Handbook of Meat Processing

428 Chapter 24

a role in the control of obesity, reduction of

the risk of diabetes, and modulation of bone

metabolism.

Histidyl Dipeptides

Various endogenous antioxidants, including

tocopherols, ubiquinone, cartenoids, ascorbic

acid, glutathione, lipoic acid, uric acid,

spermine, carnosine, and anserine, have been

found in skeletal muscle (Decker et al. 2000 ).

Both carnosine ( β - alanyl - L - histidine) and

anserine (N - β - alanyl - 1 - methyl - L - histidine)

are antioxidative histidyl dipeptides (Fig.

24.4 ) and are the most abundant antioxida-

tives in meats. Consumption of antioxidant -

rich foods prevents oxidative damage in our

body (Lindsay 2000 ). This action is attrib-

uted to neutralization and reduced release

of free radicals by antioxidants (Langseth

2000 ). Antioxidant activities of carnosine

and anserine may result from their ability to

chelate transition metals such as copper

(Brown 1981 ).

The concentrations of carnosine and

anserine vary depending on animal species

and the parts of the meat. The concentration

of carnosine in meat ranges from 500 mg/kg

in chicken thigh to 2,700 mg/kg in pork

shoulder. Anserine is especially abundant in

this CLA isomer due to its anticarcinogenic
activity. Commercially available supple-
ments utilized for many studies are usually
mixtures of several CLA isomers (e.g.,
c 9, t 11: 41%; t 10, c 12: 44%; t 9, t 11/ t 10, t 12:
7%). Some studies have shown that the
t 10, c 12 isomer (Fig. 24.3 , bottom) exhibits
stronger physiological activities than those of
the c 9, t 11 - isomer. However, most animal
products such as beef and cow ’ s milk contain
only trace amounts of the t 10, c 12 CLA
isomer.
The CLA content of animal products is
changed by several factors, such as breed,
age, and feed composition (Dhiman et al.
2005 ). CLA content in grass - fed animal
products is more than three times greater than
that in products from animals fed a diet of
50% hay and silage with 50% grain. CLA
content was also reported to be higher in beef
from cattle fed a diet containing soy oil
(Lorenzen et al. 2007 ). CLA content of foods
is increased by heat treatments, such as
cooking and processing (Herzallah et al.
2005 ). Also, lactic acid bacteria promote the
formation of CLA. The effect of lactic acid
bacteria on the formation of CLA in media
and fermented dairy products has been
studied (Alonso et al. 2003 ; Coakley et al.
2003 ; Sieber et al. 2004 ; Xu et al. 2005 ).
Such bacterial conversion would be expected
in fermented meat products.
Epidemiological studies have suggested
that high intakes of high - fat dairy foods and
CLA may reduce the risk of colorectal cancer
(Larsson et al. 2005 ). Besides anticarcino-
genic activities, CLA has anti - artherioscle-
rotic, antioxidative, and immunomodulative
activities (Azain 2003 ). CLA may also play

H 2 N

H

N

HN

N

O

O

OH H^2 N

H

N

N

N

O

O

OH

Figure 24.4. Structures of carnosine (left) and anser-

ine (right).

COOH

COOH

Figure 24.3. Structures of conjugated linoleic acid isomers. Top: c 9, t 11 - isomer; bottom: t 10, c 12 - isomer.