Alejandro Poveda-Arteaga

This narrative review aims to provide a comprehensive overview of meat color in vacuum-packaged beef, focusing on intrinsic and extrinsic discoloration mechanisms throughout the whole beef production process. The review describes fundamental knowledge about wet-aging, vacuum-packaging, meat color, consumer acceptance, and postmortem metabolism. It also explains the intrinsic discoloration mechanisms, involving various chemical and biochemical oxidizing processes of myoglobin. These mechanisms are also influenced by muscle type and composition. Further, extrinsic discoloration mechanisms. These mechanisms include microbiology, slaughtering, vacuum packaging and its application, and storage. This review summarizes all fundamentals necessary to understand the biochemistry of meat color and provides a comprehensive overview of possible discoloration mechanisms and causes in beef. The knowledge acquired is applied to the vacuum-packaged beef production chain and offers valuable insights for developing effective prevention strategies. Important findings are that the extrinsic factors are currently easier to influence than intrinsic factors. There are knowledge gaps in relation to discoloration and mitochondrial metabolism, reducing systems of meat, and oxygen concentration in packaging. Also, the influence of the microbiome on discoloration and postmortem metabolism of the meat and the influence of the living conditions and feed on color-stabilizing intrinsic factors of the meat should be further investigated.

Intrinsic factors of vacuum-packaged, discolored beef samples found in the early stages of wet aging at the slaughterhouse were measured and compared to a control group. The aim was to identify possible differences in intrinsic factors that could explain the discolorations. L *, a *, b * values, and myoglobin redox state levels were measured to characterize the extent of discoloration and the oxidation state of myoglobin. pH value, redox potential, total reducing activity, and the concentrations of lactate, α -tocopherol, β -carotene, and NAD ⁺ /NADH were analyzed to identify differences. Significant ( p < 0.05) differences and correlations were observed in color values and myoglobin redox states between the control and discolored samples, e.g., a * = 11.21 (control) and 9.42 (discolored); metmyoglobin = 0.79 (control) and 1.01 (discolored). Except for directly color-related parameters, only a significant difference in lactate concentration was observed (3.90 mg/g (control) and 5.60 mg/g (discolored) without a significant change in pH [5.60 (control) and 5.61 (discolored)]. Since lactate is reported to stabilize the color of meat rather than causing discoloration, the cause of the discoloration might be attributed to a multifactorial interaction of intrinsic parameters, or extrinsic parameters during the slaughtering, deboning, cutting, and packaging process. Although the cause of the discoloration could not be identified, this study displays important data on the interactions between intrinsic parameters. Therefore, this study can be considered an exploratory investigation that lays the foundation for further research to identify the causes of discoloration.

The influence of a 1% oxygen atmosphere on the color stability of modified atmosphere packaged beef was investigated. Beef silverside slices were packed under 1%, 20%, and 70% oxygen atmospheres and stored at 2 °C for 14 days. Color and reflection data were measured non-invasively. The L*a*b* values were analyzed, the color difference ΔE₂₀₀₀, and the levels of myoglobin (Mb), deoxy-(DMb), oxy-(OMb), and metmyoglobin (MMb) were calculated. The 1% oxygen atmosphere resulted in a rapid MMb formation from 0.63 (day 0) to 1.27 (day 8) (p < 0.05). The other samples showed slight increases from 0.65 to 0.80 MMb (20%) and 0.65 to 0.79 MMb (70%). On day 10, the 20% oxygen sample showed an increased MMb formation (1.33 MMb). The 70% atmosphere resulted in a final value of 0.91 MMb after 14 days. These results show that an oxygen content of 1% accelerates the formation of MMb at an early stage. A higher oxygen content in the packaging delays MMb development through OMb formation, which masks MMb creation, to a certain extent. Measuring the packaged meat pieces over a 14-day storage period provides detailed insights into the development of Mb formation and critical points during storage.