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Consumption of oxygen by the muscles of beef animals and related species. II. Consumption of oxygen by post‐rigor muscle
Author(s) -
Bendall J. R.,
Taylor A. A.
Publication year - 1972
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.2740230606
Subject(s) - oxygen , chemistry , respiratory quotient , enthalpy , nad+ kinase , mitochondrion , reaction rate constant , biochemistry , food science , kinetics , thermodynamics , organic chemistry , physics , quantum mechanics , enzyme
The oxygen consumption rate (o.c.r.) of post‐rigor beef muscle, unlike the pre‐rigor o.c.r., is virtually unaffected by the degree of comminution of the muscle. It has a constant enthalpy of activation (ΔH*) of 18.2 ± 0.3 kcal/mol, which is nearly double the value for pre‐rigor muscle and is close to the enthalpy of activation of the mitochondrial NAD + ‐linked oxidation of pyruvate (∼19 kcal/mol). The latter mitochondrial rate (m.r.) appears to be the step which determines the post‐rigor o.c.r., unlike the pre‐rigor state where the rate of turnover of ATP (a.t.r.) is rate‐determining, except below 15 °C. This is because the potential post‐rigor a.t.r. is too high for the mitochondrial electron‐transport chain to keep pace with it under the prevailing conditions of low pH. The post‐rigor o.c.r. can be doubled at all times of storage up to 6 weeks by addition of an ATP supplement. The o.c.r. declines exponentially from the second day of storage onwards and reaches about 10% of its initial level after about 6 weeks storage of the muscle at 2 °C. This is shown to parallel the decline in the m.r. on storage and is evidently due to partly irreversible impairment of mitochondrial function and not to loss of NAD + . The respiratory quotient (r.q.) in the post‐rigor state is 1.0 at low pH and falls to ∼0.5 on raising the pH to 7.2, due to initial production and subsequent oxidation of α‐glycerol phosphate and pyruvate in equal amounts. There are species differences in the magnitude of the post‐rigor o.c.r., possibly due to differing mitochondrial contents. The exponential decay of the o.c.r. during storage goes far to explain the increasing depth of penetration of the oxymyoglobin layer which forms on exposing a surface of meat to air or oxygen and which gives the exposed meat an attractive bright red appearance.