Food Lipids: Chemistry, Nutrition, and Biotechnology

column for water saturation of the oil phase, Posorske et al. (89) produced a cocoa
butter substitute from palm stearin and coconut oil. These authors found that decreasing
the flow rates to increase the total product concentration caused a decrease
in productivity. Decreasing the flow rates to as to increase product levels from 20%
to 29% leads to a significant decrease in productivity. Fixed bed reactors are more
efficient than batch reactors but are prone to fouling and compression. Dissolution
of the oil in an organic solvent to reduce viscosity for flow through the packed bed
may be required (89). In addition, the substrate has to be treated to remove any
particulates, inhibitors, and poisons that can build up over time and inactivate the
lipase (8). Macrae (9) found that after treatment of palm oil midfraction and stearic
acid to remove particulates, inhibitors, and poisons, acidolysis reached completion
after 400 hours and there was not appreciable loss in lipase activity even after 600
hours of operation. Wisdom et al. (91) performed a pilot scale reaction using a 2.9-
L fixed bed reactor to esterify shea oleine with stearic acid. It was found that with
high-quality substrates, only a small loss of activity was exhibited after 3 days with
the production of 50 kg of product. However, when a lower grade shea oil was used,
there was rapid inactivation of the lipase.
The kinetics of a packed bed reactor are assumed to be the same as for a
soluble lipase, where
dS V max[S]
� =
dt K�m � [S]
This can be rearranged and integrated to
[S ]X = K� ln(1 � X) �
0 m
k E
cat T
Q
where [S0] is the initial substrate concentration, X is the fraction of substrate that has
been converted to product at any given time (1 � [S]/[S0]), Q is the volumetric flow
rate, and E T is the total number of moles of enzyme present in the packed bed
(80,92). The residence time, �, is based on the porosity of the packed bed and is
defined as (93):
P
� = Vtot Q
where Vtot is the volume of the reactor, P is the porosity of the bed, and Q is the
flow rate of the substrate.
The porosity of the bed in a fixed bed reactor can produce internal transfer
limitations. Ison et al. (84) studied the effects of pore size on lipase activity in a
fixed bed reactor using Spherosil with a mean pore size of 1480 A˚ and Duolite with
a mean pore size of 190 A˚ . The larger pore size of the Spherosil was found to
produce a decrease in lipase activity. This loss in activity was due to the higher
degree of enzyme loading during immobilization, making some of the lipase inaccessible
to substrate. With the smaller pore size of Duolite, the lipase was immobilized
only on the surface of the support, eliminating internal mass transfer limitations.
B. Stirred Batch Reactor
A stirred batch reactor is a common system used in laboratory experiments with
lipase-catalyzed interesterification due to its simplicity and low cost. No addition
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