Effect of pectinmethylesterase on the flow behavior of fresh valencia orange pulp
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Orange pulp has a complex flow behavior displaying slippage at very low shear rates (0.6-0.9 s-1), in addition to changing rapidly with storage time. That change was attributed to pectinmethylesterase (PME) activity in unpasteurized orange pulp but had not been characterized. Flow behavior of orange pulp was fitted to power law at shear rates smaller than those where slippage occurred. Shear stress-controlled rotational rheology tests were conducted on fresh orange pulp stored for 0 to 48 h at 4 °C. Flow behavior index (n) was 0.32, independent of storage time (p>0.05). Consistency coefficient (K) increased 65.5% after 48 h storage (119.7 to 198.1 Pa·sn). Pressure drop was determined in a pilot scale flow system as a function of flow rate for ~650 g·L-1 orange pulp stored for 0 to 72 h at 22 °C. Pressure drop increased non-linearly with storage time and was inclined to level off after 36 h due to the completion of deesterification of pectin. At 0.8 GPM (5.05×10-5 m3·s-1), the pressure drop due to major friction increased 51.1% (607.2 to 917.4 kPa) as storage time increased from 0 to 72 h and the power requirement increased from 30.3 to 45.9 W.