Effects of Light and Oxygen Conditions on Nonenzymatic Metmyoglobin Reduction In Vitro

Abstract

Previous research indicated that inherently present electron donors and carriers contribute to nonenzymatic metmyoglobin reduction. However, limited knowledge is currently available on how light and oxygen influence nonenzymatic metmyoglobin reduction. The objective of this study was to evaluate the effect of light and oxygen levels on nonenzymatic metmyoglobin reduction in vitro. Two experiments were conducted using equine metmyoglobin solution at pH 5.6 (represents typical postmortem muscle pH) with different electron donors and electron carriers in a 96-well plate. A gas blend of 80% oxygen and 20% carbon dioxide or a pure 99.9% nitrogen gas was bubbled in phosphate buffers and myoglobin solutions to create 2 oxygen levels (low oxygen [4%] and high oxygen [160%]). The desired dissolved oxygen content was measured using a NeoFox oxygen probe (atmospheric oxygen level was 20% oxygen). There were significant effects of electron donors, carriers, and light on nonenzymatic metmyoglobin reduction. Ascorbate and nicotinamide adenine dinucleotide reduced form (NADH) in the presence of methylene blue and ethylenediaminetetraacetic acid (EDTA) exhibited a greater nonenzymatic metmyoglobin reduction in light than dark. An increase in nonenzymatic metmyoglobin-reducing activity (P<0.0001) was observed for the combination of NADH+methylene blue+EDTA in the high-oxygen condition in comparison with the low-oxygen levels. The results indicate that light and oxygen levels increase nonenzymatic metmyoglobin reduction. Characterizing the cofactors required for nonenzymatic metmyoglobin reduction and understanding the conditions conducive to reduction enhance knowledge related to meat color changes.

Keywords

• meat color
• non-enzymatic metmyoglobin reduction
• myoglobin
• cofactors