BLBS102-c09 BLBS102-Simpson March 21, 2012 11:15 Trim: 276mm X 219mm Printer Name: Yet to Come
194 Part 2: Biotechnology and Enzymologydeterioration of seafood postharvest (Lopez-Amaya and
Marangoni 2000b).
Sphingomyelin (SM) phosphodiesterase (also known as sph-
ingomyelinase or SMase) is a hydrolytic enzyme involved in
sphingolipid metabolism and is responsible for the formation
of ceramide (and phosphocholine) from sphingomyelin in re-
sponse to cellular stresses. However, SMase is usually treated
separately from “regular” lipases.Some Applications of LipasesDairy Products Lipases occur naturally in milk and have been
shown to be present in the milk of the cow, goat, sheep, sow,
donkey, horse, camel, and humans. Perhaps, the natural role of
lipases in mammalian milks is to aid digestion for the young
suckling. However, in dairy products, lipases play an important
role in flavor development: for example, “membrane” lipases
can produce undesirable rancidity in freshly drawn milks. In
processed milk and milk products, this may not be expected to
pose a problem due to the high pH range for milk lipase activity
(pH 6–9), the low thermal stability of the lipases, and their inabil-
ity to survive pasteurization treatments. In some dairy products,
post-process lipolysis is desirable to produce the flavors nor-
mally associated with such products, such as butterfat, cheddar
cheese, blue cheese, and Roquefort cheese. In these products,
supplementation with microbial lipases is done to facilitate the
ripening process. During “ripening,” the added lipases break
down milk fat into free fatty acids. Different types of lipases con-
tribute to distinctive flavors. In this regard, lipases that release
short-chain fatty acids (i.e., C4–C6) produce “sharp” flavors in
food products, while the lipases furnishing long-chain fatty acid
(>C12) tend to elicit more subtle tastes (Schmidt and Verger
1998). For example, cheddar cheese has higher levels of butyric
acid (C4:0) versus milk fat (Bills and Day 1964). In this regard,
lipases fromPenicillium roqueforti,A. niger,Rhizopus arrhizus,
andCandida cylindraceahave been found to be very useful (Ha
and Lindsay 1993). Although free fatty acids produce distinctive
flavors in cheeses and other dairy products, controlling of lipol-
ysis after the desired transformation has been achieved in the
product is necessary because excessive lipolysis could induce
objectionable rancid flavors in the products (McSweeney and
Sousa 2000).Oleo Products Oleo products are spreads prepared mostly
from vegetable oils and used as a substitute for butter. The term
covers a broad spectrum of products ranging from margarines
to specialty fats, shortenings, and lard substitutes. The making
of oleo products takes advantage of the capacity of lipases to
catalyze interesterification reactions that enable modifications
in acylglycerols from fats and oils. An example is the mak-
ing of cocoa butter equivalents. Cocoa butter has 1-palmitoyl-
2-oleoyl-3-stearoyl-glycerol (POS) or 1,3-distearoyl-2-oleoyl-
glycerol (SOS) as its key components and is widely used in
making chocolates and candies. Palm oil mid fraction with its
predominant TG as 1,3-dipalmitoyl-2-oleoyl-glycerol has been
used as common substrates to mimic cocoa butter by mixing it
with co-substrates such as tristearin. In the presence of lipase,interesterification reactions proceed, whereby fatty acids insn-1
andsn-3 positions are interchanged to produce POS and/or SOS.
Some commercially available fungal lipases, e.g., lipozyme pro-
duced by Novozymes fromMucor mieheiand Enzymatix F3
produced fromRhizopus sp.by Gist-brocades have been shown
to be able to carry out such product-simulating interesterification
reactions (Bloomer et al. 1983). ImmobilizedRhizopus arrhizus
lipase has been utilized to produce cocoa butter equivalent from
oils, and the substrate conversion rate was significantly increased
by addition of defatted soy lecithin (Mojovic et al. 1993). ́
Lipase-catalyzed interesterifications are also employed to
produce shortenings devoid oftrans-fatty acids. Shortenings
are usually produced by the hydrogenating of vegetable oils
and the process formstrans-fatty acids as common compo-
nents. Lipozyme TLIM fromThermomyces lanuginosuspro-
ducestrans-fatty acids-free shortening from high oleic acid sun-
flower oil and fully hydrogenated soybean oil (Li et al. 2010).
Trans-fatty acids-free shortening was also formed from palm
stearin and rice bran oil by using the same lipozyme.Lipases in Human Health and DiseaseIn humans, lipase breaks down dietary fats in food so they can
be absorbed in the intestines. The enzyme is primarily produced
in the pancreas but is also produced in the mouth and stomach.
Proper digestion of dietary fat is important prior to their absorp-
tion because the end products must be carried in an aqueous
milieu (blood and lymph) in which fats are not soluble.
The importance of lipase in the gastrointestinal tract is due to
the fact that it is the primary agent for splitting fats into free fatty
acids and glycerol. Gastric lipases digest pre-emulsified fats in
foods such as egg yolk and cream; however, emulsification in the
small intestine followed by lipolysis is the basis for the proper
digestion of dietary fats and oils. Emulsification is effected by
the action of bile salts produced by the liver and results in the
breakdown of the large fat molecules into tiny droplets, which
provide lipases with an increased surface area to act on. If bile
is insufficient or when the liver is not stimulated to produce
bile, fats remain in such large particles that enzymes cannot
readily combine with; hence, fat digestion is incomplete and fat
absorption is markedly reduced. Most people produce enough
pancreatic lipase for this purpose; however, individuals with
cystic fibrosis, Crohn’s disease, or celiac disease may not have
sufficient lipase to assure proper absorption and assimilation of
the lipid breakdown products.
Lipases control cell permeability so that nutrients can enter
while waste exit. Lipase-deficient individuals have reduced cell
permeability; thus, nutrients cannot enter into cells nor can waste
metabolites leave. For example, diabetics are lipase-deficient
and glucose entry into their cells is impaired, while waste or
unwanted substances tend to accumulate in the cells. When li-
pase is deficient, individuals may suffer health defects including
a tendency toward high cholesterol, high TGs, difficulty in los-
ing weight, diabetes or glucosuria, and ultimately cardiovascular
diseases.
In humans, inhibition of digestive lipases is important for the
control of obesity. The inhibitors act by targeting gastric and