Food Lipids: Chemistry, Nutrition, and Biotechnology

lanuginosa, C. antarctica B, Rhizopus delemar, and G. candidum, all of which are
commercially available. Many of these lipases have relatively high specific activities:
3485 U/mg for Mucor miehei lipase A (12) and 7638 U/mg for Rhizopus delemar
(18) (see Table 1 for other examples). Lipases that have received the most attention
are mainly those having relatively high activities or certain properties that make them
commercially attractive. Other than additional strains of known lipase producers,
there seems to be no pattern among the fungi or yeasts from a taxonomic point of
view that would direct future studies on where to find prolific lipase producers or
lipases with specific properties.
Lipases have been modified using either chemical or molecular approaches to
alter their properties and to identify structure–activity relationships. For example,
lipases have been chemically modified with polyethylene glycol to render them more
soluble in organic media. Recently, Kodera et al. (154) produced amphipathic chainshaped
and copolymer derivatives of lipases from Pseudomonas fragi or P. cepacia
that were soluble in aqueous and hydrophobic media and exhibited catalytic activities
for esterification and transesterification reactions, as well as for hydrolysis. The modified
lipase showed preference for the R isomer of secondary alcohols in esterification
reactions.
Molecular approaches have been used to increase the production of a lipase
from the fungus Rhizopus delemar (130). The gene for this lipase codes for a preproenzyme
that is posttranslationally modified to the mature enzyme. A cloned cDNA
for the precursor polypeptide of the lipase (155) was altered by site-directed mutagenesis
to produce fragments that code for the proenzyme and mature enzyme (130).
When inserted into E. coli BL21 (DE3), the quantities of lipase from a 1-L culture
exceeded those obtained from the fungal culture by 100-fold. Other examples of
gene modification of lipases are given in Sec. V.D.
C. Production Synthesis/Modification
There are many examples of uses for lipases in product synthesis/modification. One
of the major areas of interest is in the use of lipase-catalyzed interesterification to
improve the nutritional value, or alter the physical properties, of vegetable or fish
oils. This is achieved, for example, by increasing the content of docosahexaenoic
acid (DHA) or eicosapentaenoic acid (EPA) of these oils. These long chain �3 (n-
3) fatty acids have been incorporated into several vegetable oils using a lipase from
Mucor miehei (45,156), medium chain triglycerides (46), and cod-liver oil (157). The
n-3 fatty acid content of menhaden and anchovy oils (158) and tuna oil (120,159)
has also been increased by lipase-catalyzed interesterification. Another fatty acid of
interest is �-linolenic acid (GLA), which is applicable in a wide range of clinical
disorders. GLA has been enriched in evening primrose and borage oils by several
fungal lipases (47,48).
Other research involving synthesis/modification includes the synthesis of monoand
diglycerides (49,50) including regioisomerically pure products (51,52), synthesis
of acetylated glucose (53), modification of phospholipids into biosurfactants (54),
hydrolysis of phosphatidylcholine (43), and production of high value specialty fats
such as cocoa butter substitutes or hardened vegetable oils with butterfat properties
(151). The production of high-value fats takes advantage of the 1,3-specificity of
lipases that could not be achieved by chemical synthesis (44). Some recent examples
of research involving synthesis/modification by lipases were given in Table 2.
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