Dietary supplementation of livestock with vitamin E results in improved quality of meat subsequently obtained from these animals. The effect is especially noteworthy in cattle, in which the primary effects are delayed discoloration and lipid oxidation. A threshold level of alpha-tocopherol in muscle ensures a detectable effect; dietary strategies for attaining this threshold must consider tocopherol status of cattle arriving at the feedyard and duration and level of supplementation. The alpha-tocopherol concentration in muscle must be determined before proper interpretation of experimental results can be made. Muscles vary in their color stability, and this relative difference is not changed by vitamin E supplementation. Several in vitro models have been used to characterize the interaction between alpha-tocopherol, lipid oxidation, and oxymyoglobin oxidation. Alpha-tocopherol seems to exert its color-stabilizing effect by indirectly delaying oxymyoglobin oxidation via direct inhibition of lipid oxidation. However, recent results demonstrating a protective effect of alpha-tocopherol toward oxymyoglobin in low-oxygen atmospheres indicate that additional mechanisms may exist. A better understanding of the fundamental bases for protection of water-soluble myoglobin by lipid-soluble alpha-tocopherol is needed to optimize this beneficial effect.

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To better understand the mechanism by which camosine inhibits myoglobin oxidation in salted ground pork, interactions of camosine with ferrylmyoglobin (ferMb), metmyoglobin (metMb) and oxymyoglobin (oxyMb) were investigated. Camosine (O-50 n-&l; pH 5.0-7.5) accelerated the conversion of metMb to oxyMb at pH 2 7.0 and carnosine concentrations 2 25 mM. Camosine (l-50 mM) also accelerated the conversion of oxyMb to metMh with its formation rates increasing with decreasing pH and increasing camosine concentrations. Camosine (l-25 mM) inhibited ferMb-catalyzed oxidation of phosphatidylcholine liposomes 1676% and reduced the ferMh electron paramagnetic resonance signal 24-43%. Results suggested that the color stabilizing effects of camosine were related to its antioxidant activity.

Supernatants (105,000 ϫ g) of oxidized phosphatidylcholine (PC) liposomes contained higher levels of thiobarbituric acid-reactive substances, and caused greater metmyoglobin formation when combined with oxymyoglobin than those of controls (C) or PC plus tocopherol (PCT) (PϽ0.05). Products of PC liposome oxidation crossed dialysis membranes (mol wt cut-off ϭ 500 Dalton) and accelerated the oxidation of oxymyoglobin more than C or PCT (PϽ0.05). The addition of known oxidation products of oleic acid and linoleic acid, fatty acids typical of PC, accelerated oxymyoglobin oxidation relative to controls (PϽ0.05). Results demonstrated that oxidation products of PC were prooxidative towards oxymyoglobin.