Food Biochemistry and Food Processing (2 edition)

BLBS102-c16 BLBS102-Simpson March 21, 2012 10:54 Trim: 276mm X 219mm Printer Name: Yet to Come

16 Biochemistry of Processing Meat and Poultry 311

02

0.25

0.3

0.35

0

0.05

0.1

0.15

0.2

0.25

02040608

Activity (U/g

× 1000)

Glucuronidase

N acetyl glucosamidase

0

80

Time (d)

N

Figure 16.9.Evolution ofβ-glucuronidase and

N-acetyl-β-glucosaminidase during the processing of a

dry-fermented sausage (Toldra, unpublished data). ́

of process, and extent of cooking (Toldr ́a 2002). The generation

rate observed during in vitro incubations of muscle lipases with

pure phospholipids is the following (in order of importance):

linoleic>oleic>linolenic>palmitic>stearic>arachidonic

acid. Lipolysis may also vary depending on the type of muscle, as

oxidative and glucolytic muscles exhibit different lipase activity

(Flores et al. 1996). The generation of free short-chain fatty acids

is very low due to the lack of adequate substrate (Motilva et al.

1993b). Studies comparing pale, soft, exudative (PSE) versus

normal pork reported that phospholipase A2 activity was higher

and well correlated with the occurrence of the PSE syndrome

(Chen et al. 2010). Reverse correlation was also reported for

the antioxidant activity of glutathione peroxidase (Chen et al.

2010). The physical and chemical conditions in the muscle and

adipose tissue, especially during cooking, may affect the enzyme

activity (see Tables 16.3 and 16.4). The evolution of muscle

lipases during aging of pork meat is shown in Figure 16.11.

Lipolysis in Fermented Meats

Depending on the raw materials, type of product, and processing

conditions, the degree of contribution of endogenous and micro-

bial origin lipases will vary (Toldr ́a 2007). The relative impor-

tance of both enzyme systems has been checked with mixtures

of antibiotics and antimycotics used in sterile meat model sys-

tems ( Molly et al. 1997). The results showed a minimal effect of

antibiotics, and it was concluded that lipolysis is mainly brought

about by muscle and adipose tissue lipases (60–80% of total

free fatty acids generated), even though some variability might

be found, depending on the batch and the presence of specific

strains (Molly et al. 1997). Other authors have also observed

that fatty acids are released in higher amounts when starters are

added, but that there is significant lipolysis in the absence of mi-

crobial starters (Montel et al. 1993, Hierro et al. 1997). When pH

drops during fermentation, the action of muscle lysosomal acid

lipase and acid phospholipase becomes very important. Some

strains are selected as starters based on their contribution to

lipolysis. So,Micrococcaceaepresent a highly variable amount

of extra- and intracellular lipolytic enzymes, dependent on the

strain and type of substrate (Casaburi et al. 2008). The action of

the extracellular enzymes on the hydrolysis of triacylglycerols

becomes more important after 15–20 days of ripening (Ordonez ̃

et al. 1999). Other microorganisms used as starters areStaphy-

lococcus warneri,which gives the highest lipolytic activity, and

Triacylglycerols

In muscle and adipose tissue: In muscle tissue:

Diacylglycerols

Lipase Phospholipids

Phospholipases

Monoacylglycerols

Lipase Lysophospholipids

Lysophospholipase

Free

fatty acids

Free

fatty acids

Monoacylglycerol lipase

Oxidation

Volatile compounds

Volatile compounds

Oxidation

Figure 16.10.General scheme of lipolysis during the processing of meat and meat products.