- Email: [email protected]
κ-carrageenan composite aqueous and emulsion systems: Effect of NaCl
Journal Pre-proofs Flocculation behavior and gel properties of egg yolk/κ-carrageenan composite aqueous and emulsion systems: effect of NaCl Junhua Li, Lilan Xu, Yujie Su, Cuihua Chang, Yanjun Yang, Luping Gu PII: DOI: Reference:
S0963-9969(20)30015-6 https://doi.org/10.1016/j.foodres.2020.108990 FRIN 108990
To appear in:
Food Research International
Received Date: Revised Date: Accepted Date:
14 October 2019 29 November 2019 6 January 2020
Please cite this article as: Li, J., Xu, L., Su, Y., Chang, C., Yang, Y., Gu, L., Flocculation behavior and gel properties of egg yolk/κ-carrageenan composite aqueous and emulsion systems: effect of NaCl, Food Research International (2020), doi: https://doi.org/10.1016/j.foodres.2020.108990
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier Ltd.
1
Flocculation behavior and gel properties of egg yolk/κ-carrageenan
2
composite aqueous and emulsion systems: effect of NaCl
3 4
Junhua Lia, b, c, #, Lilan Xua, b, c, #, Yujie Su a, b , c, Cuihua Chang a, b, c, Yanjun Yang a, b, c, *,
5
Luping Gu a, b, c, *
6
a State
7
214122, PR China
8
b
9
China
Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu,
School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122, PR
10
c
11
Jiangnan University, Wuxi, Jiangsu, 214122, PR China
Collaborative Innovation Center of Food Safety and Quality Control in Jiangsu Province,
12 13 14 15
*Corresponding author.
16
E-mail address: [email protected]; [email protected]
17
#
These authors contributed equally.
18 19 20 21 22 23 24 25 1
26
ABSTRACT
27
In this study, the influence of NaCl on the flocculation behavior and gel properties of
28
egg yolk/κ-carrageenan mixed dispersions or emulsions were studied. As a result of NaCl
29
incorporation, there was a decrease in the mean droplet size, zeta potential, degree of
30
flocculation and viscosity of the mixed dispersions/emulsions, and the onset point of gelation
31
was also brought forward. Increasing the concentration of NaCl led to a significant increase
32
in gel strength and decrease in gel cohesiveness. Results from low field nuclear magnetic
33
resonance (LF-NMR) confirmed that the addition of NaCl could significantly reduce the
34
hydration ability of gel molecules and increase the content of immobilized water of hydrogels
35
as the gel strength increased, while the water holding capacity of emulsion gels was
36
depressed with the incorporation of oil. These findings suggested the flocculation state and
37
gel properties of egg yolk/κ-carrageenan mixed dispersions/emulsions can be tailored by
38
adjusting NaCl for food formulations.
39
Keywords: Egg yolk, κ-carrageenan, flocculation behavior, rheological characteristics,
40
low-field nuclear magnetic resonance
41 42 43 44 45 46
2
47
1. Introduction
48
Hydrogels, constructed from one or more polymers such as protein and polysaccharide
49
suspended in water, are useful in the formation of novel food structure or as bioactive
50
delivery systems (AbaeeMohammadian & Jafari, 2017; Francis & Chidambaram, 2019;
51
Gravelle et al., 2019; Valverde et al., 2016). Nonetheless, one drawback of hydrogels in
52
practical applications is the limited solubility for lipophilic components. Up to date, many
53
oil-soluble nutrients such as lutein are usually added to the emulsion delivery systems to
54
improve their stability and bioavailability (SteinerMcClements & Davidov-Pardo, 2018; Su et
55
al., 2020). Among different emulsion systems, emulsion gels, existed as both an emulsion and
56
a gel, exhibit great potential applications in the improvement of thermo-dynamic stability,
57
texture modification, and encapsulation of both lipophilic and hydrophilic components
58
(Montes de Oca-Ávalos et al., 2016; Pintado et al., 2018; TorresMurray & Sarkar, 2016). So
59
it is promising for emulsion gels to be used as food material in the development of the
60
fortified foods.
61
Emulsion gels are common soft solid materials and are complex colloids formed by
62
matrices of polymeric gels into which emulsion droplets are incorporated (Geremias-Andrade
63
et al., 2016). The emulsion gel could be fabricated from the food-grade proteins or
64
polysaccharides. The properties of emulsion gels are highly dependent on the polymers used.
65
Recent developments of protein and polysaccharide hybrid delivery system and fat replacer
66
have attracted much attention (de Souza Paglarini et al., 2018; Gaber et al., 2018;
67
SerdaroğluNacak & Karabıyıkoğlu, 2017; Sun et al., 2015). A previous study has
3
68
demonstrated the beneficial effects of a polysaccharide on the improvement of gelling and
69
emulsifying properties of soy protein hydrolysates under certain conditions (Lopes-da-Silva
70
& Monteiro, 2019). Increasing carrageenan could improve the stability of the emulsion and
71
hardness of the surimi emulsion gels (Panyathitipong & Puechkamut, 2010). Compared with
72
simple protein-based emulsion gel system, protein-polysaccharide based emulsion gel
73
showed better oil/water stability (Khalesi et al., 2019; Liu et al., 2016). This may be ascribed
74
to the fact that polysaccharide could increase thickness of interfacial layer and viscosity of
75
aqueous phase to improve emulsion stability (Zang et al., 2019). Meanwhile, polysaccharide
76
could form gels in the presence of saline ions due to ion bridging interaction (Kara et al.,
77
2006), which has a positive effect on the properties of emulsion gels.
78
Egg yolk was often used as the main amphiphilic component in medium/high internal
79
phase emulsions like salad dressings or mayonnaise due to their excellent emulsifying
80
properties. All constituents of yolk proteins (low-density lipoproteins (LDL), high-density
81
lipoproteins (HDL), livetin and phosvitin) have a strong propensity to adsorb at the oil–water
82
interface and have been applied in the fabrication of emulsion (Castellani et al., 2006; Gmach
83
et al., 2019; Zhou et al., 2016). Furthermore, it was found that the presence of NaCl in
84
solution could change the aggregated state of egg yolk granules, leading to an improvement
85
of emulsion stability (AntonBeaumal & Gandemer, 2000). Our previous study demonstrated
86
that the emulsifying activity and stability of yolk exhibited an increase trend when the
87
concentration of NaCl was less than 1.8% (approximately 0.3 M) (Li, Wang, Li et al., 2018).
88
Carrageenan was a kind of linear, sulfated polysaccharide extracted from various species
4
89
of the Rhodophyta. Owing to its excellent bulking, gelling or thickening properties,
90
carrageenan was widely used as a food additive in the production of processed foods,
91
including dairy products, water-based foods, meat products and beverages (Prajapati et al.,
92
2014). It was reported that the types and concentrations of cation played important roles in
93
the formation of κ-carrageenan gel (LaiWong & Lii, 2000; Rochas & Rinaudo, 1984).
94
Although Na+ is not considered as the specific ions that affect the gelation of κ-carrageenan,
95
it is still efficient to prepare gels with the necessary structure and rheological properties in the
96
present of NaCl (Yampol’skaya et al., 2009).
97
Previous studies had showed the importance of electrostatic interactions in the degree of
98
compatibility between egg yolk and κ-carrageenan and the viscoelastic properties of mixed
99
egg yolk/κ-carrageenan gels at different pH and polysaccharide concentrations (Aguilar et al.,
100
2011; Aguilar et al., 2017). However, the flocculation behavior and hydrogel or emulsion gel
101
properties of egg yolk/κ-carrageenan hybrid systems have not been sufficiently studied,
102
particularly in different NaCl conditions. Both the functional properties of egg yolk and
103
κ-carrageenan are highly dependent on salt concentration used. Therefore, the objective of the
104
present study was to evaluate the emulsifying and gelling properties of egg
105
yolk/κ-carrageenan hybrid system under different concentrations of NaCl. The possible
106
mechanism of gelation in this system affected by NaCl and oil fill was also discussed. The
107
results obtained from this study may contribute to the development of hydrogel/emulsion
108
gel-based food products specifically designed for functional applications, such as
109
replacement of dietary saturated fats or enhanced delivery of lipophilic nutrients.
5
110
2. Materials and Methods
111
2.1. Materials
112
Fresh hen eggs and sunflower oil were purchased from a local market. Egg yolk
113
(average solid content: 50.5%, protein content: 17.5%, pH 6.4) was carefully separated from
114
egg white. κ-carrageenan (CAS number: 11114-20-8) and NaCl were obtained from Aladdin
115
Industrial Corporation (Shanghai, China). All other reagents used were of analytical grade
116
and were used without further purification.
117
2.2. Sample preparation
118
The mixed aqueous dispersions of egg yolk/κ-carrageenan were prepared according to
119
the following procedure. Briefly, 5 g egg yolk and 1 g κ-carrageenan were dispersed in 90
120
mL of deionized water and then adjusted to pH 7.0 with 0.1 M NaOH solution in a magnetic
121
stirrer (150 rpm) at room temperature for 2 h. Then, dissolve NaCl in above mixture and
122
dilute with deionized water to 100 mL to obtain the final mixed dispersions with the different
123
NaCl concentrations (0.0, 0.1, 0.2 and 0.3 M) in the mixture above. What needs to be pointed
124
out was that the concentrations of egg yolk and κ-carrageenan used in this study were based
125
on preliminary tests which had confirmed the emulsion gel can form under these conditions.
126
Samples of mixed aqueous dispersions were termed as 0.0W, 0.1W, 0.2W and 0.3W
127
according to the NaCl content of each sample. The oil-in-water emulsions (named as 0.0O,
128
0.1O 0.2Oand 0.3O) were prepared by homogenizing the above mixed dispersions with
129
sunflower oil (60% water phase: 40% oil phase, v/v) utilizing a high-speed mixer (IKA T25,
130
Germany) at 11,000 rpm for 4 min at room temperature.
6
131
The hydrogels and emulsion gels based on egg yolk and κ-carrageenan were prepared as
132
follows: the mixed dispersions and oil-in-water emulsions as described above were separately
133
added to glass beaker, heated in a water bath at 90 °C for 30 min, and then
134
immediately cooled down using tap water to induce gel formation. The obtained hydrogels
135
and emulsion gels were kept overnight at 4 ℃ prior to analysis.
136
2.3. Particle size and zeta potential
137
Droplet size, polydispersity index and zeta potential of mixed dispersions and emulsions
138
were determined by dynamic light scattering (DLS) using a Zetasizer Nano-ZS90 (Malvern
139
Instruments, Worcestershire, UK) at a fixed detector angle of 173°. Results were described as
140
z-average particle diameter (size, nm) for droplet size, polydispersity index (PDI) for particle
141
size distribution and zeta-potential (mV) for particle electric charge data, respectively. Prior
142
to each measurement, samples were diluted with deionized water to the final concentration of
143
0.025% (w/v) egg yolk and 0.005% (w/v) κ-carrageenan minimize multiple scattering effects.
144
All above measurements were conducted with 4 replicates at room temperature
145
2.4. Confocal laser scanning microscopy (CLSM)
146
The microstructure of the samples before gelation was observed using confocal laser
147
scanning microscopy (LSM710, Zeiss, Oberkochen, Germany). Samples applied in
148
observation were dyed using a mixed staining solution containing fluorescein isothiocyanate
149
(FITC) solution (0.1 g/L) and Nile Red (0.1 g/L) and then smeared over the microscopy slide
150
and gently covered with a glass slip. Samples were excited at 488 nm and detected
151
sequentially at 500-550 (FITC channel) and 600-700 nm (Nile red channel). Representative
7
152
images were chosen from at least three similar images.
153
2.5. Rheological characteristics
154
The flow behavior and gelation process of yolk/κ-carrageenan dispersions or emulsions
155
were studied using a DHR-3 rheometer (TA Instruments, USA) equipped with a steel
156
cone-plate geometry (diameter: 6 cm, angle: 4o, truncation: 53 µm). Each sample was
157
carefully deposited over the plateau of the rheometer. Samples were held at 25 ℃ for 60 s to
158
equilibrate before data collection. Apparent viscosity (η) of the samples was recorded at shear
159
rates (γ) over the range of 0.1 – 300 s-1 for 5 min at 25 ℃.
160
The gelation protocol involved successive heating and cooling cycles. For each
161
measurement, 4 mL of solution or emulsion was carefully transferred onto the steel plateau.
162
After the plateau has been brought to contact with the cone, a thin layer of low-viscosity
163
silicone oil was spread on the edge of plate to prevent water evaporation during
164
measurements. Heat gelation was induced at the 1 Hz and 0.1% strain by: (1) equilibrating
165
the sample at 25 ℃ for 1 min; (2) heating the sample to 90 ℃ at a rate of 10 K/min; (3)
166
cooling at a rate of 10 K/min from 90 ℃ to 25 ℃; and holding at 25 oC for 5 min. The onset
167
of gelation temperature was designated as the beginning of exponential growth regime of the
168
storage modulus (G´) (Anton et al., 2001). The gelation rate was calculated by linear fitting
169
approach that data was intercepted from the first 20 seconds right after the onset of gelation
170
temperature. All tests were performed in duplicate.
171
2.6. Textural analysis
172
Textural properties of the mixed hydrogels and emulsion gels were analyzed using 8
173
compression and penetration tests. The compression test is useful in assessing the cohesive
174
property of gels, while the penetration test is better for assessing density and compactness
175
(Lee & Chung, 1989). They can reflect the gel textural properties from different aspects. The
176
compression test, texture profile analysis (TPA), was performed at ambient temperature with
177
a TA-XT plus Texture Analyzer (Texture Technologies Corp., UK) and a 1 kg load cell. The
178
mixed gels were cylinders with 15 mm height and 20 mm diameter. Each sample was
179
compressed axially in two consecutive cycles of 50% compression, 5 s interval, with a flat
180
plunger 25 mm in diameter (SMS-P/25). The cross-head moved at a constant speed of 2 mm/s.
181
TPA curves were recorded and hardness and cohesiveness of samples were calculated.
182
Hardness was defined by peak force during the first compression cycle. Cohesiveness was
183
calculated as the ratio of the area under the second curve to the area under the first curve. Six
184
replicates were conducted for each sample.
185
A penetration test was also carried out using the TA-XT plus Texture Analyzer at
186
ambient temperature. A P/0.5 plunger with a diameter of 5 mm was used to penetrate 50% of
187
the sample length (sample size: 25 mm diameter×12 mm length) and the first peak of the
188
curve was used as fracture force. The results were expressed in terms of the fracture force (g)
189
and fracture distance (mm) (Tabilo-Munizaga & Barbosa-Cánovas, 2004). Six replicates were
190
conducted for each sample.
191
2.7. Low field nuclear magnetic resonance (LF-NMR) measurements
192
Low field nuclear magnetic resonance measurements (NMI20-Analyst, Niumag Electric
193
Corporation, Shanghai, China) were performed according to the previous method (Li, Wang, 9
194
Zhang et al., 2018) with minor modification. The cylindrical gel sample (15 mm height, 20
195
mm diameter) was placed in a glass tube and inserted in the NMR probe. The spin–spin
196
relaxation time (T2) was measured using Carr-Purcell-Meiboom-Gill (CPMG) sequences.
197
Typical parameters were as follows: echo time of 0.8 ms and waiting time of 5000 ms. Data
198
from 10000 echoes were acquired as 4 scan repetitions. Each measurement was performed in
199
twice. The T2 relaxation curve was fitted to a multi-exponential curve with included MultiExp
200
Inv Analysis software. LF-NMR measurements were conducted with three replicates for each
201
sample.
202
2.8. Statistical analysis
203
Statistical analysis was performed using the statistical program SPSS for Windows
204
(SPSS Inc., Chicago, IL, U.S.A.). One-way analysis of variance (ANOVA) was carried out,
205
and the comparison of means was performed using Duncan’s multiple range tests. Significant
206
differences were determined at P < 0.05.
207
3. Results and discussion
208
3.1. Particle size and zeta potential
209
The z-average particle size and PDI obtained from mixed dispersions and emulsions
210
were presented in Fig.1a. For the control sample egg yolk (EY), the particle size decreased
211
after adding NaCl (EY+), coinciding with a sharp drop in PDI. This result was consistent
212
with a previous study which demonstrated that the disruption of egg yolk granules after
213
addition of NaCl occurred (Anton et al., 2000). However, there is no obvious decrease in
214
particle size of κ-carrageenan after adding salt, although the PDI decreased, suggesting that
10
215
small amount of large aggregates was dissociated. Correspondingly, the particle size and PDI
216
of the mixed dispersions were decreased as the concentration of NaCl increased.
217
Interestingly, the particle size of the mixed dispersions was more dependent on κ-carrageenan
218
than egg yolk. This might be ascribed to the stabilization effect of κ-carrageenan on egg yolk
219
dispersions. It was note that the PDI of egg yolk/κ-carrageenan mixed dispersions was
220
obviously higher than that of egg yolk or κ-carrageenan dispersions, indicating the
221
occurrence of complex coacervation between egg yolk and κ-carrageenan. Furthermore, the
222
particle size and PDI of egg yolk/κ-carrageenan composite emulsions were decreased with
223
the increase of NaCl concentration. These results suggested that emulsions formulated by
224
disrupted yolk/κ-carrageenan complex were more homogenous than those made with the egg
225
yolk/κ-carrageenan hybrid system without NaCl.
226
The zeta potential of the mixed dispersions and emulsions were measured to analyze the
227
changes in surface potential with the increase level of NaCl. As shown in Fig. 1b, there was
228
no obvious difference of zeta potential between the mixed dispersions and emulsions at the
229
same concentration of NaCl but increasing NaCl concentrations indeed led to lower values of
230
zeta potential in each series of samples. This result was in agreement with a previous study,
231
which reported that the increase of ionic strength leads to lower zeta potential values for
232
κ-carrageenan solution (Carneiro-da-Cunha et al., 2011). The negative charge of
233
κ-carrageenan was significantly higher than egg yolk and this accounted for the low particle
234
size of egg yolk/κ-carrageenan mixed dispersions (as shown in Fig. 1a) where κ-carrageenan
235
provided enough electrostatic repulsion for egg yolk components. The zeta potential of the 11
236
mixed dispersions or emulsions was slightly higher than the simple egg yolk or κ-carrageenan
237
dispersions. This phenomenon could be due to the fact that the mixture of two kinds of
238
charged particles possessed the higher surface charge compared to the single charged
239
particles. As previously mentioned (Aguilar et al., 2017), increasing content of charged
240
particles (κ-carrageenan) in the egg yolk/k carrageenan hybrid systems showed an apparent
241
effect on the zeta potential.
242
3.2. Confocal laser scanning microscopy (CLSM)
243
CLSM was applied to illustrate the microstructure of the mixed dispersions and
244
emulsions fabricated by egg yolk and κ-carrageenan. The oil phase was stained by Nile red
245
while other components were dyed with FITC. Fig. 2 displayed the CLSM images of mixed
246
dispersions or emulsions before and after addition of NaCl (0.3 M). Apparently, the
247
aggregates of egg yolk or κ-carrageenan exhibited a dramatic decrease after addition of NaCl,
248
which was in accordance with the results obtained from dynamic light scattering. For the egg
249
yolk/κ-carrageenan mixed dispersions, the flocculation behaviors can be easily observed due
250
to the formation of the large highlighted flocculates. After addition of NaCl, the flocculation
251
phenomenon was obviously lessened. This result may be owed to two main factors: decreased
252
zeta potential and dissociation of egg yolk or κ-carrageenan aggregates. The former reduced
253
the interaction among egg yolk components and κ-carrageenan molecules and the latter
254
resulted in reduced possibility of large flocs formation. For the emulsions, the formation of
255
oil-in-water emulsions could be confirmed because the red fluorescence from nile red was
256
visualized in the interior of the droplets whereas the green fluorescence from FITC was 12
257
located at the perimeter of the droplets. The distribution of oil droplet of the egg
258
yolk/κ-carrageenan hybrid emulsion with 0.3 M NaCl was more homogenous than that of the
259
emulsion without NaCl. This is inconsistent with the whey protein stabilized o/w emulsions
260
containing xanthan gum at pH 7 (Sriprablom et al., 2019), which reported that the droplet
261
aggregation of emulsions was exacerbated at high ionic strengths (200 and 250 mM NaCl)
262
due to a decrease in the droplet zeta-potential. This opposite trend could be attributed to the
263
improving emulsifying properties of egg yolk when the NaCl concentration is increased (Li,
264
Wang, Li et al., 2018), leading to the formation of homogenous emulsified droplets thereby
265
preventing droplet aggregation.
266
3.3. Rheological characteristics
267
The flow behaviors of the mixed dispersions or emulsions were presented in Fig. 3. The
268
results showed that all samples showed a shear-thinning flow behavior. Fig. 3a showed that
269
with an increase in the level of NaCl, the viscosity of the mixed dispersions decreased. This
270
was due to the fact that strong hydration cation Na+ was unconducive to the hydration of
271
carrageenan molecules, leading to a decrease in hydrodynamic volume and viscometric
272
expansion factor of polysaccharide molecules (BrunchiMorariu & Bercea, 2014). Another
273
reason for this phenomenon is that the raised concentrations of counter-ions made the
274
polysaccharide molecules contracted and expressed as lower viscosities owing to the charge
275
shielding effect (Hao et al., 2018). As shown in Figs. 3a and 3b, the viscosity of emulsions
276
(shown in Fig. 3b) was elevated to the higher level than that of the mixed dispersions (shown
277
in Fig. 3a). Despite the existence of adverse effect from NaCl, the apparent viscosity of
13
278
emulsions (at 150 s-1, shown in Table 1) increased as the incorporation of sunflower oil into
279
the mixed dispersions. The natural high viscosity of plant oil and the unaltered concentration
280
of polysaccharide in aqueous phase may be the reason for the viscosity changes of emulsions.
281
The development of storage modulus (G´) during the thermal/cooling cycle of
282
yolk/κ-carrageenan dispersions and emulsions was shown in Fig. 4. For the mixed
283
dispersions (Fig. 4a), the higher the salt concentration was, the greater the gelation
284
temperature was (the beginning of the kinetics). In addition, Table 1 showed that the gelation
285
rates calculated from the slope of 20 s data point right after the onset of gelation were 0.02 Pa
286
s-1, 0.78 Pa s-1, 13.4 Pa s-1 and 31.1 Pa s-1 for the sample 0.0W, 0.1W, 0.2W and 0.3W,
287
respectively. The addition of NaCl reduced the net negative charge and thus lowered the
288
repulsive force among molecules, making the aggregation, entanglement and network
289
formation of gel molecules more prone to occur. The addition of NaCl may favor the
290
aggregation of carrageenan molecules by the competitive hydration, leading to the rapid
291
formation of gel network (Lai et al., 2000).
292
For the gelation behavior of emulsion samples, a similar pattern with the mixed
293
dispersions was observed during the heating/cooling process, although the terminal G' value
294
was lower. Furthermore, there was no obvious difference in the gelation point for both group
295
samples when the salt concentration was at the same level. This result may be due to the same
296
concentration of κ-carrageenan existed in water phase for both group samples. However, the
297
gelation rate of emulsions was significantly lower than the mixed dispersions under the same
298
concentration of NaCl. This result implied that the existence of oil may dilute the
14
299
concentration of κC in whole gel system and reduce the interaction of gel molecules.
300
Previous study had demonstrated that the gel storage (G’ at 1 rad/s) underwent an obvious
301
increase with the addition of κC into egg yolk gel (Aguilar et al., 2011). From the above
302
results, it can be clearly concluded that the gelation point of κC was related to the solution
303
environment whereas the gelation rate tend to be more dependent on the concentration of gel
304
molecules.
305
3.4. Textural analysis
306
The large-strain compression test - texture profile analysis (TPA), a simple and rapid
307
analytical technique, has been commonly used in the food industry. It is vital to explore the
308
possible application of ingredients in food products or develop a new food product. As
309
shown in Fig. 5a, the hardness of mixed hydrogels and emulsion gels showed a fluctuant
310
trend with the increasing NaCl level. Similar phenomenon was reported in other study that
311
with increasing cation concentration, the hardness of carrageenan systems increased to a
312
maximum value at a certain polysaccharide concentration and then decreased (Thrimawithana
313
et al., 2010). The cohesiveness of all gel samples showed a declining trend with the increase
314
of NaCl concentrations. The decrease of gel cohesiveness of κ-carrageenan could be related
315
to the formation of the aggregated structure with large voids with the addition of NaCl
316
(Walther et al., 2006). Decreased cohesiveness means that gels are brittle and easily broken
317
when gels are swallowed or homogenized. This feature was conducive to the formation of
318
micronized gel particles that is useful to prepare a fat analogue (Li et al., 2014). The
319
accelerated gelation rate and decreased particle size after the addition of NaCl in systems
15
320
might go against the tight entanglement among gel molecule chains, leading to the decrease
321
in the deformation tolerance of the resultant gels. Notably, this changes differ from the
322
previous G' response patterns which can be ascribed to the small strain (0.1%) used in the
323
rheological test.
324
The gum–salt interaction presented differences in gel fracture force and fracture distance
325
(Fig. 5b). The fracture distance exhibited the same changes as the above cohesiveness, while
326
the fracture force of all gels showed an increase with the increase in NaCl concentrations
327
except for the mixed hydrogel containing 0.3M NaCl (sample 0.3W). Furthermore, salt-free
328
gels presented the lowest fracture force values. It can be also clearly seen from Fig. 5b that
329
the fracture force of emulsion gels (0.0O, 0.1O, 0.2O and 0.3O) was obviously lower than
330
that of the mixed hydrogels (0.0W, 0.1W, 0.2W and 0.3W). This is consistent with the
331
observation from the above result of rheology. A possible explanation is that the decrease of
332
contact area of plunger with samples used in puncture test minimizes the effect of decreased
333
gel cohesiveness on the fracture force. Therefore, the results of fracture test show a better
334
agreement with those of rheological test than that of texture profile analysis.
335
3.5. LF-NMR spin–spin relaxation measurements
336
Low field NMR has been extensively used to study proton mobility in
337
protein/polysaccharide gel systems (Shao et al., 2016; Ye et al., 2019). Fig. 6 and Table 2
338
showed that four peaks were identified in the hydrogels or gelled emulsions through the
339
multi-exponential fitting of a T2 distribution which was used to assess relaxation time of
340
hydrogen protons. These four relaxation components: T2b (1-10 ms) has been assigned to the
16
341
water that exists in macromolecular structures or water of hydration; T21 (30-150 ms) mainly
342
refers to water that is tightly associated with macromolecules or oil existed in the gel
343
network; T22 (300–1000 ms) represents immobilized water which is located in the gel
344
network; and T23 (>1000 ms) can be designated as the free water (Au et al., 2015; Li, Li et
345
al., 2018; Shao et al., 2016). Fig. 6 and Table 2 showed the T2 relaxation spectra and
346
relaxation parameters of mixed hydrogels or emulsion gels at different level of NaCl. It can
347
be found that the T2b, T21 and T22 of the mixed hydrogels showed a declining trend with the
348
addition of NaCl, signifying that the addition of NaCl could strengthen the water holding
349
capacity of gels by increasing the gel strength. The proportion of peak area represented the
350
content of the four components of H proton in the mixed hydrogels or emulsion gels. PT2b,
351
PT21, PT22 and PT23 represent the areas of relaxation times T2b, T21, T22 and T23
352
respectively. As shown in Table 2, the PT2b and PT21 component of hydrogels (0.0W, 0.1W,
353
0.2W and 0.3W) decreased from 0.64%/3.78% (0.0% NaCl) to 0.09%/1.46% (3.0% NaCl),
354
indicating that the addition of NaCl decreased the hydration effects of protein/polysaccharide
355
molecules. Accordingly, the PT22 component of immobilized water increased with the
356
addition of NaCl.
357
For emulsion gel system, the existence of oil in gel structure had an immense impact on
358
the stability of water in yolk/κ-carrageenan emulsion gels. The relaxation time of T21 peak
359
for salty emulsion gels showed a significant increase after adding oil as compared to the
360
corresponding hydrogel samples while the related areas of relaxation was significantly
361
increased. The PT21 proportion was approximately consistent with amount of oil added.
17
It
362
was notable that there was an additional T23 peak for sample 0.0O. Furthermore, the PT21 of
363
0.0O was the minimum while the corresponding PT22 was the maximum among all emulsion
364
gels. These results indicated the emulsion gel without NaCl (0.0O) that possessed weakest gel
365
strength cannot effectively hold water/oil. As the NaCl concentration increased, the T22 and
366
PT22 simultaneously increased along with the decrease of T21 and PT21, indicating the oil
367
and water holding capacity of emulsion gels decreased. Based on the cumulative results
368
above, a possible mechanism could be proposed to explain the above phenomenon. With the
369
rise of salt concentration, the water holding capacity of hydrogels increased due to the
370
enhanced gel network, although the hydration capacity of gel molecules decreased. After
371
incorporation of oil in hydrogels, the repulsion effect of oil against water was further
372
strengthened by the increase of gel strength, leading to the instability of immobilized water in
373
gel network.
374
4. Conclusions
375
The concentration of NaCl had a significant effect on the flocculation behavior. As the
376
NaCl concentration increased, the decreased particle size and zeta potential were beneficial to
377
the decrease of aggregation level of egg yolk/κ-carrageenan mixed dispersions and the
378
increase of the oil droplets’ uniformity in emulsions, leading to the formation of a stiffer gel.
379
Meanwhile, the viscosity of the mixed dispersions decreased and the onset of gelation was
380
also brought forward with the increase of NaCl. LF-NMR analysis indicated that the
381
hydration ability of gel molecules tended to decrease after addition of NaCl which promoted
382
the aggregation of κ-carrageenan in the process of gel formation. After incorporation of oil in 18
383
the mixed dispersions, the gelation rate was decreased. Furthermore, the repulsion effect of
384
oil against water was also strengthened by the increase of gel strength, leading to the decrease
385
in water holding capacity of emulsion gels. However, more studies are still needed to know
386
about the behavior of the systems and their application by testing more variables besides the
387
NaCl concentration. In summary, the flocculation behavior and gel properties of egg
388
yolk/κ-carrageenan mixed dispersions/emulsion can be modulated by NaCl. And this will be
389
the base for the subsequent preparation of fat analogues and delivery carriers of nutrients.
390 391
Acknowledgments
392
This work was supported by the National Key Research and Development Program of
393
China (No. 2018YFD0400303), the Natural Science Foundation of Jiangsu Province for the
394
Youth (No. BK20180610), the National Natural Science Foundation for the Youth of China
395
(No. 31801483), the Fundamental Research Funds for the Central Universities
396
(JUSRP11902), and the project of China Scholarship Council.
397 398
References
399
Abaee, A., Mohammadian, M., & Jafari, S. M. (2017). Whey and soy protein-based
400
hydrogels and nano-hydrogels as bioactive delivery systems. Trends in Food Science
401
& Technology, 70, 69-81.
402
Aguilar, J. M., Batista, A. P., Nunes, M. C., Cordobés, F., Raymundo, A., & Guerrero, A.
403
(2011). From egg yolk/κ-Carrageenan dispersions to gel systems: Linear
19
404
viscoelasticity and texture analysis. Food Hydrocolloids, 25 (4), 654-658.
405
Aguilar, J. M., Cordobés, F., Raymundo, A., & Guerrero, A. (2017). Thermal gelation of
406
mixed egg yolk/kappa-carrageenan dispersions. Carbohydrate Polymers, 161,
407
172-180.
408
Anton, M., Beaumal, V., & Gandemer, G. (2000). Adsorption at the oil-water interface and
409
emulsifying properties of native granules from egg yolk : effect of aggregated state.
410
Food Hydrocolloids, 14 (4), 327-335.
411
Anton, M., Le Denmat, M., Beaumal, V., & Pilet, P. (2001). Filler effects of oil droplets on
412
the rheology of heat-set emulsion gels prepared with egg yolk and egg yolk fractions.
413
Colloids and Surfaces B: Biointerfaces, 21 (1–3), 137-147.
414
Au, C., Acevedo, N. C., Horner, H. T., & Wang, T. (2015). Determination of the gelation
415
mechanism of freeze–thawed hen egg yolk. Journal of Agricultural and Food
416
Chemistry, 63 (46), 10170-10180.
417
Brunchi, C.-E., Morariu, S., & Bercea, M. (2014). Intrinsic viscosity and conformational
418
parameters of xanthan in aqueous solutions: Salt addition effect. Colloids and
419
Surfaces B: Biointerfaces, 122, 512-519.
420
Carneiro-da-Cunha, M. G., Cerqueira, M. A., Souza, B. W. S., Teixeira, J. A., & Vicente, A.
421
A. (2011). Influence of concentration, ionic strength and pH on zeta potential and
422
mean hydrodynamic diameter of edible polysaccharide solutions envisaged for
423
multinanolayered films production. Carbohydrate Polymers, 85 (3), 522-528.
424
Castellani, O., Belhomme, C., Davidbriand, E., Guerindubiard, C., & Anton, M. (2006).
20
425
Oil-in-water emulsion properties and interfacial characteristics of hen egg yolk
426
phosvitin. Food Hydrocolloids, 20 (1), 35-43.
427
de Souza Paglarini, C., de Figueiredo Furtado, G., Biachi, J. P., Vidal, V. A. S., Martini, S.,
428
Forte, M. B. S., Cunha, R. L., & Pollonio, M. A. R. (2018). Functional emulsion gels
429
with potential application in meat products. Journal of Food Engineering, 222, 29-37.
430
Francis, F. P., & Chidambaram, R. (2019). Hybrid hydrogel dispersed low fat and heat
431
resistant chocolate. Journal of Food Engineering, 256, 9-17.
432
Gaber, M., Mabrouk, M. T., Freag, M. S., Khiste, S. K., Fang, J.-Y., Elkhodairy, K. A., &
433
Elzoghby, A. O. (2018). Protein-polysaccharide nanohybrids: Hybridization
434
techniques and drug delivery applications. European Journal of Pharmaceutics and
435
Biopharmaceutics, 133, 42-62.
436
Geremias-Andrade, M. I., Souki, P. B. G. N., Moraes, C. F. I., & Pinho, C. S. (2016).
437
Rheology of emulsion-filled gels applied to the development of food materials. Gels,
438
2 (3), 1-18.
439
Gmach, O., Bertsch, A., Bilke-Krause, C., & Kulozik, U. (2019). Impact of oil type and pH
440
value on oil-in-water emulsions stabilized by egg yolk granules. Colloids and
441
Surfaces A: Physicochemical and Engineering Aspects, 581, 123788.
442
Gravelle, A. J., Nicholson, R. A., Barbut, S., & Marangoni, A. G. (2019). Dataset on the
443
elastic modulus of heat-set whey protein isolate/xanthan gum mixed biopolymer
444
hydrogels filled with glass microspheres: A model particle-filled composite food
445
system. Data in Brief, 25, 104066.
21
446
Hao, Z.-q., Chen, Z.-j., Chang, M.-c., Meng, J.-l., Liu, J.-y., & Feng, C.-p. (2018).
447
Rheological properties and gel characteristics of polysaccharides from fruit-bodies of
448
Sparassis crispa. International Journal of Food Properties, 21 (1), 2283-2295.
449
Kara, S., Arda, E., Kavzak, B., & Pekcan, Ö. (2006). Phase transitions of κ-carrageenan gels
450
in various types of salts. Journal of Applied Polymer Science, 102 (3), 3008-3016.
451
Khalesi, H., Emadzadeh, B., Kadkhodaee, R., & Fang, Y. (2019). Effect of Persian gum on
452
whey protein concentrate cold-set emulsion gel: Structure and rheology study.
453
International Journal of Biological Macromolecules, 125, 17-26.
454
Lai, V. M. F., Wong, P. A. L., & Lii, C. Y. (2000). Effects of cation properties on sol-gel
455
transition and gel properties of κ-carrageenan. Journal of Food Science, 65 (8),
456
1332-1337.
457 458
Lee, C. M., & Chung, K. H. (1989). Analysis of surmi gel properties by compression and penetration tests. Journal of Texture Studies, 20 (3), 363-377.
459
Li, J., Li, X., Wang, C., Zhang, M., Xu, Y., Zhou, B., Su, Y., & Yang, Y. (2018).
460
Characteristics of gelling and water holding properties of hen egg white/yolk gel with
461
NaCl addition. Food Hydrocolloids, 77, 887-893.
462
Li, J., Wang, C., Li, X., Su, Y., Yang, Y., & Yu, X. (2018). Effects of pH and NaCl on the
463
physicochemical and interfacial properties of egg white/yolk. Food Bioscience, 23,
464
115-120.
465
Li, J., Wang, C., Zhang, M., Zhai, Y., Zhou, B., Su, Y., & Yang, Y. (2018). Effects of
466
selected phosphate salts on gelling properties and water state of whole egg gel. Food
22
467 468 469
Hydrocolloids, 77, 1-7. Li, J., Wang, Y., Jin, W., Zhou, B., & Li, B. (2014). Application of micronized konjac gel for fat analogue in mayonnaise. Food Hydrocolloids, 35, 375-382.
470
Liu, Q.-R., Qi, J.-R., Yin, S.-W., Wang, J.-M., Guo, J., Feng, J.-L., Cheng, M., Cao, J.,
471
Weng, J.-Y., & Yang, X.-Q. (2016). The influence of heat treatment on acid-tolerant
472
emulsions prepared from acid soluble soy protein and soy soluble polysaccharide
473
complexes. Food Research International, 89, 211-218.
474
Lopes-da-Silva, J. A., & Monteiro, S. R. (2019). Gelling and emulsifying properties of soy
475
protein hydrolysates in the presence of a neutral polysaccharide. Food Chemistry,
476
294, 216-223.
477
Montes de Oca-Ávalos, J. M., Huck-Iriart, C., Candal, R. J., & Herrera, M. L. (2016).
478
Sodium caseinate/sunflower oil emulsion-based gels for structuring food. Food and
479
Bioprocess Technology, 9 (6), 981-992.
480
Panyathitipong, W., & Puechkamut, Y. (2010). Effect of tofu powder and carrageenan on
481
functionality and physical characteristics of surimi emulsion gel. Kasetsart J (Nat
482
Sci), 44, 671-679.
483
Pintado, T., Herrero, A. M., Jiménez-Colmenero, F., Pasqualin Cavalheiro, C., &
484
Ruiz-Capillas, C. (2018). Chia and oat emulsion gels as new animal fat replacers and
485
healthy bioactive sources in fresh sausage formulation. Meat Science, 135
486
(Supplement C), 6-13.
487
Prajapati, V. D., Maheriya, P. M., Jani, G. K., & Solanki, H. K. (2014). Carrageenan: a
23
488
natural seaweed polysaccharide and its applications. Carbohydrate Polymers, 105,
489
97-112.
490 491
Rochas, C., & Rinaudo, M. (1984). Mechanism of gel formation in κ‐carrageenan. Biopolymers: Original Research on Biomolecules, 23 (4), 735-745.
492
Serdaroğlu, M., Nacak, B., & Karabıyıkoğlu, M. (2017). Effects of beef fat replacement with
493
gelled emulsion prepared with olive oil on quality parameters of chicken patties.
494
Korean journal for food science of animal resources, 37 (3), 376.
495
Shao, J., Deng, Y., Jia, N., Li, R., Cao, J., Liu, D., & Li, J. (2016). Low-field NMR
496
determination of water distribution in meat batters with NaCl and polyphosphate
497
addition. Food Chemistry, 200, 308-314.
498
Sriprablom, J., Luangpituksa, P., Wongkongkatep, J., Pongtharangkul, T., & Suphantharika,
499
M. (2019). Influence of pH and ionic strength on the physical and rheological
500
properties and stability of whey protein stabilized o/w emulsions containing xanthan
501
gum. Journal of Food Engineering, 242, 141-152.
502 503
Steiner, B. M., McClements, D. J., & Davidov-Pardo, G. (2018). Encapsulation systems for lutein: A review. Trends in Food Science & Technology, 82, 71-81.
504
Su, J., Guo, Q., Chen, Y., Dong, W., Mao, L., Gao, Y., & Yuan, F. (2020). Characterization
505
and formation mechanism of lutein pickering emulsion gels stabilized by
506
β-lactoglobulin-gum arabic composite colloidal nanoparticles. Food Hydrocolloids,
507
98, 105276.
508
Sun, L., Chen, W., Liu, Y., Li, J., & Yu, H. (2015). Soy protein isolate/cellulose nanofiber
24
509
complex gels as fat substitutes: rheological and textural properties and extent of cream
510
imitation. Cellulose, 22 (4), 2619-2627.
511
Tabilo-Munizaga, G., & Barbosa-Cánovas, G. V. (2004). Color and textural parameters of
512
pressurized and heat-treated surimi gels as affected by potato starch and egg white.
513
Food Research International, 37 (8), 767-775.
514
Thrimawithana, T. R., Young, S., Dunstan, D. E., & Alany, R. G. (2010). Texture and
515
rheological characterization of kappa and iota carrageenan in the presence of counter
516
ions. Carbohydrate Polymers, 82 (1), 69-77.
517
Torres, O., Murray, B. S., & Sarkar, A. (2016). Emulsion microgel particles: Novel
518
encapsulation strategy for lipophilic molecules. Trends in Food Science and
519
Technology, 55, 98-108.
520
Valverde, D., Laca, A., Estrada, L. N., Paredes, B., Rendueles, M., & Díaz, M. (2016). Egg
521
yolk and egg yolk fractions as key ingredient for the development of a new type of
522
gels. International Journal of Gastronomy and Food Science, 3, 30-37.
523
Walther, B., Lorén, N., Nydén, M., & Hermansson, A.-M. (2006). Influence of κ-carrageenan
524
gel structures on the diffusion of probe molecules determined by transmission
525
electron microscopy and NMR diffusometry. Langmuir, 22 (19), 8221-8228.
526
Yampol’skaya, G., Elenskii, A., Pan’kina, N., Tarasevich, B., & Kulichikhin, V. (2009).
527
Properties of carrageenan gels with immobilized lysozyme. Colloid Journal, 71 (2),
528
271.
529
Ye, T., Dai, H., Lin, L., & Lu, J. (2019). Employment of κ-carrageenan and high pressure
25
530
processing for quality improvement of reduced NaCl surimi gels. Journal of Food
531
Processing and Preservation, 43 (9), e14074.
532
Zang, X., Wang, J., Yu, G., & Cheng, J. (2019). Addition of anionic polysaccharides to
533
improve the stability of rice bran protein hydrolysate-stabilized emulsions. LWT, 111,
534
573-581.
535
Zhou, M., Wang, T., Hu, Q., & Luo, Y. (2016). Low density lipoprotein/pectin complex
536
nanogels as potential oral delivery vehicles for curcumin. Food Hydrocolloids, 57,
537
20-29.
538 539 540 541 542 543 544 545 546 547 548 549 550
26
551 552 553
Figure captions:
554
Fig. 1. Z-average particle size, polydispersity index (a) and zeta potential (b) of egg yolk and
555
κ-carrageenan composite dispersions and emulsions at different NaCl concentrations (0.0, 0.1,
556
0.2 and 0.3 mol/L). Four reference samples: egg yolk (EY), egg yolk with 0.3 M NaCl (EY+),
557
κ-carraggeenan (κC) and κ-carraggeenan with 0.3 M NaCl (κC+). Colum graphs represent the
558
z-average particle size (a) and zeta potential (b); scatter graph represents the polydispersity
559
index. Error bars represent standard deviations from four replicates. Different uppercase or
560
lowercase letters indicate significant differences (P < 0.05).
561
Fig. 2. The CLSM observations of egg yolk and/or κ-carrageenan dispersions and emulsion
562
prepared without and with 0.3 M NaCl. Green and red micrographs were dyed by fluorescein
563
isothiocyanate (FITC) and nile red (NR), respectively.
564
Fig. 3. Flow curves of egg yolk and κ-carrageenan composite dispersions (a) and emulsions
565
(b) at the NaCl concentrations ranged from 0.0 to 0.3 M.
566
Fig. 4. Changes in the storage moduli (G´) of egg yolk and κ-carrageenan composite
567
dispersions (a) and emulsions (b) under different NaCl concentrations (0.0, 0.1, 0.2 and 0.3
568
M) with temperature.
569
Fig. 5. Textural analysis of egg yolk/κ-carrageenan composite hydrogels and emulsion gels.
570
(a) Texture profile analysis (TPA); (b) Puncture test. Colum graphs represent the hardness (a)
571
and fracture force (b); scatter graphs represent the cohesiveness (a) and fracture distance (b).
27
572
Error bars represent standard deviations from six replicates. Different uppercase or lowercase
573
letters indicate significant differences (P < 0.05).
574
Fig. 6. The curves of relaxation time T2 of egg yolk and κ-carrageenan composite hydrogels
575
(a) and emulsion gels (b) at different NaCl concentrations.
576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592
28
593 594
Z-average particle size Polydispersity index
A
5000
D
b
bc
b
E
2500
b
b E c
cd
c
500
FG
F
0.4
G H
e
I
0.2 0
595
0
Zeta potential (mV)
-10
f
g
-20 -30 -40
e
-50
Zeta potentiala
E EY Y +
-60
d a
ab
596 597
c
a
a
b
c
kC kC 0. + 0W 0. 1W 0. 2W 0. 3W 0. 0O 0. 1O 0. 2O 0. 3O
b
0.6
d
d F
0.8
C
Fig. 1
29
Polydispersity index
B
a
E EY Y + kC kC 0. + 0W 0. 1W 0. 2W 0. 3W 0. 0O 0. 1O 0. 2O 0. 3O
Z-average particle size (nm)
a 7500
598 599
Fig. 2
600 601
30
Viscosity (Pa.s)
a100
0.0W 0.1W 0.2W 0.3W
10
1
0.1
0
50
602
100 150 200 Shear rate (1/s)
250
Viscosity (Pa.s)
b100
604
0.0O 0.1O 0.2O 0.3O
10
1
0.1 603
300
0
50
100 150 200 Shear rate (1/s)
Fig. 3
605
31
250
300
100
a2000
80 60
G' (Pa)
0.0W 0.1W 0.2W 0.3W Temperature
1000 500
Temperature (C)
1500
40 20
0 0
200
400 600 Time (s)
800
1000 1200
606
100
b 750 G' (Pa)
450
60
0.0O 0.1O 0.2O 0.3O Temperature
300 150
40 20
0 0
200
400 600 Time (s)
607 608
Fig. 4
32
800
1000 1200
Temperature (C)
80
600
a A b
400
b
B
C
0.6
300 c
200
f
100
0.4
d
e
D
g
E F
G
0.2
H
0.0
0 0 .0
609
b
W .1 W .2 W .3 W .0 O .1 O .2 O .3 O 0 0 0 0 0 0 0
350
Fracture force (g)
Fracture force (g) Fracture distance (mm)
A a
300
6
B
C
5
b
250 200
4
150
c
100 50
G
d
G
f
c
E
F
d
D
3 e
2
0 0 .0
W .1 W .2 W .3 W .0 O .1 O .2 O .3 O 0 0 0 0 0 0 0
610 611 612
0.8
Fig. 5
33
Fracture distance (mm)
Hardness (g)
Hardness (g) Cohesiveness
Cohesiveness
a500
a300
0.0W 0.1W 0.2W 0.3W
Proportion
250 200 150 100 50 0 1
10
100 1000 Time (ms)
10000
100 1000 Time(ms)
10000
613
b140
0.0O 0.1O 0.2O 0.3O
120
Proportion
100 80 60 40 20 0 1
10
614 615 616 617 618 619 620
Fig. 6
34
621 622
Table 1 Parameters of the rheological characteristics of egg yolk and κ-carrageenan mixed dispersions/hydrogels and emulsions/emulsion
623
gels (b) at different NaCl concentrations 0.0W
0.1W
0.2W
0.3W
0.0O
0.1O
0.2O
0.3O
Viscosity (Pa.s at150 s-1) 0.40±0.02c 0.25±0.01e 0.20±0.01f 0.18±0.01f 0.65±0.03a 0.52±0.03b 0.33±0.02d 0.25±0.02e
624
Onset of gelation (℃)
25.4±1.0d
32.5±1.0b
34.5±0.6a
25.5±1.3d
Gelation rate (Pa s-1)
0.02±0.01g 0.78±0.08e 13.4±0.9b
31.1±1.5a
0.09±0.07g 0.51±0.10f
28.4±1.1c
Different lowercase in the same row indicate significant differences (P < 0.05).
625 626 627 628 629 630 631 632 633 634 635 636 637 35
28.4±1.2c
32.5±1.2b
35.5±0.8a
4.92±0.45d 6.16±0.75c
638
Table 2 T2 relaxation parameters of mixed hydrogels or emulsion gels with different NaCl
639
0.0W
0.1W
0.2W
0.3W
0.0O
T2b
7.07±0.00d
6.44±0.20e
3.37±0.11f
2.55±0.08g
T21
81.85±0.00b
78.15±2.40c
54.00±1.78f
32.48±1.08g
T22
787.62±0.00a 752.06±24.0b 685.67±23.0c 654.71±20.9d 382.74±0.0f 519.65±16.59e 752.06±24.01b 752.06±24.0b
T23
58.72±1.8e
0.2O
0.3O
7.75±0.20b
9.01±0.22a
7.31±0.20c
124.06±3.96a
77.52±2.30c
72.32±2.25d
3783.46±6.3
PT2b
0.64±0.01a
0.46±0.01b
0.16±0.01e
0.09±0.01f
PT21
3.78±0.05e
3.65±0.04f
2.23±0.2g
1.46±0.15h
PT22
95.58±0.10d
95.89±0.15c
97.61±0.3b
98.45±0.3a
0.08±0.01f
0.27±0.01c
0.24±0.01d
21.48±0.1d
35.41±0.1a
31.88±0.2b
30.78±0.15c
78.21±0.08e
64.51±0.05h
67.85±0.04g
68.98±0.08f
0.31±0.01 640
0.1O
Different lowercase in the same row indicate significant differences (P < 0.05).
641 642
36
643 644
Graphical abstract
645 646
37
Highlights
647 648
1. Addition of NaCl could lessen the flocculation of egg yolk and κ-carrageenan.
649
2. The viscoelasticity of hydrogels depended on the aggregation of gel molecules.
650
3. The decreased hydration ability of gel molecules against the water/oil trapping.
651
4. Water holding capacity of emulsion gels was depressed by oil.
652
Author Contribution Statement
653 654 655
Junhua Li and Lilan Xu: Conceptualization, Methodology, Investigation, Writing- Original draft preparation
656
Yujie Su and Cuihua Chang: Writing- Reviewing and Editing.
657
Yanjun Yang and Luping Gu: Supervision
658 659 660
Conflict of interest statement
661
The authors declare no conflict of interest.
662
38
S0963-9969(20)30015-6 https://doi.org/10.1016/j.foodres.2020.108990 FRIN 108990
To appear in:
Food Research International
Received Date: Revised Date: Accepted Date:
14 October 2019 29 November 2019 6 January 2020
Please cite this article as: Li, J., Xu, L., Su, Y., Chang, C., Yang, Y., Gu, L., Flocculation behavior and gel properties of egg yolk/κ-carrageenan composite aqueous and emulsion systems: effect of NaCl, Food Research International (2020), doi: https://doi.org/10.1016/j.foodres.2020.108990
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier Ltd.
1
Flocculation behavior and gel properties of egg yolk/κ-carrageenan
2
composite aqueous and emulsion systems: effect of NaCl
3 4
Junhua Lia, b, c, #, Lilan Xua, b, c, #, Yujie Su a, b , c, Cuihua Chang a, b, c, Yanjun Yang a, b, c, *,
5
Luping Gu a, b, c, *
6
a State
7
214122, PR China
8
b
9
China
Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu,
School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu, 214122, PR
10
c
11
Jiangnan University, Wuxi, Jiangsu, 214122, PR China
Collaborative Innovation Center of Food Safety and Quality Control in Jiangsu Province,
12 13 14 15
*Corresponding author.
16
E-mail address: [email protected]; [email protected]
17
#
These authors contributed equally.
18 19 20 21 22 23 24 25 1
26
ABSTRACT
27
In this study, the influence of NaCl on the flocculation behavior and gel properties of
28
egg yolk/κ-carrageenan mixed dispersions or emulsions were studied. As a result of NaCl
29
incorporation, there was a decrease in the mean droplet size, zeta potential, degree of
30
flocculation and viscosity of the mixed dispersions/emulsions, and the onset point of gelation
31
was also brought forward. Increasing the concentration of NaCl led to a significant increase
32
in gel strength and decrease in gel cohesiveness. Results from low field nuclear magnetic
33
resonance (LF-NMR) confirmed that the addition of NaCl could significantly reduce the
34
hydration ability of gel molecules and increase the content of immobilized water of hydrogels
35
as the gel strength increased, while the water holding capacity of emulsion gels was
36
depressed with the incorporation of oil. These findings suggested the flocculation state and
37
gel properties of egg yolk/κ-carrageenan mixed dispersions/emulsions can be tailored by
38
adjusting NaCl for food formulations.
39
Keywords: Egg yolk, κ-carrageenan, flocculation behavior, rheological characteristics,
40
low-field nuclear magnetic resonance
41 42 43 44 45 46
2
47
1. Introduction
48
Hydrogels, constructed from one or more polymers such as protein and polysaccharide
49
suspended in water, are useful in the formation of novel food structure or as bioactive
50
delivery systems (AbaeeMohammadian & Jafari, 2017; Francis & Chidambaram, 2019;
51
Gravelle et al., 2019; Valverde et al., 2016). Nonetheless, one drawback of hydrogels in
52
practical applications is the limited solubility for lipophilic components. Up to date, many
53
oil-soluble nutrients such as lutein are usually added to the emulsion delivery systems to
54
improve their stability and bioavailability (SteinerMcClements & Davidov-Pardo, 2018; Su et
55
al., 2020). Among different emulsion systems, emulsion gels, existed as both an emulsion and
56
a gel, exhibit great potential applications in the improvement of thermo-dynamic stability,
57
texture modification, and encapsulation of both lipophilic and hydrophilic components
58
(Montes de Oca-Ávalos et al., 2016; Pintado et al., 2018; TorresMurray & Sarkar, 2016). So
59
it is promising for emulsion gels to be used as food material in the development of the
60
fortified foods.
61
Emulsion gels are common soft solid materials and are complex colloids formed by
62
matrices of polymeric gels into which emulsion droplets are incorporated (Geremias-Andrade
63
et al., 2016). The emulsion gel could be fabricated from the food-grade proteins or
64
polysaccharides. The properties of emulsion gels are highly dependent on the polymers used.
65
Recent developments of protein and polysaccharide hybrid delivery system and fat replacer
66
have attracted much attention (de Souza Paglarini et al., 2018; Gaber et al., 2018;
67
SerdaroğluNacak & Karabıyıkoğlu, 2017; Sun et al., 2015). A previous study has
3
68
demonstrated the beneficial effects of a polysaccharide on the improvement of gelling and
69
emulsifying properties of soy protein hydrolysates under certain conditions (Lopes-da-Silva
70
& Monteiro, 2019). Increasing carrageenan could improve the stability of the emulsion and
71
hardness of the surimi emulsion gels (Panyathitipong & Puechkamut, 2010). Compared with
72
simple protein-based emulsion gel system, protein-polysaccharide based emulsion gel
73
showed better oil/water stability (Khalesi et al., 2019; Liu et al., 2016). This may be ascribed
74
to the fact that polysaccharide could increase thickness of interfacial layer and viscosity of
75
aqueous phase to improve emulsion stability (Zang et al., 2019). Meanwhile, polysaccharide
76
could form gels in the presence of saline ions due to ion bridging interaction (Kara et al.,
77
2006), which has a positive effect on the properties of emulsion gels.
78
Egg yolk was often used as the main amphiphilic component in medium/high internal
79
phase emulsions like salad dressings or mayonnaise due to their excellent emulsifying
80
properties. All constituents of yolk proteins (low-density lipoproteins (LDL), high-density
81
lipoproteins (HDL), livetin and phosvitin) have a strong propensity to adsorb at the oil–water
82
interface and have been applied in the fabrication of emulsion (Castellani et al., 2006; Gmach
83
et al., 2019; Zhou et al., 2016). Furthermore, it was found that the presence of NaCl in
84
solution could change the aggregated state of egg yolk granules, leading to an improvement
85
of emulsion stability (AntonBeaumal & Gandemer, 2000). Our previous study demonstrated
86
that the emulsifying activity and stability of yolk exhibited an increase trend when the
87
concentration of NaCl was less than 1.8% (approximately 0.3 M) (Li, Wang, Li et al., 2018).
88
Carrageenan was a kind of linear, sulfated polysaccharide extracted from various species
4
89
of the Rhodophyta. Owing to its excellent bulking, gelling or thickening properties,
90
carrageenan was widely used as a food additive in the production of processed foods,
91
including dairy products, water-based foods, meat products and beverages (Prajapati et al.,
92
2014). It was reported that the types and concentrations of cation played important roles in
93
the formation of κ-carrageenan gel (LaiWong & Lii, 2000; Rochas & Rinaudo, 1984).
94
Although Na+ is not considered as the specific ions that affect the gelation of κ-carrageenan,
95
it is still efficient to prepare gels with the necessary structure and rheological properties in the
96
present of NaCl (Yampol’skaya et al., 2009).
97
Previous studies had showed the importance of electrostatic interactions in the degree of
98
compatibility between egg yolk and κ-carrageenan and the viscoelastic properties of mixed
99
egg yolk/κ-carrageenan gels at different pH and polysaccharide concentrations (Aguilar et al.,
100
2011; Aguilar et al., 2017). However, the flocculation behavior and hydrogel or emulsion gel
101
properties of egg yolk/κ-carrageenan hybrid systems have not been sufficiently studied,
102
particularly in different NaCl conditions. Both the functional properties of egg yolk and
103
κ-carrageenan are highly dependent on salt concentration used. Therefore, the objective of the
104
present study was to evaluate the emulsifying and gelling properties of egg
105
yolk/κ-carrageenan hybrid system under different concentrations of NaCl. The possible
106
mechanism of gelation in this system affected by NaCl and oil fill was also discussed. The
107
results obtained from this study may contribute to the development of hydrogel/emulsion
108
gel-based food products specifically designed for functional applications, such as
109
replacement of dietary saturated fats or enhanced delivery of lipophilic nutrients.
5
110
2. Materials and Methods
111
2.1. Materials
112
Fresh hen eggs and sunflower oil were purchased from a local market. Egg yolk
113
(average solid content: 50.5%, protein content: 17.5%, pH 6.4) was carefully separated from
114
egg white. κ-carrageenan (CAS number: 11114-20-8) and NaCl were obtained from Aladdin
115
Industrial Corporation (Shanghai, China). All other reagents used were of analytical grade
116
and were used without further purification.
117
2.2. Sample preparation
118
The mixed aqueous dispersions of egg yolk/κ-carrageenan were prepared according to
119
the following procedure. Briefly, 5 g egg yolk and 1 g κ-carrageenan were dispersed in 90
120
mL of deionized water and then adjusted to pH 7.0 with 0.1 M NaOH solution in a magnetic
121
stirrer (150 rpm) at room temperature for 2 h. Then, dissolve NaCl in above mixture and
122
dilute with deionized water to 100 mL to obtain the final mixed dispersions with the different
123
NaCl concentrations (0.0, 0.1, 0.2 and 0.3 M) in the mixture above. What needs to be pointed
124
out was that the concentrations of egg yolk and κ-carrageenan used in this study were based
125
on preliminary tests which had confirmed the emulsion gel can form under these conditions.
126
Samples of mixed aqueous dispersions were termed as 0.0W, 0.1W, 0.2W and 0.3W
127
according to the NaCl content of each sample. The oil-in-water emulsions (named as 0.0O,
128
0.1O 0.2Oand 0.3O) were prepared by homogenizing the above mixed dispersions with
129
sunflower oil (60% water phase: 40% oil phase, v/v) utilizing a high-speed mixer (IKA T25,
130
Germany) at 11,000 rpm for 4 min at room temperature.
6
131
The hydrogels and emulsion gels based on egg yolk and κ-carrageenan were prepared as
132
follows: the mixed dispersions and oil-in-water emulsions as described above were separately
133
added to glass beaker, heated in a water bath at 90 °C for 30 min, and then
134
immediately cooled down using tap water to induce gel formation. The obtained hydrogels
135
and emulsion gels were kept overnight at 4 ℃ prior to analysis.
136
2.3. Particle size and zeta potential
137
Droplet size, polydispersity index and zeta potential of mixed dispersions and emulsions
138
were determined by dynamic light scattering (DLS) using a Zetasizer Nano-ZS90 (Malvern
139
Instruments, Worcestershire, UK) at a fixed detector angle of 173°. Results were described as
140
z-average particle diameter (size, nm) for droplet size, polydispersity index (PDI) for particle
141
size distribution and zeta-potential (mV) for particle electric charge data, respectively. Prior
142
to each measurement, samples were diluted with deionized water to the final concentration of
143
0.025% (w/v) egg yolk and 0.005% (w/v) κ-carrageenan minimize multiple scattering effects.
144
All above measurements were conducted with 4 replicates at room temperature
145
2.4. Confocal laser scanning microscopy (CLSM)
146
The microstructure of the samples before gelation was observed using confocal laser
147
scanning microscopy (LSM710, Zeiss, Oberkochen, Germany). Samples applied in
148
observation were dyed using a mixed staining solution containing fluorescein isothiocyanate
149
(FITC) solution (0.1 g/L) and Nile Red (0.1 g/L) and then smeared over the microscopy slide
150
and gently covered with a glass slip. Samples were excited at 488 nm and detected
151
sequentially at 500-550 (FITC channel) and 600-700 nm (Nile red channel). Representative
7
152
images were chosen from at least three similar images.
153
2.5. Rheological characteristics
154
The flow behavior and gelation process of yolk/κ-carrageenan dispersions or emulsions
155
were studied using a DHR-3 rheometer (TA Instruments, USA) equipped with a steel
156
cone-plate geometry (diameter: 6 cm, angle: 4o, truncation: 53 µm). Each sample was
157
carefully deposited over the plateau of the rheometer. Samples were held at 25 ℃ for 60 s to
158
equilibrate before data collection. Apparent viscosity (η) of the samples was recorded at shear
159
rates (γ) over the range of 0.1 – 300 s-1 for 5 min at 25 ℃.
160
The gelation protocol involved successive heating and cooling cycles. For each
161
measurement, 4 mL of solution or emulsion was carefully transferred onto the steel plateau.
162
After the plateau has been brought to contact with the cone, a thin layer of low-viscosity
163
silicone oil was spread on the edge of plate to prevent water evaporation during
164
measurements. Heat gelation was induced at the 1 Hz and 0.1% strain by: (1) equilibrating
165
the sample at 25 ℃ for 1 min; (2) heating the sample to 90 ℃ at a rate of 10 K/min; (3)
166
cooling at a rate of 10 K/min from 90 ℃ to 25 ℃; and holding at 25 oC for 5 min. The onset
167
of gelation temperature was designated as the beginning of exponential growth regime of the
168
storage modulus (G´) (Anton et al., 2001). The gelation rate was calculated by linear fitting
169
approach that data was intercepted from the first 20 seconds right after the onset of gelation
170
temperature. All tests were performed in duplicate.
171
2.6. Textural analysis
172
Textural properties of the mixed hydrogels and emulsion gels were analyzed using 8
173
compression and penetration tests. The compression test is useful in assessing the cohesive
174
property of gels, while the penetration test is better for assessing density and compactness
175
(Lee & Chung, 1989). They can reflect the gel textural properties from different aspects. The
176
compression test, texture profile analysis (TPA), was performed at ambient temperature with
177
a TA-XT plus Texture Analyzer (Texture Technologies Corp., UK) and a 1 kg load cell. The
178
mixed gels were cylinders with 15 mm height and 20 mm diameter. Each sample was
179
compressed axially in two consecutive cycles of 50% compression, 5 s interval, with a flat
180
plunger 25 mm in diameter (SMS-P/25). The cross-head moved at a constant speed of 2 mm/s.
181
TPA curves were recorded and hardness and cohesiveness of samples were calculated.
182
Hardness was defined by peak force during the first compression cycle. Cohesiveness was
183
calculated as the ratio of the area under the second curve to the area under the first curve. Six
184
replicates were conducted for each sample.
185
A penetration test was also carried out using the TA-XT plus Texture Analyzer at
186
ambient temperature. A P/0.5 plunger with a diameter of 5 mm was used to penetrate 50% of
187
the sample length (sample size: 25 mm diameter×12 mm length) and the first peak of the
188
curve was used as fracture force. The results were expressed in terms of the fracture force (g)
189
and fracture distance (mm) (Tabilo-Munizaga & Barbosa-Cánovas, 2004). Six replicates were
190
conducted for each sample.
191
2.7. Low field nuclear magnetic resonance (LF-NMR) measurements
192
Low field nuclear magnetic resonance measurements (NMI20-Analyst, Niumag Electric
193
Corporation, Shanghai, China) were performed according to the previous method (Li, Wang, 9
194
Zhang et al., 2018) with minor modification. The cylindrical gel sample (15 mm height, 20
195
mm diameter) was placed in a glass tube and inserted in the NMR probe. The spin–spin
196
relaxation time (T2) was measured using Carr-Purcell-Meiboom-Gill (CPMG) sequences.
197
Typical parameters were as follows: echo time of 0.8 ms and waiting time of 5000 ms. Data
198
from 10000 echoes were acquired as 4 scan repetitions. Each measurement was performed in
199
twice. The T2 relaxation curve was fitted to a multi-exponential curve with included MultiExp
200
Inv Analysis software. LF-NMR measurements were conducted with three replicates for each
201
sample.
202
2.8. Statistical analysis
203
Statistical analysis was performed using the statistical program SPSS for Windows
204
(SPSS Inc., Chicago, IL, U.S.A.). One-way analysis of variance (ANOVA) was carried out,
205
and the comparison of means was performed using Duncan’s multiple range tests. Significant
206
differences were determined at P < 0.05.
207
3. Results and discussion
208
3.1. Particle size and zeta potential
209
The z-average particle size and PDI obtained from mixed dispersions and emulsions
210
were presented in Fig.1a. For the control sample egg yolk (EY), the particle size decreased
211
after adding NaCl (EY+), coinciding with a sharp drop in PDI. This result was consistent
212
with a previous study which demonstrated that the disruption of egg yolk granules after
213
addition of NaCl occurred (Anton et al., 2000). However, there is no obvious decrease in
214
particle size of κ-carrageenan after adding salt, although the PDI decreased, suggesting that
10
215
small amount of large aggregates was dissociated. Correspondingly, the particle size and PDI
216
of the mixed dispersions were decreased as the concentration of NaCl increased.
217
Interestingly, the particle size of the mixed dispersions was more dependent on κ-carrageenan
218
than egg yolk. This might be ascribed to the stabilization effect of κ-carrageenan on egg yolk
219
dispersions. It was note that the PDI of egg yolk/κ-carrageenan mixed dispersions was
220
obviously higher than that of egg yolk or κ-carrageenan dispersions, indicating the
221
occurrence of complex coacervation between egg yolk and κ-carrageenan. Furthermore, the
222
particle size and PDI of egg yolk/κ-carrageenan composite emulsions were decreased with
223
the increase of NaCl concentration. These results suggested that emulsions formulated by
224
disrupted yolk/κ-carrageenan complex were more homogenous than those made with the egg
225
yolk/κ-carrageenan hybrid system without NaCl.
226
The zeta potential of the mixed dispersions and emulsions were measured to analyze the
227
changes in surface potential with the increase level of NaCl. As shown in Fig. 1b, there was
228
no obvious difference of zeta potential between the mixed dispersions and emulsions at the
229
same concentration of NaCl but increasing NaCl concentrations indeed led to lower values of
230
zeta potential in each series of samples. This result was in agreement with a previous study,
231
which reported that the increase of ionic strength leads to lower zeta potential values for
232
κ-carrageenan solution (Carneiro-da-Cunha et al., 2011). The negative charge of
233
κ-carrageenan was significantly higher than egg yolk and this accounted for the low particle
234
size of egg yolk/κ-carrageenan mixed dispersions (as shown in Fig. 1a) where κ-carrageenan
235
provided enough electrostatic repulsion for egg yolk components. The zeta potential of the 11
236
mixed dispersions or emulsions was slightly higher than the simple egg yolk or κ-carrageenan
237
dispersions. This phenomenon could be due to the fact that the mixture of two kinds of
238
charged particles possessed the higher surface charge compared to the single charged
239
particles. As previously mentioned (Aguilar et al., 2017), increasing content of charged
240
particles (κ-carrageenan) in the egg yolk/k carrageenan hybrid systems showed an apparent
241
effect on the zeta potential.
242
3.2. Confocal laser scanning microscopy (CLSM)
243
CLSM was applied to illustrate the microstructure of the mixed dispersions and
244
emulsions fabricated by egg yolk and κ-carrageenan. The oil phase was stained by Nile red
245
while other components were dyed with FITC. Fig. 2 displayed the CLSM images of mixed
246
dispersions or emulsions before and after addition of NaCl (0.3 M). Apparently, the
247
aggregates of egg yolk or κ-carrageenan exhibited a dramatic decrease after addition of NaCl,
248
which was in accordance with the results obtained from dynamic light scattering. For the egg
249
yolk/κ-carrageenan mixed dispersions, the flocculation behaviors can be easily observed due
250
to the formation of the large highlighted flocculates. After addition of NaCl, the flocculation
251
phenomenon was obviously lessened. This result may be owed to two main factors: decreased
252
zeta potential and dissociation of egg yolk or κ-carrageenan aggregates. The former reduced
253
the interaction among egg yolk components and κ-carrageenan molecules and the latter
254
resulted in reduced possibility of large flocs formation. For the emulsions, the formation of
255
oil-in-water emulsions could be confirmed because the red fluorescence from nile red was
256
visualized in the interior of the droplets whereas the green fluorescence from FITC was 12
257
located at the perimeter of the droplets. The distribution of oil droplet of the egg
258
yolk/κ-carrageenan hybrid emulsion with 0.3 M NaCl was more homogenous than that of the
259
emulsion without NaCl. This is inconsistent with the whey protein stabilized o/w emulsions
260
containing xanthan gum at pH 7 (Sriprablom et al., 2019), which reported that the droplet
261
aggregation of emulsions was exacerbated at high ionic strengths (200 and 250 mM NaCl)
262
due to a decrease in the droplet zeta-potential. This opposite trend could be attributed to the
263
improving emulsifying properties of egg yolk when the NaCl concentration is increased (Li,
264
Wang, Li et al., 2018), leading to the formation of homogenous emulsified droplets thereby
265
preventing droplet aggregation.
266
3.3. Rheological characteristics
267
The flow behaviors of the mixed dispersions or emulsions were presented in Fig. 3. The
268
results showed that all samples showed a shear-thinning flow behavior. Fig. 3a showed that
269
with an increase in the level of NaCl, the viscosity of the mixed dispersions decreased. This
270
was due to the fact that strong hydration cation Na+ was unconducive to the hydration of
271
carrageenan molecules, leading to a decrease in hydrodynamic volume and viscometric
272
expansion factor of polysaccharide molecules (BrunchiMorariu & Bercea, 2014). Another
273
reason for this phenomenon is that the raised concentrations of counter-ions made the
274
polysaccharide molecules contracted and expressed as lower viscosities owing to the charge
275
shielding effect (Hao et al., 2018). As shown in Figs. 3a and 3b, the viscosity of emulsions
276
(shown in Fig. 3b) was elevated to the higher level than that of the mixed dispersions (shown
277
in Fig. 3a). Despite the existence of adverse effect from NaCl, the apparent viscosity of
13
278
emulsions (at 150 s-1, shown in Table 1) increased as the incorporation of sunflower oil into
279
the mixed dispersions. The natural high viscosity of plant oil and the unaltered concentration
280
of polysaccharide in aqueous phase may be the reason for the viscosity changes of emulsions.
281
The development of storage modulus (G´) during the thermal/cooling cycle of
282
yolk/κ-carrageenan dispersions and emulsions was shown in Fig. 4. For the mixed
283
dispersions (Fig. 4a), the higher the salt concentration was, the greater the gelation
284
temperature was (the beginning of the kinetics). In addition, Table 1 showed that the gelation
285
rates calculated from the slope of 20 s data point right after the onset of gelation were 0.02 Pa
286
s-1, 0.78 Pa s-1, 13.4 Pa s-1 and 31.1 Pa s-1 for the sample 0.0W, 0.1W, 0.2W and 0.3W,
287
respectively. The addition of NaCl reduced the net negative charge and thus lowered the
288
repulsive force among molecules, making the aggregation, entanglement and network
289
formation of gel molecules more prone to occur. The addition of NaCl may favor the
290
aggregation of carrageenan molecules by the competitive hydration, leading to the rapid
291
formation of gel network (Lai et al., 2000).
292
For the gelation behavior of emulsion samples, a similar pattern with the mixed
293
dispersions was observed during the heating/cooling process, although the terminal G' value
294
was lower. Furthermore, there was no obvious difference in the gelation point for both group
295
samples when the salt concentration was at the same level. This result may be due to the same
296
concentration of κ-carrageenan existed in water phase for both group samples. However, the
297
gelation rate of emulsions was significantly lower than the mixed dispersions under the same
298
concentration of NaCl. This result implied that the existence of oil may dilute the
14
299
concentration of κC in whole gel system and reduce the interaction of gel molecules.
300
Previous study had demonstrated that the gel storage (G’ at 1 rad/s) underwent an obvious
301
increase with the addition of κC into egg yolk gel (Aguilar et al., 2011). From the above
302
results, it can be clearly concluded that the gelation point of κC was related to the solution
303
environment whereas the gelation rate tend to be more dependent on the concentration of gel
304
molecules.
305
3.4. Textural analysis
306
The large-strain compression test - texture profile analysis (TPA), a simple and rapid
307
analytical technique, has been commonly used in the food industry. It is vital to explore the
308
possible application of ingredients in food products or develop a new food product. As
309
shown in Fig. 5a, the hardness of mixed hydrogels and emulsion gels showed a fluctuant
310
trend with the increasing NaCl level. Similar phenomenon was reported in other study that
311
with increasing cation concentration, the hardness of carrageenan systems increased to a
312
maximum value at a certain polysaccharide concentration and then decreased (Thrimawithana
313
et al., 2010). The cohesiveness of all gel samples showed a declining trend with the increase
314
of NaCl concentrations. The decrease of gel cohesiveness of κ-carrageenan could be related
315
to the formation of the aggregated structure with large voids with the addition of NaCl
316
(Walther et al., 2006). Decreased cohesiveness means that gels are brittle and easily broken
317
when gels are swallowed or homogenized. This feature was conducive to the formation of
318
micronized gel particles that is useful to prepare a fat analogue (Li et al., 2014). The
319
accelerated gelation rate and decreased particle size after the addition of NaCl in systems
15
320
might go against the tight entanglement among gel molecule chains, leading to the decrease
321
in the deformation tolerance of the resultant gels. Notably, this changes differ from the
322
previous G' response patterns which can be ascribed to the small strain (0.1%) used in the
323
rheological test.
324
The gum–salt interaction presented differences in gel fracture force and fracture distance
325
(Fig. 5b). The fracture distance exhibited the same changes as the above cohesiveness, while
326
the fracture force of all gels showed an increase with the increase in NaCl concentrations
327
except for the mixed hydrogel containing 0.3M NaCl (sample 0.3W). Furthermore, salt-free
328
gels presented the lowest fracture force values. It can be also clearly seen from Fig. 5b that
329
the fracture force of emulsion gels (0.0O, 0.1O, 0.2O and 0.3O) was obviously lower than
330
that of the mixed hydrogels (0.0W, 0.1W, 0.2W and 0.3W). This is consistent with the
331
observation from the above result of rheology. A possible explanation is that the decrease of
332
contact area of plunger with samples used in puncture test minimizes the effect of decreased
333
gel cohesiveness on the fracture force. Therefore, the results of fracture test show a better
334
agreement with those of rheological test than that of texture profile analysis.
335
3.5. LF-NMR spin–spin relaxation measurements
336
Low field NMR has been extensively used to study proton mobility in
337
protein/polysaccharide gel systems (Shao et al., 2016; Ye et al., 2019). Fig. 6 and Table 2
338
showed that four peaks were identified in the hydrogels or gelled emulsions through the
339
multi-exponential fitting of a T2 distribution which was used to assess relaxation time of
340
hydrogen protons. These four relaxation components: T2b (1-10 ms) has been assigned to the
16
341
water that exists in macromolecular structures or water of hydration; T21 (30-150 ms) mainly
342
refers to water that is tightly associated with macromolecules or oil existed in the gel
343
network; T22 (300–1000 ms) represents immobilized water which is located in the gel
344
network; and T23 (>1000 ms) can be designated as the free water (Au et al., 2015; Li, Li et
345
al., 2018; Shao et al., 2016). Fig. 6 and Table 2 showed the T2 relaxation spectra and
346
relaxation parameters of mixed hydrogels or emulsion gels at different level of NaCl. It can
347
be found that the T2b, T21 and T22 of the mixed hydrogels showed a declining trend with the
348
addition of NaCl, signifying that the addition of NaCl could strengthen the water holding
349
capacity of gels by increasing the gel strength. The proportion of peak area represented the
350
content of the four components of H proton in the mixed hydrogels or emulsion gels. PT2b,
351
PT21, PT22 and PT23 represent the areas of relaxation times T2b, T21, T22 and T23
352
respectively. As shown in Table 2, the PT2b and PT21 component of hydrogels (0.0W, 0.1W,
353
0.2W and 0.3W) decreased from 0.64%/3.78% (0.0% NaCl) to 0.09%/1.46% (3.0% NaCl),
354
indicating that the addition of NaCl decreased the hydration effects of protein/polysaccharide
355
molecules. Accordingly, the PT22 component of immobilized water increased with the
356
addition of NaCl.
357
For emulsion gel system, the existence of oil in gel structure had an immense impact on
358
the stability of water in yolk/κ-carrageenan emulsion gels. The relaxation time of T21 peak
359
for salty emulsion gels showed a significant increase after adding oil as compared to the
360
corresponding hydrogel samples while the related areas of relaxation was significantly
361
increased. The PT21 proportion was approximately consistent with amount of oil added.
17
It
362
was notable that there was an additional T23 peak for sample 0.0O. Furthermore, the PT21 of
363
0.0O was the minimum while the corresponding PT22 was the maximum among all emulsion
364
gels. These results indicated the emulsion gel without NaCl (0.0O) that possessed weakest gel
365
strength cannot effectively hold water/oil. As the NaCl concentration increased, the T22 and
366
PT22 simultaneously increased along with the decrease of T21 and PT21, indicating the oil
367
and water holding capacity of emulsion gels decreased. Based on the cumulative results
368
above, a possible mechanism could be proposed to explain the above phenomenon. With the
369
rise of salt concentration, the water holding capacity of hydrogels increased due to the
370
enhanced gel network, although the hydration capacity of gel molecules decreased. After
371
incorporation of oil in hydrogels, the repulsion effect of oil against water was further
372
strengthened by the increase of gel strength, leading to the instability of immobilized water in
373
gel network.
374
4. Conclusions
375
The concentration of NaCl had a significant effect on the flocculation behavior. As the
376
NaCl concentration increased, the decreased particle size and zeta potential were beneficial to
377
the decrease of aggregation level of egg yolk/κ-carrageenan mixed dispersions and the
378
increase of the oil droplets’ uniformity in emulsions, leading to the formation of a stiffer gel.
379
Meanwhile, the viscosity of the mixed dispersions decreased and the onset of gelation was
380
also brought forward with the increase of NaCl. LF-NMR analysis indicated that the
381
hydration ability of gel molecules tended to decrease after addition of NaCl which promoted
382
the aggregation of κ-carrageenan in the process of gel formation. After incorporation of oil in 18
383
the mixed dispersions, the gelation rate was decreased. Furthermore, the repulsion effect of
384
oil against water was also strengthened by the increase of gel strength, leading to the decrease
385
in water holding capacity of emulsion gels. However, more studies are still needed to know
386
about the behavior of the systems and their application by testing more variables besides the
387
NaCl concentration. In summary, the flocculation behavior and gel properties of egg
388
yolk/κ-carrageenan mixed dispersions/emulsion can be modulated by NaCl. And this will be
389
the base for the subsequent preparation of fat analogues and delivery carriers of nutrients.
390 391
Acknowledgments
392
This work was supported by the National Key Research and Development Program of
393
China (No. 2018YFD0400303), the Natural Science Foundation of Jiangsu Province for the
394
Youth (No. BK20180610), the National Natural Science Foundation for the Youth of China
395
(No. 31801483), the Fundamental Research Funds for the Central Universities
396
(JUSRP11902), and the project of China Scholarship Council.
397 398
References
399
Abaee, A., Mohammadian, M., & Jafari, S. M. (2017). Whey and soy protein-based
400
hydrogels and nano-hydrogels as bioactive delivery systems. Trends in Food Science
401
& Technology, 70, 69-81.
402
Aguilar, J. M., Batista, A. P., Nunes, M. C., Cordobés, F., Raymundo, A., & Guerrero, A.
403
(2011). From egg yolk/κ-Carrageenan dispersions to gel systems: Linear
19
404
viscoelasticity and texture analysis. Food Hydrocolloids, 25 (4), 654-658.
405
Aguilar, J. M., Cordobés, F., Raymundo, A., & Guerrero, A. (2017). Thermal gelation of
406
mixed egg yolk/kappa-carrageenan dispersions. Carbohydrate Polymers, 161,
407
172-180.
408
Anton, M., Beaumal, V., & Gandemer, G. (2000). Adsorption at the oil-water interface and
409
emulsifying properties of native granules from egg yolk : effect of aggregated state.
410
Food Hydrocolloids, 14 (4), 327-335.
411
Anton, M., Le Denmat, M., Beaumal, V., & Pilet, P. (2001). Filler effects of oil droplets on
412
the rheology of heat-set emulsion gels prepared with egg yolk and egg yolk fractions.
413
Colloids and Surfaces B: Biointerfaces, 21 (1–3), 137-147.
414
Au, C., Acevedo, N. C., Horner, H. T., & Wang, T. (2015). Determination of the gelation
415
mechanism of freeze–thawed hen egg yolk. Journal of Agricultural and Food
416
Chemistry, 63 (46), 10170-10180.
417
Brunchi, C.-E., Morariu, S., & Bercea, M. (2014). Intrinsic viscosity and conformational
418
parameters of xanthan in aqueous solutions: Salt addition effect. Colloids and
419
Surfaces B: Biointerfaces, 122, 512-519.
420
Carneiro-da-Cunha, M. G., Cerqueira, M. A., Souza, B. W. S., Teixeira, J. A., & Vicente, A.
421
A. (2011). Influence of concentration, ionic strength and pH on zeta potential and
422
mean hydrodynamic diameter of edible polysaccharide solutions envisaged for
423
multinanolayered films production. Carbohydrate Polymers, 85 (3), 522-528.
424
Castellani, O., Belhomme, C., Davidbriand, E., Guerindubiard, C., & Anton, M. (2006).
20
425
Oil-in-water emulsion properties and interfacial characteristics of hen egg yolk
426
phosvitin. Food Hydrocolloids, 20 (1), 35-43.
427
de Souza Paglarini, C., de Figueiredo Furtado, G., Biachi, J. P., Vidal, V. A. S., Martini, S.,
428
Forte, M. B. S., Cunha, R. L., & Pollonio, M. A. R. (2018). Functional emulsion gels
429
with potential application in meat products. Journal of Food Engineering, 222, 29-37.
430
Francis, F. P., & Chidambaram, R. (2019). Hybrid hydrogel dispersed low fat and heat
431
resistant chocolate. Journal of Food Engineering, 256, 9-17.
432
Gaber, M., Mabrouk, M. T., Freag, M. S., Khiste, S. K., Fang, J.-Y., Elkhodairy, K. A., &
433
Elzoghby, A. O. (2018). Protein-polysaccharide nanohybrids: Hybridization
434
techniques and drug delivery applications. European Journal of Pharmaceutics and
435
Biopharmaceutics, 133, 42-62.
436
Geremias-Andrade, M. I., Souki, P. B. G. N., Moraes, C. F. I., & Pinho, C. S. (2016).
437
Rheology of emulsion-filled gels applied to the development of food materials. Gels,
438
2 (3), 1-18.
439
Gmach, O., Bertsch, A., Bilke-Krause, C., & Kulozik, U. (2019). Impact of oil type and pH
440
value on oil-in-water emulsions stabilized by egg yolk granules. Colloids and
441
Surfaces A: Physicochemical and Engineering Aspects, 581, 123788.
442
Gravelle, A. J., Nicholson, R. A., Barbut, S., & Marangoni, A. G. (2019). Dataset on the
443
elastic modulus of heat-set whey protein isolate/xanthan gum mixed biopolymer
444
hydrogels filled with glass microspheres: A model particle-filled composite food
445
system. Data in Brief, 25, 104066.
21
446
Hao, Z.-q., Chen, Z.-j., Chang, M.-c., Meng, J.-l., Liu, J.-y., & Feng, C.-p. (2018).
447
Rheological properties and gel characteristics of polysaccharides from fruit-bodies of
448
Sparassis crispa. International Journal of Food Properties, 21 (1), 2283-2295.
449
Kara, S., Arda, E., Kavzak, B., & Pekcan, Ö. (2006). Phase transitions of κ-carrageenan gels
450
in various types of salts. Journal of Applied Polymer Science, 102 (3), 3008-3016.
451
Khalesi, H., Emadzadeh, B., Kadkhodaee, R., & Fang, Y. (2019). Effect of Persian gum on
452
whey protein concentrate cold-set emulsion gel: Structure and rheology study.
453
International Journal of Biological Macromolecules, 125, 17-26.
454
Lai, V. M. F., Wong, P. A. L., & Lii, C. Y. (2000). Effects of cation properties on sol-gel
455
transition and gel properties of κ-carrageenan. Journal of Food Science, 65 (8),
456
1332-1337.
457 458
Lee, C. M., & Chung, K. H. (1989). Analysis of surmi gel properties by compression and penetration tests. Journal of Texture Studies, 20 (3), 363-377.
459
Li, J., Li, X., Wang, C., Zhang, M., Xu, Y., Zhou, B., Su, Y., & Yang, Y. (2018).
460
Characteristics of gelling and water holding properties of hen egg white/yolk gel with
461
NaCl addition. Food Hydrocolloids, 77, 887-893.
462
Li, J., Wang, C., Li, X., Su, Y., Yang, Y., & Yu, X. (2018). Effects of pH and NaCl on the
463
physicochemical and interfacial properties of egg white/yolk. Food Bioscience, 23,
464
115-120.
465
Li, J., Wang, C., Zhang, M., Zhai, Y., Zhou, B., Su, Y., & Yang, Y. (2018). Effects of
466
selected phosphate salts on gelling properties and water state of whole egg gel. Food
22
467 468 469
Hydrocolloids, 77, 1-7. Li, J., Wang, Y., Jin, W., Zhou, B., & Li, B. (2014). Application of micronized konjac gel for fat analogue in mayonnaise. Food Hydrocolloids, 35, 375-382.
470
Liu, Q.-R., Qi, J.-R., Yin, S.-W., Wang, J.-M., Guo, J., Feng, J.-L., Cheng, M., Cao, J.,
471
Weng, J.-Y., & Yang, X.-Q. (2016). The influence of heat treatment on acid-tolerant
472
emulsions prepared from acid soluble soy protein and soy soluble polysaccharide
473
complexes. Food Research International, 89, 211-218.
474
Lopes-da-Silva, J. A., & Monteiro, S. R. (2019). Gelling and emulsifying properties of soy
475
protein hydrolysates in the presence of a neutral polysaccharide. Food Chemistry,
476
294, 216-223.
477
Montes de Oca-Ávalos, J. M., Huck-Iriart, C., Candal, R. J., & Herrera, M. L. (2016).
478
Sodium caseinate/sunflower oil emulsion-based gels for structuring food. Food and
479
Bioprocess Technology, 9 (6), 981-992.
480
Panyathitipong, W., & Puechkamut, Y. (2010). Effect of tofu powder and carrageenan on
481
functionality and physical characteristics of surimi emulsion gel. Kasetsart J (Nat
482
Sci), 44, 671-679.
483
Pintado, T., Herrero, A. M., Jiménez-Colmenero, F., Pasqualin Cavalheiro, C., &
484
Ruiz-Capillas, C. (2018). Chia and oat emulsion gels as new animal fat replacers and
485
healthy bioactive sources in fresh sausage formulation. Meat Science, 135
486
(Supplement C), 6-13.
487
Prajapati, V. D., Maheriya, P. M., Jani, G. K., & Solanki, H. K. (2014). Carrageenan: a
23
488
natural seaweed polysaccharide and its applications. Carbohydrate Polymers, 105,
489
97-112.
490 491
Rochas, C., & Rinaudo, M. (1984). Mechanism of gel formation in κ‐carrageenan. Biopolymers: Original Research on Biomolecules, 23 (4), 735-745.
492
Serdaroğlu, M., Nacak, B., & Karabıyıkoğlu, M. (2017). Effects of beef fat replacement with
493
gelled emulsion prepared with olive oil on quality parameters of chicken patties.
494
Korean journal for food science of animal resources, 37 (3), 376.
495
Shao, J., Deng, Y., Jia, N., Li, R., Cao, J., Liu, D., & Li, J. (2016). Low-field NMR
496
determination of water distribution in meat batters with NaCl and polyphosphate
497
addition. Food Chemistry, 200, 308-314.
498
Sriprablom, J., Luangpituksa, P., Wongkongkatep, J., Pongtharangkul, T., & Suphantharika,
499
M. (2019). Influence of pH and ionic strength on the physical and rheological
500
properties and stability of whey protein stabilized o/w emulsions containing xanthan
501
gum. Journal of Food Engineering, 242, 141-152.
502 503
Steiner, B. M., McClements, D. J., & Davidov-Pardo, G. (2018). Encapsulation systems for lutein: A review. Trends in Food Science & Technology, 82, 71-81.
504
Su, J., Guo, Q., Chen, Y., Dong, W., Mao, L., Gao, Y., & Yuan, F. (2020). Characterization
505
and formation mechanism of lutein pickering emulsion gels stabilized by
506
β-lactoglobulin-gum arabic composite colloidal nanoparticles. Food Hydrocolloids,
507
98, 105276.
508
Sun, L., Chen, W., Liu, Y., Li, J., & Yu, H. (2015). Soy protein isolate/cellulose nanofiber
24
509
complex gels as fat substitutes: rheological and textural properties and extent of cream
510
imitation. Cellulose, 22 (4), 2619-2627.
511
Tabilo-Munizaga, G., & Barbosa-Cánovas, G. V. (2004). Color and textural parameters of
512
pressurized and heat-treated surimi gels as affected by potato starch and egg white.
513
Food Research International, 37 (8), 767-775.
514
Thrimawithana, T. R., Young, S., Dunstan, D. E., & Alany, R. G. (2010). Texture and
515
rheological characterization of kappa and iota carrageenan in the presence of counter
516
ions. Carbohydrate Polymers, 82 (1), 69-77.
517
Torres, O., Murray, B. S., & Sarkar, A. (2016). Emulsion microgel particles: Novel
518
encapsulation strategy for lipophilic molecules. Trends in Food Science and
519
Technology, 55, 98-108.
520
Valverde, D., Laca, A., Estrada, L. N., Paredes, B., Rendueles, M., & Díaz, M. (2016). Egg
521
yolk and egg yolk fractions as key ingredient for the development of a new type of
522
gels. International Journal of Gastronomy and Food Science, 3, 30-37.
523
Walther, B., Lorén, N., Nydén, M., & Hermansson, A.-M. (2006). Influence of κ-carrageenan
524
gel structures on the diffusion of probe molecules determined by transmission
525
electron microscopy and NMR diffusometry. Langmuir, 22 (19), 8221-8228.
526
Yampol’skaya, G., Elenskii, A., Pan’kina, N., Tarasevich, B., & Kulichikhin, V. (2009).
527
Properties of carrageenan gels with immobilized lysozyme. Colloid Journal, 71 (2),
528
271.
529
Ye, T., Dai, H., Lin, L., & Lu, J. (2019). Employment of κ-carrageenan and high pressure
25
530
processing for quality improvement of reduced NaCl surimi gels. Journal of Food
531
Processing and Preservation, 43 (9), e14074.
532
Zang, X., Wang, J., Yu, G., & Cheng, J. (2019). Addition of anionic polysaccharides to
533
improve the stability of rice bran protein hydrolysate-stabilized emulsions. LWT, 111,
534
573-581.
535
Zhou, M., Wang, T., Hu, Q., & Luo, Y. (2016). Low density lipoprotein/pectin complex
536
nanogels as potential oral delivery vehicles for curcumin. Food Hydrocolloids, 57,
537
20-29.
538 539 540 541 542 543 544 545 546 547 548 549 550
26
551 552 553
Figure captions:
554
Fig. 1. Z-average particle size, polydispersity index (a) and zeta potential (b) of egg yolk and
555
κ-carrageenan composite dispersions and emulsions at different NaCl concentrations (0.0, 0.1,
556
0.2 and 0.3 mol/L). Four reference samples: egg yolk (EY), egg yolk with 0.3 M NaCl (EY+),
557
κ-carraggeenan (κC) and κ-carraggeenan with 0.3 M NaCl (κC+). Colum graphs represent the
558
z-average particle size (a) and zeta potential (b); scatter graph represents the polydispersity
559
index. Error bars represent standard deviations from four replicates. Different uppercase or
560
lowercase letters indicate significant differences (P < 0.05).
561
Fig. 2. The CLSM observations of egg yolk and/or κ-carrageenan dispersions and emulsion
562
prepared without and with 0.3 M NaCl. Green and red micrographs were dyed by fluorescein
563
isothiocyanate (FITC) and nile red (NR), respectively.
564
Fig. 3. Flow curves of egg yolk and κ-carrageenan composite dispersions (a) and emulsions
565
(b) at the NaCl concentrations ranged from 0.0 to 0.3 M.
566
Fig. 4. Changes in the storage moduli (G´) of egg yolk and κ-carrageenan composite
567
dispersions (a) and emulsions (b) under different NaCl concentrations (0.0, 0.1, 0.2 and 0.3
568
M) with temperature.
569
Fig. 5. Textural analysis of egg yolk/κ-carrageenan composite hydrogels and emulsion gels.
570
(a) Texture profile analysis (TPA); (b) Puncture test. Colum graphs represent the hardness (a)
571
and fracture force (b); scatter graphs represent the cohesiveness (a) and fracture distance (b).
27
572
Error bars represent standard deviations from six replicates. Different uppercase or lowercase
573
letters indicate significant differences (P < 0.05).
574
Fig. 6. The curves of relaxation time T2 of egg yolk and κ-carrageenan composite hydrogels
575
(a) and emulsion gels (b) at different NaCl concentrations.
576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592
28
593 594
Z-average particle size Polydispersity index
A
5000
D
b
bc
b
E
2500
b
b E c
cd
c
500
FG
F
0.4
G H
e
I
0.2 0
595
0
Zeta potential (mV)
-10
f
g
-20 -30 -40
e
-50
Zeta potentiala
E EY Y +
-60
d a
ab
596 597
c
a
a
b
c
kC kC 0. + 0W 0. 1W 0. 2W 0. 3W 0. 0O 0. 1O 0. 2O 0. 3O
b
0.6
d
d F
0.8
C
Fig. 1
29
Polydispersity index
B
a
E EY Y + kC kC 0. + 0W 0. 1W 0. 2W 0. 3W 0. 0O 0. 1O 0. 2O 0. 3O
Z-average particle size (nm)
a 7500
598 599
Fig. 2
600 601
30
Viscosity (Pa.s)
a100
0.0W 0.1W 0.2W 0.3W
10
1
0.1
0
50
602
100 150 200 Shear rate (1/s)
250
Viscosity (Pa.s)
b100
604
0.0O 0.1O 0.2O 0.3O
10
1
0.1 603
300
0
50
100 150 200 Shear rate (1/s)
Fig. 3
605
31
250
300
100
a2000
80 60
G' (Pa)
0.0W 0.1W 0.2W 0.3W Temperature
1000 500
Temperature (C)
1500
40 20
0 0
200
400 600 Time (s)
800
1000 1200
606
100
b 750 G' (Pa)
450
60
0.0O 0.1O 0.2O 0.3O Temperature
300 150
40 20
0 0
200
400 600 Time (s)
607 608
Fig. 4
32
800
1000 1200
Temperature (C)
80
600
a A b
400
b
B
C
0.6
300 c
200
f
100
0.4
d
e
D
g
E F
G
0.2
H
0.0
0 0 .0
609
b
W .1 W .2 W .3 W .0 O .1 O .2 O .3 O 0 0 0 0 0 0 0
350
Fracture force (g)
Fracture force (g) Fracture distance (mm)
A a
300
6
B
C
5
b
250 200
4
150
c
100 50
G
d
G
f
c
E
F
d
D
3 e
2
0 0 .0
W .1 W .2 W .3 W .0 O .1 O .2 O .3 O 0 0 0 0 0 0 0
610 611 612
0.8
Fig. 5
33
Fracture distance (mm)
Hardness (g)
Hardness (g) Cohesiveness
Cohesiveness
a500
a300
0.0W 0.1W 0.2W 0.3W
Proportion
250 200 150 100 50 0 1
10
100 1000 Time (ms)
10000
100 1000 Time(ms)
10000
613
b140
0.0O 0.1O 0.2O 0.3O
120
Proportion
100 80 60 40 20 0 1
10
614 615 616 617 618 619 620
Fig. 6
34
621 622
Table 1 Parameters of the rheological characteristics of egg yolk and κ-carrageenan mixed dispersions/hydrogels and emulsions/emulsion
623
gels (b) at different NaCl concentrations 0.0W
0.1W
0.2W
0.3W
0.0O
0.1O
0.2O
0.3O
Viscosity (Pa.s at150 s-1) 0.40±0.02c 0.25±0.01e 0.20±0.01f 0.18±0.01f 0.65±0.03a 0.52±0.03b 0.33±0.02d 0.25±0.02e
624
Onset of gelation (℃)
25.4±1.0d
32.5±1.0b
34.5±0.6a
25.5±1.3d
Gelation rate (Pa s-1)
0.02±0.01g 0.78±0.08e 13.4±0.9b
31.1±1.5a
0.09±0.07g 0.51±0.10f
28.4±1.1c
Different lowercase in the same row indicate significant differences (P < 0.05).
625 626 627 628 629 630 631 632 633 634 635 636 637 35
28.4±1.2c
32.5±1.2b
35.5±0.8a
4.92±0.45d 6.16±0.75c
638
Table 2 T2 relaxation parameters of mixed hydrogels or emulsion gels with different NaCl
639
0.0W
0.1W
0.2W
0.3W
0.0O
T2b
7.07±0.00d
6.44±0.20e
3.37±0.11f
2.55±0.08g
T21
81.85±0.00b
78.15±2.40c
54.00±1.78f
32.48±1.08g
T22
787.62±0.00a 752.06±24.0b 685.67±23.0c 654.71±20.9d 382.74±0.0f 519.65±16.59e 752.06±24.01b 752.06±24.0b
T23
58.72±1.8e
0.2O
0.3O
7.75±0.20b
9.01±0.22a
7.31±0.20c
124.06±3.96a
77.52±2.30c
72.32±2.25d
3783.46±6.3
PT2b
0.64±0.01a
0.46±0.01b
0.16±0.01e
0.09±0.01f
PT21
3.78±0.05e
3.65±0.04f
2.23±0.2g
1.46±0.15h
PT22
95.58±0.10d
95.89±0.15c
97.61±0.3b
98.45±0.3a
0.08±0.01f
0.27±0.01c
0.24±0.01d
21.48±0.1d
35.41±0.1a
31.88±0.2b
30.78±0.15c
78.21±0.08e
64.51±0.05h
67.85±0.04g
68.98±0.08f
0.31±0.01 640
0.1O
Different lowercase in the same row indicate significant differences (P < 0.05).
641 642
36
643 644
Graphical abstract
645 646
37
Highlights
647 648
1. Addition of NaCl could lessen the flocculation of egg yolk and κ-carrageenan.
649
2. The viscoelasticity of hydrogels depended on the aggregation of gel molecules.
650
3. The decreased hydration ability of gel molecules against the water/oil trapping.
651
4. Water holding capacity of emulsion gels was depressed by oil.
652
Author Contribution Statement
653 654 655
Junhua Li and Lilan Xu: Conceptualization, Methodology, Investigation, Writing- Original draft preparation
656
Yujie Su and Cuihua Chang: Writing- Reviewing and Editing.
657
Yanjun Yang and Luping Gu: Supervision
658 659 660
Conflict of interest statement
661
The authors declare no conflict of interest.
662
38