Rheology of Pomelo Juice
The proximate analysis studies on pomelo juice provide useful data for its juice processing industry. The studies on the physico-chemical properties such as water activity, pH and density make better prediction of its behavior at the relevant processing concentration and temperature. The Pomelo j...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English English |
| Published: |
2009
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/5818/1/FK_2009_30a.pdf |
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| Summary: | The proximate analysis studies on pomelo juice provide useful data for its juice
processing industry. The studies on the physico-chemical properties such as water
activity, pH and density make better prediction of its behavior at the relevant
processing concentration and temperature. The Pomelo juice is found to have high
moisture content which contributes to high water activity and specific heat of
capacity. Also, the PH of pomelo juice obtained indicates that pomelo juice is acidic
fluid. The predictions of density yielded high regression coefficient. In general, the
density increases with increasing concentration but decreases with temperature
increase. The density of pomelo juice also presented a stronger dependence on
concentration than the temperature.
Rheology is the science of deformation and flow behavior of fluid. Knowledge of
rheological properties of fluid and their variation with temperature and concentration
have been globally important for industrialization of food technology for quality,
understanding the texture, process engineering application, correlation with sensory evaluation, designing of transport system , equipment design (heat
exchanger and evaporator), deciding pump capacity and power requirement for
mixing.
The aim of this study was to determine the rheological behavior of pomelo juice at
different concentrations (20-60.4 Brix) and temperatures (23-60°C) by using a
rotational Haake Rheostress 600 rheometer and a cone and plate geometry sensor
(35mm diameter, 2° cone angle), with a gap distance of 0.105 mm. Shear rates
employed ranged from 0-1000 s-1.
o
Pomelo juice was found to exhibit both Newtonian and Non-Newtonian behavior.
For lower concentration the Newtonian behavior is observed while at higher
concentration Non-Newtonian behavior was observed. Standard error (SE) method
was selected on the basis to carry out the error analysis due to the best fit model. For
the four models the values of SE show that the Herschel-Bulkley and Power Law
models perform better than the Bingham and Casson models but Herschel-Bulkley
model is true at higher concentration.
The experimental data of apparent viscosity versus shear rate were successfully
described by the Power-law model. The model parameters; flow behavior index, n
varied in the range of 0.65-0.89, whereas the values for the consistency coefficient,
K, were in the range of 0.004-0.3 (Pa. ). Apparent viscosity and consistency
coefficient of pomelo juice increased with increasing concentration and decreasing
temperature. The effect of temperature on n was found to be significant but did not follow any descriptive trend.
The effect of temperature on pomelo juice is best described by the applicability of
the Arrhenius model related to apparent viscosity, η at a constant shear rate of
100s −1 or the consistency index of the power law model. Activation energies (
a Ε ) of
the pomelo juice appeared in the range of 9103.83-23391.43 J/mol as the pomelo
juice concentration was increased from 20 to 60.4 o Brix.
The relationship between η or K of pomelo juice concentration was explained by
exponential and power functions while pomelo juice observed that at higher
concentration will have higher viscosity.
The master-curve was investigated for comparing data from different products at a
reference temperature of 40 . Multiple regression analysis indicated Master-Curve
presents good agreement for pomelo juice at all concentrations studied with R 2 >0.8.
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Response surface methodology (RSM) was applied to investigate the effects of the
three main independent parameters; rotation, temperature and time on the pomelo
juice concentration and optimizing the operating conditions of the treatment process.
Values of parameters required to obtain efficiency of concentration pomelo juice are
suggested based on rotation speed (60-120 rpm), temperature (40-60 ) and time
(5-60 min).
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It is clear from the result that the concentration increased when the temperature, rotation speed and time increased. It can be inferred that any parameters,
individually, had positive effect on increase of concentration. The main effects of
parameters are in following order: Main effect of time> temperature> rotation speed. |
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