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ORIGINAL ARTICLE
Comparative study of block cryoconcentration in pomegranate
juice: Centrifugation versus vacuum
Flor M. Vásquez-Castillo
1
| Eduard Hernández
1
| Milber O. Ureña-Peralta
2
|
Isabel Achaerandio
1
1
Departament d'Enginyeria Agroalimentària i Biotecnologia, Universitat Politècnica de Catalunya (UPC) Barcelonatech, Barcelona, Spain
2
Departamento de Ingeniería de Alimentos, Facultad de Industrias Alimentarias, Universidad Nacional Agraria La Molina, Lima, Peru
Correspondence
Eduard Hernández, Departament d'Enginyeria
Agroalimentària i Biotecnologia, Universitat
Politècnica de Catalunya (UPC) Barcelonatech,
C/Esteve, Terradas, 8, 08860, Castelldefels,
Barcelona, Spain.
Email: eduard.hernandez@upc.edu
Funding information
Universidad Nacional Agraria La Molina;
Universitat Politècnica de Catalunya
Abstract
Block cryoconcentration is a technique that can be applied to obtain fruit juice concen-
trates while preserving their nutritional, bioactive and organoleptic properties. Until
now, the investigations present both the centrifugation and vacuum cryoconcentration
method independently for different matrices, but with different purposes such as
observing the effect of the initial freezing temperature, the freezing direction, whether
radial or unidirectional, the effect of several cycles of cryoconcentration, comparing
cryoconcentration with other concentration methods, etc. However, there is no study
that compares both methods in the same matrix considering some common parameters
such as cryoconcentration time. The objective of this research work was to compare
two block centrifugation methods, centrifugation-assisted (CABC) and vacuum-assisted
(VABC). A factorial experimental design was used. The operation conditions evaluated
were 110 RCF and 2360 RCF, and 10 and 70 kPa at the same time conditions (4 and
12 min). Pomegranate juice was frozen at 20C unidirectionally for 48 h before treat-
ments. For the response studied—concentration index (CI), solute yield (SY, %) and effi-
ciency (Eff, %)—CABC at 110 RCF for 12 min showed the best overall results
(SY =59.2% and Eff =84.3%) and the desirability was .91. For VABC at 10 kPa for
12 min, the desirability was .98 but SY was lower. In both methods, the CI in one cycle
was up to 3.0. The advantage of both systems is that in one cycle the CI, SY and Eff
were higher than those obtained by other investigations on pomegranate juice.
Practical applications
Cryoconcentration is an emerging technology for concentrating a food solute in a
solution based on the separation of ice crystals from a freeze-concentrated solution.
The nutritional and sensory quality of cryoconcentrated fruit juices is higher than
those concentrated conventionally by means of evaporation due to the low proces-
sing temperatures. Consumer demand for food rich in bioactive components for a
healthy lifestyle is growing. With the use of the block freeze concentration technique,
Received: 7 October 2022 Revised: 28 June 2023 Accepted: 4 August 2023
DOI: 10.1111/jfpe.14435
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any
medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
© 2023 The Authors. Journal of Food Process Engineering published by Wiley Periodicals LLC.
J Food Process Eng. 2023;46:e14435. wileyonlinelibrary.com/journal/jfpe 1of12
https://doi.org/10.1111/jfpe.14435
it is possible to produce a pomegranate juice concentrate with excellent nutritional
properties. Two techniques for assisted block cryoconcentration of pomegranate
juice—vacuum and centrifugal—were compared in a single cycle. Both methods
showed better performance in once cycle than other cryoconcentration methods at
lab scale. The generated knowledge in this study can be easily adapted for the juice
industry in order to improve the process parameters of block freeze concentration in
the elaboration of concentrated pomegranate juice.
KEYWORDS
block freeze concentration, desirability, efficiency, freezing rate, Punica granatum, solute yield
1|INTRODUCTION
Pomegranate fruits have high antioxidant capacity due to their antho-
cyanin and phenolic compound content. Punicalagin, the main ellagi-
tannin in pomegranate juice, promotes some beneficial properties for
health because it reduces the effects of oxidative stress in cells. The
evidence of the benefits of pomegranate phytochemicals has been
recently reviewed (Laurindo et al., 2022). There are different varieties
of pomegranate; the ‘Wonderful’cultivar is the most consumed for its
organoleptic characteristics as well as for its higher antioxidant activ-
ity, polyphenol content and very high acidity compared to the ‘Mollar
de Elche’accessions, as demonstrated by Mena et al. (2011).
Cryoconcentration is a method for concentrating a food solute in
a solution based on the separation of pure ice crystals from a freeze-
concentrated solution. As compared to evaporation and membrane
technology, freeze concentration has some significant potential
advantages for producing a high-quality concentrate because the pro-
cess occurs at low temperatures where no vapor/liquid interface
exists, resulting in no loss of volatiles (Petzold et al., 2013).
As the temperature below the freezing point decreases, the water
becomes ice and the solids content of the juice becomes more con-
centrated. After the juice is frozen, this concentrate can be extracted
by gravitational methods, by centrifugation and by vacuum. The cryo-
concentrated solution has better nutritional, organoleptic and bioac-
tive characteristics than the original fresh juice (Guerra-Valle
et al., 2021).
There are different types of cryoconcentration: suspension, pro-
gressive and block cryoconcentration; of all of them, the simplest
technique and that giving better results is block cryoconcentration. To
improve the technique, it has been complemented by gravitational-
assisted thawing and microwave-assisted thawing (Aider et al., 2008;
Aider & de Halleux, 2008), by shaking (Iritani et al., 2013) and by ultra-
sound (Kawasaki et al., 2006). Suspension cryoconcentration is cur-
rently being used in the industry; the disadvantage is that it requires
costly equipment and the operation is carried out in several steps:
nucleation, growth and crystal separation (Petzold et al., 2013). The
advantage of block cryoconcentration is that the design of the equip-
ment is simpler (Miyawaki, 2018) and the process is a single step
(Petzold & Aguilera, 2013). For this reason, other techniques with
fewer costs and better yields are being studied at laboratory and pilot
scale, including centrifugation-assisted block cryoconcentration
(CABC) and vacuum-assisted block cryoconcentration (VABC). Some
research groups have worked with both techniques independently for
several food products, with promising results, such as sucrose solu-
tions both by VABC (Petzold et al., 2013) and CABC (Petzold &
Aguilera, 2013), blueberry juice by VABC (Orellana-Palma, Petzold,
Andana, et al., 2017) and by CABC (Casas-Forero et al., 2021;
Orellana-Palma, Petzold, Guerra-Valle, & Astudillo-Lagos, 2017;
Petzold et al., 2015; Santana et al., 2020), and orange juice by VABC
(Petzold et al., 2017,2019) and by CABC (Orellana-Palma, González, &
Petzold, 2019; Orellana-Palma, Petzold, Andana, et al., 2017). How-
ever, to the authors’knowledge, the two methods have not been
compared to evaluate which of them gives better results. On the
other hand, investigations of the cryoconcentration of pomegranate
juice have used gravity-assisted cryoconcentration and microwave
(Khajehei et al., 2015), CABC (Orellana-Palma et al., 2021) and a BL-
20 crystallizer (Burdo et al., 2021). To fill this gap, the main aim of this
research work was to compare the CABC and VABC methods in
pomegranate juice to evaluate which of them the better obtains the
concentration index, solute yield and efficiency of concentration.
2|MATERIALS AND METHODS
2.1 |Materials
Fresh fruits of ‘Wonderful’pomegranate (Punica granatum) from
southern Israel were obtained at Mercabarna (Barcelona). The average
weight of fruits was 450 ± 50 g.
2.2 |Experimental procedure
Two methods of block cryoconcentration (BC) were compared: CABC
and VABC, and two factors were studied for each technique (centrifu-
gation speed–time and vacuum pressure–time, respectively). The
experimental design is indicated in Table 1, which was chosen consid-
ering previous investigations. Preliminary tests showed that if the
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ASQUEZ-CASTILLO ET AL.
vacuum pressure of 10 kPa is applied for more than 12 min, vacuum
pressure loss occurs due to the formation of pores in the top of the
ice block. In total, 24 tests were carried out considering three
replications.
The following response variables were calculated: concentration
index (CI), solute yield (SY) and efficiency (Eff ).
2.2.1 | Freezing procedure
The juice was extracted using a Moulinex Juice extractor, then it was
vacuum-filtered with filter paper of approximately 10 μm of porosity
using a Büchner funnel and Kitasato flask.
Juice solutions (45 g) contained in plastic centrifugal tubes (inter-
nal diameter D=27 mm) were covered with a thermal insulation
made of elastomeric foam (8 mm thickness, thermal conductivity
k=.035 Wm
1
K
1
) so the heat transfer during freezing occurred
axially from top to bottom as recommended (Orellana-Palma, Petzold,
Andana, et al., 2017). These samples were frozen in a static freezer at
20C (Arcon Freezer model THC 520 ANI) for 48 h (Figure 1).
During freezing, the temperature in the samples was measured
using K thermocouples (NiCr-Ni) connected to a Testo Data logger
(176T4) at the geometric center of samples. The freezing rate
(mmmin
1
) was calculated as the thickness divided by the freezing
time (assuming that freezing occurs from one side) (Ramaswamy &
Marcotte, 2005).
2.2.2 | CABC
The frozen samples were removed from the freezer and immediately
placed in a refrigerated centrifuge (HETTICH ROTANTA 460 R, Tut-
tlingen, Germany) operated at 20 ± 1C, using two centrifugation
speeds: 1000 and 4600 rpm (110 and 2360 RCF, respectively) for
4 and 12 min, to force the separation of the solutes from the frozen
samples. Then the tip of the centrifuge tube is cut, the concentrate is
extracted weighed it and measure its concentration of total soluble
solids, the frozen fraction remaining in the tube is weighed, thawed,
and total soluble solids are measured.
2.2.3 | VABC
This procedure was carried out following Petzold and Aguilera
(2013). The samples were removed from the freezer, cut at the bot-
tom of the tube and immediately taken to a suction stage generated
by a vacuum pump (Comecta model, Spain; pump rate: 3.6 m
3
h
1
;
vacuum limit: .1 mbar). The absolute pressures used were 10 and
70 kPa (91.3 and 31.3 kPa vacuum pressure), for 4- and 12-min.
Vacuum pressure was monitored visually with the vacuum manom-
eter of the pump and an external manometer during the
experiment.
In both cryoconcentration methods, the weight and concentration
of the initial juice, concentrate and ice fraction were measured at
20 ± 2C with a refractometer (ATAGO DBX-55A, Tokyo, Japan) with
a precision of ±.1Brix.
TABLE 1 Experimental design. Experiment Cryoconcentration Time (min)
1 CABC 1000 rpm 110 RCF 4
2 CABC 1000 rpm 12
3 CABC 4600 rpm 2360 RCF 4
4 CABC 4600 rpm 12
5 VABC 10 kPa Absolute pressures 4
6 VABC 10 kPa 12
7 VABC 70 kPa 4
8 VABC 70 kPa 12
Abbreviations: CABC, centrifugation assisted block cryoconcentration; VABC, vacuum assisted block
cryoconcentration.
FIGURE 1 Freezing condition of pomegranate juice samples. The
samples were frozen in a static freezer at 20C for 48 h.
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2.3 |Process parameter calculations
2.3.1 | Concentration index
CI is a variable used to evaluate the increase in concentration at the
end of the BC process. It is the relation between the final concentra-
tion of the solute in the concentrated liquid and the initial
concentration of the sample, as shown in Equation (1):
CI ¼Cs
C0
ð1Þ
where C
S
and C
0
are the percentage of soluble solids (Brix) in the
concentrated and initial solutions, respectively (Orellana-Palma,
Takhar, & Petzold, 2019).
2.3.2 | Solute yield
SY was defined as the relationship between the mass of total soluble
solids present in the separated concentrated fraction and the mass of
total soluble solids present in the initial sample, as seen in Equation (2)
(Miyawaki et al., 2012; Moreno et al., 2014):
SY ¼ms
m0
100 ð2Þ
2.3.3 | Efficiency of concentration
The efficiency was defined as the increase in the concentration of the
solution relative to the quantity of total soluble solids remaining in
the frozen fraction, Equation (3) (Hernández et al., 2010).
Eff %ðÞ¼
CsCf
Cs
100 ð3Þ
2.3.4 | Validation of results
The experimental results were validated with a mass balance after the
BC process (W
e
) (Equation (4)). Those were compared with the pre-
dicted value (W
p
) according to Equation (5) (Petzold et al., 2015).
We¼Mf
MfþMc
ð4Þ
WP¼CsC0
CsCf
ð5Þ
where W
e
is the experimental value of the ice mass ratio (kg ice/kg ini-
tial sample), W
p
is the predicted value of the ice mass ratio (kg ice/kg
initial sample), M
f
is the ice mass (kg) and M
c
is the mass (kg) of the
concentrated sample.
Finally, the root mean square (RMS) was calculated by Equation (6)
to determine the fit between the experimental and predicted values)
for Nexperimental points subjected to cryoconcentration.
RMS %ðÞ¼100 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
PWeWp
ðÞ=We
½
2
N
sð6Þ
2.3.5 | Statistical design and analysis
A2
2
factorial analysis for two response variables was performed to
observe the significant factors and the adjusted model equations in
both cryoconcentration methods. Then, a categorical multifactor
design was performed using ANOVA to assess if there were signifi-
cant differences between the treatments. A multiple range test with
the Bonferroni method with a 95% confidence interval was used to
compare set of means. Desirability was used as an indicator to evalu-
ate which response variables have to be taken into consideration and
thus find the model equation adjusted to those factor conditions.
To find the final freezing time, the optimization method of no sig-
nificant variation in kinetics (NSVK) was used (Daza-La Plata
et al., 2020). The STATGRAPHICS Centurion 19
®
program was used.
The data were expressed as a mean ± standard deviation.
3|RESULTS AND DISCUSSION
3.1 |Freezing curve
Figure 2shows the freezing curve of the pomegranate juice samples.
The average freezing point was 2.1 ± .1C, which is within the range
of most fruit juices of 1to2C and the freezing point decreases as
FIGURE 2 Freezing curve of the pomegranate juice sample (three
independent experiments).
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ASQUEZ-CASTILLO ET AL.
the juice is more concentrated (Ramaswamy & Marcotte, 2005)sothe
average subcooling point of 2.6 ± .5C can be observed. That value is
very common in solutions such as fruit juices since the more viscous
and colloidal the solution, the lower the average subcooling point
(Barreiro & Sandoval, 2006). There are several methods to measure the
freezing time, as mentioned by Ramaswamy and Marcotte (2005). One
of them is the procedure applied by Rayman Ergün et al. (2021)who
considers the freezing time as the time taken to reach a temperature of
15Cfrom0
C at the cold point. Taking into account this definition,
in our experiment the freezing rate was .176 mmmin
1
(2.93 μms
1
).
On the other hand, Barreiro and Sandoval (2006)andOrrego(2003)
define the freezing time of a food as the time that elapses from when it
starts freezing until it reaches the temperature of the freezer. In our
case, the time to start freezing was 102 min and the final freezing time
was 660 min determined according to the NSVK method (Figure 2).
The freezing rate was .145 mmmin
1
(2.42 μms
1
). These values
show, based on freezing front propagation, a moderate freezing rate
(Ramaswamy & Marcotte, 2005). In addition, these values of freezing
rate were lower than the critical value (approximately 8 μms
1
)
reported by Moreno et al. (2014) who stated that velocities higher
than 8 μms
1
promote a faster freezing process. In cryoconcentra-
tion, that leads to the formation of occluded solutes in the ice that
avoid the separation of the concentrated solution from the ice matrix.
3.2 |Evaluation of CABC
Figure 3shows the Pareto diagram that resulted from the factorial
analysis considering the three response variables CI, SY and Eff. In the
CABC system, only time had a significant effect on CI, with
R
2
=85.8% (Figure 3a). As shown in Figure 3b,c, time and the interac-
tion time–centrifugation speed had a significant effect on SY and Eff,
with R
2
=97% (p< 0.05).
For this analysis, the desirability function was .604, which was
not close to 1; due to this and because CI only expresses how many
times the product has been concentrated but without considering the
solids that remain in the ice, a factorial design was used considering
only two response variables, SY and Eff in the CABC. In this case, time
and the interaction centrifugation speed–time had a significant effect
on SY and Eff, with R
2
=97.4% and 96.7%, respectively. With this
analysis, the desirability function was .91, very close to 1. The best
results were obtained at 1000 rpm (110 RCF) and 12 min (Figure 4).
There were significant differences between the treatments for
the studied response variables: CI, SY and Eff. The initial juice had
15.8Brix, reaching a maximum concentration of 50.9Brix in a single
step, with a CI of 3.2 to 3.0 in CABC; the treatments at 1000 rpm
(110 RCF) for 4 min and 4600 rpm (2360 RCF) for 4 min had the high-
est CI values. The longer the centrifugation time, the higher the dilu-
tion in the concentration fraction, decreasing its total soluble solids
content. Those phenomena might be due to the increase in the tem-
perature inside the tube. Similar results were obtained by Orellana-
Palma, González, and Petzold (2019) with orange juice at 1600 RCF
for 14 min, they got 3.1.
Most investigations have obtained CI values in the range of 1.4–
2.8 in a single cycle in various fruit juices such as blueberry juice 1.8
(Casas-Forero et al., 2021), 1.54 (Petzold et al., 2015), orange juice
1.8 (Orellana-Palma, Petzold, Andana, et al., 2017), calafate juice 1.86
FIGURE 3 Pareto diagram for (a) CI, (b) SY, and (c) Eff by CABC.
FIGURE 4 Estimated response surface for CABC.
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ASQUEZ-CASTILLO ET AL.5of12
(Orellana-Palma et al., 2020), pomegranate juice 2.0 (Orellana-Palma
et al., 2021), apple juice 2.3 (Orellana-Palma et al., 2020), murta juice
1.8 and arrayan juice 2.0 (Guerra-Valle et al., 2021), pomelo juice 1.71
(Das et al., 2020), prickly pear juice 2.4 (Márquez-Montes et al., 2023)
and maqui aqueous extract 2.16 (Bastías-Montes et al., 2019,2022).
Vidal-San Martín et al. (2021) used a centrifugation-filtration assisted
cryoconcentration method (C-FABC) with an aqueous extract of
maqui and calafate (10.5 and 6.8Brix, respectively). CI of 5.1 and 5.8
were obtained, respectively, at 4000 rpm for 10 min in a frozen sam-
ple of 350 mL. Eff was higher than 96%. The high values of CI and Eff,
in this work, they may be due to the addition of the filter that helps in
the separation and recovery process.
Regarding SY, in our experiment 59.2 ± 3.9% was obtained for
the treatment at 1000 rpm (110 RCF) for 12 min; the other treat-
ments yielded less than 40%. This result was higher than that found
for blueberry juice, 45% by Casas-Forero et al. (2021)andfororange
juice, 42% (Orellana-Palma et al., 2018),butitwaslowerthanforthe
juices of murta, 72% and arrayan, 82% (Guerra-Valle et al., 2021),
pomelo, 61% (Das et al., 2020), and blueberry, 67% and pineapple,
66% (Petzold et al., 2015). Under these same centrifugation condi-
tions, the Eff obtained was 84.3 ± 1.5%, very similar to that obtained
for arrayan juice, 82% at 1878.24 RCF for 20 min (Guerra-Valle
et al., 2021). However, in our experiments, the Eff obtained was
higher than the majority of the published results, whose range fluc-
tuates between 46% and 78%, for juices such as blueberry, 78%
(Casas-Forero et al., 2021), 48% (Petzold et al., 2015), pineapple,
58.7% (Petzold et al., 2015), orange, 83.5% (Orellana-Palma, Petzold,
Andana, et al., 2017), calafate, 69 and 76% (Orellana-Palma
et al., 2020), murta, 76% (Guerra-Valle et al., 2021), prickly pear,
65% (Márquez-Montes et al., 2023) and pomelo, 73.7% (Das
et al., 2020).
The investigations that applied C-FABC in three cycles obtained a
higher Eff in the range of 95–99% in the third step (Bastías-Montes
et al., 2019,2022), that is 15% higher than the efficiency obtained in
one cycle by CABC (Figure 5c) although, in the previous research
works, the CI achieved was close to 2. In our experiments, the final
fraction was concentrated three times (Figure 5a). Given the three
variables of the process, the best treatment was at 1000 rpm
(110 RCF) for 12 min, that is, at a lower speed and for a longer time
(Figure 5). The higher the centrifugation speed, the higher breakage of
the ice crystals may occur. The crystals may become smaller, there-
fore, there will be greater tortuosity, that may prevent the exit of all
the concentrate. Consequently, the SY and Eff are lower. It should be
noted that in our experiment the centrifugation force increases by
21 when the centrifugation speed increases 4.6 times. Simultaneously
at a higher centrifugation speed, regardless of time, diffusion mecha-
nism may take place that lead the concentrate to return to the frozen
fraction and therefore low solute recovery and efficiency is obtained.
At the lower speed and shorter time (1000 rpm and 4 min) there is
very little time for the soluble solids content to be separated from the
sample, and at the higher speed (4600 rpm either at 4 or 12 min)
the centrifugation force might cause the ice to break and melt; that is
why SY and Eff are lower.
The equations of the fitted model are:
SY ¼23:3343 þ:0140509xþ7:37199y–:00166782xy,
R2adjusted from 95:2%
Eff ¼63:3343 þ:00369907xþ1:89884y–:000457176xy,
R2adjusted from 94%
where x=centrifugation speed (rpm) and y=time (min).
FIGURE 5 (a) CI, (b) SY, and (c) Eff by CABC.
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3.3 |Evaluation of VABC
Figure 6shows the Pareto diagram that resulted from the factorial
analysis considering the three response variables CI, SY, and Eff, in
which both factors and their interaction had significant effects for SY
and Eff.
In the VABC, it was possible to concentrate samples from 15.8 to
54.7Brix, with the treatments at 10 kPa for 4 min and 10 kPa for
12 min obtaining the highest CI. These values were higher than the
reported results in 15% (w/w) sucrose solution, 2.8 (Petzold
et al., 2013), wine, 2.63 (Petzold et al., 2016) and orange juice, 2.3 at
60 min (Petzold et al., 2019). The absolute vacuum pressure used in
our work and short time may help increase the CI. However, Orellana-
Palma, Petzold, Pierre, and Pensaben (2017) reached a CI of 4.2 in
blueberry juice at 80 kPa for 10 min. Regarding SY, it was 47.3 ± 1.2%
for the treatment of 10 kPa for 12 min. The solids yield was higher
than the value obtained by Orellana-Palma, Petzold, Pierre, and Pen-
saben (2017) at 80 kPa for 20 min, 40% for blueberry juice and lower
than for sucrose solution at 15% (Petzold et al., 2013). An Eff of
81.9% was obtained, higher than that obtained by Petzold et al.
(2013) for a 15% (w/w) sucrose solution, 78%; but it was lower than
for wine, 90% obtained by Petzold et al. (2016) and for blueberry
juice, 84% (Orellana-Palma, Petzold, Pierre, & Pensaben, 2017).
Figure 7shows the comparison of the four VABC treatments for the
three response variables. A maximum average CI of 3.4 and 3.3 was
obtained with the treatments of 10 kPa for 4 min and 10 kPa for 12 min,
showing no significant differences (p> 0.05); the mean maximum values
of SY and Eff were 47.3% and 81.9%, respectively (10 kPa for 10 min).
In the VABC, the desirability function considering the three response
variables was .86, and considering only SY and Eff it reached a value of
.98 with a vacuum pressure of 10 kPa and a time of 12 min (Figure 8).
The fitted model equations are:
SY ¼4:25833 –:0375xþ4:65903y–:0334028xy,
R2adjusted from 98:7%
Eff ¼70:7417 –:0858333xþ1:04375y–:00395833xy,
R2adjusted from 99:2%
where x=vacuum pressure (kPa) and y=time (min).
FIGURE 6 Pareto diagram for (a) CI, (b) SY, and (c) Eff by VABC.
FIGURE 7 (a) CI, (b) SY, and (c) Eff by VABC.
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ASQUEZ-CASTILLO ET AL.7of12
3.4 |Comparison between CABC and VABC
The eight treatments were compared applying a categorical multifac-
tor design and multiple range test by the Bonferroni method
(p< 0.05). A maximum CI of 3.4 was obtained with VABC at 10 kPa
for 4 min. CI values were between 3.0 and 3.4 (p< 0.05); however,
the maximum difference was 12% (Table 2). This method is recom-
mended to obtain a high concentration of soluble solids, although SY
and Eff were lower than for CABC (1000 rpm for 12 min).
In our one-step experiments, CI values, 3.1 are similar to those
obtained by Orellana-Palma et al. (2021); however, they obtained the
same value after three cycles of centrifugation. In addition, Khajehei
et al. (2015), obtained a CI of 2 in four cycles of cryoconcentration
assisted by gravity and by microwave. Moreover, Burdo et al. (2021)
obtained a CI of 2.2. If we take into account some functional aspects
of each method, in CABC the sample is closed and placed in a dark
environment, which helps the phytochemicals not to oxidize or suffer
degradation, which does not happen with VABC because it operates
in open-system to facilitate the extraction.
As shown in Figure 9, in the CABC system, soluble solids such as
sucrose, glucose, fructose and others are concentrated in the lower
part of the tube so that it is easier to extract them; consequently, SY
and Eff are better. On the other hand, in the VABC system those solu-
ble solids are dispersed and it is more difficult to extract them, so that
CI, SY and Eff turn out to be lower. It is probable that the results
obtained in our investigation have been better than others, due to the
composition of the fruit with which the juice is obtained, since
the higher the soluble fiber content (mostly pectin) the juice has a
higher viscosity, which generates structure of smaller ice crystals that
occlude soluble solids, which will be more difficult to separate (either
by centrifugation or vacuum) due to greater tortuosity. For example,
the pomegranate is one of the fruits that contains less soluble dietary
fiber, .5%, while the apple has .9% (Ramulu & Rao, 2003), orange 2%
and blueberries 2.8% (Marlett & Vollendorf, 1994); murta contains
.32%–1.14% pectin (L
opez et al., 2018). It should also be noted that
the way the sample is prepared can influence the results, for example,
the pomegranate juice was filtered on filter paper with a porosity
approximate than 10 μm, in which insoluble solids are retained while
in other investigations the sample was filtered with a fine-mesh nylon
cloth (.8 mm mesh), so while the juice contains more insoluble solids,
the extraction of soluble solids becomes more difficult, the freezing
time of the sample may also have influenced, since at longer
freezing time the ice becomes more stable, which favors the extrac-
tion of soluble solids, in our case it was 48 h while in other investiga-
tions it was 12 h.
FIGURE 8 Estimated response surface for desirability VABC.
TABLE 2 CI, SY, and Eff for the eight treatments.
Treatments CI SY Eff
CABC
1000 rpm (110 RCF)
4 min 3.1 ± .0
def
18.4 ± .2
de
73.3 ± .5
d
12 min 3.0 ± .0
d
59.2 ± 3.9
a
84.3 ± 1.5
a
4600 rpm (2360 RCF)
4 min 3.2 ± .0
bc
40.1 ± 1.3
b
79.5 ± .3
bc
12 min 3.1 ± .1
cd
37.7 ± 2.1
b
77.9 ± 1.0
c
VABC
10 kPa
4 min 3.4 ± .1
a
12.7 ± 1.8
cd
73.9 ± .5
d
12 min 3.3 ± .0
ab
47.3 ± 1.2
b
81.9 ± .3
ab
70 kPa
4 min 3.0 ± .1
d
2.4 ± .5
d
67.8 ± .3
e
12 min 3.2 ± .0
b
20.9 ± 2.7
c
73.9 ± .6
d
Note: Different superscript letters indicate significant differences
(p≤0.05) among treatments.
Abbreviations: CABC, centrifugation assisted block cryoconcentration;
VABC, vacuum assisted block cryoconcentration.
FIGURE 9 Scheme of the position of soluble solids in the tube:
(a) VABC and (b) CABC.
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´
ASQUEZ-CASTILLO ET AL.
3.5 |Validation of experimental results
To validate the experimental results, a mass balance of each cryocon-
centration treatment was done, which was compared with the theo-
retical values (Equation (6) and Appendix 1).
The ice mass ratio (W) is lower in treatment 2: CABC 1000 rpm
for 12 min. Good fitting was observed between experimental (W
e
)
and predicted (W
p
) ice mass proportions in the eight treatments
(Figure 10). The RMS values for CABC and VABC were .78% and
.63%, which were less than 25%, which is what Lewicki (2000) consid-
ered as an acceptable fit, much less than the 7.3%, 5%, 2% and 4.9%
reported by Hernández et al. (2010), Sánchez et al. (2010) and Petzold
and Aguilera (2013), respectively.
4|CONCLUSIONS
Both cryoconcentration methods (CABC and VABC) are suitable to
concentrate pomegranate juice in one cycle. SY and Eff were chosen
as the parameters to obtain a desirability close to 1, while CI repre-
sents the level of concentration that can be reached. CABC at
1000 rpm (110 RCF) for 12 min obtained a concentration of 47.9Brix
with an SY of 59.2% and average Eff of 84.3% in a single cycle. For
VABC at 10 kPa and 12 min, values of CI and Eff were similar but SY
was remarkably lower. The advantage of both systems is that in one
cycle the performance is more satisfactory than other cryoconcentra-
tion methods with two or more operational cycles.
Efforts have to be made in the design of the cryoconcentration
equipment and scale-up, together with recovery of the solutes
retained in the ice block to translate the technology to an industrial
scale. Both systems may lead to reduce equipment design and
improve energy efficiency compared with current industrial cryocon-
centration devices.
NOMENCLATURE
C
0
solute concentration in the initial sample (Brix)
CABC centrifugation-assisted block cryoconcentration
C
f
solute concentration in the ice fraction (Brix)
C-FABC centrifugation-filtration assisted cryoconcentration
CI concentration Index
C
s
solute concentration in the concentrated (Brix)
Eff efficiency (%)
kthermal conductivity (Wm
1
K
1
)
M
c
concentrate mass (kg)
M
f
ice mass (kg)
m
0
mass of solute in the initial sample (kg)
m
s
mass of solute in the concentrate (kg)
NSVK no significant variation in kinetics
RCF relative centrifuge force (g)
RMS root mean square (%)
rpm revolutions per minute
SY solute yield (%)
VABC vacuum-assisted block cryoconcentration
Wice mass ratio (kg/kg)
W
e
experimental ice mass ratio (kg/kg)
W
p
predicted ice mass ratio (kg/kg)
AUTHOR CONTRIBUTIONS
Flor M. Vásquez-Castillo: Conceptualization; data curation; formal
analysis; investigation; methodology; software; writing and editing.
Isabel Achaerandio: Conceptualization; data curation; investigation;
methodology; supervision; writing –review and editing. Milber
O. Ureta-Peralta: Validation, Formal analysis, Visualization. Eduard
Hernandez: Conceptualization; data curation; investigation; method-
ology; supervision; writing –review and editing.
ACKNOWLEDGMENTS
Flor M. Vásquez-Castillo thanks God and PRONABEC for the scholar-
ship granted to carry out this research as part of the doctorate in Tec-
nología Agroalimentaria y Biotecnología at the Universitat Politècnica
de Catalunya (UPC), and the authors from both the UPC and UNALM
for their valuable contributions for its execution.
CONFLICT OF INTEREST STATEMENT
The authors declare no conflict of interest.
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available on
request from the corresponding author. The data are not publicly
available due to privacy or ethical restrictions.
ORCID
Eduard Hernández https://orcid.org/0000-0002-5337-6947
Milber O. Ureña-Peralta https://orcid.org/0000-0002-0716-0176
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How to cite this article: Vásquez-Castillo, F. M., Hernández, E.,
Ureña-Peralta, M. O., & Achaerandio, I. (2023). Comparative
study of block cryoconcentration in pomegranate juice:
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AP PE N D I X 1: Primary experimental values
No.
Conditions
Treatment
Initial sample Concentrated fraction Ice fraction Validation of results (mass balance)
Speed centrifugation (rpm)/
vacuum pressure (kPa)
Time
(min)
Initial
weight
Initial
soluble
solids
Concentrate
weight (g)
Soluble solids
from concentrate
Ice
weight
(g)
Soluble
solids
from ice
Predicted
value
Experimental
value
Root mean
square (RMS)
W
0
C
0
W
c
C
s
W
i
C
f
V
p
=
(C
s
C
0
)/
(C
s
C
f
)V
e
=W
i
/W
0
((V
e
V
p
)/
W
e
)
2
1 1000 rpm 4 A 45.01 15.80 2.70 49.00 42.35 13.20 .927 .941 .00
2 1000 rpm 4 A 45.00 15.80 2.60 49.80 42.31 13.50 .937 .940 .00
3 1000 rpm 4 A 45.01 15.80 2.60 50.40 42.29 13.20 .930 .940 .00
4 1000 rpm 12 B 45.00 15.80 9.42 48.10 35.40 6.80 .782 .787 .00
5 1000 rpm 12 B 45.00 15.80 8.41 48.30 36.30 7.60 .799 .807 .00
6 1000 rpm 12 B 45.00 15.80 8.54 47.20 36.34 8.10 .803 .808 .00
7 4600 rpm 4 C 45.00 15.80 5.89 50.10 38.83 10.10 .858 .863 .00
8 4600 rpm 4 C 45.00 15.80 5.59 50.50 39.14 10.30 .863 .870 .00
9 4600 rpm 4 C 45.00 15.80 5.46 50.90 39.47 10.60 .871 .877 .00
10 4600 rpm 12 D 45.01 15.80 5.40 49.60 39.42 10.80 .871 .876 .00
11 4600 rpm 12 D 45.01 15.80 5.75 49.20 39.08 10.50 .863 .868 .00
12 4600 rpm 12 D 45.01 15.80 5.29 47.90 39.49 11.10 .872 .877 .00
13 10 kPa 4 E 45.01 15.80 1.40 54.70 43.60 14.30 .963 .969 .00
14 10 kPa 4 E 45.01 15.80 1.89 53.50 43.10 13.70 .947 .958 .00
15 10 kPa 4 E 45.01 15.80 1.75 53.00 43.21 14.10 .956 .960 .00
16 10 kPa 12 F 45.00 15.80 6.47 52.53 38.38 9.50 .854 .853 .00
17 10 kPa 12 F 45.00 15.80 6.17 52.93 38.71 9.70 .859 .860 .00
18 10 kPa 12 F 45.00 15.80 6.54 52.27 38.35 9.30 .849 .852 .00
19 70 kPa 4 G 45.00 15.80 .27 47.10 44.73 15.10 .978 .994 .00
20 70 kPa 4 G 45.00 15.80 .39 48.50 44.65 15.50 .991 .992 .00
21 70 kPa 4 G 45.01 15.80 .40 47.40 44.66 15.40 .988 .992 .00
22 70 kPa 12 H 45.00 15.80 3.36 50.70 41.70 12.90 .923 .927 .00
23 70 kPa 12 H 45.00 15.80 2.81 50.60 42.23 13.50 .938 .938 .00
24 70 kPa 12 H 45.00 15.80 2.60 51.65 42.39 13.50 .940 .942 .00
Sum (P)/N.000
Root .007
RMS % .713
12 of 12 V
´
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