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Article Type
Research article
Article Title
Improved flowability and wettability of whey protein-fortified skim milk powder
via fluidized bed agglomeration
Running Title (within 10 words)
Fluidized bed agglomeration of WPI-fortified SMP
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Chan Won Seo1,
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1. R&D center, Seoul Dairy Cooperative, Ansan 15407, Korea
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Chan Won Seo (https://orcid.org/0000-0003-0787-2007)
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Chan Won Seo
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Abstract
Recently, protein-fortified milk powders are being widely consumed in Korea to prevent
sarcopenia, and the demand for high-protein food powders is continuously increasing in the
Korean market. However, spray-dried milk proteins have poor flowability and wettability owing
to their fine particle sizes and high inter-particle cohesive forces. Fluidized bed agglomeration is
widely used to improve the instant properties of food powders. This study investigated the effect
of fluidized bed agglomeration on whey protein isolate (WPI)-fortified skim milk powder (SMP)
at different SMP/WPI ratios. The fluidized bed process increased the particle size distribution,
and agglomerated particles with grape-like structures were observed in the SEM images. As the
size increased, the Carr index (CI) and Hausner ratio (HR) values of the agglomerated WPI-
fortified SMP particles exhibited excellent flowability (CI: <15) and low cohesiveness (HR:
<1.2). In addition, agglomerated WPI-fortified SMP particles exhibited the faster wetting time
than the instant criterion (<20 s). As a result, the rheological and physical properties of the WPI-
fortified SMP particles were effectively improved by fluidized bed agglomeration. However, the
fluidized bed agglomeration process led to a slight change in the color properties. The L*
(lightness) value decreased, and the b* (yellowness) value increased because of the Maillard
reaction. The apparent viscosity (ηa,10) and consistency index (K) values of the rehydrated
solutions (60 g/ 180 mL water) increased with the increasing WPI ratio. These results may be
useful for formulating protein-fortified milk powder with better instant properties.
Keywords
whey protein, milk powder, sarcopenia, fluidized bed, agglomeration
Introduction
Globally, the population of people over the age of 65 is expected to rapidly increase from
524 million in 2010 to nearly 1.5 billion in 2050. Rapid aging is accompanied by degenerative
diseases, such as sarcopenia, which is characterized by a reduction in muscle mass and strength
(Liao et al., 2019; Park et al., 2021). Dietary protein supplementation is important for preventing
muscle loss, and milk proteins are widely used because of their functional, nutritional, and
sensorial properties. In particular, whey protein is well known as an effective stimulant for
promoting muscle protein synthesis because it is rapidly digestible and contains all essential
amino acids (EAA) and branch-chain amino acids (BCAA) (Gilmartin et al., 2020; Kobayashi et
al., 2016). Englund et al. (2017) found that whey protein supplementation (20 g) for six months
in 78.5 ± 5.4 years old elderly people could promote an increase in muscle density, compared to
the control group. Mori et al. (2018) also reported a positive effect of whey protein
supplementation (22.3 g) with exercise on muscle mass in women aged 65–80 years. Therefore,
high-protein supplements are a growing market with a drastic increase in the elderly population,
and milk proteins can be used as ideal ingredients for sarcopenia prevention.
Dairy-based powder products are required for instant properties related to rapid dispersion
without the formation of lumps. However, spray-dried milk proteins have poor flowability and
wettability because of their fine particle size and high inter-particle cohesive forces, resulting in
slow reconstitution and lump formation problems (Atalar and Yazici, 2019; Ji et al., 2017). The
fluidized bed agglomeration process can be used to solve these problems to help produce instant
food powder. Fluidized bed agglomeration is defined as the size enlargement from small fine
particles to large porous particles, and it can improve physical properties, such as size
distribution, flowability, mixing capacity, and dispersibility (Atalar and Yazici, 2021; Park and
Yoo, 2020). Currently, protein-fortified milk powders are consumed in Korea to prevent
sarcopenia. The demand for high-protein powder products is continuously increasing in the
Korean market, and most of these products are manufactured by the dry blending method that
simply blends dairy powders, protein powders and other powdered ingredients such as vitamins
and minerals (Kang et al., 2020; Jang and Oh, 2021). Some researchers have studied the effects
of the fluidized bed agglomeration process on dairy powders such as skim milk powder (SMP)
(Turchiuli et al., 2013), milk protein isolate (MPI) (Ji et al., 2015; Wu et al., 2020), and whey
protein isolate (WPI) (Ji et al., 2017). However, the effect of the fluidized bed agglomeration
process in mixed systems of skim milk powder and milk protein has not yet been studied. Thus,
in this study, the improved rheological and physical properties of whey protein isolate (WPI)-
fortified skim milk powder (SMP) produced by a fluidized bed process were investigated, and
the influence of the SMP/WPI ratio on fluidized bed agglomeration was also examined.
Materials and Methods
Materials
Skim milk powder (SMP, 37% protein and 49% lactose) was supplied by the Seoul Dairy
Cooperative (Ansan, Korea), and whey protein isolate (WPI; Hilmar™ 9410, 89% protein and
0.1% lactose) was obtained from Hilmar Ingredients Inc. (CA, USA). The SMP was mixed with
WPI at ratios of 9:1 (SMP9/WPI1), 8:2 (SMP8/WPI2), and 7:3 (SMP7/WPI3) to manufacture
agglomerated WPI-fortified SMP samples.
Fluidized bed agglomeration process
The fluidized bed agglomeration process was performed according to the method of
Barkouti et al. (2013) with slight modification. One kilogram of raw powder was poured into a
conical product vessel, and agglomeration of milk powder was conducted using a fluid bed
granulator (Fluid Bed Lap system, Einsystem Co., Ltd., Cheonan, Korea). The temperature of the
injected air was set to 95 ± 1°C, and the product temperature in the vessel was maintained at 55 ±
1°C. Distilled water was used as the binder solution, which was pumped at a flow rate of 10
mL/min and sprayed using a fluid spray nozzle at a pressure of 1.5 bar. After spraying with
distilled water for 30 min, the agglomerated milk powder was dried using hot air (55°C) for 10
min. The SMP without WPI also agglomerated under the same conditions and was used as the
control sample.
Measurement of particle size distribution
The size distributions of the raw and agglomerated WPI-fortified SMP particles were
measured using a laser diffraction particle size analyzer (Mastersizer 3000, Malvern Instruments
Ltd., Worcestershire, UK). The D[3,2] (surface-weighted mean) and span (dispersion index)
values were used to determine the size distribution of the agglomerated WPI-fortified SMP
particles and were calculated from equations (1) and (2), respectively:
D[3,2] =
(1)
span =
(2)
where di is the average diameter of the i class interval, and ni is the number of particles with
diameter di. Dv10, Dv50, and Dv90 are the average particle sizes at 10%, 50%, and 90% of the
cumulative size distribution, respectively.
Scanning electron microscopy (SEM) analysis
The microstructure of raw and agglomerated milk powders was investigated using
scanning electron microscopy (SEM) (Genesis-1000, EmCrafts, Seoul, Korea). Powder samples
were attached to SEM stubs using double-sided adhesive carbon tape and coated with gold under
vacuum prior to observation. SEM analysis was performed at an accelerating voltage of 20 kV
and 200 × magnification.
Flowability and cohesiveness measurement
The flowability and cohesiveness of the WPI-fortified SMP particles were measured using
the Carr index (CI) and Hausner ratio (HR), respectively, which were calculated using the bulk
density (ρbulk) and tapped density (ρtapped). ρbulk and ρtapped were calculated as the mass/volume
ratio of the powder samples before and after 1250 taps, respectively, using a tap density
volumeter (BT-301, Bettersize Instrument Ltd., Dandong, China), and CI and HR values were
calculated from equations (3)–(4):
CI =
(3)
HR =
(4)
Powder flowability (%) based on the CI value was classified as follows: <15 very good, 15–20
good, 20–35 fair, 35–45 bad, and >45 very bad. Powder cohesiveness based on the HR value is
classified follows: <1.2 low, 1.2–1.4 intermediate, >1.4 high (Atalar and Yazici, 2018; Szulc and
Lenart, 2013).
Wettability measurement
The wetting time (tw) was used to evaluate the hydration properties of raw and
agglomerated WPI-fortified SMP particles. As described by Atalar and Yazici (2018), the
required time to complete wetting and immersion of 5 g powders in 100 mL distilled water (23 ±
1°C) was measured as the wetting time.
Color analysis
Color analysis of the raw and agglomerated WPI-fortified SMP samples was performed
using a “Colorflex” colorimeter (Hunter Associates Laboratory Inc., Reston, VA, USA), which
was calibrated using a standard white tile (x = 80.32; y = 85.18; z = 89.28) before measurement.
The results were described using EasyMatchQC ver 4.77 software in terms of L* (lightness
index) ranging from 0 (dark) to +100 (light), a* (redness index) ranging from -60 (green) to +60
(red), and b* (yellowness index) ranging from -60 (blue) to +60 (yellow), according to the
international color system.
Rheological measurement of rehydrated milk beverages
Agglomerated milk powder (60 g) was dissolved in 180 mL of drinking water to
investigate the rheological properties of the rehydrated milk beverages. Rheological
measurements were performed using a HAKKE Roto Visco-1 (Thermo Fisher Scientific, MA,
USA) equipped with a cone-plate geometry, and data were obtained at a shear rate range of 0.4
to 100 s–1. The data were fitted to the following power-law model to describe the flow behavior
of rehydrated solutions:
σ = Kγn (5)
where σ is the shear stress (Pa), γ is the shear rate (s–1), K is the consistency index, and n is the
flow behavior index. The apparent viscosity (ηa,10) of the sample was calculated at 10 s–1 using
the K and n values obtained from the power-law model.
Statistical analysis
All experiments were conducted in triplicates, and data are expressed as the mean ±
standard deviation. Statistical analysis was performed using one-way ANOVA, followed by
Tukey's test using the IBM SPSS Statistics 24 software suite (IBM Software, NY, USA). The
significance level was set at p < 0.05.
Results and Discussion
Particle size and distribution
Particle size and distribution are important characteristics of food powders and can be
closely linked to other physical properties, such as density, flowability, and reconstitution. The
particle size distribution profiles of the raw and agglomerated WPI-fortified SMP samples are
presented in Fig. 1, which shows that the particle size distribution of raw SMP and WPI-fortified
SMP samples moved to the large size region as they agglomerated. These results indicate that the
particle size of the powders was increased by the fluidized bed process. In principle, fluidized
bed agglomeration is performed by spraying the binder solution onto the powders flowing
upward by airflow. This process consists of three steps:1) wetting, 2) coalescence and 3)
consolidation (Atalar and Yazici, 2021; Lim et al., 2021). The raw particles are fluidized by
rising hot air, and their surfaces are wetted by a sprayed binder solution, which makes them bind
together by the formation of liquid bridges owing to the collision of sticky particles, which then
turns liquid bridges into solid bridges, leading to the anchoring of the agglomerated particles
(Atalar and Yazici, 2019; Barkouti et al., 2013). Therefore, the fluidized bed process can
effectively produce agglomerated milk powder.
The particle size and distribution values (D[3,2], Dv10, Dv50, Dv90, and span) of the raw
and agglomerated WPI-fortified SMP samples are listed in Table 1. The D[3,2] values of raw
powders exhibited similar D[3,2] values, which were about 61.6-63.0 µm. But, the D[3,2] values
of the agglomerated powders increased in the order SMP7/WPI3 (147%) < SMP8/WPI2 (164%)
< SMP9/WPI1 (186%) < SMP (208%), and other particle size values (Dv10, Dv50, and Dv90)
also showed a similar tendency. In general, fluidized bed agglomeration is influenced by powder
composition, particle size, binder type, and process conditions (Barkouti et al., 2013; Park and
Yoo, 2020). In this study, the agglomeration of the WPI-fortified SMP samples may be strongly
affected by the powder composition because the fluidized bed agglomeration process was carried
out under the same conditions. According to Atalar and Yazici (2019), hydrophilic sugars such
as lactose can improve the wettability of food powders, promoting the formation of liquid
bridges between particles. Therefore, SMP with high lactose content can be more easily
agglomerated by the fluidized bed process than WPI with low lactose content.
One purpose of fluidized bed agglomeration is to achieve a uniform particle size
distribution. In general, the span value is used to assess the homogeneity and polydispersity of
food powders (Chever et al., 2017). The span values of raw WPI-fortified SMP samples
decreased from 2.02 to 1.84 with the increase in WPI ratio. This result can be explained by the
increase in Dv50 values, as shown in Table 1. After the fluidized bed process, the span values of
the agglomerated SMP and WPI-fortified SMP samples were in the range of 1.58-1.63, and the
span values of the agglomerated powders were much lower than those of the raw powders. This
reduction in span values indicates a narrow size distribution with homogenous particles. From
these results, it was found that WPI enrichment could slightly suppress the agglomeration of
SMP by the reduction of liquid bridges between particles due to the decrease in hydrophilic
sugar content, but it was concluded that the fluidized bed agglomeration process can effectively
improve the particle size distribution.
Particle morphology
SEM analysis was used to visualize the microstructures of the SMP and WPI-fortified
SMP particles. Fig. 2 shows the SEM images of the raw and agglomerated powders with
different structures. The raw SMP (Fig.2A) and WPI (Fig.2B) showed small spherical particles,
which are typical of milk powders produced by spray dryers (Atalar and Yazici, 2019). Some
particles were connected; thus, the particle size distribution was approximately 30-200 mm,
consistent with the particle size distribution results shown in Table 1. The fluidized bed
agglomeration process had noticeable effects on the size and shape of the SMP and WPI-fortified
SMP particles. The SMP was effectively agglomerated by the fluidized bed process, which led to
a grape-like structure with high porosity (Fig.2C). This result can be attributed to the better
intermolecular interactions between the SMP particles during the fluidized bed process.
Generally, a highly porous structure can improve the reconstitution properties of food powders
because it allows water to penetrate easily into the void spaces of agglomerated particles (Ji et
al., 2015; Lee and Yoo, 2021; Wu et al., 2020). WPI-fortified SMP particles (Fig.2D) were
partially agglomerated by the fluidized bed process, resulting in the formation of smaller
agglomerated particles than agglomerated SMP particles. This result may be due to the lower
compatibility between the SMP and WPI particles, which can be explained by the lower
wettability of the WPI particles than that of the SMP particles, as described previously. These
results suggest that the microstructure of SMP is strongly affected by the fluidized bed
agglomeration process and that the enrichment of WPI particles can influence the agglomeration
of SMP particles.
Density, flowability and cohesiveness
The physical properties of the raw and agglomerated WPI-fortified SMP samples are
presented in Table 2. The bulk density (ρbulk) and tapped density (ρtapped) of raw powders were in
the range of 0.48-0.64 g/cm3 and 0.63-0.78 g/cm3, respectively, and both ρbulk and ρtapped values
decreased to 0.38-0.45 g/cm3 and 0.47-0.51 g/cm3 after fluidized bed agglomeration process,
respectively. These results were similar to those by Ji et al. (2017), which reported that WPI
powders agglomerated using a lecithin solution as a binder. According to Chever et al. (2017),
the fluidized bed process produces a powder with a lower density owing to additional voids
caused by the formation of porous structures during the agglomeration process (Ji et al., 2015;
Wu et al., 2020). Therefore, the lower ρbulk and ρtapped values of the agglomerated WPI-fortified
SMP particles can be attributed to the additional voids within the porous structure of the
agglomerated powders by the fluidized bed process.
The ability to flow easily is an important property related to transfer, weighing, storage,
and blending (Lee and Yoo, 2021). The flowability and cohesiveness of food powders can be
described using the Carr index (CI) and Hausner ratio (HR), respectively. As shown in Table 2,
the CI values of the raw SMP showed good flowability (CI:15-20) and increased from 18.2 to
22.5 as the WPI ratio increased, indicating fair flowability (CI:20-25). The HR values of the raw
powders exhibited intermediate cohesiveness (HR:1.2-1.4) and increased with increasing WPI
ratio. In contrast, the CI and HR values of the agglomerated powders decreased with increasing
WPI ratio, and the CI and HR values of the agglomerated WPI-fortified SMP particles exhibited
very good flowability (CI: <15) and low cohesiveness (HR: <1.2). These results indicate that the
physical properties of WPI-fortified SMP particles can be improved by the fluidized bed
agglomeration process. The improved flowability and cohesiveness of the agglomerated powders
can be explained by the increased particle size, which can reduce the particle surface area and
decrease friction between the particles (Lim et al., 2021; Park and Yoo, 2020). However, the
fluidized bed process did not improve the CI and HR values of the agglomerated SMP samples.
This result may be due to the lower ρbulked and ρtapped values of agglomerated SMP particles as
compared to the WPI-fortified particles (Lee and Yoo, 2020). From these results, it was
suggested that the physical properties of SMP particles are greatly affected by the addition of
WPI particles and that the fluidized bed agglomeration process can effectively improve the
flowability and cohesiveness of WPI-fortified SMP particles.
Wettability
Wettability of powders is defined as its ability to overcome surface tension at the interface
between liquid and particles, and good wettability is very important for powder products because
it is closely related to the hydration properties (Atalar and Yazici, 2018; Ji et al., 2017). The
hydration properties of raw and agglomerated WPI-fortified SMP particles were shown in Fig. 3
and Table 2. The raw SMP and WPI-fortified SMP particles had a long wetting time (tw) of >120
s and floated on the water surface with lump formation, as shown in Fig 3. According to
Nascimento et al. (2021), fine particles can penetrate into spaces between large particles and lead
to more compact powders. These compact particles do not allow water to penetrate inside the
particles, which can form lumps and float on water surface. In contrast, agglomerated SMP and
WPI-fortified SMP particles displayed faster wetting, as demonstrated by the decrease in wetting
time to 4.33-14.3 s. The same effect was also observed in other studies of isolated protein
powders, such as milk protein isolate (Wu et al., 2020), pea protein isolate (Nascimento et al.,
2021), and soy protein isolate (Machado et al., 2014). This improved wettability can be
explained by the large particle size and the porous structure of agglomerated particles. As
previously described, the large porous structure can allow water to easily penetrate into the void
spaces of agglomerated particles, facilitating the wetting of powders (Custodio et al., 2020; Wu
et al., 2020). Although wetting time of agglomerated WPI-fortified SMP particles increased from
4.67 s to 14.3 s with increasing WPI ratio, they showed the faster wetting time than the instant
criterion (<20 s) described by Chever et al. (2017). Consequently, the rehydration properties of
WPI-fortified SMP particles can be effectively improved by the fluidized bed agglomeration
process.
Color properties
Color is a significant factor in the sensory aspect of food powders, and the changes in the
color parameters (L*, a*, and b*) of raw and agglomerated powders are summarized in Table 3.
The L* value decreased with an increase in the WPI ratio, and the agglomerated powders had
lower L* values than the raw powders, indicating that the color became darker owing to fluidized
bed agglomeration. Similar results were observed by Lee et al. (2021), who reported that the L*
value of carboxymethyl cellulose (CMC) powder decreased from 88.3 to 83.7 after fluidized bed
agglomeration. This result can be attributed to the increase in particle size. According to Sakhare
et al. (2014), larger particle size can decrease the whiteness of food powder. In the case of b*
values, agglomerated powders have higher values than raw powders, indicating that fluidized bed
agglomeration can increase the yellowness of milk powders. The higher b* value of
agglomerated powders can be explained by the brown pigments produced by the Maillard
reaction, which can be accelerated at high temperatures because of hot air (Zulueta et al., 2013).
Consequently, the color properties of dairy-based food powders can be influenced by the
fluidized bed agglomeration process, which can lead to a decrease in the L* value and an
increase in the b* value owing to the Maillard reaction.
Flow behavior of rehydrated milk beverages
The shear stress (σ) versus shear rate (γ) data were applied to the power law model to
describe the flow behavior of rehydrated milk beverages with agglomerated powders, and the
experimental results were well fitted to the power law model with high R2 (0.97–0.98), as shown
in Table 4. The rehydrated solutions with the SMP and SMP9/WPI1 samples exhibited
Newtonian behavior with flow behavior index values of close to 1 (n = 0.98–1.02). The n value
decreased slightly with increasing WPI ratio, and the rehydrated solution with the SMP7/WPI3
sample showed little shear-thinning behavior (n = 0.76). Similar results were reported by Bazinet
et al. (2004), who found that the WPI dispersion exhibited shear-thinning behavior above a
concentration of 10 %. This shear-thinning behavior of the WPI solution can be explained by the
breakdown of weak bonds, such as hydrogen and ionic bonds, in the protein network at high
shear rates, which can lead to a decrease in viscosity (González Tello et al., 2009; Tang et al.,
1993). The apparent viscosity (ηa,10) and consistency index (K) values of rehydrated solutions
were also influenced by the enrichment of WPI and increased with an increase in the WPI ratio.
The higher viscosity of the rehydrated solution containing the SMP7/WPI3 sample may be
attributed to the higher concentration of protein aggregates. According to Morison and Mackay
(2001), the viscosity of whey protein solutions is governed by whey protein and depends on the
protein concentration. Therefore, these results indicate that the SMP/WPI ratio can influence the
flow behavior of rehydrated milk beverages with agglomerated WPI-fortified SMP samples.
Conclusion
The high-protein dairy powder is being consumed to prevent sarcopenia. However, spray-
dried milk proteins have poor flowability and wettability owing to their fine particle sizes and
high inter-particle cohesive forces. This study aimed to investigate the effect of fluidized bed
agglomeration on SMP fortified with WPI with varying SMP/WPI ratios to resolve these
problems. The fluidized bed process increased the particle size distribution, and SEM images of
the agglomerated particles showed a grape-like structure with high porosity, which can
contribute to good reconstitution properties. The Carr index (CI) and Hausner ratio (HR) values
of agglomerated WPI-fortified SMP particles exhibited very good flowability (CI: <15) and low
cohesiveness (HR: <1.2) compared to raw WPI-fortified SMP particles. In addition,
agglomerated WPI-fortified SMP particles exhibited the faster wetting time than the instant
criterion (<20 s). However, the level of agglomeration decreased with increasing WPI ratio,
resulting in a slight decrease in particle size and wettability. Therefore, it can be recommended
that the SMP with a high ratio of WPI (SMP7/WPI3) requires the longer agglomeration time in
the fluidized bed process. However, the extension of agglomeration time should be carefully
considered from a color point of view, because the fluidized bed process can decease the L*
(lightness) value and increase the b* (yellowness) value due to the Maillard reaction. Although
WPI enrichment can slightly suppress the agglomeration of SMP particles, the fluidized bed
agglomeration process can effectively improve the physical properties such as particle size
distribution, flowability, and wettability of WPI-fortified SMP particles. In addition, the
rehydrated milk beverage with the agglomerated SMP7/WPI3 sample (60 g in 180 mL water)
can be expected to provide approximately 19.3 g of whey protein and a total of 31.7 g of
proteins. Therefore, these results may be useful in formulating protein-fortified dairy powders
with better instant property.
Conflicts of Interest
The authors have declared no conflicts of interest for this article.
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Table 1. Size distribution of raw and agglomerated WPI-fortified SMP particles with different
SMP/WPI ratios.
Sample
D[3,2]
Dv10
Dv50
Dv90
span
[µm]
[µm]
[µm]
[µm]
Raw
powder
WPI
61.6 ± 0.59a
29.2 ± 0.35a
109 ± 1.53a
218 ± 2.52a
1.73 ± 0.01a
SMP
63.0 ± 0.47a
33.5 ± 0.15b
87.7 ± 0.60b
211 ± 4.62ab
2.02 ± 0.04b
SMP9/WPI1
62.4 ± 0.21a
33.1 ± 0.15bc
90.8 ± 0.35b
203 ± 1.73ab
1.87 ± 0.02c
SMP8/WPI2
62.7 ± 0.49a
32.5 ± 0.20bc
95.6 ± 0.93c
210 ± 2.00ab
1.86 ± 0.01c
SMP7/WPI3
61.9 ± 0.58a
31.7 ± 0.32c
97.1 ± 1.06c
210 ± 2.08ab
1.84 ± 0.01c
Agglomerated
powder
SMP
131 ± 2.31b
73.6 ± 1.21d
169 ± 3.06d
345 ± 7.55c
1.61 ± 0.02d
SMP9/WPI1
116 ± 1.53c
66.3 ± 0.91e
160 ± 2.31e
322 ± 6.35d
1.60 ± 0.01d
SMP8/WPI2
103 ± 0.58d
59.3 ± 0.21f
151 ± 1.53f
306 ± 2.52e
1.63 ± 0.01d
SMP7/WPI3
90.7 ± 1.59e
52.7 ± 0.76g
137 ± 1.15g
269 ± 2.00f
1.58 ± 0.01d
Values are the means of three measurements + SD.
Mean values in the same line with different letters are significantly different (p < 0.05).
The SMP (skim milk powder) was mixed with WPI (whey protein isolate) at different ratios of
9:1 (SMP9/WPI1), 8:2 (SMP8/WPI2), and 7:3 (SMP7/WPI3).
Table 2. Density and flow properties of raw and agglomerated WPI-fortified SMP particles with
different SMP/WPI ratios.
Sample
ρbulk
ρtapped
CI
HR
tw
[g/cm3]
[g/cm3]
[%]
[s]
Raw
powder
SMP
0.64 ± 0.01a
0.78 ± 0.01a
18.2 ± 0.75a
1.22 ± 0.01a
>120
SMP9/WPI1
0.57 ± 0.01b
0.70 ± 0.01b
18.9 ± 0.75a
1.23 ± 0.01a
>120
SMP8/WPI2
0.52 ± 0.01c
0.66 ± 0.01c
20.7 ± 1.43ab
1.26 ± 0.02ab
>120
SMP7/WPI3
0.48 ± 0.01d
0.63 ± 0.01d
22.5 ± 2.12b
1.29 ± 0.04b
>120
Agglomerated
powder
SMP
0.38 ± 0.01e
0.47 ± 0.00e
18.1 ± 0.73a
1.22 ± 0.01a
4.33 ± 0.58a
SMP9/WPI1
0.45 ± 0.00f
0.51 ± 0.01f
11.8 ± 1.39c
1.13 ± 0.02c
4.67 ± 0.58a
SMP8/WPI2
0.44 ± 0.01f
0.50 ± 0.00f
11.2 ± 0.80c
1.13 ± 0.01c
5.67 ± 1.15a
SMP7/WPI3
0.45 ± 0.01f
0.50 ± 0.01f
8.99 ± 1.36c
1.10 ± 0.02c
14.3 ± 2.08b
Values are the means of three measurements + SD.
Mean values in the same column with different letters are significantly different (p < 0.05).
The SMP (skim milk powder) was mixed with WPI (whey protein isolate) at different ratios of
9:1 (SMP9/WPI1), 8:2 (SMP8/WPI2), and 7:3 (SMP7/WPI3).
Table 3. Color properties of raw and agglomerated WPI-fortified SMP samples with different
SMP/WPI ratios.
Sample
Color
L*
a*
b*
Raw
powder
SMP
95.3 ± 0.11a
-3.39 ± 0.05a
18.5 ± 0.12a
SMP9/WPI1
94.8 ± 0.09b
-2.94 ± 0.06b
18.1 ± 0.09a
SMP8/WPI2
94.5 ± 0.05c
-2.36 ± 0.02c
17.1 ± 0.03b
SMP7/WPI3
94.3 ± 0.06de
-2.11 ± 0.03d
16.8 ± 0.07b
Agglomerated
powder
SMP
94.2 ± 0.12ef
-3.53 ± 0.07e
21.2 ± 0.43c
SMP9/WPI1
94.0 ± 0.06fg
-3.11 ± 0.02f
20.5 ± 0.10d
SMP8/WPI2
93.9 ± 0.08gh
-2.59 ± 0.03g
19.5 ± 0.37e
SMP7/WPI3
93.8 ± 0.05h
-2.15 ± 0.04d
18.4 ± 0.15a
Values are the means of three measurements + SD.
Mean values in the same column with different letters are significantly different (p < 0.05).
The SMP (skim milk powder) was mixed with WPI (whey protein isolate) at different ratios of
9:1 (SMP9/WPI1), 8:2 (SMP8/WPI2), and 7:3 (SMP7/WPI3).
Table 4. Flow behavior of rehydrated milk beverages with agglomerated WPI-fortified SMP
samples.
Sample
Apparent viscosity
power law
ηa,10 [mPa s]
n
K [mPa sn]
R2
SMP
7.14 ± 0.45a
1.02 ± 0.07a
6.72 ± 1.55a
0.98
SMP9/WPI1
8.10 ± 1.02a
0.98 ± 0.02a
8.58 ± 1.35a
0.98
SMP8/WPI2
8.94 ± 0.44b
0.91 ± 0.02b
10.9 ± 0.72b
0.97
SMP7/WPI3
11.0 ± 0.68c
0.76 ± 0.03c
19.2 ± 2.22c
0.98
Values are the means of three measurements + SD.
Mean values in the same column with different letters are significantly different (p < 0.05).
The SMP (skim milk powder) was mixed with WPI (whey protein isolate) at different ratios of
9:1 (SMP9/WPI1), 8:2 (SMP8/WPI2), and 7:3 (SMP7/WPI3).
FIGURE LEGENDS
Fig. 1. Particle size distribution of raw and agglomerated WPI-fortified SMP particles with
different SMP/WPI ratios: (A) SMP, (B) SMP9/WPI1, (C) SMP8/WPI2, and (D) SMP7/WPI3.
Fig. 2. Scanning electron microscopy images of raw and agglomerated particles at 200 ×
magnification: (A) raw SMP, (B) raw WPI, (C) agglomerated SMP, and (D) agglomerated
SMP7/WPI3.
Fig. 3. Wettability of SMP and WPI-fortified SMP particles with different SMP/WPI ratios: (A)
Raw powder, (B) Agglomerated powder.
Fig. 1.
Fig. 2.
Fig. 3.
