B. Arendt · H. Skibsted · H.J. Andersen ( )  Department of Dairy and Food Science, Royal Veterinary and Agricultural University, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark Present address:  Department of Product Quality, Danish Institute of Animal Science, Research Centre Foulum, P.O. Box 39, DK-8830 Tjele, Denmark Z Lebensm Unters Forsch A (1997) 204: 7—12  Springer-Verlag 1997 ORIGINAL PAPER Bianca Arendt · Leif H. Skibsted · Henrik J. Andersen Antioxidative activity of nitrite in metmyoglobin induced lipid peroxidation Received: 8 March 1996 Abstract The antioxidative activity of nitrite in met- myoglobin (MMb)-initiated lipid peroxidation in linoleic acid emulsions was examined using oxygen consumption measurement. Nitrite decreased MMb- induced lipid peroxidation with increasing con- centrations. The antioxidative effect of nitrite was independent of pH in the range 6.3—5.5, and 1% NaCl did not seem to influence the antioxidative activity of nitrite. Furthermore, nitrite reduced MMb denatura- tion during MMb-induced peroxidation of linoleic acid. Thermal analysis using differential scanning calorimetry showed that nitrite increased the denatura- tion temperature of MMb. However, direct complexa- tion between nitrite and the iron center of MMb could not be confirmed using chromatographic methods and analysis of UV-visible spectra of mixtures of nitrite and MMb. The observed results can rather be explained by a weak reversible interaction between nitrite and MMb such as binding of nitrite at the entrance to the haem cavity protecting MMb against heat denaturation and protecting both MMb and the fatty acids against oxi- dative degradation. Key words Lipid peroxidation · Metmyoglobin ·Nitrite · Antioxidative activity Introduction Nitrite is recognized as a unique additive in meat prod- ucts, as it has an anti-microbial effect, contributes to color and flavor formation, protects against oxidative processes, which otherwise may cause the development of rancidity and formation of off-flavors. Even though the antioxidative activity of nitrite has been realized for many years, the underlying mechanism is only poorly understood. Four different mechanisms have been proposed for the antioxidative effect of nitrite in meats: (1) It stabilizes the lipid fraction in meats by reaction with the carbon—carbon double bonds, as the amount of reacted nitrite increases with the number of double bonds in lipid model systems [1, 2]. (2) It forms a stable complex by coordination to the iron center of haem proteins and thereby prevents catalytic breakdown of hydroperoxides by the haem proteins [3, 4]. (3) It chelates trace metals which might be possible pro-oxidants in lipid peroxidation [5, 6]. (4) It reacts with meat constituents forming nitroso and nitrosyl compounds, which possess antioxidative activity [7, 8]. Haem compounds are now recognized as main initiators of lipid peroxidation in meats [9 —12]. Any interaction between haem compounds and nitrite which diminishes haem-catalyzed lipid peroxidation will therefore be of interest. Regardless of whether such an interaction proceeds through a direct interaction be- tween the haem protein and nitrite [3, 4] through forma- tion of antioxidative nitrosyl compounds [7, 8] or by any other mechanism, it is necessary to characterize the mechanism(s) and the conditions under which these in- teractions are active to optimize the oxidative stability of cured meats with minimal use of nitrite in view of the toxicological aspect of addition of nitrite to meats [13]. The object of the present study was to investigate the effect of nitrite in MMb-induced lipid peroxidation and to demonstrate and characterize possible interactions between nitrite and MMb as part of our ongoing re- search on the coupling between oxidation of pigment and lipids in meat and meat products.