Food Chemistry

12.3 Muscle Tissue: Composition and Function 585

acceptable (early stages of microbial infestation),
20–50 inferior quality and>50 spoiled meat.
The BAI values of fermented meat products
are naturally higher; a limit of 500 mg/kg was
proposed for salami.
Other biogenic amines are spermidine [N-(3-
aminopropyl)-1,4-butandiamine] and spermine [N,
N′-bis-(3-aminopropyl)-1,4-butandiamine], which
are biogenetically formed from putrescine and
belong to the constituents of meat. The main
compound is spermine, with a concentration in
the range of 25–65 mg/kg.

12.3.6 Guanidine Compounds

Creatine and creatinine (I and II, respectively; cf.
Formula 12.23) are characteristic constituents of
muscle tissue and their assay is used to detect the
presence of meat extract in a food product. Crea-
tine is present in fresh beef at 0.3–0.6% and cre-
atinine at 0.02–0.04%.
In living muscle, 50–80% of creatine is in the
phosphorylated form, creatine phosphate (III, cf.
Formula 12.23), which is in equilibrium with
ATP. The reaction rate is highly influenced by
the enzyme creatine phosphokinase. Creatine
phosphate serves as an energy reservoir (free
energy of hydrolysis, G^0 =− 42 .7kJ/mole;
of ATP: G^0 = − 29 .7kJ/mole). Creatine
phosphate has a higher phosphoryl group transfer
potential than ATP. Hence, when muscle is
stimulated for a prolonged period in the absence
of glycolysis or respiration, the supply of creatine
phosphate will become depleted within a couple
of hours by maintaining the ATP concentration.
This is especially the case in post-mortem
muscle, when the ATP supply has declined
significantly through oxidative respiration.

(12.23)

12.3.7 Quaternary Ammonium Compounds

Choline and carnitine are present in muscle tissue

at 0.02–0.06% and 0.05–0.2%, respectively (on

a fresh weight basis). Choline is synthesized from

serine with colamine as an intermediary product

(cf. Reactions 12.24) and carnitine is obtained

from lysine throughε-N-trimethyllysine and bu-

tyrobetaine (cf. Reactions 12.25).

The carnitine fatty acid esters, which are in equi-

librium with long chain acyl-CoA molecules in

living muscle tissue, are of biochemical import-

ance. The carnitine fatty acid ester, but not the

acyl-CoA ester, can traverse the inner mitochon-

drial membrane. After the fatty acid is oxidized

within the mitochondria, carnitine is instrumental

in transporting the generated acetic acid out of the

mitochondria.

(12.24)

(12.25)