Enzymes as Biocatalysts for Lipid-based Bioproducts Processing - Food and Industrial Bioproducts and Bioprocessing - page 334

Reaction temperature is well known for its effect on enzyme activity. Most lipases are
active in the temperature range 40-75 °C. Within this temperature range, higher temperature
usually increases the reaction rate. Nevertheless, lipases are deactivated faster at higher
reaction temperature due to protein denaturation. Cheong and co-workers (2007) found that
1,3-specific lipase from RML was quite stable at 65 °C and could be reused in at least ten
continuous batches of enzymatic partial hydrolysis (120 h) to produce DAG without significant
loss of catalytic activity.
Reactor design has a significant effect on the enzymatic production efficiency of partial
acylglycerols. For example, enzymatic glycerolysis involves the reaction between oil and
glycerol, which are immiscible. A stirred tank batch reactor that provides efficient mechanical
stirring is preferable in such a reaction to enhance mass transfer and reaction rate.
Nevertheless, enzyme support material may be broken down by the strong mechanical
stirring, resulting in lower recoverability and reusability of the enzyme (Xu et al ., 2007b ).
Packed-bed reactors, which usually comprise of pumping the reaction substrates through a
column containing a bed of enzyme, are beneficial in terms of recoverability and reusability
of enzyme. However, it may not be suitable for use in enzymatic glycerolysis, as glycerol
may coat the enzyme bed, resulting in decrease of mass transfer and reaction rate.
Nonetheless, it can be used in other enzymatic reactions where strong mechanical stirring is
not required, such as enzymatic partial hydrolysis (Cheong et al ., 2007 ).
Enzymatic processing for synthesis of partial acylglycerols has been a regular feature in
lipid technology. In fact, numerous enzymatic processes have been patented for industrial
scale DAG production (Lai et al ., 2004). Although it may seem that the subject has been
heavily and thoroughly investigated, a few reaction-related problems still persist. One such
problem is low product conversion due to immiscible reaction substrates. A few studies have
been conducted to improve the miscibility of reaction substrates, such as employing novel
reaction media, namely compressed n-butane and sodium dioctyl sulfosuccinate (AOT) sur-
factant (Valerio et al ., 2009), and also introducing sonochemical irradiation to the enzymatic
reaction (Babicz et al ., 2010). Besides that, purification of the partial acylglycerol product
is also worth studying, as the final products from enzymatic processing usually contain a
mixture of glycerol, FFA, MAG, DAG and TAG. Xu (2004b) has conducted extensive stud-
ies on purification of partial acylglycerol products using short path distillation technology.
In fact, this technology has been used industrially for production of DAG oil. Nevertheless,
other problems persist in regards to coloration and possible development of carcinogenic
glycidol fatty acid esters during the heat treatment. The coloration of oil can be easily solved
through an adsorption/bleaching process (Minoru et al ., 2010). Thus, it will be beneficial to
investigate other purification methods or elimination of the glycidol fatty acid esters.

14.4.2 Enzymatic processing of bioactive compounds
Described as non-nutritional microconstituents of plants with significant biological activity
(Patil et al ., 2009 ; Saura-Calixto and Gon , 2009), bioactive compounds have been widely

linked to the maintenance and improvement of human health, such as prevention of cardiovas-
cular disease and various cancers. Current research suggests that the ability to protect against
oxidative damage is yet another key attribute of bioactive compounds (Balsano and Alisi,
2009; Madhuri and Pandey, 2009). Polyphenols, ascorbic acid, carotenoids and limonoids are
just some examples of bioactive compounds present in foods such as fruits and vegetables,
wine, tea, oilseeds and cocoa (Rice-Evans et al ., 1996). Due largely to their natural origin and
healthy properties, the overall demand for these compounds continues to expand.

ĩ