Light wavelengths that induce oxidation of oxymyoglobin in meat

Light wavelengths that induce meat discoloration and the photoreceptors in the meat were studied. We investigated the effects of the light wavelength on the oxidation rate of myoglobin (Mb) by exposing Mb extracts or model solutions containing Mb to light at specific wavelengths with a bandwidth of 5 nm using a fluorescence spectrophotometer. The wavelengths examined comprised 385, 415, 445, 460, 490, 525, 555, 580, 605, 630,660, and 750 nm. In the Mb extracts, Mb oxidation was induced through exposure to the light at 445 and 580–605 nm; Mb was insensitive to light at 445 nm. Mitochondria, containing cytochrome a and cytochrome a3 with absorption peaks at 448 and 600 nm, and riboflavin with fluorescence at 450 nm were studied as 445 nm receptors. Mitochondria significantly oxidized Mb via cytochrome c oxidation through complex IV activity; however, no 445 nm-specific photo sensitivity effects were observed. In contrast, riboflavin increased the Mb oxidation rate induced via exposure to the light at 450 nm in a concentration-dependent manner (minimum concentration: 38.4 μg L⁻¹). While native mitochondria did not show 445 nm-specific photosensitivity effects on Mb, supernatants of heated mitochondria conferred 445 nm-wavelength sensitivity to Mb. Riboflavin concentration in this supernatant was 182 ± 60 μg L⁻¹. The Mb photosensitivity spectrum with 473 μg L⁻¹ riboflavin had two peaks at 445 nm and 580 nm, which were similar to those of Mb extract. These results suggest that mitochondrial damage affects the meat discoloration through the release of cytochrome c and riboflavin.