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Effect of high hydrostatic pressure on formation and rheological properties of inulin gels
Journal Pre-proof Effect of high hydrostatic pressure on formation and rheological properties of inulin gels Anna Florowska, Tomasz Florowski, Barbara Sokołowska, Monika Janowicz, Lech Adamczak, Dorota Pietrzak PII:
S0023-6438(19)31337-4
DOI:
https://doi.org/10.1016/j.lwt.2019.108995
Reference:
YFSTL 108995
To appear in:
LWT - Food Science and Technology
Received Date: 12 September 2019 Revised Date:
25 December 2019
Accepted Date: 26 December 2019
Please cite this article as: Florowska, A., Florowski, T., Sokołowska, B., Janowicz, M., Adamczak, L., Pietrzak, D., Effect of high hydrostatic pressure on formation and rheological properties of inulin gels, LWT - Food Science and Technology (2020), doi: https://doi.org/10.1016/j.lwt.2019.108995. 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. © 2019 Published by Elsevier Ltd.
CRediT author statement Anna Florowska: conceptualization, methodology, investigation, writing - original draft, writing - review & editing, visualization, supervision; Tomasz Florowski: conceptualization, writing - review & editing; Barbara Sokołowska: methodology, writing - review & editing; Monika Janowicz: investigation, visualization; Lech Adamczak: formal analysis, visualization; Dorota Pietrzak: investigation.
1
Effect of high hydrostatic pressure on formation and rheological properties of inulin gels
2
Anna Florowskaa*, Tomasz Florowskia, Barbara Sokołowskab,c, Monika Janowicza, Lech
3
Adamczaka, Dorota Pietrzaka
4
a
5
Life Sciences-SGGW, 159c Nowoursynowska Street, Warsaw 02-787, Poland
6
b
7
Biotechnology, 36 Rakowiecka Street, Warsaw 02-532, Poland
8
c
9
Warsaw 01-142, Poland
10 11 12
Department of Food Technology, Faculty Institute of Food Sciences, Warsaw University of
Department of Microbiology, prof. Wacław Dąbrowski Institute of Agricultural and Food
Institute of High Pressure Physic of Polish Academy of Sciences, 29/37 Sokołowska Street,
*Corresponding author: Anna Florowska: [email protected]
13
Abstract: The aim of the study was to determine the possibility of using high hydrostatic
14
pressure (HHP) for induction of inulin gels and to compare properties of the obtained gels
15
with gels induced traditionally by thermal or shear force treatment. HHP (500 MPa) induced
16
inulin gelation regardless of the time treatment (5-20 min) and inulin concertation (20-25
17
g/100g). Obtained by HHP gels differ from traditional gels, had different microstructure and
18
distribution of primary particles. In consequences HHP gels, comparing with thermally and
19
mechanically induced ones, weare less firm and spreadable and weare characterized by a
20
higher yield stress as well as stability and lower L* colour parameter. Those differences
21
properties may allow using inulin gels for creating new, innovative products, than those made
22
with traditionally induced inulin gels. It was also found that exposure time to HHP was not
23
influencing deteriorating physical properties of inulin gels, what gives opportunity to
24
sterilized preserved product with inulin gels with by HHP without the risk of deterioration of
25
properties.
26
Keywords: inulin gel, high hydrostatic pressure, gelation
27
28
1.
Introduction
29
Inulin is well known prebiotic fibre having functional, health-promoting attributes,
30
composed of a mixture of oligo- and polysaccharides constituted of fructose molecules linked
31
by β-(2/1)-D-fructosyl-fructose bonds of various length, terminated generally by a single
32
glucose molecule linked by an α-D- glucopyranosoyl bond (Roberfroid, 1999, Florowska,
33
Krygier, Florowski, & Dłużewska, 2016). Inulin can be obtained by: water extraction from
34
plants, in which inulin is a reserve carbohydrate occurring naturally (e.g. from chicory roots);
35
enzymatically - from sucrose by inulosucrase type fructosyltransferase mainly derived from
36
bacteria (Bacillus species 217C–11); and recently also with the genetic modification (GMO)
37
technics which are used to grow plants that produce the inulin (e.g. potatoes, sugar beet, rice).
38
Method of inulin production determines its average degree of polymerization (DP) and in
39
consequences also its physicochemical properties as solubility, viscosity or melting
40
temperatures that influenced texture forming properties of inulin (Mensink, Frijlink, van der
41
Voort Maarschalk, & Hinrichs, 2015). In turns textural properties of inulin determine its
42
usage in food products not only as a pro-healthy functional ingredient but also as bulking and
43
gelling agent and factor increasing viscosity, which leads to body and mouthfeel improvement
44
especially of low fat food products (Crittenden & Playne, 1996, O'Brien, Mueller, Scannell, &
45
Arendt, 2003, Salvatore, Pes, Mazzarello, & Pirisi, 2014). Inulin’s fat replacing ability, results
46
from its capability to form, from the water solutions, microcrystalline gel network, which in
47
the mouth is perceptible as having a smooth, creamy texture, very similar to fat (Chiavaro,
48
Vittadini, & Corradini, 2007).
49
Gel forming ability of inulin depends on DP, inulin concentration, and the type of
50
induction as well as crystallization conditions. Inulin (DP ≥ 10) can form a gel network from
51
water solution when its concentration exceeds 10–15 g/100g, but completely gelatinized,
52
stable gels are obtained from inulin water solutions with a minimum concentration of 20
53
g/100g. The most often used in food industry are gels obtained either by thermal treatment of
54
inulin’s solution, or by applying shear forces (Kim, Faqih, & Wang, 2001, Glibowski &
55
Wasko, 2008). The method of gels’ induction determines gel characteristic and the possibility
56
of using it as a fat substitute (Glibowski, 2010). Thermally induced gel can form the network
57
structure among the molecular chains through entanglement of molecules into ten times
58
smaller particles as compared to that obtained by mechanical induction, whereas mechanically
59
induced gels are formed with hydrogen bond and van der Waals interactions among particles
60
(aggregates of molecules) in dispersion. Gels that were inducted by thermal treatment are
61
characterised by large primary particles, w What in consequence causes that thermally
62
induced gel formats ion white, creamy structure with a short spreadable texture, which can
63
easily be incorporated into foods to replace fat by up to 100%. Whereas inulin gels that were
64
induced by shear forces (by stirring, nonthermal technology) had smaller the average size of
65
the primary particles, and more numerous what cause the formation of gels with - have
66
softener gel structure (Kim et al., 2001, Beccard et al., 2019). Conditions of gel induction in
67
those two methods might also determine the properties and usage of obtained gels. Too high
68
temperature used in thermal methods or too intensive stirring can cause inulin hydrolysis or
69
decreasing the number of seeding crystals what in consequence cause deterioration of gel
70
firmness or even inhibited inulin’s gelation (Kim et al., 2001, Bot, Erle, Vreeker, & Agterof,
71
2004, Glibowski & Wasko, 2008). That is why in the creation of new textural properties of
72
inulin gels new technologies are being developed. Examples of such induction are a
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subjection of inulin’s water solutions to microfluidization treatments under 30 MPa (Ronkart
74
et al., 2010) or using high-pressure homogenization (HPH) with pressure amounted 103 MPa
75
(Alvarez-Sabatel, de Marãnón, & Arboleya, 2015). Another method, which gaining
76
increasingly popularity in food industry at present, although is not described in the literature
77
as inulin induction method, is high hydrostatic pressure treatment (HHP). HHP is a non-
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thermal process which is used in food industry as an alternative method to heat pasteurization,
79
or blanching (Rahman, 2007) able to induce structural changes of biomacromolecules,
80
including protein denaturation (Khan, Mu, Zhang, & Arogundade, 2014). Commercially
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pasteurized foods by HHP are being exposed to pressures around 400–600 MPa (Ramirez,
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Saraiva, Lamela, & Torres, 2009). The high hydrostatic pressure, besides destroying
83
microorganisms and inactivating enzymes, also affect the physicochemical properties of
84
products (Khan et al., 2014), i.e. pectin conversion (Jolie et al., 2012), and modulate the
85
microstructure of crystalline lipid droplets (Sevdin, Yucel, & Alpas, 2017), as well as sensory
86
properties like colour and flavour (Oey, Lille, Van Loey, & Hendrickx, 2008). Although high
87
pressure inulin gel induction was not the subject of publication so far, but there are several
88
materials on gelation of other polysaccharides, including starch (Li et al., 2015, Yang et al.,
89
2016, Hu, Zhang, Jin, Xu, & Chen, 2017), glucomannan (Moreno, Herranz, Borderías, &
90
Tovar, 2016) or pectin (Peng et al., 2016). All authors agreed that HHP treatment is a method
91
for achieving complete gelatinization of polysaccharides and can modificate gel structure and
92
rheological behaviour. Therefore the aim of the study was to determine the possibility of HHP
93
inulin gel induction and its influence on the properties of obtained gels.
94
2.
Material and methods
95
2.1.
Materials
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Inulin Orafti® HPX (average degree of polymerisation DP≥23) purchased from
97
BENEO GmbH (Mannheim, Germany).
98
2.1.1. Formation of inulin gels
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In thermally induced gel formation method inulin (20 and 25 g/100g) was dissolved
100
in distilled water (80 °C) using a heating magnetic stirrer (for approximately 5 minutes). Then
101
the solutions were cooled at 20 °C. In mechanically induced gel formation inulin (20 and 25
102
g/100g) was suspended in distilled water (20 °C) using a magnetic stirrer. Then inulin
103
suspensions were homogenized by laboratory homogenizer Ultra-Turax T25 (Janke&Kunkel
104
IKA Labortechnik, Staufen, Germany). Homogenization lasted for 5 min at rotational speed
105
of 8.000 min-1. After inductions thermally and mechanically induced sols were poured into
106
plastic cylindrical bottles (50 ml) and all probes were stored at chilled temperature (8 °C) for
107
24 h till the structure was build.
108
By high hydrostatic pressure (HHP) gel formation were induce by suspending inulin (20
109
and 25 g/100g) in distilled water (20 °C) using a magnetic stirrer. Then poured into plastic
110
cylindrical bottles (50 ml) and exposed to pressure of 500 MPa at a temperature 20 °C for 5,
111
10, 20 min. Pressure build-up time up to 500 MPa was in 100 s and the release time was 2–4
112
s. The pressurization times reported do not include the build-up and release times. Samples
113
were subjected to high pressure at the Institute of High Pressure Physics, The Polish Academy
114
of Science, using U 4000/65 (Unipress) apparatus. The apparatus U4000/65, designed and
115
produced by the Laboratory of High Pressure Equipment, is fully automatized, and is
116
provided with a data acquisition system. Pressure is generated by a hydraulically driven
117
reciprocating boxer-type high-pressure pump and is released using a hydraulically driven
118
high-pressure valve. The working volume of the treatment chamber was 0.95 L. As the
119
pressure-transmitting fluid were used distilled water and polypropylene glycol (1:1). After
120
inductions probes were stored at chilled temperature (8 °C) for 24 h till the structure was
121
build.
122
After 24 h the degree of inulin gels formation, rheological properties and colour parameters of
123
obtained gels were tested. Inulin gels were produced in three experimental replicates at
124
separate times.
125
2.2.
126
2.2.1. Volumetric Gel Index (VGI)
Methods
127
The VGI was used as a parameter for optimizing the formation of inulin gel. The
128
volumetric gel index (VGI) was expressed as the volume of gel (VG) over the total volume of
129
samples (VT) multiplied by 100 (Kim et al., 2001).
130
2.2.2. Microstructure
131
Changes in the structure of inulin gels were determined based on the analysis of
132
sample images using an electron scanning microscope (FEI Quanta 200 ESEM, USA)
133
equipped with an energy dispersive spectrometer (EDS) and digital image recording.
134
Previously freeze-dried inulin gels were crushed, applied to a carbon band and sprayed with
135
gold, and microscopically examined to determine differences in the gels structure. Specimens
136
were observed at pressures of 100–133 Pa, under accelerating voltage of 25 or 30 kV.
137
Graphical elaboration of gel structure were performed using MultiScan v.18.03 software
138
(Computer Scanning System).
139
2.2.3. Textural properties
140
Textural properties were measured using a texture analyser (TA.XT Plus, Stable Micro
141
Mixtures, UK) with a 5 kg load cell at 20 °C. The probe used for gel firmness (N) and
142
adhesiveness (Ns) measurement was a cylindrical of 0.5-cm diameter (P/0.5R) and operating
143
at speed of 1.0 mm/s. The sample height was 50 mm in a cylindrical container with a diameter
144
of about 50 mm. The trigger force was 1 g and the probe penetrated the inulin gel with a total
145
displacement of 8 mm. The probe used for spreadability measurement was a TTC
146
Spreadability Rig. The test speed and distance were set to 3.0 mm/s and 20 mm, respectively.
147
The reported values in all textural parameters represent the averages of six replicates. The
148
values of texture attributes were analysed from the resulting graphs using the Exponent
149
version 6.1.4.0 equipment software.
150
2.2.4. Yield stress
151
Yield stress were measured using a rheometer (DV3T, Brookfield, Middleboro, USA)
152
at 20 °C. The spindle used for gel yield stress (Pa*s ) was a vane spindles V74 with a torque
153
range HA. The sample height was 50 mm in a cylindrical container with a diameter of about
154
50 mm, the test speed was 0.10 RMP. The reported values represent the averages of six
155
replicates. The values of texture attributes were analysed from the resulting graphs using the
156
equipment software.
157
2.2.5. Determination of physical stability
158
The physical stability of inulin gels was analysed with LUMiSizer 6120-75 (L.U.M.
159
GmbH, Berlin, Germany) - an analytical centrifuge by measuring the intensity of transmitted
160
near infrared light in suspension. Stability was shown as a space and time related transmission
161
profile over the sample length. The instrumental parameters used for the measurement were as
162
follows: wavelength 870 nm, volume 1.8 mL of dispersion; light factor: 1; 1500 rpm;
163
experiment time, 15 h 10 min; interval time 210 s; temperature 20 °C. To simply assess the
164
physical stability of inulin gels, the instability index was calculated by the delivered software
165
(SepView 6.0; LUM, Berlin, Germany).
166
2.2.6. Colour parameters
167
The L*, a*, and b* colour components were determined with use of CIEL*a*b* at the
168
surface of inulin gel, using a Minolta CR-200 colorimeter (Minolta, Japan; light source D65,
169
observer 2°, a measuring head hole of 8 mm). In order to determine the colour differences
170
between HHP induced gels and gels induced by standard methods, i.e. thermally and
171
mechanically, the parameter of total colour difference ∆E was also calculated (Mokrzycki, &
172
Tatol, 2011). ∆ =
173
∗
−
∗
) +(
∗
−
∗
) +(
∗
−
∗
)
Where:
174
∗
175
∗
176
(
,
∗
,
∗
,
∗
refers to the colour parameters of gels induced by standard methods, ,
∗
refers to the colour parameters of HHP induced gels.
2.2.7. Statistical analysis
177
The results were statistically analysed using Statistica 13.3 (TIBICO Software Inc.).
178
To determine the significance of differences between the average values of yield stress,
179
firmness, adhesiveness, spreadability, colour parameters of inulin gels mechanically,
180
thermally and HHP induced multifactor analysis of variance was used. Significant differences
181
between mechanical, thermal an HHP induction, as well as length of HHP treatment and
182
inulin concentration and were verified using Tukey’s test at significant level α=0.05.
183
Significant differences in analysed gel parameters for different inulin concentration were
184
verified using the t-Student test at significant level α=0.05.
185
3.
Results and discussion
186
3.1.
Effect of HHP treatment on gel formation of inulin
187
Under investigated conditions - mechanical, thermal, and high hydrostatic pressure
188
(500 MPa), independently from inulin concentration and treatment time (HHP), from inulin
189
water solutions the homogeneous gel structures were formed (VGI = 100 %, table 1). That
190
indicates that HHP might be an alternative method of inulin’s gel induction.
191
3.2.
Effect of HHP treatment on the structure of inulin gels
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To observe the inulin gels structure electron microscopy was used. Scanning electron
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microscopy images (Figure 1) showed the influence of HHP on inulin gel structure.
194
Mechanically and thermally induced inulin gels had a tridimensional granular-like structure.
195
During pressure treatment, morphological changes took place including disorganization of gel
196
structures. After HHP treatment the smooth surface of the gel become uneven and lost its
197
granular structure, also the microstructure of gels compressed, aggregated and larger areas of
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disordered structures were formed. This might be due to induced the inulin nuclei partly
199
breakage or/and increasing the susceptibility of inulin chains to undergo a hydrolysis process
200
(Ronkart et al., 2010). The changes in the inulin gel structure under HHP depended also on
201
the treatment time. While time of HHP extend inulin gels granules were packed tighter with
202
melting on the surface of granules and after 20 minutes of HHP the granulated structure was
203
almost invisible. This results are in accordance with HHP treatment of other polysaccharides
204
such as starch (Colussi et al., 2018) or pectin (Peng et al., 2016). According to Kim et al.
205
(2001) the size of inulin particles is corelated with sandy texture of gels, the bigger particles
206
are the more sandy mouthfeel of a product occur. Larger inulin particles are obtained by the
207
mechanical treatment (Figure. 1) so the process like HHP investigated in this research or other
208
pressure treatments like micro-fluidization (Ronkart et al., 2010) or HPH (Alvarez-Sabatel et
209
al., 2015) might contribute to the formation of smoother texture even without heating the
210
product what is extremally important in introducing inulin gels as a fat replacement into
211
specific, non-thermal treated food products.
212
3.3.
Effect of HHP treatment on textural properties and yield stress of inulin gels
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A significant impact on the ability to form inulin gel network and physical properties
214
of the obtained gels have a crystallisation conditions such as: inulin concentration, DP or
215
temperature of inulin solution which affect the size of primary particles in inulin gel network
216
and further gel formation Crystallization conditions such as: inulin concentration, DP or
217
temperature of inulin solution which affect the size of primary particles in inulin gel network
218
have a significant impact on the ability to form inulin gel networks and the physical properties
219
of the obtained gels (Bot et al., 2004, Beccard et al., 2019). This might have consequences in
220
terms of the gel functional properties and thus also on its use in food industry. Comparing
221
inulin gels, obtained by traditional methods (mechanical and thermal) with HHP methods,
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significant (P<0.05) gel firmness losses were found in HHP treated samples regardless of
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inulin concentration (table 1). Although there are no study on inulin solutions treated by HHP
224
it is well known that polysaccharides under HHP are being modified in the way that firmness
225
of product is degraded, the confirmation of this can be found in the study on materials built
226
with polysaccharides such as carrots (Araya et al., 2007), broccoli (Christiaens et al., 2011),
227
asparagus (Yi et al., 2016) treated by HHP. Additionally, almost none changes in firmness
228
was detected after extending treatment time from 5 to 20 minutes. What might suggest that
229
longer HHP treatment does not cause the inulin chain degradation like it occurs in thermal
230
induced gels (Glibowski & Wasko, 2008). It was stayed that adhesiveness of inulin gels is
231
strongly corelated with the inulin concentration, higher adhesiveness of inulin gels was found
232
in the gels containing 25 g/100g of inulin compared with 20 g/100g regardless to the
233
induction method (table 1). Similarly observed Chiavaro et al., (2007) testing inulin gels
234
obtained from inulin’s with different chemical composition (oligo-polysaccharides profile).
235
The HHP induced gels are similar in adhesiveness to those obtained by mechanical forces
236
while thermally induced gels are twice as adhesive. The reasons for this might be in
237
differences in the structure of inulin gels induced by different methods, which probably
238
results from different gelation mechanisms. HHP induced gel are probably formed the same,
239
as mechanically induced gels - by the intermolecular hydrogen bonds which are probably
240
mediated through the bridging water molecules in cross-linking junctions as it was proposed
241
for carrageenan (Steyer, Bera, Massaux, Sindic, Blecker & Deroanne, 1999). Obtained results
242
might also suggested that the HHP treatment had no effect on the molecular structure of
243
inulin, what was confirmed already for other polysaccharide such as starch (Katopo, Song, &
244
Jane, 2002, Li & Zhu, 2018).
245
As inulin gels have creamy appearance, and spreadable texture, with properties
246
resembling that of a fat crystal network in oil, its usage as fat replacer is very likely (Franck,
247
2002). That is why investigating the spredability of inulin gels is very important.
248
Spreadability (dynamic property), is a deformation under an external load, and the term to
249
describe the ease with which a spread can be applied in a thin layer to bread. Applied HHP
250
treatment did significantly affect the spredability of inulin gels. Firmness value in spredability
251
test for gels induce by HHP were much higher, regardless of the inulin concentration, than for
252
those obtained by thermal or mechanical treatment (table 1). Those higher spreadability
253
values might occurs due to the compressed structure developed under High Hydrostatic
254
Pressure treatment what is also visible on scanning electron microscopy images (Figure 1).
255
Similar observation was conducted by Vega-Gálvez et al. (2011) in the case of structural
256
polysaccharides (pectin, cellulose, and hemicellulose) located within the cell walls.
257
Yield stress is an initial resistance to flow under stress. For inulin gels it was reported
258
that yield stress (table 1) depends on the inulin concentration; the higher the solution
259
concentration, the greater the yield stress was. It also depends on the induction method, what
260
was more visible in gels containing 25 g/100g of inulin. The highest yield stress was noted for
261
inulin gels obtained by HHP treatment. What is more, yield stress of inulin gels containing
262
25 g/100g of inulin depends also on the HHP treatment time. The longer probes were kept
263
under pressure the higher yield stress was. Extending the treatment of HHP resulted in higher
264
yield stress of obtained gels. According to literature data the pressure holding time has an
265
effect on the overall texture of processed products (Ludikhuyze & Hendrickx, 2001, Vega-
266
Gálvez et al., 2011). In a case of the yield stress, which is the minimum force needed to drive
267
certain sample to flow (Mezger, 2006), it might be assumed that the increase of yield stress
268
for longer HHP treatment was also, like spredability, due to compressed structure developed
269
under High Hydrostatic Pressure treatment (Figure 1). These results are consistent with those
270
obtained by other authors that investigated the HHP treatment on viscosity, or yield stress of
271
xanthan gum (Dolz, Hernández, Delegido, Alfaro, & Muñoz, 2007) or pectin (Peng et al.,
272
2016), similar observations were made also for inulin solution treated with pressure
273
homogenisation (103-296 MPa) (Alvarez-Sabatel et al., 2015).
274
3.4.
Effect of HHP on stability of inulin gel
275
The effect of HHP treatment on gels’ stability was examined with the multi-sample
276
analytical centrifuge based on the STEP technology (space-time resolved extinction profiles).
277
Destabilization progression of process are shown on Figure 2. Inulin gels showed
278
sedimentation mechanism due to increase of transmission profiles on the bottom of cell. As
279
Glampedaki, Petzold, Dutschk, Miller, & Warmoeskerken (2012) proved the higher the
280
sedimentation rate, the lower the stability of products. The separation behavior of inulin gels
281
dependent less on the inulin concentration than on type of the induction. HHP treatment
282
allowed to obtained, for higher inulin concentration (25 g/100g), more stable inulin gels (with
283
lower instability index) compared with thermal and mechanical induction (Figures 3 & 4). It
284
may result from more compact structure of inulin HHP induce gels. Moreover it was observed
285
that extension of HHP treatment time, regardless to the inulin concetration, resulted in
286
increased stability of inulin gels. This can be explained by the influence of length of HHP
287
time treatment on the microstructure of obtained inulin gels. The extend time of HHP
288
treatment results besides the compression also in tighter packed granules of inulin gels with
289
melting on the surface of granules. The changes are visible in scanning electron microscopy
290
images (Figure 1). This results are in accordance with HHP treatment of other
291
polysaccharides such as starch (Colussi et al., 2018) or pectin (Peng et al., 2016).
292
3.5.
Effect of HHP on colour parameters of inulin gel
293
The lightness of the investigated inulin gels, regardless of the gel’s induction type,
294
depended on the inulin’s concertation concentration (table 2). The results are similar to that
295
obtained by Alvarez-Sabatel et al., (2018), whose observed that the increasement of inulin
296
concentration from 20 to 25 g/100g significantly increases the gel lightness. Inulin gels
297
obtained by HHP treatment are darker than gels obtained thermally or mechanically (table 2).
298
Although, there are no information about influence of HHP on colour parameters of inulin
299
gels, there are other polysaccharides that darker after HHP treatment like starch (Tabilo-
300
Munizaga & Barbosa-Canovas, 2004), glucomannan (Moreno et al., 2016) or Jerusalem
301
artichoke extracts (Kim, Fan, Chung, & Han, 2010). For other colour parameters (a*, b*)
302
differences between average values for different inulin gel induction methods were not big,
303
although inulin gels induced by HHP, especially with longer time treatment, were
304
characterized by lower a* value, when compare with mechanical induced gels. Basing on
305
comprehensive analysis of the effect of the applied gel induction method, using the total
306
colour difference parameter (∆E), it was found that although the differences in colour between
307
HHP induced gels and gels obtained by standard methods of induction were visible to the
308
unexperienced observer (∆E> 2), HHP-induced gels were more similar in colour to thermally
309
induced gels (2 <∆E <3.5) than to mechanically induced gels. Comparing colour between
310
HHP and mechanically induced gel it was found that parameter of total colour difference ∆E
311
was 3.5 <∆E <5 indicating that the differences in colour were noticed.
312
4. Conclusions
313
High pressure treatment of inulin’s solution might be an interesting alternative beyond
314
thermal and mechanical inulin gel inductions to produce food with novel textures, and with
315
better nutritional and functional ingredients retention. Inulin gels obtained by HHP method
316
comparing with described in literature (thermal and mechanical) methods weare significantly
317
darker and less firm as well as less spreadable regardless of inulin concentration and HHP
318
time treatment. but more stable. It was also found that HHP inducted gels had smoother, with
319
visible lower granular, compressed and aggregated structure. Extended exposure time to HHP
320
caused changes in inulin gels properties such as higher yield stress and stability as well as
321
obtaining tighter packed gels structure with melting on the surface. was not influencing
322
physical properties of inulin gels, what gives opportunity to sterilized product with HHP
323
without the risk of deterioration of inulin gel properties. Therefore HHP inulin’s gelling
324
induction as non-thermal method gives an opportunity to applied inulin gels in products where
325
their application was so far impossible.
326
327
328
5
References
329
1. Alvarez-Sabatel, S., de Marañón, I. M., & Arboleya, J.-C. (2018). Impact of oil and
330
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Table 1: Physical properties of inulin gels obtained by mechanical, thermal an HHP induction Inulin concentration Method of gel induction
20 g/100g
25 g/100g
Mechanical Thermal HHP 500 MPa 5 min HHP 500 MPa 10 min HHP 500 MPa 20 min Mechanical Thermal HHP 500 MPa 5 min HHP 500 MPa 10 min HHP 500 MPa 20 min
VGI [%] 100a 100a 100a 100a 100a 100a 100a 100a 100a 100a
Firmness [N]
Adhesiveness [Ns]
Spreadability [N]
Yield stress [Pa]
2.72b# ± 0.24 2.88b# ± 0.20 1.19a#± 0.01 1.15a# ± 0.01 1.47a# ± 0.02 5.65c# ± 0.41 7.44d# ± 0.65 3.13ab# ± 0.01 2.72a# ± 0.02 3.59b# ± 0.02
-0.65b# ± 0.21 -1.31a# ± 0.08 -0.58b# ± 0.01 -0.52bc# ± 0.06 -0.54bc# ± 0.01 -1.20bc# ± 0.11 -3.33a# ± 0.21 -1.25bc# ± 0.08 -1.15c# ± 0.01 -1.22c# ± 0.01
0.51a ± 0.08 1.96ab# ± 0.16 5.73d# ± 1.72 4.90cd# ± 0.01 5.40d# ± 0.09 1.80a ± 0.27 5.49b# ± 0.53 10.76c# ± 0.27 12.13d# ± 0.01 12.15d# ± 0.26
270.1a# ± 11.4 410.9a# ± 14.5 582.7b# ± 10.3 650.0b# ± 7.2 617.6b# ± 3.5 690.1a# ± 15.6 840.6b# ± 14.2 1061.4c# ± 8.4 1452.9d# ± 47.5 1646.0e# ± 36.7
Values are mean ± SD (n=3). a, b, …- values followed by the same letter within a column for the same inulin concentration do not differ significantly according to Tukey’s test (P<0,05),. #- values with # within a column for the same induction method differ significantly according to Tukey’s test the t-Student test (P<0,05).
Table 2: Colour parameters of inulin gels obtained by mechanical, thermal an HHP induction ∆E
Colour parameters Inulin concentration Method of gel induction
20 g/100g
25 g/100g
Mechanical Thermal HHP 500 MPa 5 min HHP 500 MPa 10 min HHP 500 MPa 20 min Mechanical Thermal HHP 500 MPa 5 min HHP 500 MPa 10 min HHP 500 MPa 20 min
L*
a*
b*
89.53b# ± 1.26 89.17b# ± 0.09 86.29a# ± 0.21 86.39a# ± 0.26 85.39a# ± 0.13 92.29c# ± 0.84 90.04b# ± 0.31 88.03a# ± 0.12 87.88a# ± 0.15 87.81a#± 0.35
-1.31b ± 0.13 -1.54ab ± 0.02 -1.41ab# ± 0.03 -1.42ab# ± 0.07 -1.64a ± 0.10 -1.29b ± 0.12 -1.62a ± 0.13 -1.66a# ± 0.03 -1.63a# ± 0.03 -1.63a ± 0.06
2.19c ± 0.22 0.64ab# ± 0.06 0.91ab# ± 0.07 0.56ab# ± 0.05 0.96b# ± 0.35 2.57b ± 0.53 1.27a# ± 0.11 2.48b# ± 0.03 2.35b# ± 0.08 2.44b# ± 0.05
Comp. mechanical 1,91± 0,13 3,56± 1,18 3,61± 1,01 4,41± 1,11 2,73± 0,70 4,31± 0,71 4,46± 0,93 4,52± 0,66
Comp. thermal 1,91± 0,13 2,90± 0,22 2,79± 0,35 3,28± 0,18 2,73± 0,70 2,36± 0,32 2,42± 0,37 2,54± 0,25
Values are mean ± SD (n=3). a, b, …- values followed by the same letter within a column for the same inulin concentration do not differ significantly according to Tukey’s test (P<0,05),. #- values with # within a column for the same induction method differ significantly according to Tukey’s test the t-Student test (P<0,05).
Figure 1: Influence of HHP on inulin gel structure in comparison with thermal and mechanical induction
20g/100g; thermal
25g/100g; thermal
20g/100g; mechanical
25g/100g; mechanical
20g/100g; HHP 5 min
25g/100g; HHP 5 min
20g/100g; HHP 10 min
25g/100g; HHP 10 min
20g/100g; HHP 20 min
25g/100g; HHP 20 min
Figure 2. Transmission profiles of inulin gels formed from solutions with inulin concentrations 20 and 25 g/100g, obtained by thermal, mechanical, and HHP induction presented enabling LUMiSizer® analysis
Figure 3: Influence of HHP on stability of 20 g/100g inulin gels in comparison with thermal and mechanical induction
Figure 4: Influence of HHP on stability of 25 g/100g inulin gels in comparison with thermal and mechanical induction
Highlights HHP (500 MPa) induced inulin gelation regardless of the time treatment (5-20 min). HHP gels, comparing with thermally and mechanically induced ones, are less firm and spreadable. HHP induction increased yield stress and stability of inulin gels. HHP induction gave gels with the uneven surface and less granular structure. HHP gels had unique properties which may allow using it in creating new products.
S0023-6438(19)31337-4
DOI:
https://doi.org/10.1016/j.lwt.2019.108995
Reference:
YFSTL 108995
To appear in:
LWT - Food Science and Technology
Received Date: 12 September 2019 Revised Date:
25 December 2019
Accepted Date: 26 December 2019
Please cite this article as: Florowska, A., Florowski, T., Sokołowska, B., Janowicz, M., Adamczak, L., Pietrzak, D., Effect of high hydrostatic pressure on formation and rheological properties of inulin gels, LWT - Food Science and Technology (2020), doi: https://doi.org/10.1016/j.lwt.2019.108995. 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. © 2019 Published by Elsevier Ltd.
CRediT author statement Anna Florowska: conceptualization, methodology, investigation, writing - original draft, writing - review & editing, visualization, supervision; Tomasz Florowski: conceptualization, writing - review & editing; Barbara Sokołowska: methodology, writing - review & editing; Monika Janowicz: investigation, visualization; Lech Adamczak: formal analysis, visualization; Dorota Pietrzak: investigation.
1
Effect of high hydrostatic pressure on formation and rheological properties of inulin gels
2
Anna Florowskaa*, Tomasz Florowskia, Barbara Sokołowskab,c, Monika Janowicza, Lech
3
Adamczaka, Dorota Pietrzaka
4
a
5
Life Sciences-SGGW, 159c Nowoursynowska Street, Warsaw 02-787, Poland
6
b
7
Biotechnology, 36 Rakowiecka Street, Warsaw 02-532, Poland
8
c
9
Warsaw 01-142, Poland
10 11 12
Department of Food Technology, Faculty Institute of Food Sciences, Warsaw University of
Department of Microbiology, prof. Wacław Dąbrowski Institute of Agricultural and Food
Institute of High Pressure Physic of Polish Academy of Sciences, 29/37 Sokołowska Street,
*Corresponding author: Anna Florowska: [email protected]
13
Abstract: The aim of the study was to determine the possibility of using high hydrostatic
14
pressure (HHP) for induction of inulin gels and to compare properties of the obtained gels
15
with gels induced traditionally by thermal or shear force treatment. HHP (500 MPa) induced
16
inulin gelation regardless of the time treatment (5-20 min) and inulin concertation (20-25
17
g/100g). Obtained by HHP gels differ from traditional gels, had different microstructure and
18
distribution of primary particles. In consequences HHP gels, comparing with thermally and
19
mechanically induced ones, weare less firm and spreadable and weare characterized by a
20
higher yield stress as well as stability and lower L* colour parameter. Those differences
21
properties may allow using inulin gels for creating new, innovative products, than those made
22
with traditionally induced inulin gels. It was also found that exposure time to HHP was not
23
influencing deteriorating physical properties of inulin gels, what gives opportunity to
24
sterilized preserved product with inulin gels with by HHP without the risk of deterioration of
25
properties.
26
Keywords: inulin gel, high hydrostatic pressure, gelation
27
28
1.
Introduction
29
Inulin is well known prebiotic fibre having functional, health-promoting attributes,
30
composed of a mixture of oligo- and polysaccharides constituted of fructose molecules linked
31
by β-(2/1)-D-fructosyl-fructose bonds of various length, terminated generally by a single
32
glucose molecule linked by an α-D- glucopyranosoyl bond (Roberfroid, 1999, Florowska,
33
Krygier, Florowski, & Dłużewska, 2016). Inulin can be obtained by: water extraction from
34
plants, in which inulin is a reserve carbohydrate occurring naturally (e.g. from chicory roots);
35
enzymatically - from sucrose by inulosucrase type fructosyltransferase mainly derived from
36
bacteria (Bacillus species 217C–11); and recently also with the genetic modification (GMO)
37
technics which are used to grow plants that produce the inulin (e.g. potatoes, sugar beet, rice).
38
Method of inulin production determines its average degree of polymerization (DP) and in
39
consequences also its physicochemical properties as solubility, viscosity or melting
40
temperatures that influenced texture forming properties of inulin (Mensink, Frijlink, van der
41
Voort Maarschalk, & Hinrichs, 2015). In turns textural properties of inulin determine its
42
usage in food products not only as a pro-healthy functional ingredient but also as bulking and
43
gelling agent and factor increasing viscosity, which leads to body and mouthfeel improvement
44
especially of low fat food products (Crittenden & Playne, 1996, O'Brien, Mueller, Scannell, &
45
Arendt, 2003, Salvatore, Pes, Mazzarello, & Pirisi, 2014). Inulin’s fat replacing ability, results
46
from its capability to form, from the water solutions, microcrystalline gel network, which in
47
the mouth is perceptible as having a smooth, creamy texture, very similar to fat (Chiavaro,
48
Vittadini, & Corradini, 2007).
49
Gel forming ability of inulin depends on DP, inulin concentration, and the type of
50
induction as well as crystallization conditions. Inulin (DP ≥ 10) can form a gel network from
51
water solution when its concentration exceeds 10–15 g/100g, but completely gelatinized,
52
stable gels are obtained from inulin water solutions with a minimum concentration of 20
53
g/100g. The most often used in food industry are gels obtained either by thermal treatment of
54
inulin’s solution, or by applying shear forces (Kim, Faqih, & Wang, 2001, Glibowski &
55
Wasko, 2008). The method of gels’ induction determines gel characteristic and the possibility
56
of using it as a fat substitute (Glibowski, 2010). Thermally induced gel can form the network
57
structure among the molecular chains through entanglement of molecules into ten times
58
smaller particles as compared to that obtained by mechanical induction, whereas mechanically
59
induced gels are formed with hydrogen bond and van der Waals interactions among particles
60
(aggregates of molecules) in dispersion. Gels that were inducted by thermal treatment are
61
characterised by large primary particles, w What in consequence causes that thermally
62
induced gel formats ion white, creamy structure with a short spreadable texture, which can
63
easily be incorporated into foods to replace fat by up to 100%. Whereas inulin gels that were
64
induced by shear forces (by stirring, nonthermal technology) had smaller the average size of
65
the primary particles, and more numerous what cause the formation of gels with - have
66
softener gel structure (Kim et al., 2001, Beccard et al., 2019). Conditions of gel induction in
67
those two methods might also determine the properties and usage of obtained gels. Too high
68
temperature used in thermal methods or too intensive stirring can cause inulin hydrolysis or
69
decreasing the number of seeding crystals what in consequence cause deterioration of gel
70
firmness or even inhibited inulin’s gelation (Kim et al., 2001, Bot, Erle, Vreeker, & Agterof,
71
2004, Glibowski & Wasko, 2008). That is why in the creation of new textural properties of
72
inulin gels new technologies are being developed. Examples of such induction are a
73
subjection of inulin’s water solutions to microfluidization treatments under 30 MPa (Ronkart
74
et al., 2010) or using high-pressure homogenization (HPH) with pressure amounted 103 MPa
75
(Alvarez-Sabatel, de Marãnón, & Arboleya, 2015). Another method, which gaining
76
increasingly popularity in food industry at present, although is not described in the literature
77
as inulin induction method, is high hydrostatic pressure treatment (HHP). HHP is a non-
78
thermal process which is used in food industry as an alternative method to heat pasteurization,
79
or blanching (Rahman, 2007) able to induce structural changes of biomacromolecules,
80
including protein denaturation (Khan, Mu, Zhang, & Arogundade, 2014). Commercially
81
pasteurized foods by HHP are being exposed to pressures around 400–600 MPa (Ramirez,
82
Saraiva, Lamela, & Torres, 2009). The high hydrostatic pressure, besides destroying
83
microorganisms and inactivating enzymes, also affect the physicochemical properties of
84
products (Khan et al., 2014), i.e. pectin conversion (Jolie et al., 2012), and modulate the
85
microstructure of crystalline lipid droplets (Sevdin, Yucel, & Alpas, 2017), as well as sensory
86
properties like colour and flavour (Oey, Lille, Van Loey, & Hendrickx, 2008). Although high
87
pressure inulin gel induction was not the subject of publication so far, but there are several
88
materials on gelation of other polysaccharides, including starch (Li et al., 2015, Yang et al.,
89
2016, Hu, Zhang, Jin, Xu, & Chen, 2017), glucomannan (Moreno, Herranz, Borderías, &
90
Tovar, 2016) or pectin (Peng et al., 2016). All authors agreed that HHP treatment is a method
91
for achieving complete gelatinization of polysaccharides and can modificate gel structure and
92
rheological behaviour. Therefore the aim of the study was to determine the possibility of HHP
93
inulin gel induction and its influence on the properties of obtained gels.
94
2.
Material and methods
95
2.1.
Materials
96
Inulin Orafti® HPX (average degree of polymerisation DP≥23) purchased from
97
BENEO GmbH (Mannheim, Germany).
98
2.1.1. Formation of inulin gels
99
In thermally induced gel formation method inulin (20 and 25 g/100g) was dissolved
100
in distilled water (80 °C) using a heating magnetic stirrer (for approximately 5 minutes). Then
101
the solutions were cooled at 20 °C. In mechanically induced gel formation inulin (20 and 25
102
g/100g) was suspended in distilled water (20 °C) using a magnetic stirrer. Then inulin
103
suspensions were homogenized by laboratory homogenizer Ultra-Turax T25 (Janke&Kunkel
104
IKA Labortechnik, Staufen, Germany). Homogenization lasted for 5 min at rotational speed
105
of 8.000 min-1. After inductions thermally and mechanically induced sols were poured into
106
plastic cylindrical bottles (50 ml) and all probes were stored at chilled temperature (8 °C) for
107
24 h till the structure was build.
108
By high hydrostatic pressure (HHP) gel formation were induce by suspending inulin (20
109
and 25 g/100g) in distilled water (20 °C) using a magnetic stirrer. Then poured into plastic
110
cylindrical bottles (50 ml) and exposed to pressure of 500 MPa at a temperature 20 °C for 5,
111
10, 20 min. Pressure build-up time up to 500 MPa was in 100 s and the release time was 2–4
112
s. The pressurization times reported do not include the build-up and release times. Samples
113
were subjected to high pressure at the Institute of High Pressure Physics, The Polish Academy
114
of Science, using U 4000/65 (Unipress) apparatus. The apparatus U4000/65, designed and
115
produced by the Laboratory of High Pressure Equipment, is fully automatized, and is
116
provided with a data acquisition system. Pressure is generated by a hydraulically driven
117
reciprocating boxer-type high-pressure pump and is released using a hydraulically driven
118
high-pressure valve. The working volume of the treatment chamber was 0.95 L. As the
119
pressure-transmitting fluid were used distilled water and polypropylene glycol (1:1). After
120
inductions probes were stored at chilled temperature (8 °C) for 24 h till the structure was
121
build.
122
After 24 h the degree of inulin gels formation, rheological properties and colour parameters of
123
obtained gels were tested. Inulin gels were produced in three experimental replicates at
124
separate times.
125
2.2.
126
2.2.1. Volumetric Gel Index (VGI)
Methods
127
The VGI was used as a parameter for optimizing the formation of inulin gel. The
128
volumetric gel index (VGI) was expressed as the volume of gel (VG) over the total volume of
129
samples (VT) multiplied by 100 (Kim et al., 2001).
130
2.2.2. Microstructure
131
Changes in the structure of inulin gels were determined based on the analysis of
132
sample images using an electron scanning microscope (FEI Quanta 200 ESEM, USA)
133
equipped with an energy dispersive spectrometer (EDS) and digital image recording.
134
Previously freeze-dried inulin gels were crushed, applied to a carbon band and sprayed with
135
gold, and microscopically examined to determine differences in the gels structure. Specimens
136
were observed at pressures of 100–133 Pa, under accelerating voltage of 25 or 30 kV.
137
Graphical elaboration of gel structure were performed using MultiScan v.18.03 software
138
(Computer Scanning System).
139
2.2.3. Textural properties
140
Textural properties were measured using a texture analyser (TA.XT Plus, Stable Micro
141
Mixtures, UK) with a 5 kg load cell at 20 °C. The probe used for gel firmness (N) and
142
adhesiveness (Ns) measurement was a cylindrical of 0.5-cm diameter (P/0.5R) and operating
143
at speed of 1.0 mm/s. The sample height was 50 mm in a cylindrical container with a diameter
144
of about 50 mm. The trigger force was 1 g and the probe penetrated the inulin gel with a total
145
displacement of 8 mm. The probe used for spreadability measurement was a TTC
146
Spreadability Rig. The test speed and distance were set to 3.0 mm/s and 20 mm, respectively.
147
The reported values in all textural parameters represent the averages of six replicates. The
148
values of texture attributes were analysed from the resulting graphs using the Exponent
149
version 6.1.4.0 equipment software.
150
2.2.4. Yield stress
151
Yield stress were measured using a rheometer (DV3T, Brookfield, Middleboro, USA)
152
at 20 °C. The spindle used for gel yield stress (Pa*s ) was a vane spindles V74 with a torque
153
range HA. The sample height was 50 mm in a cylindrical container with a diameter of about
154
50 mm, the test speed was 0.10 RMP. The reported values represent the averages of six
155
replicates. The values of texture attributes were analysed from the resulting graphs using the
156
equipment software.
157
2.2.5. Determination of physical stability
158
The physical stability of inulin gels was analysed with LUMiSizer 6120-75 (L.U.M.
159
GmbH, Berlin, Germany) - an analytical centrifuge by measuring the intensity of transmitted
160
near infrared light in suspension. Stability was shown as a space and time related transmission
161
profile over the sample length. The instrumental parameters used for the measurement were as
162
follows: wavelength 870 nm, volume 1.8 mL of dispersion; light factor: 1; 1500 rpm;
163
experiment time, 15 h 10 min; interval time 210 s; temperature 20 °C. To simply assess the
164
physical stability of inulin gels, the instability index was calculated by the delivered software
165
(SepView 6.0; LUM, Berlin, Germany).
166
2.2.6. Colour parameters
167
The L*, a*, and b* colour components were determined with use of CIEL*a*b* at the
168
surface of inulin gel, using a Minolta CR-200 colorimeter (Minolta, Japan; light source D65,
169
observer 2°, a measuring head hole of 8 mm). In order to determine the colour differences
170
between HHP induced gels and gels induced by standard methods, i.e. thermally and
171
mechanically, the parameter of total colour difference ∆E was also calculated (Mokrzycki, &
172
Tatol, 2011). ∆ =
173
∗
−
∗
) +(
∗
−
∗
) +(
∗
−
∗
)
Where:
174
∗
175
∗
176
(
,
∗
,
∗
,
∗
refers to the colour parameters of gels induced by standard methods, ,
∗
refers to the colour parameters of HHP induced gels.
2.2.7. Statistical analysis
177
The results were statistically analysed using Statistica 13.3 (TIBICO Software Inc.).
178
To determine the significance of differences between the average values of yield stress,
179
firmness, adhesiveness, spreadability, colour parameters of inulin gels mechanically,
180
thermally and HHP induced multifactor analysis of variance was used. Significant differences
181
between mechanical, thermal an HHP induction, as well as length of HHP treatment and
182
inulin concentration and were verified using Tukey’s test at significant level α=0.05.
183
Significant differences in analysed gel parameters for different inulin concentration were
184
verified using the t-Student test at significant level α=0.05.
185
3.
Results and discussion
186
3.1.
Effect of HHP treatment on gel formation of inulin
187
Under investigated conditions - mechanical, thermal, and high hydrostatic pressure
188
(500 MPa), independently from inulin concentration and treatment time (HHP), from inulin
189
water solutions the homogeneous gel structures were formed (VGI = 100 %, table 1). That
190
indicates that HHP might be an alternative method of inulin’s gel induction.
191
3.2.
Effect of HHP treatment on the structure of inulin gels
192
To observe the inulin gels structure electron microscopy was used. Scanning electron
193
microscopy images (Figure 1) showed the influence of HHP on inulin gel structure.
194
Mechanically and thermally induced inulin gels had a tridimensional granular-like structure.
195
During pressure treatment, morphological changes took place including disorganization of gel
196
structures. After HHP treatment the smooth surface of the gel become uneven and lost its
197
granular structure, also the microstructure of gels compressed, aggregated and larger areas of
198
disordered structures were formed. This might be due to induced the inulin nuclei partly
199
breakage or/and increasing the susceptibility of inulin chains to undergo a hydrolysis process
200
(Ronkart et al., 2010). The changes in the inulin gel structure under HHP depended also on
201
the treatment time. While time of HHP extend inulin gels granules were packed tighter with
202
melting on the surface of granules and after 20 minutes of HHP the granulated structure was
203
almost invisible. This results are in accordance with HHP treatment of other polysaccharides
204
such as starch (Colussi et al., 2018) or pectin (Peng et al., 2016). According to Kim et al.
205
(2001) the size of inulin particles is corelated with sandy texture of gels, the bigger particles
206
are the more sandy mouthfeel of a product occur. Larger inulin particles are obtained by the
207
mechanical treatment (Figure. 1) so the process like HHP investigated in this research or other
208
pressure treatments like micro-fluidization (Ronkart et al., 2010) or HPH (Alvarez-Sabatel et
209
al., 2015) might contribute to the formation of smoother texture even without heating the
210
product what is extremally important in introducing inulin gels as a fat replacement into
211
specific, non-thermal treated food products.
212
3.3.
Effect of HHP treatment on textural properties and yield stress of inulin gels
213
A significant impact on the ability to form inulin gel network and physical properties
214
of the obtained gels have a crystallisation conditions such as: inulin concentration, DP or
215
temperature of inulin solution which affect the size of primary particles in inulin gel network
216
and further gel formation Crystallization conditions such as: inulin concentration, DP or
217
temperature of inulin solution which affect the size of primary particles in inulin gel network
218
have a significant impact on the ability to form inulin gel networks and the physical properties
219
of the obtained gels (Bot et al., 2004, Beccard et al., 2019). This might have consequences in
220
terms of the gel functional properties and thus also on its use in food industry. Comparing
221
inulin gels, obtained by traditional methods (mechanical and thermal) with HHP methods,
222
significant (P<0.05) gel firmness losses were found in HHP treated samples regardless of
223
inulin concentration (table 1). Although there are no study on inulin solutions treated by HHP
224
it is well known that polysaccharides under HHP are being modified in the way that firmness
225
of product is degraded, the confirmation of this can be found in the study on materials built
226
with polysaccharides such as carrots (Araya et al., 2007), broccoli (Christiaens et al., 2011),
227
asparagus (Yi et al., 2016) treated by HHP. Additionally, almost none changes in firmness
228
was detected after extending treatment time from 5 to 20 minutes. What might suggest that
229
longer HHP treatment does not cause the inulin chain degradation like it occurs in thermal
230
induced gels (Glibowski & Wasko, 2008). It was stayed that adhesiveness of inulin gels is
231
strongly corelated with the inulin concentration, higher adhesiveness of inulin gels was found
232
in the gels containing 25 g/100g of inulin compared with 20 g/100g regardless to the
233
induction method (table 1). Similarly observed Chiavaro et al., (2007) testing inulin gels
234
obtained from inulin’s with different chemical composition (oligo-polysaccharides profile).
235
The HHP induced gels are similar in adhesiveness to those obtained by mechanical forces
236
while thermally induced gels are twice as adhesive. The reasons for this might be in
237
differences in the structure of inulin gels induced by different methods, which probably
238
results from different gelation mechanisms. HHP induced gel are probably formed the same,
239
as mechanically induced gels - by the intermolecular hydrogen bonds which are probably
240
mediated through the bridging water molecules in cross-linking junctions as it was proposed
241
for carrageenan (Steyer, Bera, Massaux, Sindic, Blecker & Deroanne, 1999). Obtained results
242
might also suggested that the HHP treatment had no effect on the molecular structure of
243
inulin, what was confirmed already for other polysaccharide such as starch (Katopo, Song, &
244
Jane, 2002, Li & Zhu, 2018).
245
As inulin gels have creamy appearance, and spreadable texture, with properties
246
resembling that of a fat crystal network in oil, its usage as fat replacer is very likely (Franck,
247
2002). That is why investigating the spredability of inulin gels is very important.
248
Spreadability (dynamic property), is a deformation under an external load, and the term to
249
describe the ease with which a spread can be applied in a thin layer to bread. Applied HHP
250
treatment did significantly affect the spredability of inulin gels. Firmness value in spredability
251
test for gels induce by HHP were much higher, regardless of the inulin concentration, than for
252
those obtained by thermal or mechanical treatment (table 1). Those higher spreadability
253
values might occurs due to the compressed structure developed under High Hydrostatic
254
Pressure treatment what is also visible on scanning electron microscopy images (Figure 1).
255
Similar observation was conducted by Vega-Gálvez et al. (2011) in the case of structural
256
polysaccharides (pectin, cellulose, and hemicellulose) located within the cell walls.
257
Yield stress is an initial resistance to flow under stress. For inulin gels it was reported
258
that yield stress (table 1) depends on the inulin concentration; the higher the solution
259
concentration, the greater the yield stress was. It also depends on the induction method, what
260
was more visible in gels containing 25 g/100g of inulin. The highest yield stress was noted for
261
inulin gels obtained by HHP treatment. What is more, yield stress of inulin gels containing
262
25 g/100g of inulin depends also on the HHP treatment time. The longer probes were kept
263
under pressure the higher yield stress was. Extending the treatment of HHP resulted in higher
264
yield stress of obtained gels. According to literature data the pressure holding time has an
265
effect on the overall texture of processed products (Ludikhuyze & Hendrickx, 2001, Vega-
266
Gálvez et al., 2011). In a case of the yield stress, which is the minimum force needed to drive
267
certain sample to flow (Mezger, 2006), it might be assumed that the increase of yield stress
268
for longer HHP treatment was also, like spredability, due to compressed structure developed
269
under High Hydrostatic Pressure treatment (Figure 1). These results are consistent with those
270
obtained by other authors that investigated the HHP treatment on viscosity, or yield stress of
271
xanthan gum (Dolz, Hernández, Delegido, Alfaro, & Muñoz, 2007) or pectin (Peng et al.,
272
2016), similar observations were made also for inulin solution treated with pressure
273
homogenisation (103-296 MPa) (Alvarez-Sabatel et al., 2015).
274
3.4.
Effect of HHP on stability of inulin gel
275
The effect of HHP treatment on gels’ stability was examined with the multi-sample
276
analytical centrifuge based on the STEP technology (space-time resolved extinction profiles).
277
Destabilization progression of process are shown on Figure 2. Inulin gels showed
278
sedimentation mechanism due to increase of transmission profiles on the bottom of cell. As
279
Glampedaki, Petzold, Dutschk, Miller, & Warmoeskerken (2012) proved the higher the
280
sedimentation rate, the lower the stability of products. The separation behavior of inulin gels
281
dependent less on the inulin concentration than on type of the induction. HHP treatment
282
allowed to obtained, for higher inulin concentration (25 g/100g), more stable inulin gels (with
283
lower instability index) compared with thermal and mechanical induction (Figures 3 & 4). It
284
may result from more compact structure of inulin HHP induce gels. Moreover it was observed
285
that extension of HHP treatment time, regardless to the inulin concetration, resulted in
286
increased stability of inulin gels. This can be explained by the influence of length of HHP
287
time treatment on the microstructure of obtained inulin gels. The extend time of HHP
288
treatment results besides the compression also in tighter packed granules of inulin gels with
289
melting on the surface of granules. The changes are visible in scanning electron microscopy
290
images (Figure 1). This results are in accordance with HHP treatment of other
291
polysaccharides such as starch (Colussi et al., 2018) or pectin (Peng et al., 2016).
292
3.5.
Effect of HHP on colour parameters of inulin gel
293
The lightness of the investigated inulin gels, regardless of the gel’s induction type,
294
depended on the inulin’s concertation concentration (table 2). The results are similar to that
295
obtained by Alvarez-Sabatel et al., (2018), whose observed that the increasement of inulin
296
concentration from 20 to 25 g/100g significantly increases the gel lightness. Inulin gels
297
obtained by HHP treatment are darker than gels obtained thermally or mechanically (table 2).
298
Although, there are no information about influence of HHP on colour parameters of inulin
299
gels, there are other polysaccharides that darker after HHP treatment like starch (Tabilo-
300
Munizaga & Barbosa-Canovas, 2004), glucomannan (Moreno et al., 2016) or Jerusalem
301
artichoke extracts (Kim, Fan, Chung, & Han, 2010). For other colour parameters (a*, b*)
302
differences between average values for different inulin gel induction methods were not big,
303
although inulin gels induced by HHP, especially with longer time treatment, were
304
characterized by lower a* value, when compare with mechanical induced gels. Basing on
305
comprehensive analysis of the effect of the applied gel induction method, using the total
306
colour difference parameter (∆E), it was found that although the differences in colour between
307
HHP induced gels and gels obtained by standard methods of induction were visible to the
308
unexperienced observer (∆E> 2), HHP-induced gels were more similar in colour to thermally
309
induced gels (2 <∆E <3.5) than to mechanically induced gels. Comparing colour between
310
HHP and mechanically induced gel it was found that parameter of total colour difference ∆E
311
was 3.5 <∆E <5 indicating that the differences in colour were noticed.
312
4. Conclusions
313
High pressure treatment of inulin’s solution might be an interesting alternative beyond
314
thermal and mechanical inulin gel inductions to produce food with novel textures, and with
315
better nutritional and functional ingredients retention. Inulin gels obtained by HHP method
316
comparing with described in literature (thermal and mechanical) methods weare significantly
317
darker and less firm as well as less spreadable regardless of inulin concentration and HHP
318
time treatment. but more stable. It was also found that HHP inducted gels had smoother, with
319
visible lower granular, compressed and aggregated structure. Extended exposure time to HHP
320
caused changes in inulin gels properties such as higher yield stress and stability as well as
321
obtaining tighter packed gels structure with melting on the surface. was not influencing
322
physical properties of inulin gels, what gives opportunity to sterilized product with HHP
323
without the risk of deterioration of inulin gel properties. Therefore HHP inulin’s gelling
324
induction as non-thermal method gives an opportunity to applied inulin gels in products where
325
their application was so far impossible.
326
327
328
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Table 1: Physical properties of inulin gels obtained by mechanical, thermal an HHP induction Inulin concentration Method of gel induction
20 g/100g
25 g/100g
Mechanical Thermal HHP 500 MPa 5 min HHP 500 MPa 10 min HHP 500 MPa 20 min Mechanical Thermal HHP 500 MPa 5 min HHP 500 MPa 10 min HHP 500 MPa 20 min
VGI [%] 100a 100a 100a 100a 100a 100a 100a 100a 100a 100a
Firmness [N]
Adhesiveness [Ns]
Spreadability [N]
Yield stress [Pa]
2.72b# ± 0.24 2.88b# ± 0.20 1.19a#± 0.01 1.15a# ± 0.01 1.47a# ± 0.02 5.65c# ± 0.41 7.44d# ± 0.65 3.13ab# ± 0.01 2.72a# ± 0.02 3.59b# ± 0.02
-0.65b# ± 0.21 -1.31a# ± 0.08 -0.58b# ± 0.01 -0.52bc# ± 0.06 -0.54bc# ± 0.01 -1.20bc# ± 0.11 -3.33a# ± 0.21 -1.25bc# ± 0.08 -1.15c# ± 0.01 -1.22c# ± 0.01
0.51a ± 0.08 1.96ab# ± 0.16 5.73d# ± 1.72 4.90cd# ± 0.01 5.40d# ± 0.09 1.80a ± 0.27 5.49b# ± 0.53 10.76c# ± 0.27 12.13d# ± 0.01 12.15d# ± 0.26
270.1a# ± 11.4 410.9a# ± 14.5 582.7b# ± 10.3 650.0b# ± 7.2 617.6b# ± 3.5 690.1a# ± 15.6 840.6b# ± 14.2 1061.4c# ± 8.4 1452.9d# ± 47.5 1646.0e# ± 36.7
Values are mean ± SD (n=3). a, b, …- values followed by the same letter within a column for the same inulin concentration do not differ significantly according to Tukey’s test (P<0,05),. #- values with # within a column for the same induction method differ significantly according to Tukey’s test the t-Student test (P<0,05).
Table 2: Colour parameters of inulin gels obtained by mechanical, thermal an HHP induction ∆E
Colour parameters Inulin concentration Method of gel induction
20 g/100g
25 g/100g
Mechanical Thermal HHP 500 MPa 5 min HHP 500 MPa 10 min HHP 500 MPa 20 min Mechanical Thermal HHP 500 MPa 5 min HHP 500 MPa 10 min HHP 500 MPa 20 min
L*
a*
b*
89.53b# ± 1.26 89.17b# ± 0.09 86.29a# ± 0.21 86.39a# ± 0.26 85.39a# ± 0.13 92.29c# ± 0.84 90.04b# ± 0.31 88.03a# ± 0.12 87.88a# ± 0.15 87.81a#± 0.35
-1.31b ± 0.13 -1.54ab ± 0.02 -1.41ab# ± 0.03 -1.42ab# ± 0.07 -1.64a ± 0.10 -1.29b ± 0.12 -1.62a ± 0.13 -1.66a# ± 0.03 -1.63a# ± 0.03 -1.63a ± 0.06
2.19c ± 0.22 0.64ab# ± 0.06 0.91ab# ± 0.07 0.56ab# ± 0.05 0.96b# ± 0.35 2.57b ± 0.53 1.27a# ± 0.11 2.48b# ± 0.03 2.35b# ± 0.08 2.44b# ± 0.05
Comp. mechanical 1,91± 0,13 3,56± 1,18 3,61± 1,01 4,41± 1,11 2,73± 0,70 4,31± 0,71 4,46± 0,93 4,52± 0,66
Comp. thermal 1,91± 0,13 2,90± 0,22 2,79± 0,35 3,28± 0,18 2,73± 0,70 2,36± 0,32 2,42± 0,37 2,54± 0,25
Values are mean ± SD (n=3). a, b, …- values followed by the same letter within a column for the same inulin concentration do not differ significantly according to Tukey’s test (P<0,05),. #- values with # within a column for the same induction method differ significantly according to Tukey’s test the t-Student test (P<0,05).
Figure 1: Influence of HHP on inulin gel structure in comparison with thermal and mechanical induction
20g/100g; thermal
25g/100g; thermal
20g/100g; mechanical
25g/100g; mechanical
20g/100g; HHP 5 min
25g/100g; HHP 5 min
20g/100g; HHP 10 min
25g/100g; HHP 10 min
20g/100g; HHP 20 min
25g/100g; HHP 20 min
Figure 2. Transmission profiles of inulin gels formed from solutions with inulin concentrations 20 and 25 g/100g, obtained by thermal, mechanical, and HHP induction presented enabling LUMiSizer® analysis
Figure 3: Influence of HHP on stability of 20 g/100g inulin gels in comparison with thermal and mechanical induction
Figure 4: Influence of HHP on stability of 25 g/100g inulin gels in comparison with thermal and mechanical induction
Highlights HHP (500 MPa) induced inulin gelation regardless of the time treatment (5-20 min). HHP gels, comparing with thermally and mechanically induced ones, are less firm and spreadable. HHP induction increased yield stress and stability of inulin gels. HHP induction gave gels with the uneven surface and less granular structure. HHP gels had unique properties which may allow using it in creating new products.