Food-grade filler particles as an alternative method to modify the texture and stability of myofibrillar gels

Abstract

A series of food grade particles were characterized for their potential as fillers in myofibrillar gels. The fillers were separated into (i) hydrophilic, insoluble, crystalline particles and (ii) starch granules. The particles used were microcrystalline cellulose, oat fiber and walnut shell flour, as well as potato and tapioca starches. Crystalline particles increased hardness and decreased recovery properties. Although all of these fillers decreased the T2 relaxation time of water, this was dependent on particle type and size. An increase in gel strength was observed with increasing filler content, which was attributed to particle crowding. Native potato starch was the most efficient at increasing liquid retention, while native tapioca was the least effective. Gel strength increased significantly only for the native potato and modified tapioca starches, but no effect on recovery attributes were observed for any of the starch varieties. The potato starches became swollen and hydrated to a similar extent during the protein gelation process, while the native tapioca starch gelatinized at higher temperatures, and the modified tapioca showed little evidence of swelling. T2 relaxometry supported this finding, as the meat batters containing native potato starch displayed two water populations, while the remaining starches displayed only a single population.

Full text

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Food-grade ller particles as an
alternative method to modify the
texture and stability of myobrillar
gels
Andrew J. Gravelle, Shai Barbut & Alejandro G. Marangoni
A series of food grade particles were characterized for their potential as llers in myobrillar gels. The
llers were separated into (i) hydrophilic, insoluble, crystalline particles and (ii) starch granules. The
particles used were microcrystalline cellulose, oat ber and walnut shell our, as well as potato and
tapioca starches. Crystalline particles increased hardness and decreased recovery properties. Although
all of these llers decreased the T2 relaxation time of water, this was dependent on particle type and
size. An increase in gel strength was observed with increasing ller content, which was attributed to
particle crowding. Native potato starch was the most ecient at increasing liquid retention, while
native tapioca was the least eective. Gel strength increased signicantly only for the native potato
and modied tapioca starches, but no eect on recovery attributes were observed for any of the starch
varieties. The potato starches became swollen and hydrated to a similar extent during the protein
gelation process, while the native tapioca starch gelatinized at higher temperatures, and the modied
tapioca showed little evidence of swelling. T2 relaxometry supported this nding, as the meat batters
containing native potato starch displayed two water populations, while the remaining starches
displayed only a single population.
Finely comminuted meat products such as frankfurter-type sausages and bologna can be described as a discrete
fat phase embedded in a thermally-set protein gel network1, 2. e chopping, or comminution process is per-
formed under saline conditions to facilitate extraction of the salt-soluble (predominantly myobrillar) proteins.
Some of these proteins associate at the surface of the fat globules, forming an interfacial protein lm (IPF), thus
embedding the fat droplets within the gel matrix, as well as acting to physically restrain or stabilize the droplets
during the thermal gelation process1. As a result, these types of products are commonly referred to as meat emul-
sions, or meat batters.
Comminuted meat products have a relatively high fat content (oen 20–30% or greater), and as this fat gen-
erally comes from animal sources which are rich in saturated fatty acids, these products oen contain a signif-
icant amount of saturates. Although there has been conicting evidence on the role of saturated fats on human
health in recent years, consumption trends have been steered towards mono- and poly-unsaturated fats3, and both
fat- and calorie-reduced products remain popular with consumers. As a result, there have been many strategies
explored for both reducing fat content and utilizing fats with more favorable lipid proles4, 5. e main target of
such strategies has been to decrease the caloric content or incorporate liquid vegetable oils, while maintaining
product performance (e.g. yield, stability) and mimicking desirable sensory attributes, such as texture and per-
ceived juiciness.
e addition of carbohydrates has been the dominant strategy used to retain sensory properties of com-
minuted meats when reducing fat content, as they can serve to improve the water holding capacity of the meat
protein6. Starches are commonly used across the meat industry to retain moisture either by acting as bulking
agents through the formation of hydrogels. Starches are a popular ingredient because they are inexpensive, and
their composition and functional properties vary with plant source; the latter of which can be further tailored
by various physical or chemical modications. e use of starches as water binding agents in comminuted meats
is well established4, 6, 7; however, various modied and underutilized sources of starch are still being actively
Department of Food Science, University of Guelph, Guelph, ON, Canada. Correspondence and requests for materials
should be addressed to A.G.M. (email: amarango@uoguelph.ca)
Received: 12 June 2017
Accepted: 30 August 2017
Published: xx xx xxxx
OPEN

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investigated8, 9. Other hydrocolloids such as dietary bres10–12, gums13, 14, and cellulose derivatives15, 16 have also
been explored, and are still of interest in current literature.
In addition to reducing the caloric content of comminuted meats through fat reduction, strategies for achiev-
ing an improved lipid prole have represented an alternative approach to improving the nutritional prole of
these products5. Such strategies have included using oils from plant sources which have been pre-emulsied
with non-meat proteins17, 18, or structured via non-traditional means, including oil in water emulsions19, 20, gelled
emulsions (i.e. the oil is dispersed in a hydrogel)11, or oleogelators (i.e. directly structuring the oil)21, 22.
Traditionally, the mechanism by which fat globules are stabilized in a comminuted meat system was thought
to be via either emulsication or physical entrapment1. However, it was recently proposed that the capillary forces
arising from the water lled channels present throughout protein network are responsible for the water holding
ability of these so materials23, 24, as well as stabilizing the fat phase. In a recent study, our group demonstrated
that incorporating micron-sized glass beads in a lean comminuted chicken meat batter can serve to enhance
the performance of the resulting composite gel by providing support to the capillary network25. e addition of
these particles as a model insoluble hydrophilic ller dramatically decreased liquid expulsion and improved the
integrity of the protein gel network; i.e. increased texture prole analysis (TPA) parameters and decreased the
occurrence of microfractures induced by uid migration. Under the capillarity hypothesis23, it would be expected
that providing support to the capillary network would also serve to stabilize the embedded lipid droplets24, which
could assist with reformulating comminuted meat products with improved lipid proles. erefore, the goal of
this work was to investigate the feasibility of using food-grade hydrophilic, insoluble ller particles to serve as
analogs for glass beads. e particles selected were microcrystalline cellulose (MCC, 2 sizes), oat ber, and wal-
nut shell our. To contrast the crystalline particles (which are not aected by the thermal gelation process), two
types of starches were investigated as llers. Although starches arecommonly used to improve liquid retention
in comminuted meats, they are generally not viewed as particulate llers, as they swell and gelatinize during
thermal processing. However, if the granules maintain some crystallinity and structural integrity, it may be useful
to interpret their inuence on the meat protein gel in terms of particle-lled composite materials. To this end,
native potato and tapioca starches were selected as llers, as they vary in both size and gelatinization temperature.
Furthermore, a modied version of each starch variety was also investigated, to determine how modifying the
gelatinization temperature aected their impact on the composite meat protein gel.
Results and Discussion
Crystalline ller particles. Liquid loss and large deformation properties. Fluid losses (fat and water) are
commonly used as an indicator of stability in comminuted meat products6, 26, as uid retention contributes to
important attributes such as juiciness and rmness. e liquid loss during thermal gelation of the composites
containing crystalline ller particles is presented in Fig.1A, and is reported as the wt% relative to the meat batter
(note: no fat loss was observed). In the absence of ller, the comminuted meat gels exuded ~9 wt% liquid. In
commercial products such as frankfurters, emulsied fat binds to the protein network, acting as an ‘active’ ller,
thus contributing to the stability of the protein network, and aiding in moisture retention1, 24. As no fat was added
to the lean chicken breast meat in the present work, this level of uid loss suggests the gel matrix was relatively
stable. e addition of crystalline ller particles had little impact on further improving gel stability across the
range of ller content investigated (mf = 0–0.15). e only notable exception was MCC-105, which produced a
signicant decrease in liquid loss relative to the unlled sample at mf of 0.10 and 0.15. is result is in line with
previous work published by our group using hydrophilic glass microspheres of varying sizes as model ller parti-
cles in comminuted chicken meat batters25, 27. Glass beads ~4 μm in diameter completely arrested liquid expulsion
at low incorporation levels (volume fraction <0.05); however, the ability of these particles to stabilize the water
phase rapidly diminished with increasing particle size, requiring a much higher ller content to eliminate liquid
losses. erefore,as all of the particles presented in Fig.1 were selected for their crystalline nature and insolubility
in water, the inuence of the ~15 μm MCC-105 particles can likely be attributed to their smaller size (relative to
the other particles), and the associated increased surface area available to interact with water. is point will be
further addressed in the following subsections.
Figure1B and C respectively depict the large deformation Hardness and Resilience, as measured by uniaxial
compression to 50% of the sample’s original height. For all varieties of crystalline particles under investigation,
a relatively high mf is required to produce a signicant increase in Hardness relative to the unlled gel (Oat:
mf ≥ 0.10; MCC-102, MCC-105, Walnut: mf = 0.15). Previous work has indicated that the textural properties
of comminuted meat batters can be enhanced by stabilizing the water phase; however, an increase in composite
Hardness occurred for all particle types, irrespective of their ability to decrease liquid losses. High ller load-
ing can also result in particle-particle contacts, and when the ller particles are signicantly stier than the
surrounding matrix, such contacts will have a greater capacity to withstand deformation, thus resulting in the
observed increase in Hardness27. erefore, the observed increase in the strength of the composites with a high
ller content can be attributed to stress-loading of the rigid particles during the deformation process as a result
of ller crowding. Similar to the observed increase in gel strength here, Rayment et al. reported an increase in
the viscosity of MCC-lled guar galactomannan solutions prepared with an increasing volume fraction ller28.
Furthermore, Schuh et al. demonstrated that the rmness of full-fat comminuted meat batters gradually increased
when incorporating low concentrations of MCC (0.3–2.0 wt%)16. In contrast, equivalent concentrations of car-
boxymethyl cellulose greatly decreased the rmness of these composites and drastically altered the microstruc-
ture of the protein network. ese results indicate the surface chemistry of the ller particles strongly inuences
their compatibility with the gel network, and furthermore suggests the crystalline llers investigated here were
relatively compatible with the meat protein network (as no decrease in gel strength was observed).
The incorporation of rigid particles in a flexible matrix can contribute to stress concentration at the
particle-matrix interface during deformation, which has been shown to act as a nucleation point for

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microfractures29. Such debonding from the matrix during deformation has also been shown in particle-lled food
gels in which the modulus of the ller and matrix are comparable. Plucknett et al. characterized the debonding of
spherical maltodextrin particles embedded in a continuous gelatin matrix by confocal microscopy30, 31, indicating
weak adhesion can also contribute to fracture at the interface. At higher ller concentrations, ller-ller contacts
can result in particles slipping past one another during compression, thus having a negative impact on the recov-
ery of the composite material. Such behavior is observed in the Resilience of the composites with increasing mf in
Fig.1C. For all particle types, the Resilience decreased with increasing mf, and this eect was more pronounced
in the composites containing the walnut and oat particles. e reduced impact of the MCC particles on the
Resilience may be attributed to their thin, rectangular shape. During incorporation, some of the particles would
become oriented so that they either reduce stress concentration at the interface (i.e., orienting with their at face
parallel to the axis of compression), and some may align favorably with neighboring particles to reduce the occur-
rence of particle slips. Interestingly, despite the fact that the MCC-105 particles were able to improve the stability
of the matrix (i.e. increased liquid retention), the textural properties of these composites did not show any stark
dierences from the other crystalline llers.
e Resilience is dened as the ratio of work exerted by the material during the decompression of the rst cycle
relative to that of the compressionstage; i.e. the instantaneous recovery of the material. erefore, the observed
decrease in Resilience with increasing ller content is consistent with the proposed mechanism of increasing
composite Hardness at high mf without an associated decrease in liquid loss. Furthermore, an analogous behavior
Figure 1. Post-gelation liquid loss (A), and texture prole analysis Hardness (B) and Resilience (C) of
the composite meat protein gels containing crystalline particles as llers. Fillers denoted in legend are
microcrystalline cellulose (larger particles: MCC-102; smaller particles: MCC-105), oat ber (Oat), and walnut
shell our (Walnut).

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to that depicted in Fig.1C was observed for the Cohesiveness and Springiness TPA parameters, which also incor-
porate the recovery of the material aer a second compression (see Supplementary Material, Fig.S1).
Microstructure. Light micrographs of the crystalline particle-lled meat protein gels (mf = 0.10) are presented
in Fig.2. A PAS stain was used to highlight the carbohydrate-based ller particles (purple), and the surrounding
matrix was counter-stained with H&E (pink). e le column of Fig.2 depicts micrographs of the composites
acquired in brighteld mode, while the right column depicts the same location imaged under polarized light.
Figure 2. Light micrographs of composite meat protein gels containing crystalline particles as llers (mass
fraction ller, mf = 0.10). Panels (A,C,E,G) were taken in brighteld mode, and those in Panels (B,D,F,H) were
taken with polarized light. e ller particles incorporated were MCC-102 (A,B), MCC-105 (C,D), oat ber
(E,F), and walnut shell our (G,H). All images were acquired using a 10x objective.

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ese images indicate the crystallinity of the particles was maintained aer being subjected to the thermal gela-
tion procedure. is was further conrmed by dispersing each class of particles in water and acquiring images
both before and aer mimicking the thermal gelation process (see Supplementary Material, Fig.S2). e particles
appeared unaected by the heat treatment, and no evidence of swelling was noted.
All particle types appeared to be well distributed throughout the protein matrix, and no evidence of orien-
tation due to the preparation process was noted. It can be seen that the smaller MCC-105 particles are highly
dispersed throughout the gel network relative to the other particles, which corroborates well with their ability to
decrease liquid losses at higher mf. e MCC-102, walnut, and oat particles which did not provide any improve-
ment in uid retention, all appear to be comparable in size. is further reinforces the hypothesis that the ability
of hydrophilic, insoluble ller particles to improve stability in a comminuted meat product is dictated by the
available ller surface area27, 32.
e micrographs of the composites containing oat ber show that the particles are particularly disconnected
from the surrounding protein network (Fig.2E). is is also seen in the composites containing walnut shell our
particles (Fig.2G), and at higher magnication (Supplementary Material,Fig.S3), is also observed in the samples
prepared with MCC-102 and even the MCC-105, albeit to a much lesser extent. Interestingly, the oat particles
also produced the greatest increase in TPA Hardness (Fig.1B) at high concentrations, and both the oat- and
walnut particles had signicantly lower Resilience values than those containing MCC at equivalent mf (Fig.1C).
A similar trend was also seen in the Cohesiveness (Supplementary Material,Fig.S1B), indicating the apparent
discontinuity between the particles and protein matrix is detrimental to the recovery of the composite gels.
e free space between the particles and protein matrix noted above may suggest that the myobrillar proteins
have a limited ability to adhere to these llers during gelation, allowing free water to pool around the particles.
However, as these llers do not appear to be tightly embedded within the gel network, this interaction would
not serve as an ecient means to stabilize the water phase, which is in agreement with the observed liquid losses
presented in Fig.1A. In contrast, the small size of the MCC-105 particles allows them to become more eciently
integrated into the gel network. Moreover, the available surface area increases dramatically with decreasing par-
ticle size, and it can be seen that the ller is more evenly distributed throughout the gel, resulting in a greater
capacity to stabilize the liquid phase. is observation is in line with our previously published results using glass
microspheres of varying sizes27, 33.
T2 relaxometry. T2 relaxometry has been utilized in various meat systems to provide an indication of how the
mobility of the aqueous phase is aected by various parameters, such as processing conditions and formulation
changes34–36. Here we have investigated the eect of ller type and mf on the relative mobility of water, both in a
bulk state, and in the context of the comminuted meat batters. Figure3 depicts the T2 relaxation proles of each
ller type at varying mf,and the corresponding peak relaxation times are presented in Table 1. All measurements
Figure 3. T2 relaxation proles of crystalline ller particles dispersed in a 0.5 wt% xanthan gum solution prior
to (solid lines) and post-thermal treatment (dashed lines); MCC-102 (A), MCC-105 (B), oat ber (C), and
walnut shell our (D). e mass fraction ller content is denoted in the legend in Panel B. Note: Control (no
ller) is only depicted in Panel A.

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were performed both before and aer mimicking the thermal gelation procedure used to prepare the commi-
nuted meat products. Note that all bulk water measurements were carried out using a 0.5 wt% xanthan gum
solution which was used to keep the particles suspended throughout the duration of the measurement. For all
ller types, the relaxation time of the dominant peak decreases with increasing mf, both pre- and post-thermal
treatment. In all cases, the relaxation time increases moderately aer heating. As this is also observed in the con-
trol solution (Fig.3A, gray curves), and no discernable dierences are noted in the microstructure of the particles
aer thermal treatment (Supplementary Material, Fig.S2), these shis can be attributed to the eect of heating
on the xanthan solution.
e T2 relaxation proles presented in Fig.3 indicate the eectiveness of the particles in decreasing the apparent
water mobility were MCC-102 < MCC-105 ≈ Oat < Walnut. e relative inuence of the llers can be attributed
to two factors; (i) the available surface area, and (ii) the chemical composition of the particles. Our group recently
reported that the peak relaxation times of the water component in glass bead-lled comminuted meat compos-
ites are shorter when smaller particles are employed, and further decrease with increasing ller content25, 33.
A similar eect has been reported in myobrillar protein gels containing sugarcane ber of varying size, where
both ller size and concentration impacted the dominant T2 relaxation times37. e oat ber and walnut shell
our should also be distinguished from the MCC, as in addition to cellulose, these particles contain other plant
structuring material, such as lignin and hemicellulose. e latter is a heterogeneous carbohydrate polymer which
may improve the interaction of the particles with water, due to its amorphous nature. e process by which these
particles are made (i.e. grinding and milling) would also be expected to produce rougher, more pitted surfaces
which would further improve their ability to interact with water. erefore, inuence of the various crystalline
llers on the peak T2 relaxation time of bulk water can be rationalized by the combined impact of particle size
and surface properties.
It is also worth noting that the presence of xanthan gum has been shown to eect the rheological properties
of particulate solutions via depletion occulation38, which may decrease the apparent T2 of the llers. e extent
of this eect would be inuenced by ller size, and any interaction between the crystalline llers and the xanthan
gum itself. erefore, when comparing T2 values of the dierent particle types, the possibility of this eect should
be kept in mind.
e T2 relaxation proles of the crystalline particle-lled meat protein batters before and aer thermal treat-
ment are depicted in Fig.4, and corresponding peak relaxation times are presented in Table1. e relaxation
proles are typical of comminuted meat systems, with a dominant peak (denoted T2,1) around 50–200 ms35, 36, 39,
which has been attributed to the water present within the comminuted protein network34. For all formulations,
the T2,1 relaxation times of the composite meat systems are shorter aer gelation34, 35, which has been attributed to
the denaturation, rearrangement, and associated contraction of the protein molecules.
Prior to gelation, the eect of the particles was analogous to that seen in the bulk state; T2,1 values decreased
with increasing ller content, and the relative impact of the ller types was consistent with that reported above
(i.e. MCC-102 < MCC-105 ≈ Oat < Walnut). Aer gelation and removal of the expelled water, there are notable
dierences between the ller types. e MCC-102 particles decreased the relaxation time of the composite from
68 to 62 ms; however, there was no longer an observed concentration eect. At mf = 0.05, the smaller MCC-105
particles produced a T2,1 value in agreement with the MCC-102, while for those formulations which exhibited
improved water retention (mf = 0.10 and 0.15), the peak relaxation time decreased marginally to ~57 ms. For
both the oat and walnut-lled gels, the T2,1 relaxation times decrease with increasing mf, consistent with the trend
observed prior to thermal treatment. Although these particles produced composites with T2,1 values equivalent
to, or shorter than the MCC-105-lled batters, neither produced an improvement in gel stability. is is in con-
trast to previous studies on glass bead-lled meat batters where a shorter T2,1 value in the uncooked batter was
Figure 4. T2 relaxation proles of composite meat protein gels containing various crystalline ller particles;
MCC-102 (A,B), MCC-105 (C,D), oat ber (E,F), and walnut our (G,H). Relaxation proles were acquired
both prior to- (A,C,E,G) and post-thermal treatment (B,D,F,H). e mass fraction ller content is denoted in
the legend in Panel A.

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indicative of reduced water mobility. In these composites, decreasing water mobility improved liquid retention by
limiting migration through the gel during heating. Furthermore, this reduced the occurrence of water channels
(i.e. microfractures), thus improving the large deformation properties of the resulting composite gel25, 33.
Here, we propose that both ller size and the surface properties (chemical composition, surface geometry,
roughness, etc.) of the particles contribute to the stability and mechanical properties of the composite gels. e
ability of the MCC-105 particles to improve water retention can be attributed to their uniform small size (~15 μm)
and homogeneous distribution throughout the network. e size of these particles is also comparable tothat of
the water channels present in nely comminuted chicken meat batters observed by SEM; ~3–4 μm, as quantied
by Stevenson et al.23. Although the walnut particles are only marginally larger (~40 μm on average) and have a
stronger interaction with water as evident by T2 relaxometry, there is a much wider size distribution, and apparent
water pooling at the interface. As noted above, such pooling may be due to the chemical composition of the plant
material (e.g. presence of hemicellulose), as well as a weak interaction with the protein gel matrix. e combina-
tion of these two factors diminishes the ability of these particles to restrict water mobility within the meat batter,
despite the apparent decrease in T2 both in bulk water and in the meat batters. is eectively diminishes the abil-
ity of the walnut particles to stabilize the water within the protein network during the gelation process, rendering
them inert at low mf. is interpretation is also consistent with the eect of the oat and MCC-105 particles which
are both orders of magnitude larger than the capillary diameter and are less eective at reducing the T2 values of
water in the meat system than the walnut particles.
Starch ller particles. Liquid loss and large deformation properties. Starches are commonly used as llers
in processed meat products to bind water which would otherwise be exuded from the product, thus improving
the textural and sensory characteristics6. Starch granules were selected as ller particles to contrast with the
crystalline ller particles described above. Potato starch and tapioca starch were selected for their similar compo-
sition (amylose:amylopectin ratio), and distinct size dierences (small and large, respectively; see Supplementary
Material, Fig.S5). Additionally, for each starch variety, a modied version designed for high temperature appli-
cations was also used. For all of the starch-lled meat batters, the protein content was decreased from 10.6%
(used for crystalline llers) to 10.25% to increase liquid expulsion, thus making the impact of the particles more
pronounced.
Liquid loss of the comminuted meat batters containing various starches is presented in Fig.5A. Overall, the
decrease in liquid loss with increasing mf occurred most rapidly with the addition of native potato starch, while
native tapioca starch required higher mf to achieve the same liquid retention. Full stabilization was achieved at
mf ≈ 0.0375 and 0.075, respectively. is may be due to the smaller granule size (decreased water holding capac-
ity), or a higher swelling and gelatinization temperature. e latter could result in some of the mobile water being
exuded from the protein network prior to the onset of swelling. e two modied starches had an equivalent,
intermediate eect on improving water retention, where the modied potato starch produced a decrease in the
water holding ability of the composite, while the modied tapioca showed improved liquid retention, relative to
their native counterparts.
e starches had a relatively minor impact on the TPA Hardness of the composite gels (see Fig.5B), and
although there was a general increase in Hardness at higher ller content, the only samples which displayed a
signicant increase from the unlled gel were those having a mf = 0.10 of either native potato starch or modi-
ed tapioca starch. e observed increase in Hardness at high mf can be attributed to a combination of particle
Filler mf
T2,1 of particles in 0.5% xanthan T2,1 of particles in meat batter
Pre-heating Post-heating Pre-heating Post-heating
MCC-102
0 1710 2040 131 73
0.05 1219 1200 120 69
0.1 630 630 107 70
0.15 357 380 100 64
MCC-105
0 1710 2040 131 73
0.05 570 645 103 65
0.1 350 410 83 60
0.15 210 240 70 56
Oat
0 1710 2040 131 73
0.05 615 675 103 65
0.1 355 445 81 58
0.15 220 260 65 50
Wal n ut
0 1710 2040 131 73
0.05 260 340 94 55
0.1 130 155 72 47
0.15 85 110 55 46
Table 1. Peak T2 relaxation values for the crystalline particles dispersed in a 0.5% xanthan solution, and
incorporated into meat batters. Relaxation times are presented for both before (Pre-) and aer (Post-) thermal
treatment. All values are reported in ms.

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crowding (outlined above), and insucient free water available to fully hydrate the starches. e latter would
result in rmer, partially swollen granules being distributed throughout the gel network, and could contribute to
the Hardness of the composite material either by traditional particle reinforcement, or ller crowding. In other
words, the partially swollen starch granules may behave in a manner analogous to a traditional particulate ller as
opposed to forming a hydrocolloid network, which would be expected under conditions of surplus water and suf-
cient heating. erefore, the signicant increase from the unlled batter seen for the native potato and modied
tapioca starches at mf = 0.10 may be attributed to the more eective wateruptake/stabilization of these starches,
as seen from the liquid loss (Fig.5A). Although this argument suggests the two modied starches should have a
similar impact on Hardness, their inuence will also depend on the gelatinization temperature of the particular
starch employed. erefore, this discrepancy will be addressed in the following section.
An alternative interpretation of the observed increase in Hardness at high mf may be that the excess starch
particles draw additional water out of the protein network during gel formation. is would produce a more
densely packed protein network, resulting in increased gel strength. However, this mechanism would eectively
produce a more concentrated protein network, which should also be expected to have an eect on other textural
parameters, which was not observed (Fig.5C and Supplementary Material, Fig.S4).
e Resilience (i.e. immediate recovery) of the composite meat batters does not deviate from the unlled con-
trol, irrespective of starch type or ller content across the entire range of mf investigated. Although the Resilience
of the composites containing the crystalline llers gradually decreased with increasing mf, the decreased rigidity
of the partially hydrated starch granules, as well as their compatibility with the protein network, resulted in an
Figure 5. Post-gelation liquid loss (A), and texture prole analysis Hardness (B) and Resilience (C) of the
composite meat protein gels containing potato starch (native: open diamonds; modied: lled diamonds)
ortapioca starch (native: open circles; modied: lled circles).

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overall neutral impact. Although it was previously noted that the presence of rigid particles may lead to stress
concentration at the interface29, the partial swelling of the granules could be expected to provide some exibility
to the ller, thus diminishing the stress concentration eect and decreasing the occurrence of microfractures at
the ller/matrix interface.
ermal behavior. e thermal proles and gelatinization temperatures (Tgel) of the various starches used as
ller particles are presented in Fig.6. e Tgel of the native potato starch (63.46 ± 0.02 °C) was lower than that
of native tapioca (68.67 ± 0.67 °C), which was only a few degrees below the nal cooking temperature of the
comminuted meat batters (72 °C). is is consistent with the observation that potato starch was more eective
at increasing water retention than tapioca. Furthermore, the modied potato starch used in this study had a
slightly higher Tgel (64.54 ± 0.11 °C), while the modied tapioca had the lowest Tgel of all the starches investigated
(56.69 ± 0.06 °C). is is also reected in the liquid loss of the composites, as the modied potato resulted in a
signicant increase in liquid expulsion than the native potato at lower mf (0.0125–0.0375), while the modied
tapioca improved liquid retention at equivalent mf. As there were no signicant dierences among the starches
at equivalent mf for both Hardness and Resilience, no conclusions could be drawn about the eect of Tgel on the
textural properties of the composites. at being said, the general trend in the data suggested that within each
starch variety, decreasing Tgel increased the TPA parameters at high mf.
Although the modied tapioca starch had the lowest peak Tgel, native potato starch had the greatest impact
on improving liquid retention. is suggests that in addition to Tgel, dierences in the structural make-up of the
two starch varieties also impacts their inuence on the water holding and textural properties of the starch-lled
comminuted meat batters. From the present work, it appears that the Tgel may be used as an indicator of how a
modication might impact the performance of a given starch variety (e.g. modied tapioca vs native tapioca);
however, this would need to be validated with a more thorough screening of various types of modied starches,
which is outside the scope of the present investigation. Furthermore, heating rates and total cooking times will
also impact the extent of swelling and gelatinization, and thus the eectiveness of the starches7, 9.
Microstructure. Micrographs of the various starch-lled comminuted meat batters (mf = 0.0125) are presented
in Fig.7. Under polarized light, only a minor amount of crystallinity was noted, indicating the granules had
undergone a signicant amount of swelling, but were not completely gelatinized. Interestingly, the size of these
partially hydrated starch particles were comparable to the untreated granules (see Supplementary Material,
Fig.S5). By mimicking the thermal gelation process in an excess of water, it was found that the native and mod-
ied potato starch granules swelled to multiple times their original size, while the tapioca starches remained
similar to that of the dry starch. Additionally, non-hydrated crystalline granules are present only in the compos-
ites containing native Tapioca (smaller particles displaying Maltese cross pattern under polarized light). is is
consistent with the thermal behavior observed by DSC which indicates the peak gelatinization occurs at ~66 °C
in the presence of excess water, while this shis to ~78 °C in the meat batter (data not shown); i.e. above the nal
cooking temperature. Despite the dierences in Tgel, the native and modied tapioca starches appear to be swol-
len to a similar extent. Furthermore, when heated in excess water under conditions mimicking the meat gelation
procedure, the modied tapioca starch showed little evidence of swelling, despite the absence of any crystallinity
(see Supplementary Material,Fig.S5). is suggests the modication made to the tapioca starch maintained the
integrity of the granule, while the lower Tgel implies the amylopectin (and possibly amylose) molecules undergo
structural rearrangement, and partially leach from the granule during the meat batter gelation procedure.
e swelling of both the native and modied potato starch particles appears to have been physically restricted
by the protein gel network, as the partially-hydrated granules are substantially smaller than when heated in excess
water (Supplementary Material,Fig.S5). ese images are consistent with previous studies40, 41, and the restricted
swelling can be attributed to the fact that the myobrillar proteins denature, aggregate, and begin to form a
three-dimensional network at temperatures between 35–50 °C2. Although this might inhibit the ability of the
Figure 6. Representative DSC thermal proles of the various starches used as ller particles in comminuted
meat products. Top to bottom: native potato, modied potato, native tapioca, modied tapioca. Peak
gelatinization temperature is denoted for each starch in the gure.

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starch to absorb water, the micrographs clearly indicate that the majority of the crystallinity is destroyed, indicat-
ing the particles are at least partially hydrated. As a result, at lower concentrations these particles become deform-
able and thus do not signicantly contribute to the large deformation properties of the composite. Although more
crystallinity is retained when a higher ller content is employed (due to the limited availability of water), these
formulations far exceed those normally used in commercial products. Modied starches able to withstand ther-
mal treatment and maintain their crystallinity in the nal product may provide an alternative means to modify
Figure 7. Light micrographs of composite meat protein gels containing native potato starch (A,B), modied
potato starch (C,D), native tapioca starch (E,F), and modied tapioca starch (G,H) as llers (mass fraction ller,
mf = 0.0125). Panels A, C, E, and G were acquired in brighteld mode, and corresponding images acquired with
a polarizing lter are shown in Panels B, D, F, and H. All images were acquired using a 10x objective.

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textural properties; however, as noted above, particle size is also a key factor in providing stability to comminuted
meat protein gels. One would therefore require a thermally stable starch with a narrow size distribution of e.g.
1–20 μm, as beyond this size range, the ability of sti inert particles to support the capillary network throughout
the protein gel rapidly diminishes32, 33.
T2 relaxometry. T2 relaxation proles of the various starch particles dispersed in xanthan gum are presented in
Fig.8. It can be seen that both the tapioca starches produced considerably shorter relaxation times than potato
starch, particularly at the low to intermediate mf tested. is dierence is also more pronounced prior to ther-
mal treatment. Consistent with the crystalline particles, the peak relaxation times increase aer mimicking the
thermal gelation process in excess water; however this was particularly apparent for the smaller tapioca starch
granules (both native and modied). is suggests that prior to heating, the inuence of the crystalline starch
granules on T2,1 is mediated by the available surface area, as seen with the two sizes of MCC particles above. In
contrast, the swollen particles are much more water-accessible, decreasing the surface-area eect, and thus the
dierences between the two starch varieties. Again, it should be noted that the presence of xanthan gum has been
shown to cause depletion occulation in starch dispersions38. It was shown this eect is more pronounced aer
gelatinization, due to the absorption of the water by the starch granules, eectively concentrating the xanthan in
the continuous phase. erefore, although these T2 values should be regarded with some skepticism, the general
trend of decreasing T2 with increasing ller content should still be expected.
e T2 relaxation proles of the starch-lled comminuted meat batters are shown in Fig.9. Similar to that seen
with the crystalline particles, prior to thermal gelation there is generally a decrease in the peak T2,1 relaxation time
with increasing mf. Aer thermal processing and removal of expelled liquid, the T2,1 of both the unlled batter
decreased from ~135 ms to ~66 ms. Unlike the crystalline llers which decreased T2,1 with increasing mf, the T2,1
peaks shied to longer relaxation times (with the notable exception of native potato starch). is suggests that the
water sequestered within the swollen starch granules is more mobile than that present in the protein gel network.
For both the tapioca starches and the modied potato starch, a minor peak at ~48 ms was also present, indicating
that when excess starch is present (i.e. there is insucient water for hydration), two distinct water populations
are observed; the faster relaxing peak associated with the water present within the protein network, and a slower
relaxing population caused by the water sequestered in the partially hydrated starch granules.
e meat batters containing native potato starch appear to have a similar splitting of the T2,1 peak; however,
for this particular starch, the split is observed at all mf investigated, including those for which liquid losses are
still observed (mf = 0.025). As mf was increased, the T2 value of both populations decreased, indicating the starch
granules have a less open structure due to the shortage of water available for hydration, and thus also marginally
decreasing the relaxation time of the water population associated with the protein matrix.
From these results, we conclude that pulsed NMR relaxometry may prove to be an interesting tool to probe
the mechanism of water binding and how ller-matrix interactions inuence the eciency of llers or binders
in comminuted meat products. Furthermore, the partially hydrated starch granules seem to behave more akin
to so ller particles than an eective water binding agent, due to either their higher gelatinization temperature
or chemical modication. It would thus be expected that increasing the gelatinization temperature of the gran-
ules would cause them to further maintain their crystalline structure, thus allowing them to behave as a rigid
Figure 8. T2 relaxation proles of native (A) and modied (B) potato starches, and native (C) and modied (D)
tapioca starches dispersed in a 0.5 wt% xanthan gum solution prior to (solid lines) and post-thermal treatment
(dashed lines). e mass fraction ller content is denoted in the legend.

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ller particle. e eect of the ller would then be mediated by the ller modulus and available surface area42.
Conversely, water binding might be improved by decreasing the gelatinization temperature via processing and/or
by selecting a starch with a naturally lower gelatinization point.
Conclusion
In the present study, we have attempted to expand on previous work showing glass microspheres can improve
the stability and large deformation properties of comminuted meat protein gels, with a size, or surface area
dependence. To this end, a series of food-grade llers were investigated, and separated into two categories; (i)
hydrophilic, insoluble, crystalline particles, and (ii) thermally sensitive starch granules. Of the crystalline llers
characterized, only the ~15 μm MCC particles improved the liquid retention of the composite meat gels, suggest-
ing the eect is surface area-mediated. Textural properties were only aected at high ller content (mf ≥ 0.10),
where all particles produced an increase in gel strength, and an associated decrease in recovery properties, indi-
cated the eect was due to particle crowding. Microstructure conrmed the particles were loosely associated with
the surrounding matrix, as evident by discontinuities at the ller/gel interface. T2 relaxometry of the raw batters
indicated the water was less mobile with increasing ller content; however, this did not necessarily translate to a
more stable product. It was found that particle size was the dominant factor in determining the inuence of the
ller on stability. It was proposed that hydrophilic llers are most eective at improving water retention when
they are comparable in size to the capillary channels present throughout the porous gel matrix.
Of the four starches investigated, it was found that the native potato starch was more eective at improving
water retention at lower mf than native tapioca, and can be attributed to its larger size and lower Tgel. ermal
analysis indicated the modied potato and tapioca starches had a higher and lower Tgel, which was correlated to a
decrease and increase in liquid retention, respectively. e native potato and modied tapioca starches also pro-
duced harder composite gels at the highest ller content investigated (mf = 0.10); however, the recovery properties
were not inuenced by the addition of any starch variety. Microstructural analysis indicated the potato starch
granules were more swollen than the tapioca, but this swelling may have been restricted by the formation of the
protein gel network.
T2 relaxometry indicated that the native potato starch more readily hydrated in the comminuted meat batter,
resulting in decreased liquid losses, and the appearance of two distinct water populations; a faster population
associated with the water within the protein network, and a slower population resulting from the water within
the partially hydrated/gelatinized starch. In contrast, the three remaining starches only exhibited this splitting of
populations at high mf, when insucient water was available for hydration. ese results suggested that the higher
gelatinization temperature of native tapioca starch and chemical modications of both the modied starches
causes them to behave akin to the hydrophilic crystalline ller particles; however, the partial gelatinization of the
granules resulted in higher liquid retention and no observed decrease in the recovery properties of the compos-
ite gels. erefore, although starches are commonly used to promote water binding by forming a hydrocolloid
network, under the processing conditions used here, the inuence of the two starch varieties on the comminuted
meat batters were similar to that of a particle-lled network. Overall, insoluble hydrophilic llers showed poten-
tial as a means to improve the stability of comminuted meat gels when the particles are of the same order of mag-
nitude as the capillary channels present throughout the protein network. As the starches were larger and less rigid
aer undergoing thermal treatment, they did not show the same potential to serve as a particulate ller in meat
batters (i.e. by supporting the capillary network). Further work should be carried out to determine if this strategy
could be applied to other polymer hydrogel systems.
Figure 9. T2 relaxation proles of composite meat protein gels containing native (A,B) and modied (C,D)
potato starches, and native (E,F) and modied (G,H) tapioca starches. Relaxation proles were acquired both
prior to- (A,C,E,G) and post-thermal treatment (B,D,F,H). e mass fraction ller content is denoted in the
legend in Panel A.

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Materials and Methods
Materials. Fresh boneless, skinless chicken breast meat (~25 kg) was purchased from a national supermarket
(Kirkland Signature, Costco Wholesale Canada Ltd., Ottawa, ON, Canada). Within 24 hrs of purchasing, all vis-
ible fat and connective tissue was removed and the meat was chopped in a bowl chopper at the low speed setting
for approximately 60 sec and mixed by hand to produce a homogeneous batch. e meat was then portioned
into ~500 g batches in bags, vacuum-packed, and stored at −20 °C until use. Protein content was determined,
in triplicate, to be 20.5 wt% using the Dumas method and a nitrogen conversion factor of 5.53 was employed43.
e pH of the chicken was determined by thoroughly mixing 5 g of defrosted meat in 45 g deionized water, and
the solution was then strained through glass wool prior to analysis. e pH of the liquid was measured to be 5.85
using a benchtop pH meter.
Two classes of llers were investigated; (i) insoluble food-grade llers, predominantly composed of crystalline
material, and (ii) hydratable starches, both native and modied. e latter group will be denoted as ‘starches’,
while the former class will be referred to as ‘crystalline llers,’ as they maintain their crystallinity through the heat-
ing/gelation process (see Supplementary Material; Fig.S2). Microcrystalline cellulose (MCC) was obtained from
JRS Pharma (Patterson, NY, USA) in two size ranges; VIVAPUR® 102 and 105 (average particle size of ~130 μm
and 15 μm, respectively, from manufacturer specications). Walnut our (“walnut”; mesh size 325) and oat ber
(“oat”; Canadian Harvest) were received from EcoShell Inc. (Corning, CA, USA) and LV Lomas (Brampton, ON,
Canada), respectively. Native tapioca starch, modied tapioca starch (PURITY® 87), and modied potato starch
(PenBind® 140) were received from Ingredion Canada (Mississauga, ON, Canada). Native potato starch was
obtained from Hela Spice Canada Inc. (Uxbridge, ON, Canada). e two modied starches used were developed
for high temperature applications; however, the nature of the chemical modication is proprietary information,
and these starches are thus simply denoted as “modied”.
Preparation of particle-lled meat protein gels. All composite meat gels were prepared in a house-
hold food processor. Batters containing crystalline particles were formulated to have a nal protein content of
10.6% in the batter (i.e. the gel phase), while the starch-lled gels had a protein content of 10.25%. e batters
were formulated independent of the mf employed so that the protein content of the gel matrix was constant
for each class of particles. is was done to ensure the physical properties of the continuous phase in the com-
posite was consistent across all mf tested. Filler particles were added on a wt% or mass fraction basis; for the
crystalline particles, a ller content of 0, 5, 10, and 15% was used, while for the starches, the meat batters were
prepared with 0, 1.25, 2.5, 3.75, 5.0, 7.5, and 10.0% ller. All llers were added aer the chopping procedure to
maintain the original size distribution, and were incorporated by hand mixing. Prior to preparation, the meat
was completely defrosted overnight under refrigerated conditions (~4 °C). e meat batters were prepared by
rst chopping two parts meat for 60 sec, followed by the addition of one part deionized water (10 sec chopping),
and 2.5% NaCl (10 sec chopping). e slurry was then held in an ice bath for 5 min to allow for the extraction of
salt-soluble myobrillar proteins. e ionic strength of the mixture during extraction was ~0.42 M. Aer extrac-
tion, the remaining water was added and the mixture was further chopped for a total of 80 sec. To ensure the
batter was chopped homogeneously, the walls and base of the food processor were scraped at regular intervals
throughout the preparation procedure. Aer chopping, the particles were thoroughly mixed into the batter by
hand (~2 min), and each sample was equilibrated under refrigeration conditions (~4 °C) for a minimum of 1 hr
prior to thermal processing. All formulations were independently prepared, and each was repeated three times
in a randomized block design.
Aer chilling, for each composite batter, 40 g samples were stued into four 50 ml polypropylene centrifuge
tubes and centrifuged at a low speed for 30 sec to remove air pockets. e composite batters were cooked by grad-
ually heating to an internal temperature of 72 °C in a water bath. e heating process took approximately 75 min
and the core temperature was monitored using a thermocouple unit fed through a rubber stopper. Upon reaching
the target temperature, the samples were transferred to an ice bath to arrest the cooking/gelation process. Once
the core temperature was below 40 °C, liquid loss was determined (see below), and the samples were then refrig-
erated overnight prior to performing texture prole analysis.
Liquid Loss. Aer the initial cooling (<40 °C), the composite gels were equilibrated to room temperature
and the excess liquid which was expelled during thermal treatment was drained and weighed. Liquid loss was
expressed as the mass of the total expelled liquid relative to the mass of the meat batter (i.e. excluding the ller)
prior to thermal treatment. Due to the low fat content of the chicken breast meat, no fat loss was observed.
Texture prole analysis (TPA). Evaluation of mechanical and textural properties of the gels was carried
out using a two cycle uniaxial compression test44. For each sample, a total of 12 cylindrical cores (height: 10 mm;
diameter: 15 mm) were compressed twice between two parallel plates to 50% of their original height using a
texture analyzer (model TA.XT2, Stable Micro Systems, Texture Technologies Corp., Scarsdale, NY, USA) out-
tted with a 30 kg load cell. e crosshead speed was xed at 1.5 mm/s and all composites were tested at room
temperature. From this test, a number of parameters were obtained, including Hardness, Resilience, Springiness,
and Cohesiveness44.
Dierential Scanning Calorimetry (DSC). e gelatinization temperature of the various starches was
evaluated using a DSC 1 instrument (Mettler-Toledo, Mississauga, ON, Canada). Approximately 1 mg of starch
powder was placed into an aluminum DSC pan, and deionized water was added to produce a ~10 mg 10% starch
solution. e pan was then hermetically sealed and heated from 20–90 °C at a rate of 5 °C/min. Peak integration
was determined using the Star Soware provided with the DSC unit.

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Light microscopy. e particle-lled myobrillar protein gels were prepared for light microscopy follow-
ing a procedure described previously45. Briey, ~3 mm thick discs were sectioned, encased in a cassette, xed
in formalin, dehydrated in a series of alcohols, embedded in a paran block. e blocks were then sectioned
in ~7–10 μm thick slices, deparanised, and stained with Periodic acid-Schi (PAS), using hematoxylin and
eosin as a counter-stain. Samples were imaged on an optical microscope (model BX60, Olympus Optical Co.,
Ltd., Japan) and images were captured with a digital camera using the cellSens soware (v1.0, Olympus Optical
Co., Ltd.). Image analysis was carried out using Image-Pro Premier v9.1 (Media Cybernetics, Inc., Rockville,
MD, USA). Images of the particles were also obtained, both immediately aer being dispersed in water, as
well as aer a 24 hr soaking period. Lastly, eect of heat treatment on particle morphology was determined by
subjecting the dispersed particles to the same thermal processing conditions used for the gelation procedure.
Particles were imaged by pipetting ~20 μl of solution onto a glass microscope slide and covering with a glass
coverslip.
Low-eld pulsed NMR spectroscopy. T2 relaxation values were obtained for the composites, both prior
to and post-gelation. e eect of the particles on the relaxation time of bulk water was also determined by
dispersing the particles in a 0.5 wt% xanthan gum solution, which was used to ensure the particles remained sus-
pended throughout the duration of the experiment. Measurements were carried out on a 20 MHz (0.47 T) mq 20
series bench-top NMR spectrometer (Bruker Corp., Milton, ON, Canada), with the sample chamber maintained
at room temperature (23 °C). e free induction decay was acquired from a Carr-Purcell-Meiboom-Gill (CPMG)
spin echo pulse train46, 47, using 32 scan repetitions. e 90° and 180° pulse lengths were optimized using an
automated calibration procedure, with characteristic values of approximately 2.6 μs and 6.2 μs, respectively. e
pulse delay τ was set to 150 μs when analyzing the particle-lled batters, and 500 μs for the particles dispersed
in xanthan. Raw meat batters and particle dispersions were transferred into small, disposable glass NMR tubes
(height: 40 mm; diameter: 7 mm). A free induction decay (FID) was collected prior to thermal treatment, and the
samples were then heated for 10 min in a water bath maintained at 72 °C and subsequently acclimated to room
temperature in a water bath at 23 °C. For the gelled meat batters, water which was expelled during heating was
decanted prior to collecting an additional FID of the thermally treated sample. No separation/sedimentation was
observed in the particle dispersions. T2 relaxation proles were obtained by processing the FID data with the
CONTIN algorithm (Bruker Corp.) which extracts multiple rate constants using an inverse Laplace transform.
e peak relaxation times were extracted using the PeakFit soware package (v4.12, Systat Soware Inc., San Jose,
CA, USA).
Graph plotting and statistical analysis. Data analysis and graph plotting was performed using GraphPad
Prism 5 (GraphPad Soware, Inc., San Diego, CA, USA). Statistical analysis was carried out within each class of
particles (crystalline or starch) using a 1-way ANOVA with a Tukey post-test.
Data availability. All data are freely available upon request to Alejandro Marangoni (amarango@uoguelph.
ca) and will be supplied in Excel sheets for inspection.
References
1. Gordon, A. & Barbut, S. Mechanisms of Meat Batter Stabilization: A eview. Crit. Rev. Food Sci. Nutr. 32, 299–332 (1992).
2. Tornberg, E. Eects of heat on meat proteins – Implications on structure and quality of meat products. Meat Sci. 70, 493–508
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Acknowledgements
is work was funded by the Natural Sciences and Engineering Research Council of Canada and the Ontario
Ministry of Agriculture, Food and Rural Aairs.
Author Contributions
Andrew Gravelle carried out the experiments, prepared the figures and wrote the manuscript. Shai Barbut
designed the experiments, supervised the project and edited the manuscript. Alejandro Marangoni designed the
experiments, supervised the project, edited the manuscript and helped develop the pulsed NMR technique used
in this work.
Additional Information
Supplementary information accompanies this paper at doi:10.1038/s41598-017-11711-1
Competing Interests: e authors declare that they have no competing interests.
Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and
institutional aliations.

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