An innovative konjac glucomannan/κ‐carrageenan mixed tensile gel

Abstract

BACKGROUND
Konjac glucomannan (KGM) showed a synergistic interaction with κ‐carrageenan (CAR), which led to the formation of a promising compound hydrocolloid gel in the food field (such as jelly). Nevertheless, the mixed gels formed by adding KGM to CAR still displayed defects in gel strength and syneresis, and would hardly meet the quality requirements of some gel foods. However, deacetylated KGM and maltodextrin (MD) have always been used in gel foods and affect their viscosity and rheological properties.

RESULTS
In our paper, different amounts of MD were first used to alter the textural properties, and the results showed that both tensile strength and elongation exhibited first an increasing and then a decreasing trend with the increasing MD proportion and achieved a maximum at a final maltodextrin proportion of 4 g kg⁻¹ in the KGM/CAR/MD system. Based on the above results, we further explored the effects of deacetylation degree of KGM on the gel properties of mixed gel system. The results revealed that, compared to the native KGM, the partial deacetylated KGM was capable of significantly improving the tensile strength and elongation of KGM/CAR mixed gel.

CONCLUSION
Our study found that the appropriate addition of MD (0.4%) and DKGM were able to alter the tensile properties of KGM/CAR mixed gel, with potential to meet the needs of consumers and further design innovative tensile gel products in the soft gel industry. © 2021 Society of Chemical Industry

Full text

Research Article
Received: 27 September 2020 Revised: 2 February 2021 Accepted article published: 11 February 2021 Published online in Wiley Online Library:
(wileyonlinelibrary.com) DOI 10.1002/jsfa.11151
An innovative konjac glucomannan/
κ-carrageenan mixed tensile gel
Di Wu,aSimin Yu,aHongshan Liang,aMohamed Eid,aBin Li,aJing Lia
*
and
Jin Maob
*
Abstract
BACKGROUND: Konjac glucomannan (KGM) showed a synergistic interaction with κ-carrageenan (CAR), which led to the forma-
tion of a promising compound hydrocolloid gel in the food field (such as jelly). Nevertheless, the mixed gels formed by adding
KGM to CAR still displayed defects in gel strength and syneresis, and would hardly meet the quality requirements of some gel
foods. However, deacetylated KGM and maltodextrin (MD) have always been used in gel foods and affect their viscosity and
rheological properties.
RESULTS: In our paper, different amounts of MD were first used to alter the textural properties, and the results showed that
both tensile strength and elongation exhibited first an increasing and then a decreasing trend with the increasing MD propor-
tion and achieved a maximum at a final maltodextrin proportion of 4 g kg
−1
in the KGM/CAR/MD system. Based on the above
results, we further explored the effects of deacetylation degree of KGM on the gel properties of mixed gel system. The results
revealed that, compared to the native KGM, the partial deacetylated KGM was capable of significantly improving the tensile
strength and elongation of KGM/CAR mixed gel.
CONCLUSION: Our study found that the appropriate addition of MD (0.4%) and DKGM were able to alter the tensile properties
of KGM/CAR mixed gel, with potential to meet the needs of consumers and further design innovative tensile gel products in the
soft gel industry.
© 2021 Society of Chemical Industry
Keywords: konjac glucomannan; deacetylation; κ-carrageenan; maltodextrin
INTRODUCTION
Konjac glucomannan (KGM), a kind of widely used natural macro-
molecular polysaccharide,
1
has been extensively applied in the
food field (such as jelly) because of its special gel properties.
2
Pre-
vious studies have reported that there were around 5–10% acety-
lated sugar residues on the main chain of KGM, which have a great
influence on hygroscopicity and gel properties.
3
Concretely, par-
tial removal of acetyl groups could eventually bring about
changes in both rheological and gel properties of KGM.
4–7
Hence
deacetylation should be of considerable interest in the food
industry for regulating the required gel properties of KGM.
κ-Carrageenan (CAR), composed of ⊎-1,3-galactopyranose and
3,6-anhydro-⊍-1,4-galactopyranose,
8
has been widely employed
as a favorable food additive such as gelling agent.
9
Certain cat-
ions, such as potassium ion, could promote the formation of
gel.
10
Nevertheless, the brittleness, low elasticity and poor
water-holding capacity of CAR have severely limited its applica-
tion in gel food.
11
It has been reported that KGM shows a synergistic interaction
with CAR, contributing to a promising hydrocolloid gel. Yuan
et al. reported that the gel formed by KGM and CAR had less brit-
tleness and higher flexibility than individually.
11
Brenner et al. also
confirmed KGM and CAR compound gels demonstrated higher
elastic moduli fracture stress compared to pure CAR.
12,13
Signifi-
cantly, KGM and CAR are representative of the synergistic effect
between the above polysaccharides, which has been applied to
the production of jelly or gelatinous food, with the aim of further
enriching the textural range in elastic polysaccharide foods.
12,14,15
Nevertheless, the mixed gels produced by adding KGM to CAR still
displayed defects in gel strength and syneresis, hardly meeting
the quality requirements of some gel foods.
16
Our previous study found that the deacetylation degree (DD) of
KGM did have an impact on the rheological and textural proper-
ties of KGM/CAR mixed gel systems.
17
Hence altering the DD of
KGM could serve as a potential method to expand the gel variety
*Correspondence to: J Li, College of Food Science and technology, Huazhong
Agricultural University, Wuhan 430070, China, E-mail: lijingfood@mail.hzau.
edu.cn; or J Mao, National Reference Laboratory for Agricultural Testing PR
China, Key Laboratory of Detection for Mycotoxins (Ministry of Agriculture),
Laboratory of Quality & Safety Risk Assessment for Oilseed Products (Ministry
of Agriculture), Oil Crops Research Institute, Chinese Academy of Agricultural
Sciences, Wuhan 430062, China. E-mail: maojin106@whu.edu.cn
aCollege of Food Science and Technology, Huazhong Agricultural University,
Wuhan, China
bNational Reference Laboratory for Agricultural Testing PR China, Key Labora-
tory of Detection for Mycotoxins (Ministry of Agriculture), Laboratory of Qual-
ity and Safety Risk Assessment for Oilseed Products (Ministry of Agricult ure), Oil
Crops Research Institute, Chinese Academy of Agricultural Sciences, Wuhan,
China
J Sci Food Agric 2021 www.soci.org © 2021 Society of Chemical Industry
1

when dealing with KGM/CAR mixed gel, to further meet the spe-
cial requirements of consumers. Furthermore, based on previous
studies, maltodextrin, a common additive in gel foods,
18
was able
to affect the viscosity and rheological properties of the mixed sys-
tem.
19
Based on such studies, we proposed a hypothesis that the
added moderate maltodextrin and the partial deacetylation of
KGM might increase the tensile strength and tensile elongation
of KGM and CAR mixed gel in order ultimately to obtain gel prod-
ucts with moderate tensile behavior.
In this paper, we explored the effects of additive maltodextrin
and DD of KGM on rheological and textural properties in the konjac
glucomannan/κ-carrageenan (KGM/CAR) mixed gel system. Tensile
strength, elongation, texture profile analysis and rheological mea-
surement were used in our paper in order to investigate the above
properties concretely. Hence, in this study, we attempted to intro-
duce an innovative tensile gel by altering the additive maltodextrin
proportion and regulating the DD of KGM, with the expectation to
meet the needs of consumers and further design innovative tensile
gel products in the soft gel food industry.
MATERIALS AND METHODS
Materials
Konjac glucomannan was kindly supplied by a local company
(Hubei Konson Konjac Gum Co. Ltd, Wuhan, China).
κ-Carrageenan was purchased from Shanghai Aladdin BioChem
Technology Co. Ltd (Shanghai, China). Maltodextrin, saccharose
and potassium chloride were obtained from Sinopharm Chemical
Reagent Co. Ltd (Shanghai, China). All other chemicals were of
analytical grade. Distilled water (electrical resistance
≈18.2 MΩcm) was used to prepare all aqueous solutions.
Preparation of deacetylated KGM (DKGM)
KGM with a series of different DD was obtained according to a
previous method.
17
Details are as follows: 40 g KGM powders
was dispersed in 50% (v/v) aqueous ethanol solution (200 mL)
and subsequently incubated in a thermostatic oscillator (40 °C,
30 min) with a stable shaking speed (150 rpm). Sodium carbonate
was then added to the above dispersion and the system was kept
for 24 h at 40 °C to complete the deacetylation reaction. Subse-
quently, the processed KGM was washed with 50%, 75% and
95% (v/v) ethanol, respectively, in order by three cycles, with the
aim to remove excess alkali (sodium carbonate). The samples
were then further dehydrated using absolute ethanol three times
and dried by vacuum drying (80 °C, 2 h). The final DKGM with a
series of DD was obtained by changing the amount of sodium
carbonate.
DD was measured with reference to a previous study, with slight
modification.
20
Concretely, the above DKGM samples (1.00 g)
were dispersed in 20 mL aqueous ethanol solution (50% v/v)
under stirring in a water bath (50 °C, 1 h). Parafilm was used out-
side the sample flasks to prevent evaporation. When the above
samples were cooled to room temperature, KOH (1 mL, 0.5 mol
L
–1
) was added to the DKGM dispersion and the dispersion was
then saponified in a thermostatic oscillator (30 °C, 48 h). Standard
HCl solution (0.02 mol L
–1
) was used to titrate excess alkali under
phenolphthalein indicator. Each group sample was repeated
three times and subsequently reported as mean value. The DD
was calculated as follows:
DD %ðÞ=V2−V1
ðÞ=V0−V1
ðÞ½×100 ð1Þ
where V
0
,V
1
and V
2
are the volume of consumed HCl for blank,
native and DKGM, respectively.
Finally, the DD of KGM samples in our article were calculated as
0.00% (DKGM0), 13.43% (DKGM1), 21.07% (DKGM2).
Preparation of DKGM/CAR mixed gel
KGM (0.45 g) and CAR (0.55 g) were dissolved in distilled water
(100 mL) with magnetic stirring for 2 h to obtain a homogeneous
system. The samples were then heated to 95 °C in a water bath for
10 min with continuous stirring and cooled to 70 °C. Saccharose
and KCl solutions were then added to the above samples to reach
afinal proportion of 100 and 0.6 g kg
−1
, respectively. Different
amounts of maltodextrin (MD) (0 wt%, 0.2 wt%，0.4 wt%，
0.6 wt%，0.8 wt% in total) were subsequently added and dis-
solved uniformly, denoted as KGM/CAR/MD or DKGMx/CAR/MD
(xrepresents the numbers corresponding to the DD in the previ-
ous subsection, and KGM and DKGM represent the native KGM
and deacetylated KGM, respectively). The above solutions were
poured into molds (30 mm ×30 mm ×10 mm) and finally cooled
to room temperature.
Tensile properties test
The method of the tensile properties test was based on a previous
study, with slight modification.
21
The mechanical properties were
studied using rectangular samples with a length of 100 mm and a
width of 10 mm. The thickness of the samples was measured as
3 mm using a vernier caliper. The cracked tension (N) and elonga-
tion (mm) of all prepared samples were determined by texture
analyzer (Stable Micro Systems Ltd, Godalming, UK) with an ATG
probe operating at room temperature with a speed of 2 mm s
−1
.
Tensile strength was then calculated as follows:
Tensile strength MPaðÞ=F=W×HðÞ ð2Þ
Elongation %ðÞ=S=L×100 ð3Þ
where Frepresents the cracked tension, Sis the cracked elonga-
tion, and W,Land Hrepresent the width, length and height of
the tested samples.
Texture profile analysis (TPA)
TPA was carried out based on a previous study, with slight modi-
fication.
22
The textural properties of gels was determined using a
texture analyzer (Stable Micro System Ltd). Samples were com-
pressed with a flat-ended cylindrical probe of 36 mm. The data
were collected over a TPA mode at a constant speed of 1 mm s
−1
.
Compressibility was 50%, with a retention interval of 5 s, using a
data acquisition rate of 200 pps and a trigger value of 5 g. Data
were replicated eight times.
Rheological measurement
Rheological measurements were performed according to our pre-
vious method.
17
Details were as follows. The rheological proper-
ties were determined with a dynamic stress rheometer
(TA Instruments, Newcastle, DE, USA) using a cone-plate mode
(gap 1 mm, diameter 40 mm). The edge of the sample was cov-
ered with a thin layer of paraffin oil to prevent moisture evapora-
tion during measurements, including temperature sweep and
steady shear test.
Deformation sweep
Deformation sweep tests were carried out first in the range of
0.01–40% and at a constant frequency of 1.0 s
−1
.
www.soci.org D Wu et al.
wileyonlinelibrary.com/jsfa © 2021 Society of Chemical Industry J Sci Food Agric 2021
2

Frequency sweep
Dynamic frequency sweep experiments were carried out at a con-
stant strain amplitude within the limits of the linear viscoelastic
region in the range of 0.1–10 Hz with a strain of 2%.
Temperature sweep
Temperature sweep tests were observed by cooling the systems
from 70 to 25 °C at a rate of 1 °C min
−1
and a strain of 2%.
Steady shear
Steady shear measurements in the range 0.1–300 s
−1
were carried
out with a constant frequency of 1 Hz and a constant temperature
of 70 °C.
Time sweep
Time sweep tests were observed with a strain of 2% and a con-
stant temperature of 25 °C.
Data analysis
The non-Newtonian flow curve of different DKC mixed solutions
may be described by a power law:
η=Kγn−1ð4Þ
Where ηis viscosity, Kis viscosity coefficient, nis flow behavior
index and γis the shear rate.
Statistical analysis
Data are expressed as the mean ±standard deviation. Statistical
comparisons were made by analysis of variance and Student's t-
test. A value of P<0.05 was considered statistically significant.
RESULTS AND DISCUSSION
Effect of MD proportion on textural properties in KGM,
CAR and MD mixed gel (denoted by KGM/CAR/MD)
Tensile testing results are exhibited in Fig. 1. As shown, there was
a gradual increasing trend in the tensile strength with increase in
MD content at first, followed by a downtrend with MD increased
to 4 g kg
−1
. That is, the tensile strength could reach a maximum
of 4 g kg
−1
for MD. A similar trend was shown regarding elonga-
tion (Fig. 1(b)), with the highest MD concentration of 4 g kg
−1
.
Since MD could formed co-gels with other materials, based on a
previous study, we hypothesized the possible reason for the
above phenomenon could be as follows: the addition of MD
might contribute to the formation of a more desired gel network,
promoting the tensile strength of gel.
23,24
However, the hardness
could also be enhanced with continuously increasing MD, making
gels brittle and, conversely, decreasing the tensile strength of
gels. With comprehensive analysis of the above results, we
selected the desired amount of MD as 4 g kg
−1
in the subsequent
study.
Effect of MD proportion on rheological properties in KGM/CAR/
MD mixed gel
Figure 2 represents shear stress and viscosity as a function of the
shear rate of KGM/CAR/MD mixed gel with different additive
amounts of MD. As exhibited in Fig. 2(a), the shear stress of all
gel samples increased sharply over the shear rate and exhibited
a steady uptrend subsequently. As shown in a previous study,
there was a nonlinear relationship between shear stress and shear
rate, indicating that all gel systems displayed pseudoplastic fluid
performance.
25
Moreover, Fig. 2(b) shows the relationship
between viscosity and shear rate and demonstrates a slightly
unstable platform of the mixed gels at first. Subsequently, there
was a gradually decreasing trend in viscosity with the growth of
shear rate. In addition, the viscosity of mixed systems was also
affected by the additive MD. The results in Fig. 2(b) show that vis-
cosity could be enhanced by adding a certain amount of
MD. Concretely, the viscosity increased gradually with increasing
MD concentration and then decreased with continually added
MD, reaching a maximal viscosity of 4 g kg
−1
of MD. Based on a
previous study, the viscosity was relevant to the additive MD
and dextrose equivalent (DE) value. Interestingly, viscosity could
be promoted by high DE value (DE value >10) and diminished
by a low value (DE value <10).
26
The DE value of the MD used
in our study was approximately 15–20. Hence the viscosity of
our gel systems could be enhanced by adding a certain amount
of MD. However, excessive added MD might also lead to a reduc-
tion in viscosity.
26
Ultimately, the optimized concentration of MD
we speculated from results was 4 g kg
−1
. The results were in
agreement with the tensile strength and elongation data.
Figure 3 shows the relationship between energy storage modu-
lus (G0), loss modulus (G00) and temperature of KGM/CAR/MD
mixed gel under different MD concentrations. All samples dis-
played roughly similar trends, with differences as follows. On
one hand, G0and G00 were both increased with decreasing temper-
ature, and G0gradually exceeded G00 at a certain temperature, after
which the gel network had been formed and the gel systems pos-
sessed solid-like properties.
27
On the other hand, the value of G0
first increased and reached a maximum (4 g kg
−1
MD), and then
dropped with enhanced MD concentration as the temperature
continued to decrease to 25 °C. In addition, the temperature of
the gel–sol transition point (G0=G00) decreased with increase in
the additive amounts of MD. The results might be interpreted that
trapping the MD inside the gel matrix might change the mobility
and network elasticity of the systems, exerting an effect on the
Figure 1. (a) Tensile strength and (b) elongation of KGM/CAR/MD mixed
gel system at different maltodextrin proportions.
An innovative konjac glucomannan/κ-carrageenan mixed tensile gel www.soci.org
J Sci Food Agric 2021 © 2021 Society of Chemical Industry wileyonlinelibrary.com/jsfa
3

free energy of mixtures and eventually impacting the tempera-
ture of the gel–sol transition point.
28
G0and G00 as a function of time are displayed at 25 °C in Fig. 4 for
mixed gels with different amounts of MD. As shown, the values of
G0were larger than the G00 values for all prepared gels during all
tested time, indicating the solid-like properties of gels at low
temperature, which was in line with the results in Fig. 3. Addition-
ally, G0first exhibited an increasing tendency, and then there was
a decreasing trend with enhanced MD concentration. In reference
to a previous study, ‘strong gels’were defined as a relatively larger
difference between G0and G00.
29
Hence the values of G0/G00 could be
used to evaluate the gel performance of our samples. That is, the
Figure 2. (a) Steady stress and (b) viscosity curves of KGM/CAR/MD mixed gel system as a function of shear rate at different maltodextrin proportions at
70 °C.
Figure 3. Storage modulus G0(solid symbols) and loss modulus G00 (open symbols) as a function of temperature for KGM/CAR/MD mixed gel at different
maltodextrin proportions. Additive maltodextrin proportions were as follows: (a) 2 g kg
−1
; (b) 4 g kg
−1
; (c) 6 g kg
−1
; (d) 8 g kg
−1
.
www.soci.org D Wu et al.
wileyonlinelibrary.com/jsfa © 2021 Society of Chemical Industry J Sci Food Agric 2021
4

larger the values, the stronger the gel properties. In our study, the
values of G0/G00 reached a maximum with an added MD concentra-
tion of 4 g kg
−1
, illustrating a favorable gel property of all gel sam-
ples. Generally speaking, the introduction of MD could further
increase the tensile properties of mixed gels with an optimized
addition of 4 g kg
−1
based on bothrheological and textural results.
Effect of different DD on textural properties in DKGMx/CAR/MD
mixed gel
The results of texture profile analysis are given in Table 1. As shown,
all results (including hardness, adhesiveness, springiness, cohesive-
ness, chewiness and resilience) exhibited a continually increasing
trend over the enhanced DD. Moreover, the mechanical properties
of DKGMx/CAR/MD mixed gel with different DD are shown in Fig. 5.
In this experiment, we selected the optimized formulation
(4 g kg
−1
MD in total) based on the above results. Figure 5(a) illus-
trates the variety of tensile distance over DD directly. As shown, the
tensile distance increased remarkably with increase in DD from
DKGM0/CAR/MD (without deacetylation of KGM) to DKGM2/CAR/
MD (partial deacetylation of KGM). In addition, the tensile strength
and elongation exhibited a steady increase with enhanced DD of
DKGMx/CAR/MD samples (Fig. 5(b, c)). A possible reason might be
that the KGM molecules with appropriate deacetylation could have
greater potential to crosslink with CAR molecules and possess a
more appropriate water binding capacity than the native KGM,
which was consistent with our previous studies.
30
Figure 4. Storage modulus G0(solid symbols) and loss modulus G00 (open symbols) as a function of time for KGM/CAR/MD mixed gel at different malto-
dextrin proportions. Additive maltodextrin proportions: (a) 2 g kg
−1
; (b) 4 g kg
−1
; (c) 6 g kg
−1
; (d) 8 g kg
−1
.
Table 1. Texture profile analysis of DKGMx/CAR/MD mixed gel system with different deacetylation degrees
Hardness Adhesiveness Springiness Cohesiveness Chewiness Resilience
DKGM0/CAR/MD 204.79 ±13.42c 18.19 ±1.45c 0.823 ±0.021b 0.591 ±0.019b 104.57 ±6.12c 0.298 ±0.005c
DKGM1/CAR/MD 239.94 ±5.03b 21.24 ±1.22b 0.833 ±0.012b 0.621 ±0.019a 118.03 ±3.14b 0.321 ±0.008b
DKGM2/CAR/MD 247.15 ±11.16a 23.41 ±1.83a 0.847 ±0.017a 0.633 ±0.012a 132.22 ±9.30a 0.344 ±0.007a
Note: In columns, means with the different lowercase letters are significantly different (P <0.05).
An innovative konjac glucomannan/κ-carrageenan mixed tensile gel www.soci.org
J Sci Food Agric 2021 © 2021 Society of Chemical Industry wileyonlinelibrary.com/jsfa
5

Effect of different DD on rheological properties in DKGMx/CAR/
MD mixed gel
Figure 6 demonstrates the steady shear curves of DKGMx/CAR/
MD gels with different DD. It was found in Fig. 6(a) that the shear
stress of all tested samples increased rapidly at lower shear rate
and shifted gradually to steady with increasing shear rate, indicat-
ing a nonlinear relationship between the shear stress and shear
rate. That is, all prepared gels behaved as a non-Newtonian
fluid.
25
As obtained from Fig. 6(b), increasing DD enlarged the vis-
cosity of the system, which could be explained by assuming that
the deacetylation promoted the aggregation of KGM within
hydrogen bonding, by which the deacetylated KGM could form
a network structure and ultimately lead to gel formation.
31
There-
fore, the viscosity of gel systems might be increased with an
enhancement of DD. Besides, the viscosity of all DKGMx/CAR/
MD samples tended to decline continuously due to the acceler-
ated shear rate to 2 s
−1
, at which the entanglement of molecular
chains was destroyed rather than rebuilt.
Figure 7 presents the G0and G00 of frequency dependence for
DKGMx/CAR/MD gels with different DD at 70 °C. As shown, both
G0and G00 were increased with the enhancement of frequency.
In addition, the molecular chains could disentangle at lower fre-
quencies because of the long periods of shaking, presenting
liquid-like behaviors (G0<G00), while the chains were entangled
under high frequencies due to the lack of mobility, thus showing
solid-like properties (G0>G00).
32,33
In addition, the crossover indi-
cated the formation of a network structure owing to the
Figure 5. (a) Photograph, (b) tensile strength and (c) elongation of
DKGMx/CAR/MD mixed gel with different deacetylation degrees.
Figure 6. (a) Steady stress and (b) viscosity curves of DKGMx/CAR/MD mixed gel system as a function of shear rate with different deacetylation degrees at
70 °C.
Figure 7. Storage modulus G0(solid symbols) and loss modulus G00 (open
symbols) as a function of frequency for DKGMx/CAR/MD mixed gel with
different deacetylation degrees.
www.soci.org D Wu et al.
wileyonlinelibrary.com/jsfa © 2021 Society of Chemical Industry J Sci Food Agric 2021
6

aggregation and association of molecular chains. In our study, the
crossover frequency occurred with increasing DD of DKGMx/CAR/
MD gels rather than the native, illustrating an enhancement of
temporary network structure of DKGMx/CAR/MD samples
because of the deacetylation of KGM. The reason for the lack of
crossover of the native KGM/CAR/MD might be the water-like
behavior and, as a consequence, the measurement of modulus
values was compromised. Moreover, the other deacetylated
KGM/CAR/MD gels had no trend towards shear thinning owing
to the stronger network structure between molecular chains.
However, there was no significant difference between the
DKGM1/CAR/MD and DKGM2/CAR/MD gels.
G0and G00 displayed a marked temperature dependence with
different DD; namely, both G0and G00 decreased with increasing
temperature (Fig. 8(a–c)). Besides, solid-like behavior was shown
at low temperatures (G0>G00) while G00 exceeded G0at high tem-
peratures, presenting liquid-like properties, which was in line with
a previous article from our lab.
30
The networks formed by the
hydrogen bonds in DKGMx/CAR/MD gels were unstable, as a con-
sequence of which the hydrogen bond forces were increasingly
weaker at high temperatures. In this situation, the hydrogen bond
forces could hardly maintain the gel structure any longer and the
systems ultimately exhibited liquid-like properties. Moreover, the
temperature at the crossover point (G0=G00) was always regarded
as the gel–sol transition temperature.
30
As shown, the crossover
points tended to lower temperature with increasing DD of KGM.
This implied that acetyl groups indeed had an important influence
on the gel behavior of DKC samples with different DD. A similar
phenomenon had been deduced by Du et al. that, although both
hydrogen bonding and hydrophobic interaction were both
responsible for the formation of KGM gels, the gel behavior was
mainly dependent on hydrophobic interaction with enhanced
DD rather than hydrogen bonding.
4
Hence the gel network
became more stable with rising DD, thus acquiring a decrease in
gel–sol transition temperature, which was due to the enhance-
ment of hydrophobic interaction.
Furthermore, Fig. 9 displays G0and G00 as a function of time for
different DKGMx/CAR/MD gels. As can be seen, the rheological
curves displayed a similar tendency among all tested samples.
Concretely, G0was always larger than G00, exhibiting solid-like
behavior. In addition, the values of G0/G00 were enhanced with
an increase in DD, indicating expectant gel properties of the par-
tially deacetylated gel samples, which was in accordance with the
above results of textural properties.
Figure 8. Storage modulus G0(solid symbols) and loss modulus G00 (open symbols) as a function of the temperature for DKGMx/CAR/MD mixed gel with
different deacetylation degrees. The deacetylation degrees of KGM were as follows: (a) DKGM0/CAR/MD; (b) DKGM1/CAR/MD; (c) DKGM2/CAR/MD.
Figure 9. Storage modulus G0(solid symbols) and loss modulus G00 (open symbols) as a function of time for DKGMx/CAR/MD mixed gel with different
deacetylation degrees. The deacetylation degrees of KGM were as follows: (a) DKGM0/CAR/MD; (b) DKGM1/CAR/MD; (c) DKGM2/CAR/MD.
An innovative konjac glucomannan/κ-carrageenan mixed tensile gel www.soci.org
J Sci Food Agric 2021 © 2021 Society of Chemical Industry wileyonlinelibrary.com/jsfa
7

CONCLUSION
The effects of added MD and DD of KGM on rheological and tex-
tural properties were explored in the KGM/CAR/MD mixed gel sys-
tem. Herein, the results revealed that the addition of maltodextrin
could endow both tensile strength and elongation with first an
increasing and then a decreasing trend, reaching a maximum at
4gkg
−1
MD. Also, DD of KGM was another critical factor that
remarkably influenced the rheological and textural properties of
KGM/CAR/MD mixed gels. Here, our results showed that partially
deacetylated KGM was able to enhance the tensile strength and
elongation of DKGM1/CAR/MD and DKGM2/CAR/MD mixed gel.
Generally speaking, this work provided an opportunity to develop
an innovative tensile gel product in order to meet the diverse
demands of consumers in the future food industry, with an opti-
mized formula of 6 g kg
−1
total KGM/CAR/MD mixed gel, partial
deacetylation of KGM and 4 g kg
−1
MD.
ACKNOWLEDGEMENTS
This work was financially supported by Hubei Provincial Natural
Science Foundation for Innovative Group (2019CFA011).
REFERENCES
1 Li G, Qi L, Li A, Ding R and Zong M, Study on the kinetics for enzymatic
degradation of a natural polysaccharide, konjac glucomannan.
Macromol Symp 216:165–178 (2004).
2 Tomczyńska-Mleko M, Brenner T, Nishinari K, Mleko S, Szwajgier D,
Czernecki T et al., Rheological properties of mixed gels: gelatin, kon-
jac glucomannan and locust bean gum. Food Sci Technol Res 20:
607–611 (2014).
3 Meada M, Shimahara H and Sugiyama N, Detailed examination of the
branched structure of konjac glucomannan. Agric Biol Chem 44:
245–252 (1980).
4 Du X, Li J, Chen J and Li B, Effect of degree of deacetylation on physi-
cochemical and gelation properties of konjac glucomannan. Food
Res Int 46:270–278 (2012).
5 Nishinari K and Zhang H, Recent advances in the understanding of
heat set gelling polysaccharides. Trends Food Sci Technol 15:
305–312 (2004).
6 Chen J, Li J and Li B, Identification of molecular driving forcesinvolved in
the gelationof konjac glucomannan: effect of degree of deacetylation
on hydrophobic association. Carbohydr Polym 86:865–871 (2011).
7 Gao S and Nishinari K, Effect of degree of acetylation on gelation of
konjac glucomannan. Biomacromolecules 5:175–185 (2004).
8 Robal M, Truus K, Volobujeva O, Mellikov E and Tuvikene R, Thermal
stability of red algal galactans: effect of molecular structure and
counterions. Int J Biol Macromol 104:213–223 (2017).
9 Loret C, Ribelles P and Lundin L, Mechanical properties of
κ-carrageenan in high concentration of sugar solutions. Food Hydro-
coll 23:823–832 (2009).
10 di Rose M, Biological properties of carrageenan. J Pharm Pharmacol 24:
89–102 (1972).
11 Yuan C, Xu D, Cui B and Wang Y, Gelation of κ-carrageenan/konjac glu-
commanan compound gel: effect of cyclodextrins. Food Hydrocol-
loids 87:158–164 (2018).
12 Brenner T, Tuvikene R, Fang Y, Matsukawa S and Nishinari K, Rheology
of highly elastic iota-carrageenan/kappa-carrageenan/xanthan/kon-
jac glucomannan gels. Food Hydrocolloids 44:136–144 (2015).
13 Brenner T and Nishinari K, Rheological effects of different interactions
in kappa-carrageenan/ locust bean gum/konjac glucomamman
gels, in Gums and Stabilisers for the Food Industry 17: The Changing
Face of Food Manufacture: The Role of Hydrocolloids, ed. by
Williams P and Phillips G. Royal Society of Chemistry, Cambridge,
UK, pp. 197–204 (2014).
14 Thomas WR, Carrageenan, in Thickening and Gelling Agents for Food,
ed. by Imeson AP. Springer, Berlin, pp. 45–59 (1992).
15 Brenner T, Wang Z, Achayuthakan P, Nakajima T and Nishinari K, Rhe-
ology and synergy of κ-carrageenan/locust bean gum/konjac gluco-
mannan gels. Carbohydr Polym 98:754–760 (2013).
16 Sokolovska I, Kambulova J and Overchuk N, Study of the water binding
in the gel systems of pectin and sodium alginate. East-Eur J Enterp
Technol 2:4–11 (2016).
17 Wu D, Yu S, Liang H, He C, Li J and Li B, The influence of deacetylation
degree of konjac glucomannan on rheological and gel properties of
konjac glucomannan/kappa-carrageenan mixed system. Food
Hydrocolloids 101:105523–105530 (2020).
18 Choi KO, Ryu J, Kwak HS and Ko S, Spray-dried conjugated linoleic acid
encapsulated with Maillard reaction products of whey proteins and
maltodextrin. Food Sci Biotechnol 19:957–965 (2010).
19 Juszczak L, Gałkowska D, Witczak T and Fortuna T, Effect of maltodex-
trins on the rheological properties of potato starch pastes and gels.
Int J Food Sci 2013:869362–869367 (2013).
20 Koroskenyi B and McCarthy SP, Synthesis of acetylated konjac gluco-
mannan and effect of degree of acetylation on water absorbency.
Biomacromolecules 2:824–826 (2001).
21 Fan L, Yang H, Yang J, Peng M and Hu J, Preparation and characteriza-
tion of chitosan/gelatin/PVA hydrogel for wound dressings. Carbo-
hydr Polym 146:427–434 (2016).
22 Chao Y, Dongyan X, Bo C and Yanli W, Gelation of kappa-carrageenan/-
konjac glucommanan compound gel: effect of cyclodextrins. Food
Hydrocolloids 87:158–164 (2019).
23 Kasapis S, Morris ER, Norton IT and Clark AH, Phase equilibria and gela-
tion in gelatin/maltodextrin systems. Part I: Gelation of individual
components. Carbohydr Polym 21:243–248 (1993).
24 Khan RS, Nickerson MT, Paulson AT and Rousseau D, Release of fluores-
cent markers from phase-separated gelatin–maltodextrin hydro-
gels. J Appl Polym Sci 121:2662–2673 (2011).
25 Cross MM, Rheology of non-Newtonian fluids: a new flow equation for
pseudoplastic systems. J Colloid Sci 20:417–437 (1965).
26 Goh KKT, Wee MSM and Hemar Y, Phase stability-induced complex
rheological behaviour of galactomannan and maltodextrin mix-
tures. Food Funct 4:627–634 (2013).
27 Song YS and Youn JR, Influence of dispersion states of carbon nano-
tubes on physical properties of epoxy nanocomposites. Carbon 43:
1378–1385 (2005).
28 Lorén N and Hermansson A-M, Phase separation and gel formation in
kinetically trapped gelatin/maltodextrin gels. Int J Biol Macromol 27:
249–262 (2000).
29 Solo-de-Zaldívar B, Tovar CA, Borderías AJ and Herranz B, Effect
of deacetylation on the glucomannan gelation process for
making restructured seafood products. Food Hydrocolloids 35:
59–68 (2014).
30 Hu Y, Tian J, Zou J, Yuan X, Li J, Liang H et al., Partial removal of
acetyl groups in konjac glucomannan significantly improved
the rheological properties and texture of konjac glucomannan
and κ-carrageenan blends. Int J Biol Macromol 123:1165–1171
(2019).
31 Maekaji K, The mechanism of gelation of konjac mannan. J Agric Chem
Soc Jpn 38:315–321 (1974).
32 Ross-Murphy SB, Physical gelation of biopolymers. Food Hydrocolloids
1:485–495 (1987).
33 Clark AH, Structural and mechanical properties of biopolymer gels.
Food Polym Gels Colloids 83:322–338 (1987).
www.soci.org D Wu et al.
wileyonlinelibrary.com/jsfa © 2021 Society of Chemical Industry J Sci Food Agric 2021
8