Peroxynitrite induced discoloration of muscle foods.

The objective of this research was to characterize the ability of peroxynitrite to cause the discoloration of meat using an in vitro oxymyoglobin system, a soluble fraction of beef muscle and minced muscle. Kinetic studies of the bolus addition of peroxynitrite (250 μM) to solutions of oxymyoglobin in phosphate buffer showed that oxidation occurred over the first 10 min producing 180 μM metmyoglobin and then slowed to the oxidation rate of the control. Addition of peroxynitrite (100-750 μM) to the soluble fraction of Longissimus dorsi muscle resulted in partial to complete discoloration of samples with 500-750 μM peroxynitrite resulting in 90-100% conversion of oxymyoglobin to metmyoglobin after 90 min. In minced L. dorsi samples, kinetic studies indicate that addition of 250 μM peroxynitrite resulted in a longer period of metmyoglobin formation than the in vitro experiment, lasting 40 min and resulting in the formation of 280 μM metmyoglobin. Antioxidants (ascorbic acid, glutathione, α-tocopherol and Trolox) were ineffective in preventing peroxynitrite-induced discoloration of minced meat, however ascorbic acid was able to partially restore color loss as the incubation period continued. The results indicate that peroxynitrite may be involved in the discoloration of muscle foods.