3.3. Effect of salt
Table 2 illustrates the effect of inorganic salts on the castor oil
hydrolysis yield. It is clear from the data that almost all the salt used
in this work deactivates the enzyme with an increase in the concentration
of the salt. However, the yield of the fatty acid product
for KCl, CaCl2 and NaCl are different for same salt concentration. It
has been observed that the extent of hydrolysis decreases with an
increase in the concentration of the salts KCl and NaCl till the concentration
of 0.01 mol/ml and 0.006 mol/ml respectively. Beyond
these concentrations, the conversion of reaction remains almost
the same for KCl and NaCl (Table 2). The yield of hydrolysis obtained
with KCl at the concentration of 0.01 mol/ml was reduced by 36%
as compared to 22% for NaCl at the concentration of 0.006 mol/ml.
However, the inhibitory effect of calcium ion increases with an
increase in the concentration from 0.01 mol/ml to 0.08 mol/ml. This
result obtained is in contradiction to previous study [4–7]. This can
be attributed to the different substrates and different sources of
the lipase used in the present study. It has been reported that with
the fungal lipase the calcium ions have no effect on hydrolysis [20]
while with the yeast lipase calcium ion have an inhibitory effect
on the hydrolysis of olive oil when lipase from C. rugosa was used
[3]. Khor et al. [13] have also showed an inhibitory effect of calcium
ion on the hydrolysis of palm oil using C. rugosa with increasing
the concentration of the calcium ions. It has been observed that calcium ion has no effect on the rate of hydrolysis in water in oil
type of system, in contrast to its positive effect observed in the oil
in water system [4]. They reported that this phenomenon is due
to the removal of fatty acid from the interface into the vigorously
stirred oil mixture, as the solubility of long chain fatty acid in oil
is relatively higher than in [21]. However, in the present study, calcium
ion gives an inhibitory effect for the same system (water in oil
type). This can again be explained in terms of differences in the substrate
and enzyme used in the present study. The fatty acid product
i.e. ricinoleic obtained has a high affinity for the enzyme and even
after high stirring and solubility in water it will not be removed
easily from enzyme oil interface.