Pumpkin puree exhibited yield stress, which decreased
exponentially with temperature (Fig. 10). The
values decreased from 24.1756 to 4.8314 Pa when the
temperature was increased from 60 C to 100 C. At
higher temperatures, due to rupture, the food structure
becomes weak resulting in the lowering of yield stress
(Steffe, 1992). The flow behavior index (n) was less than
unity and increased with temperature from 0.5832 to
0.8012. This indicated that the puree behaved as a
shear-thinning (pseudoplastic) fluid. Typical flow curves
are shown in Fig. 11. From the figure, it is evident that
the apparent viscosity (ga) was found to decrease with
increased shear rate, which also proves its pseudoplastic
or shear thinning nature. The yield stress values at selected
temperatures were incorporated into the apparent
viscosity value, and apparent viscosity-shear rate data
fitted the Herschel–Bulkley model (Eq. (6)) adequately
over the entire temperature range. The coefficients for
the Herschel–Bulkley and Power law model are given
in Table 6.
4.6. Effect of temperature on consistency index and
apparent viscosity
It is seen from Fig. 11 and Table 6 that the apparent
viscosity (ga) and consistency index (K) decreased significantly
whereas the flow behavior index value (n) increased
with an increase in puree temperature. K
Value decreased from 1.9531 to 0.6012 Pa sn (Table 6).
The Arrhenius model (Eqs. (7) and (8)) gave a satisfactory
description of the temperature dependence of
apparent viscosity (at 100 rpm) and is in agreement with
the consistency index of the Herschel–Bulkley model.
The coefficients were computed using the least-square
technique. Ega Value was found to be 13.3845 kJ/mol,
while EK was computed to be 31.9394 kJ/mol
respectively.
Pumpkin puree exhibited yield stress, which decreasedexponentially with temperature (Fig. 10). Thevalues decreased from 24.1756 to 4.8314 Pa when thetemperature was increased from 60 C to 100 C. Athigher temperatures, due to rupture, the food structurebecomes weak resulting in the lowering of yield stress(Steffe, 1992). The flow behavior index (n) was less thanunity and increased with temperature from 0.5832 to0.8012. This indicated that the puree behaved as ashear-thinning (pseudoplastic) fluid. Typical flow curvesare shown in Fig. 11. From the figure, it is evident thatthe apparent viscosity (ga) was found to decrease withincreased shear rate, which also proves its pseudoplasticor shear thinning nature. The yield stress values at selectedtemperatures were incorporated into the apparentviscosity value, and apparent viscosity-shear rate datafitted the Herschel–Bulkley model (Eq. (6)) adequatelyover the entire temperature range. The coefficients forthe Herschel–Bulkley and Power law model are givenin Table 6.4.6. Effect of temperature on consistency index andapparent viscosityIt is seen from Fig. 11 and Table 6 that the apparentviscosity (ga) and consistency index (K) decreased significantlywhereas the flow behavior index value (n) increasedwith an increase in puree temperature. KValue decreased from 1.9531 to 0.6012 Pa sn (Table 6).The Arrhenius model (Eqs. (7) and (8)) gave a satisfactorydescription of the temperature dependence ofapparent viscosity (at 100 rpm) and is in agreement withthe consistency index of the Herschel–Bulkley model.The coefficients were computed using the least-squaretechnique. Ega Value was found to be 13.3845 kJ/mol,while EK was computed to be 31.9394 kJ/molrespectively.
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