lower
than the previous notices [18]. The analysis of
alginate using GC-FID showed the diversity of
antioxidant alginate on sugar composition. For
example, fructose, fucose, rhamnose, mannose,
glucose, and galactose (Fig 6.). The thing could
form the diversity of the structure of antioxidant
alginate extracted from brown algae Sargassum
polycystum, also bioactivities of alginate that
depended on its structure characteristics [23,24].
The
13
C-NMR spectrum of antioxidant alginate
occurred 12 signals, corresponding to 12 carbon
atoms belonging to 02 monome (L-guluronic and
D-mannuronic) that was basic units forming the
alginate structure. Chemical shifts of different
sites such as C
1
, C
2
, and C
6
was 103.28, 72.64,
and 177.46, respectively, in D-mannuronic (M)
structure. The chemical shift of C
2
, C
3
, C
4
, C
5
,
and C
6
sites was 67.80, 71.79, 82.56, 69.95, and
177.65, respectively, in L-guluronic (G) structure
(Tab. 1 and Fig. 7). The significant difference in
the chemical shifts of carbon atoms in the current
study and the previous reports on the NMR of
alginate did not appear because the differences
were lower than 0.05 ppm [25], describled by
Hans et al. (1977) [26] and Peter (1988) [27].
The absorbance of the British standard solution
(1mg/ml) is D=0.473. Meanwhile, the
absorbance of the alginate sample in this study
is D=0.47. Thus, it could identify that the
purity of the obtained sample was greater
than 98 %.
4. CONCLUSION
Various extraction conditions impacted alginate
content and antioxidant activity, almost according
to the non-linear model of level 2, except for
extraction numbers and the solvent-to-material
ratio. Alginate extracting from brown algae
Sargassum polycystum grown in South-Centre of
Vietnam played a primary role in antioxidant
activity with an intrinsic viscosity and the average
molecular weight lower than the previous studies.
Sugar compositions of antioxidant alginate are
similar to the noticed alginate (glucose,
mannose, galactose, fructose, rhamnose, fucose,
and mannose). The interaction in antioxidant
alginate structure was different, so its
13
C-NMR
spectrum only exhibited chemical shifts of
C sites (C
1
, C
2
, and C
6
) of D-mannuronic (M)
and (C
2
, C
3
, C
4
, C
5
, and C
6
) of L-guluronic (G).
Alginate of brown algae Sargassum
polycystum is potential in functional-
antioxidant food and antioxidant
pharmaceuticals.
CONSENT
It is not applicable.
ETHICAL APPROVAL
It is not applicable.
DISCLAIMER
The products used for this research are
commonly and predominantly use products in our
area of research and country. There is absolutely
no conflict of interest between the authors and
producers of the products because we do not
intend to use these products as an avenue for
any litigation but for the advancement of
knowledge.
Thuat et al.; JPRI, 33(41A): 197-206, 2021; Article no.JPRI.72634
205
ACKNOWLEDGEMENTS
Thankful for the project of UDSPTM.04/20-21
and VAST03.08/20-21 are under the VAST,
chaired by Associate Professor Dang Xuan
Cuong and Dr Nguyen Dinh Thuat, for funding to
contribute to the implementation of the study.
Thankful for the project of antioxidant lignin-
alginate pharmaceutical material of the Ministry
of Industry and Trade, chaired by Associate
Professor Nguyen Xuan Hoan funded to
contribute to the implementation of the study.
COMPETING INTERESTS
Authors have declared that no competing
interests exist.
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