Food Chemistry

586 12 Meat

12.3.8 Purines and Pyrimidines

The total content of purines in fresh beef muscle
tissue is 0.1–0.25% (on a fresh weight basis).
ATP, present predominantly in living tissue,
breaks down to inosine-5′-monophosphate
(IMP) in the post-mortem stages. The break-
down rate is influenced by the condition of
the animal and by temperature. IMP is then
slowly decomposed through successive steps to
hypoxanthine, with inosine as an intermediary
product:

ATP ADP+Pin(Myosin-ATPase)

2ADP ATP+AMP(Myokinase)

AMP →IMP+NH 3 (Adenylate-deaminase)

IMP →Inosine+Pin( 5 ′−Nucleotidase)

Inosine→Hypoxanthine+Ribose(Nucleosidase)

(12.26)

Post-mortem data on the Psoas majorrabbit
muscle are given in Table 12.10. They relate to
nucleotide breakdown and to other important
muscle tissue constituents.

The changes in water holding capacity of meat
resulting from ATP transition to IMP are dealt
with in Section 12.5. Unlike purines, pyrimidine
nucleotide content in muscle is very low (Ta-
ble 12.9).

Table 12.9.Purines and pyrimidines in fresh-beef mus-
cle

Compound Content (%)

Inosine-5′-phosphate 0 .02–0. 2 a
Inosine Trace
Hypoxanthine 0 .01–0. 03
Adenosine-5′-phosphate 0 .001–0. 01
Adenosine-5′-diphosphate < 0. 3 b
Adenosine-5′-triphosphate
Nicotinamide-adenine-dinucleotide 0. 1
Guanosine-5′-phosphate 0. 002
Cytidine-5′-phosphate 0. 001
Uridine-5′-phosphate 0. 002
aUntil approx. 1 h post-mortem no IMP is found in

muscle.
bThere is a fairly rapid decrease in post-mortem con-

centration influenced by cooling and other muscle hand-
ling conditions.

Table 12.10.Post-mortem changes in the concentration

of some constituents of rabbit muscle (M. psoas)

Compound μmol/g Fresh tissue

living post-rigor

muscle muscle

Total acid-soluble phosphorus 68 68

Inorganic phosphorus < 12 > 48

Adenosine triphosphate (ATP) 9 < 1

Adenosine diphosphate (ADP) 1 < 1

Inosine monophosphate < 19

Creatine phosphate 20 < 1

Creatine 23 42

NAD/NADP 2 1

Glycogen 50 < 10

Glucose-1-phosphate < 1 < 1

Glucose-6-phosphate 5 6

Fructose-1,6-bisphosphate < 1 < 1

Lactic acid 10 100

12.3.9 Organic Acids

The predominant acid in muscle tissue is the

lactic acid formed by glycolysis (0.2–0.8% on

a fresh meat weight basis), followed by glycolic

(0.1%) and succinic acids (0.05%). Other acids

of the Krebs cycle are present in negligible

amounts.

12.3.10 Carbohydrates

The glycogen content of muscle varies greatly

(0.02–1.0% on a fresh tissue weight basis) and

is influenced by the age and condition of the

animal prior to slaugher. The rate of the post-

mortem decrease in glycogen als varies. Sugars

are only 0.1–0.15% of the weight of fresh muscle,

of which 0.1% is shared by glucose-6-phosphate

and other phosphorylated sugars. The free sugars

present are glucose (0.009–0.09%), fructose and

ribose.

12.3.11 Vitamins

Table 12.11 provides data on water-soluble vita-

mins in beef muscle.