Food Lipids: Chemistry, Nutrition, and Biotechnology

on the substrate and presence or absence of bile acids (86). Calcium effects on
microbial lipase activity may be variable depending on the enzyme source and assay
conditions. For example, stimulation of C. rugosa lipase activity was attributed to
the formation of calcium salts of fatty acid products in a normal phase emulsion,
with olive oil as the substrate but not with tributyrin; however, calcium had no effect
in an invert emulsion (109). In a nonemulsion system (i.e., without emulsifier), calcium
had no effect on C. rugosa lipase activity with olive oil as the substrate but
tended to offset the inhibitory effects of bile acid (Mozaffar and Weete, unpublished).
Human pancreatic lipase is inhibited by the bile salts, and the inhibition can
be overcome by the 10-kDa protein colipase. Bile salt coating of the substrate micelles
creates a negatively charged surface that is believed to inhibit adsorption of
the bile salt–lipase complex to the interface (110). Colipase overcomes the inhibitory
effect of the bile salts through formation of a 1:1 complex with lipase that facilitates
adsorption at bile-salt-coated interfaces (83,110). Naka and Nakamura (111) found
that although the bile salt sodium taurodeoxycholate inhibited pancreatic lipase activity
when tributyrin was the substrate, a result that has been widely reported and
cited by others, and colipase could reverse the inhibition, the bile salt actually stimulated
hydrolytic activity when triolein was the substrate. This was attributed to the
fact that triolein is a more natural substrate for the lipase than tributyrin. On the
other hand, when sodium taurocholate was added to an emulsion assay of the lipase
from C. rugosa with olive oil as the substrate, activity was progressively inhibited
from 0.1 mM to 0.8 mM concentration of the bile salt (112). Relatively high activity
at the lowest concentration was attributed to the role of the bile salt in the stabilization
of oil particles in the emulsion and providing high interfacial area for adsorption
of the lipase, and inhibition was due to interaction with the enzyme such
that adsorption was reduced.
A variety of substances have been shown to inhibit lipase activity; examples
include anionic surfactants, certain proteins, metal ions, boronic acids, phosphoruscontaining
compounds such as diethyl p-nitrophenyl phosphate, phenylmethyl sulfonylfluoride,
certain carbamates, �-lactones, and diisopropylfluorophosphate (113).
D. Selectivity
Lipases can be separated into three groups according to specificity (114,115). The
first group shows no marked specificity with respect to the position of the acyl group
on the glycerol molecule, or to the specific nature of the fatty acid component of
the substrate. Complete breakdown of the substrate to glycerol and fatty acids occurs
with nonspecific lipases. Examples of such lipases are those from C. (cylindracae)
rugosa, Corynebacterium acnes, and Staphylococcus aureus. The second group attacks
the ester bonds specifically at the 1- and 3-positions of the substrate, with
mixtures of di- and monoacylglycerols as products. Because of the instability of
intermediate 1,2-di-, 2,3-di-, and 2-monoacylglycerols (i.e., migration of the fatty
acid from the 2-position to the 1- or 3-position), these lipases may catalyze the
complete breakdown of the substrates. Most microbial lipases fall into this group;
examples include those from Aspergillus niger, Rhizopus delemar (oryzae), R.
miehei, and Mucor javanicus. Members of the third group of lipases show preference
for a specific fatty acid or chain length range, and are less common. The most widely
studied lipase in this regard is that from G. candidum, which shows specificity for
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