Food Biochemistry and Food Processing

14 Biochemistry of Processing Meat and Poultry 329

free fatty acids increases with ageing time, up to 6
months of processing (see Fig. 14.12) 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 activ-
ity is mainly influenced by pH, salt concentration,
and water activity (Motilva and Toldrá 1993), it
appears that the observed lipid hydrolysis is favored
by the same variables (salt increase and awreduc-
tion), as shown in Tables 14.3 and 14.4, that enhance
enzyme activity in vitro (Vestergaard et al. 2000,
Toldrá et al. 2004).

In the case of the adipose tissue, triacylglycerols

form the major part of this tissue (around 90%) and

are mostly hydrolyzed by neutral lipases to di- and

monoacylglycerols and free fatty acids (see Fig.

14.12), especially up to 6 months of processing

(Motilva et al. 1993a). The amount of triacylglyc-

erols decreases from about 90% to 76% (Coutron-

Gambotti and Gandemer 1999). There is a preferen-

tial 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

Table 14.3.Physical Factors Affecting Lipolytic Activity during Meat and Meat Products

Processing

Factor Typical Trend Effect on Lipolytic Enzymes

pH Near neutral pH in dry-cured ham and Favors the activity of neutral lipase,

cooked meat products neutral esterase, and hormone-

sensitive lipase

Slightly acid in aged meat Favors the activity of lysosomal acid

lipase, acid esterase, and acid phos-

pholipase

Acid pH in dry-fermented sausages Favors the activity of lysosomal acid

lipase, acid esterase, and acid phos-

pholipase

Time Short in aged meat, cooked meat Short action for enough enzyme action

products, and fermented products but significant oxidation of the

released fatty acids

Medium in dry fermented sausages and Time allows significant biochemical

long in dry-cured ham changes in dry sausages and very

important in dry-cured ham

Temperature High increase in cooking and smoking Enzymes are strongly activated by

cooking temperatures, although for a

short time

Mild temperatures in fermentation and Enzymes have time enough for their

dry curing activity even with the use of mild tem-

peratures; lipases are active even dur-

ing freezing storage of the raw meats

Water activity Slightly reduced in cooked meats Enzymes have very good conditions for

activity

Substantially reduced in dry meats Neutral muscle lipase and esterases are

affected; rest of lipolytic enzymes

remain unaffected by awdrop

Redox potential Anaerobic values in postmortem meat Slight effect on lysosomal acid lipase

and phospholipase; more intense for

rest of lipases