ISSN 0101-2061
Food Science and Technology
Rheological behavior of Brazilian Cherry (Eugenia uniflora L.) pulp at
pasteurization temperatures
Comportamento reológico da polpa de pitanga (Eugenia uniflora L.) em temperaturas de pasteurização
Alessandra Santos LOPES1*, Rafaella de Andrade MATTIETTO2, Hilary Castle de MENEZES3,
Luiza Helena Meller da SILVA1, Rosinelson da Silva PENA1
Abstract
The rheological behavior of Brazilian Cherry (Eugenia uniflora L.) pulp in the range of temperatures used for pasteurization (83 to 97 °C) was
studied. The results indicated that Brazilian Cherry pulp presented pseudoplastic behavior, and the Herschel-Bulkley model was considered
more adequate to represent the rheological behavior of this pulp in the range of temperatures studied. The fluid behavior index (n) varied
in the range from 0.448 to 0.627. The effect of temperature on the apparent viscosity was described by an equation analogous to Arrhenius
equation, and a decrease in apparent viscosity with an increase in temperature was observed.
Keywords: Brazilian cherry; fruit pulp; rheology; activation energy.
Resumo
Neste trabalho, foi estudado o comportamento reológico da polpa de pitanga na faixa de temperatura de pasteurização de 83 a 97 °C. Os
resultados indicaram que a polpa apresentou comportamento pseudoplástico e o modelo de Herschel-Bulkley foi considerado o mais adequado
para representar o comportamento reológico do produto nas temperaturas estudadas. Os índices de comportamento de fluido (n) variaram
na faixa de 0,448 a 0,627. O efeito da temperatura sobre a viscosidade aparente pôde ser descrito pela equação análoga à de Arrenhius,
observando-se a diminuição da viscosidade aparente da polpa de pitanga com o aumento da temperatura.
Palavras-chave: pitanga; polpa de fruta; reologia; energia de ativação.
1 Introduction
Brazilian Cherry is indigenous to Brazil extending over a
wide area, from the North to the South. It is found growing in the
wild along the banks of streams and in the edge the forests, but
it is also commonly grown in many parts of Brazil, mainly in the
Southeast region. Outside Brazil, Brazilian Cherry is also grown
in several countries such as United States (Florida, Hawaii, and
California), India, Ceylon, China, Algeria, France, and Cuba
(CONSOLINI; SARUBBIO, 2002; MIELKE; SCHAFFER, 2010).
Fruit pulp can be used as raw material in the food industry
to obtain various products, such as nectars, jams, ice-creams
etc., products that can also be sold directly to consumers.
Knowledge of the rheological properties of this fruit pulp
is fundamental to evaluate its quality and also for its use in
engineering to calculate flow rate, in the selection of pumps,
and determination of pressure loss in pipes, etc. (RAO; STEFFE,
1992; SARAVACOS; MAROULIS, 2001; SATO; CUNHA, 2009).
Fruit pulps are generally characterized as non-Newtonian
fluids as a result of complex interactions amongst their
components. These kinds of fluid are generally described by
empirical rheological models that represent the most convenient
rheogram fit. The most widely used models are the Power Law
(RAO; STEFFE, 1992; HOLDSWORTH, 1993; PELEGRINE;
SILVA; GASPARETTO, 2002; HAMINIUK et al., 2006) and
the Herschel–Bulkley (RAO; STEFFE, 1992; HOLDSWORTH,
1993; PELEGRINE; SILVA; GASPARETTO, 2002; DUTTA et al.,
2006).
The rheological properties of a number of fruit purees,
such as peach puree (GUERRERO; ALZAMORA, 1997),
mango puree (GUERRERO; ALZAMORA, 1997; PELEGRINE;
SILVA; GASPARETTO, 2002; DAK; VERMA; JAAFFREY,
2007), and tropical fruit puree (guava, pineapple and papaya)
(PELEGRINE; SILVA; GASPARETTO, 2002; AHMED;
RAMASWAMY, 2004; SÁNCHEZ et al., 2009) and cashew juice
(MOREIRA et al., 2005) have been determined, and the Power
Law model was used to describe the flow behavior. Until now,
however, there have been no reports on the rheological behavior
of Brazilian Cherry.
The rheological behavior of fruit juices and pulps is
associated to the levels of soluble solids in suspension and as a
function of the form, size and concentrations of the suspended
Received 27/9/2011
Accepted 31/7/2012 (005342)
1
Instituto de Tecnologia, Faculdade de Engenharia de Alimentos, Universidade Federal do Pará – UFPA, Belém, PA, Brasil, e-mail: aslopes@ufpa.br
2
Empresa Brasileira de Pesquisa Agropecuária – EMBRAPA Amazônia Oriental, CEP 66095-100, Belém, PA, Brasil
3
Universidade Estadual de Campinas – UNICAMP, CEP 13083-862, Campinas, SP, Brasil
*Corresponding author
DOI: http://dx.doi.org/10.1590/S0101-20612013005000001
26
Food Sci. Technol, Campinas, 33(1): 26-31, Jan.-Mar. 2013
Lopes et al.
particles and the structure of the system. The literature on the
rheology of fruit derivatives has established that temperature,
soluble solids concentration, pectin content, and insoluble solids
content are the main factors responsible for the rheological
behavior (RAO; STEFFE, 1992; JUSZCZAK; FORTUNA, 2004;
HAMINIUK et al., 2006).
The fruits that presented visual defects, mechanical damage, and
attack by fungi and wood pests were discarded. The extraction
process was carried out in duplicate using a BERTUZZI brush
pulper. The samples were packed in plastic bags (500 mL) and
stored under freezing temperature (–20 °C) until analyses.
Different temperatures are applied in the various steps
of fruit juice and pulp processing, for example during
pasteurization and cooling. Thus, the rheological behavior of
these fluids should be studied in the various temperature ranges
used in industrial processes (MARCOTTE; HOSHAHILI;
RAMASWAMY, 2001; SARAVACOS; MAROULIS, 2001).
2.2 Physical and physicochemical analyses
At rest, fruit pulps, which are dispersions of molecules
or asymmetric particles, show a disordered state, but when
subjected to shear stress, their molecules or particles tend to
orient themselves toward the applied force. The greater the
force applied, the greater the ordination and hence the lower
the apparent viscosity. The pseudoplastic fluids are also known
as shear-thinning fluids, since their apparent viscosity decreases
as the shear rate is increased (RAO; STEFFE, 1992; RAO, 1999;
KROKIDA; MAROULIS; SARAVACOS, 2001; SATO; CUNHA,
2009).
There are two rheological models that generally describe
the rheological behavior of fruit juice and pulps: the Ostwaldde-Waele model (or Power Law) (Equation 1) and the HerschelBulkley model (or Generalized Power Law) (Equation 2); their
difference is the inclusion of the yield stress (σo) in Equation 2
(RAO; STEFFE, 1992; HOLDSWORTH, 1993; AHMED;
RAMASWAMY, 2004).
σ = kγ n
(1)
=
σ σ o + kγ n
(2)
where: γ = shear rate (s–1), σ = shear stress (Pa), σo = yield stress
(Pa), k = consistency index (Pa.sn), and n = flow behavior index
(non-dimensional)
In the Brazilian food industry, Brazilian Cherry fruit has
mainly been used to produce pulp and juice, which shows
good economic potential due to the consumer appeal arising
from its high concentration of antioxidant compounds
(EINBOND et al., 2004; SPADA et al., 2008; CELLI; PEREIRANETTO; BETA, 2011).
The objective of the present study was to evaluate the
rheological behaviour of Brazilian Cherry pulp in the range of
pasteurization temperatures from 83 to 97 °C.
2 Materials and methods
2.1 Raw material
Brazilian Cherry fruits (9 kg) were obtained from a farm
in Valinhos, São Paulo, Brazil. Immediately after harvest, the
fruits were transported to the Pilot Plant of Food Technology
Department at UNICAMP, where they were selected, washed,
and sanitized with chlorine solution (60 mg.L–1) for 30 minutes.
Food Sci. Technol, Campinas, 33(1): 26-31, Jan.-Mar. 2013
The analyses were carried out according to AOAC methods
(ASSOCIATION... 1997): pH (method nº 981.12); total
titratable acidity (method nº 942.15); reducing and total sugars
(methods nº 925.35 and 925.36); proteins (method nº 920.152);
lipids (method nº 968.20), and ashes (method nº 940.26). Soluble
solids (ºBrix) were evaluated based on the direct reading of
degrees Brix of the sample at 20 °C using a LEICA AR200 digital
refractometer, and the total solids were determined using a
GEHAKA IV 2002 infrared moisture analyser.
2.3 Rheological characterization
The rheological analyses of the Brazilian Cherry pulp were
carried out using a BROOKFIELD RV-DV III digital rheometer
with a coaxial cylinder geometry (Ultra Low Viscosity
Adapter - ULA) and a BROOKFIELD TC500 thermostatically
controlled water bath. The analyses were carried out in triplicate
varying the velocity in both the increasing (10 to 250 rpm) and
decreasing (250 to 10 rpm) modes with increments of 10 rpm
every 15 seconds. The total run time was 6.30 minutes, within
which 50 measurements of apparent viscosity (mPa.s), shear
stress (Pa), and shear rate (s–1) were obtained. The temperatures
evaluated were 83, 85, 90, 95, and 97 °C in addition to 20 °C,
which was used as the reference temperature. Samples of
16.0 mL of Brazilian cherry pulp were used for each experiment,
and sample reuse was avoided due to the possible changes in
rheological properties after heating.
The effect of temperature on the apparent viscosity (ηa) at
a specific shear rate was evaluated by the equations analogous
to Arrhenius equation (Equation 3) (RAO; STEFFE, 1992;
MARCOTTE, HOSHAHILI; RAMASWAMY, 2001; JUSZCZAK;
FORTUNA, 2004). The Herschel-Bulkley model was used to
obtain the apparent viscosity values at different shear rates.
ηa = ηo .exp
Eat,η
R.T
(3)
where: ηa = apparent viscosity (Pa.s); ηo = constant (Pa.s);
E at, η = activation energy (J.mol –1 ); R = gas constant
(8.3144 J.mol–1.K–1); and T = temperature (K).
2.4 Statistical analysis
A non-linear fit (Quasi-Newton) was made for the
Power Law (Ostwald-de-Waele) and Generalized Power Law
(Herschel-Bulkley) models using the STATISTICA® version
5.0 software (STATSOFT…, 1995). Ascending and descending
curves were used to obtain the fits for the models, the mean value
of shear stress was calculated for each shear rate at the different
temperatures evaluated. The average values of ascending and
descending curves were used because the fluid did not present
27
Rheological behavior of pitanga pulp
thixotropy, as described by Gasparetto and Guimarães (2000).
The following statistical parameters were evaluated to determine
the adequacy of the models: coefficient of determination (R2),
chi-square (χ2), and the sum of squared residues (SSR). The
higher the value of χ2, the greater the difference between the
frequencies observed and those predicted by the model. Thus,
the model that best fitted the data was that with the highest
R2 values and the lowest for χ2 and SSR values. The Arrhenius
Equation was fitted using non-linear regression using the same
software.
juices and pulps and verified that this deviation from Newtonian
behavior was determined by the pulp content. Rao (1999) and
Sato and Cunha (2009) showed that the rheological behavior
of fruit juices and pulps was related to the levels of suspended
soluble solids as a function of the form, size, and concentration
of the suspended particles and the structure of the system. The
presence of pectic substances and/or dispersed solid particles
is responsible for the non-Newtonian behavior which can be
described by the Power Law, Herschel-Bulkley, and Bingham
models (SARAVACOS; MAROULIS, 2001; DAK; VERMA;
JAAFFREY, 2007).
3 Results and discussion
The influence of temperature on the behavior of the curves
in Figures 1 and 2 is quite pronounced; it can be seen that the
curve prepared at a temperature of 20 °C (reference temperature)
is in a distinct range of values for shear stress and viscosity when
compared to those prepared at pasteurization temperatures
(83, 85, 90, 95, and 97 °C). According to Rao and Steffe (1992),
Marcotte, Hoshahili and Ramaswamy (2001) and Juszczak and
Fortuna (2004), and many other authors, temperature is one of
the major factors that affect the viscosity of fruit pulps.
3.1 Physical and physicochemical characterization of
Brazilian Cherry pulp
Table 1 shows the results of composition obtained for the
Brazilian Cherry pulp used in this study. The major constituent
of pulp Brazilian Cherry are total sugars (7.97%), especially
reducing sugars (7.80%), which accounted for 89.7% and 87.8%
of the total solids of the pulp, respectively. Similar composition
for this fruit was observed by Lederman, Bezerra and Calado
(1992) and Santos, Silva and Alves (2006).
As observed for other fruits, the values of proteins (0.68%)
and lipids (0.49%) are below 2%. Bagetti et al. (2011) reported
values of 1.4% and 0.4% for proteins and lipids in Brazilian
cherry fruit, respectively.
3.2 Rheological behavior of Brazilian Cherry pulp
Figure 1 shows the flow curves for Brazilian Cherry pulp
at the different temperatures studied. The graph represents the
mean experimental points and their respective curves adjusted
to the Herschel-Bulkley model. Non-Newtonian behavior was
observed, as shown by the non-linearity between the shear stress
and shear rate applied. In addition, the slopes of the flow curves
decreased with an increase in shear rate, evidence of the decrease
in apparent viscosity with increase in shear rate, confirming the
pseudoplastic behavior of the Brazilian Cherry pulp.
Figure 1. Relationship between shear stress and shear rate for Brazilian
cherry pulp at different temperatures.
The majority of food fluids presents pseudoplastic behavior
the apparent viscosity decreases with an increase in shear rate
(RAO; STEFFE, 1992; SARAVACOS; MAROULIS, 2001), as can
be seen in Figure 2. Rao and Steffe (1992) and Saravacos and
Maroulis (2001) reported the pseudoplastic behavior of fruit
Table 1. Physico-chemical characterization of Brazilian Cherry pulp.
Parameter
pH
Total titratable acidity (g citric acid.100g–1)
Soluble solids (as °Brix)
Total solids (%)
Reducing sugars (g glucose.100g–1)
Total sugars (g glucose.100g–1)
Proteins (%)
Lipids (%)
Ashes (%)
*Mean of triplicate ± standard deviation (wet weight basis).
28
Value*
3.34 ± 0.01
1.23 ± 0.02
7.97 ± 0.06
8.88 ± 0.02
7.80 ± 0.03
7.97 ± 0.13
0.68 ± 0.01
0.49 ± 0.03
0.37 ± 0.00
Figure 2. Relationship between apparent viscosity and shear rate for
Brazilian cherry pulp at different temperatures.
Food Sci. Technol, Campinas, 33(1): 26-31, Jan.-Mar. 2013
Lopes et al.
The values for apparent viscosity of the Brazilian Cherry
pulp varied from 0.008 to 0.212 Pa.s (Figure 2) for the
temperature/shear rate binomials of 97 °C/306 s –1 and
20 °C/12 s–1, respectively.
Table 2 shows the values obtained for the apparent viscosity
of Brazilian Cherry pulp at shear rates of 100, 200, and 300 s–1.
As can be seen in Figure 2, a decrease in apparent viscosity is
verified when the increases in temperature and shear rate are
considered separately.
These values are relevant in industrial processing operations
when the shear rate is greater than 100 s–1 (VIDAL, 2006).
3.3 Determination of the rheological parameters of Brazilian
Cherry pulp
Table 3 presents the values for the rheological parameters
and the statistical results obtained for Brazilian Cherry pulp
at temperatures of 20, 83, 85, 90, 95 and 97 °C, from the fit for
the Power Law and Herschel-Bulkley models using the average
value of the ascending and descending curves in triplicate. It
shows that the values for the behavior index (n) are always less
than unity indicating a pseudoplastic character of the Brazilian
Cherry pulp. This rheological parameter varied from 0.346 to
0.446 for the Power Law model and from 0.448 to 0.627 for the
Herschel-Bulkley model.
Table 2. Apparent viscosity of Brazilian Cherry pulp.
Temperature
(°C)
20**
83
85
90
95
97
Apparent viscosity (mPa.s)*
100 s–1
200 s–1
300 s–1
45.98 ± 2.68a
29.10 ± 1.59a
24.67 ± 1.07a
22.53 ± 1.71b
14.96 ± 2.91b
11.21 ± 1.63b
17.75 ± 1.52bc
11.45 ± 1.04bc
9.31 ± 0.71bc
15.76 ± 1.49c
10.50 ± 1.05c
8.62 ± 0.66bc
15.57 ± 1.61c
10.39 ± 1.00c
8.52 ± 0.70c
15.61 ± 1.52c
10.43 ± 1.20c
8.53 ± 0.70c
*Mean of triplicate ± standard deviation (wet weight basis). **Reference temperature.
Mean values in the same column followed by different subscript letters are significantly
different (p < 0.05).
Table 3. Rheological and statistical parameters for Brazilian Cherry
pulp.
K (Pa.sn)
n
R2
χ2
SSR
20 °C
0.738
0.403
0.974
0.299
1.443
τo (Pa)
K (Pa.sn)
n
R2
χ2
SSR
20 °C
1.674
0.163
0.627
0.981
0.193
1.037
Power Law
83 °C
85 °C
90 °C
0.463
0.325
0.213
0.346
0.372
0.434
0.986
0.992
0.995
0.052
0.025
0.023
0.132
0.055
0.032
Herschel-Bulkley
83 °C
85 °C
90 °C
0.621
0.301
0.351
0.179
0.189
0.091
0.479
0.448
0.558
0.989
0.993
0.998
0.045
0.024
0.007
0.105
0.048
0.015
95 °C
0.201
0.442
0.996
0.019
0.025
97 °C
0.197
0.446
0.996
0.020
0.028
95 °C
0.291
0.100
0.545
0.998
0.007
0.014
97 °C
0.299
0.095
0.553
0.998
0.008
0.015
Food Sci. Technol, Campinas, 33(1): 26-31, Jan.-Mar. 2013
Pelegrine, Silva and Gasparetto (2002), Ahmed and
Ramaswamy (2004), Dutta et al. (2006), Dak, Verma and Jaaffrey
(2007) showed pseudoplastic behavior for papaya, mango, and
pineapple pulps. This effect is clearly more pronounced for whole
pulps than for those clarified by centrifugation.
According to Chin et al. (2009) and Sánchez et al. (2009),
pummelo juice concentrate and white guava puree showed
behavior index (n) values below unity at temperatures from 6
to 75 °C and 10 to 60 °C, respectively, indicating pseudoplastic
behavior.
Saravacos and Maroulis (2001) showed that the values
for the behavior index (n) for fruit purees were generally in
the range from 0.30 to 0.50. The variation in this parameter
is a function of several variables such as: variety, processing,
degree of maturity, and the method for determining rheological
parameters.
Guerrero and Alzamora (1997) and Krokida, Maroulis
and Saravacos (2001) showed that the consistency index (K)
decreased significantly at high temperatures, but the behavior
index (n) of fruit purees was not affected.
Comparing the fit for the Power Law and HerschelBulkley models, it can be seen that both models satisfactorily
represent the rheological behavior of the Brazilian Cherry
pulp. The Herschel-Bulkley model showed higher values for
the determination coefficient (R2) and lower values in the
chi-square test (χ2) and also for the sum of squared residues
(SSR). Additionally, the Herschel-Bulkley model provides three
rheological parameters (yield stress, consistency coefficient,
and flow behavior index), when compared with the Power Law
model (two parameters), which does not provide the parameter
yield stress. According Haminiuk et al. (2006), the yield stress is
an important quality control parameter in industrial processes,
particularly for comparing the overall characteristics of products
manufactured on different production lines.
Since the Herschel-Bulkley model generates more
information (yield stress) than the Power Law model, it was
chosen to describe the rheological behavior of the Brazilian
Cherry pulp.
3.4 Effect of temperature
The effect of temperature on the apparent viscosity of
Brazilian cherry pulp at a constant shear rate can be described
by the Arrhenius equation, in which the apparent viscosity
decreases with temperature (Figure 3). The apparent viscosity
values generated by Herschel-Bulkley model were used in the
construction the Arrhenius model.
The order of magnitude of the activation energy indicates
the dependence of the viscosity on the temperature (RAO;
STEFFE, 1992; RAO; TATTIYAKUL, 1999; SARAVACOS;
MAROULIS, 2001; DAK; VERMA; JAAFFREY, 2007).
According to Table 4, the variation explained around the
mean (R2) showed high values for the shear rates studied.
The values for R2 varied from 0.970 to 0.990, explaining the
experimental data using the Arrhenius equation in terms of the
29
Rheological behavior of pitanga pulp
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4 Conclusions
The rheological behavior of Brazilian Cherry pulp in the
range of pasteurization temperatures studied can be represented
by the Herschel-Bulkley equation. The fluid behavior indexes
(n) were below unity characterizing the pseudoplastic behavior
of the Brazilian Cherry pulp. The effect of temperature can
be evaluated using the Arrhenius-type equation obtaining
the activation energy values for the viscous flow of Brazilian
Cherry pulp.
Acknowledgements
The authors are grateful for the financial support provided
by CNPq (The National Council for Scientific and Technological
Development).
30
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