Food Lipids: Chemistry, Nutrition, and Biotechnology

creatic lipase is specific toward shorter chain fatty acids, while lipase from
Penicillium cyclopium is specific toward long chain fatty acids. As well, lipases from
Aspergillus niger and Aspergillus delemar are specific toward both medium chain
and short chain fatty acids (11,61). Other lipases have been found to be specific
toward fatty acids of varying lengths. Marangoni (62) found that in the hydrolysis
of butter oil, lipase from Candida rugosa showed specificity toward butyric acid
compared to Pseudomonas fluorescens lipase. With interesterification reactions in
organic media, lipases can also be specific toward certain alcohol species. A large
group of lipases from sources such as Candida cylindraceae, Mucor miehei, and
Rhizopus arrhizus have been found to be strongly specific against fatty acids containing
the first double bond from the carboxyl end at an even-numbered carbon,
such as cis-4, cis-6, and cis-8, resulting in slower esterification of these fatty acids
in comparison with other unsaturated and saturated fatty acids. Fatty acid specificity
by certain lipases can be used in the production of short chain fatty acids for use as
dairy flavors and in the concentration of EPA and DHA in fish oils by lipases with
lower activity toward these fatty acids.
III. REACTION SYSTEMS
A. Enzymatic Interesterification in Microaqueous Organic
Solvent Systems
Since the main substrates of lipases are long chain triacylglycerols, which are insoluble
in water, many experiments have been conducted in the presence of organic
solvents. Organic solvents allow the fat or oil to be solubilized and convert twophase
systems to one-phase systems (63). Stability can be improved by covalent
attachment of polyethylene glycol to free amino groups of the lipase, giving lipases
amphiphilic properties and allowing their dissolution in organic solvents (64). It has
been reported that the thermal stability of lipases can be improved in microaqueous
organic solvent systems since the lack of water prevents unfolding of the lipase at
high temperatures (65). Elliott and Parkin (65) found that porcine pancreatic lipase
had optimal activity at 50�C in an emulsion, whereas the optimum increased to 70�C
in a microaqueous organic solvent system using hexane. Lipase activity in organic
solvents depends on the nature and concentration of the substrate and source of
enzyme (63). The specific organic solvent used can dramatically affect the activity
of the lipase (66). Lipases are more active in n-hexane and isooctane than other
solvents, such as toluene, ethyl acetate, and acetylnitrile (28,44). The polarity of
solvents can be described by P, the partition coefficient of a solvent between water
and octanol. This is an indication of the hydrophobicity of the solvent. No lipase
activity is observed in solvents with a value for log P less than 2 (67,68). The
hydrophobicity of the solvent can also affect the degree of acyl migration during
interesterification using a 1,3-specific lipase. Hexane tends to promote acyl migration
due to the low solubility of free fatty acids and partial glycerides in hexane, which
forces them into the microaqueous region around the lipase, providing optimum
conditions for acyl migration. In contrast, the use of diethyl ether, in which free fatty
acids and partial glycerides are more soluble, removes the products from the microaqueous
environment and reduces the risk of acyl migration (6). Since the choice
of organic solvents based on minimization of acyl migration may conflict with max-
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