Peroxynitrite-induced oxidation of muscle foods
Peroxynitrite (ONOO−), formed from the nearly diffusion limited reaction between nitric oxide and superoxide, could be an important prooxidant in muscle foods. The objective of this dissertation was to (1) determine whether peroxynitrite caused oxidation of muscle lipids; (2) assess the potential for nitric oxide formation in muscle; and (3) examine the utility of 5-nitro-γ-tocopherol (NGT) as a peroxynitrite biomarker in muscle foods. Exogenous peroxynitrite induced oxidation of liposomes and skeletal muscle microsomes and homogenates. Skeletal muscle homogenate oxidation by reagent peroxynitrite was suppressed by metal chelators. Fresh muscle exhibited nitric oxide synthase (NOS) activity and thus the potential to produce peroxynitrite. NOS activity was reduced during refrigerated storage and by one freeze/thaw cycle. NOS activity in muscle was not affected by pH over the range of 4.5–7.4, was inhibited by 1 and 2% NaCl, and was stimulated at internal cooking temperatures up to 55°C but was completely inhibited at higher temperatures. NGT formation was induced by exogenous peroxynitrite in turkey and chicken muscle homogenates, but turkey and chicken muscle did not produce detectable levels of NGT during storage. Results of this dissertation indicate that peroxynitrite can cause lipid oxidation in muscle lipids and that post-mortem muscle has the potential to produce endogenous peroxynitrite via the activity of NOS. However, NOS was only active for the first several days of postmortem storage and no detectable NGT was observed in turkey and chicken during storage. This suggests that either no peroxynitrite is formed in post-mortem muscle or that low levels of peroxynitrite are produced which limit the detectablility of NGT using the methods employed here.