Temperature dependent electrical conductivities of ginger paste during ohmic heating
(Ahmed and Shivhare, 2001) For this study, the
paste was obtained after adding required amount
(1)
of salt (according to the experimental design) to
the puree. The pH was adjusted to 4.2 using 30%
Where, σ = electrical conductivity, mS/m
(w/v) citric acid solution. The enzymatic browning
I = electric current, A
was prevented by adding KMS at the rate of 2g/kg
of paste for treated samples. Then ginger paste was
X = distance between electrode, m
transferred to ohmic heating device and heated at
V = voltage, V
different voltage gradients (5, 7, 9, 11 and 13 v/cm)
up to 80˚C.
a = area across which current flows, m2
Measurements techniques
Results and Discussion
During ohmic heating of ginger paste, electrical
The ginger paste was ohmically heated in laboratory
conductivity is likely to change and could be a
size ohmic heating device and changes of electrical
function of temperature and time. To evaluate
conductivity with temperature were obtained. It
the effect of time on bulk and point electrical
was observed that electrical conductivity increases
conductivity, experiments were planned at the time
with increasing temperature and time of heating and
interval of 0, 5 and 10 min at four temperature levels,
bubbling was observed above 70˚C especially at high
namely, 30, 40, 50 and 60˚C.
voltage gradients. Similar electrical conductivity
changes have been observed by Castro et al. , (2004)
Point electrical conductivity
for strawberry based products.
Point electrical conductivity of ginger paste was
Time dependence of electrical conductivity
determined by Microprocessor-304 conductivity
meter using the standard conductivity probe at
Duetothestructuralchangesduringohmicheatingof
the temperatures of 30, 40, 50 and 60˚C. The ginger
product the electrical conductivity is likely to change
paste was ohmically heated at voltage gradient of 5,
with temperature and time. However, it may possible
7, 9, 11 and 13 V/cm, when temperature reached to
that ginger paste undergoes certain biochemical
the desired level (80˚C), ohmic heating device was
changes under the influence of temperature which
switched off and conductance readings were taken
influence the electrical conductivity of paste. Hence
after 10 s to avoid transient effect of electric field.
it is important to study the time dependence of point
and bulk electrical conductivity. The present study
Bulk electrical conductivity
is conducted to measure the point and bulk electrical
conductivities at different time interval of 0, 5 and
The bulk electrical conductivity was determined in
10 minute and different temperature levels namely
single experiment at voltage gradient of 5, 7, 9, 11
30, 40, 50 and 60 ˚C. Data shows that point electrical
and 13 v/cm and salt level of 0, 0.5, 1, 1.5 and 2%.
conductivity varied from 4.41 to 6.63 mS/cm while
Approximately 80g of ginger paste was filled in ETM
bulk electrical conductivity varied from 3.75 to 5.87
unit and ohmically heated up to 60˚C. The readings
mS/cm for above mentioned time interval.
of current and the area across which current flows
at particular voltage gradient were noted. The bulk
ANOVA (Table 1) for time dependence of point
electrical conductivity was calculated according to
electrical conductivity indicates that temperature
the following equation given by Palaniappan and
had significant effect on point electrical conductivity
Sastry, (1991)
at 1% level of significance which indicates that point
electrical conductivity is a function o temperature of
ohmic heating. Similarly ANOVA (Table 2) for time
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