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16 Biochemistry of Processing Meat and Poultry 31311.2
Lysosomal acid lipase
Acid esterase00.20.40.60.8Activity (U/g)Phospholipase
Lysosomal acid lipase
Acid esterase
Neutral esterase00.2051015
Time (m)Figure 16.11.Evolution of muscle lipases along the processing of
dry-cured ham (Toldra, unpublished data). ́et al. 1993b, Buscailhon et al. 1994). Furthermore, a decrease
in linoleic, arachidonic, oleic, palmitic, and stearic acids from
phospholipids is observed at early stages of processing (Martin
et al. 1999). This fact corroborates muscle phospholipases as
the most important enzymes involved in muscle lipolysis. The
amount of generated free fatty acids increases with aging time,
up to 6 months of processing (see Fig. 16.12) and is higher in
the external muscle(Semimembranosus),which contains more
salt and is more dehydrated, than in the internal muscle(Biceps
femoris).As lipase activity is mainly influenced by pH, salt
concentration, andaw(Motilva and Toldra 1993), it appears that ́
the observed lipid hydrolysis is favored by the same variables
(salt increase andawreduction), as shown in Tables 16.3 and
16.4, that enhance enzyme activity in vitro (Vestergaard et al.
2000, Toldr ́a et al. 2004).
In the case of the adipose tissue, triacylglycerols form the ma-
jor part of this tissue (around 90%) and are mostly hydrolyzed
by neutral lipases to di- and monoacylglycerols and free fatty6Oleic acid
Linoleic acid2345Free fatty acid conc (g/100g)Stearic
Oleic acid
Linoleic acid
Linolenic acid01024681012
Time (m)Stearic acidFigure 16.12.Example of the generation of some free fatty acids in
the adipose tissue during the processing of dry-cured ham (Adapted
from Motilva et al. 1993b).acids (see Fig. 16.12), especially up to 6 months of processing
(Motilva et al. 1993a). Hormone-sensitive lipase was reported
to be more stable than the adipose tissue neutral triglyceride
lipase (Xiao et al. 2010). The amount of triacylglycerols de-
creases from about 90% to 76% (Coutron-Gambotti and Gande-
mer 1999). There is a preferential hydrolysis of polyunsaturated
fatty acids, although some of them may not accumulate due to
further oxidation during processing. Triacylglycerols that are
rich in oleic and linoleic acids and are liquid at 14–18◦Cmore
hydrolyzed than triacylglycerols that are rich in saturated fatty
acids such as palmitic acid and are solid at those temperatures
(Coutron-Gambotti and Gandemer 1999). This means that the
physical state of the triacylglycerols would increase the lipolysis
rate by favoring the action of lipases at the water–oil interface.
The rate of release of individual fatty acids is as follows: linoleic
>oleic>palmitic>stearic>arachidonic (Toldr ́a 1992). The
generation rate remains high up to 10 months of processing,
when the accumulation of free fatty acids remains asymptotic or
even decreases as a consequence of further oxidative reactions.
Oleic, linoleic, stearic, and palmitic acids are those accumulated
in higher amounts because they are present in great amounts in
the triacylglycerols and have a better stability against oxidation.
Similar results for generation of oleic, linoleic and palmitic acids
were reported for Chinese Xuanwei ham (Xiao et al. 2010).OXIDATIVE REACTIONS
The lipolysis and generation of free polyunsaturated fatty acids,
susceptible to oxidation, constitute a key stage in flavor gener-
ation. The susceptibility of fatty acids to oxidation and the rate
of oxidation depend on their unsaturation (Shahidi 1998a). So,
linolenic acid (C 18:3) is more susceptible than linoleic acid (C
18:2), which is more susceptible than oleic acid (C 18:1). The
animal species have different susceptibility to autoxidation in
the following order: poultry>pork>beef>lamb (Tichiva-
gana and Morrisey 1985). Oxidation has three consecutive stages
(Shahidi 1998b). The first stage, initiation, consists in the for-
mation of a free radical. This reaction can be enzymatically
catalyzed by muscle lipoxygenase or chemically catalyzed by
light, moisture, heat, and/or metallic cations. The second stage,
propagation, consists in the formation of peroxide radicals by re-
action of the free radicals with oxygen. When peroxide radicals
react with double bonds, they form primary oxidation products,
or hydroxyperoxides, that are very unstable. Their breakdown
produces many types of secondary oxidation products by a free
radical mechanism. Some of themarepotent flavor-active com-
pounds that can impart off-flavor to meat products during cook-
ing or storage. The oxidative reactions finish by inactivation of
free radicals when they react with each other (last stage). Thus,
the result of these oxidative reactions consists in the generation
of volatile compounds responsible of final product aroma. It
is important to have a good control of these reactions because
sometimes, oxidation may give undesirable volatile compounds
with unpleasant off-flavors.
Muscle proteins may also experience some oxidative re-
actions during the processing of dry-cured ham. Dry-cured
ham presented an intermediate oxidation when compared to