Biochemical study of rapid discolouration mechanisms in Bison meat

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Fresh meat colour is an important attribute used by consumers as an indicator of freshness and wholesomeness, and any deviation of normal colour (e.g. cherry red) is indicative of poor functionality and possible spoilage. Meat colour stability is one of the major concerns in the bison industry, because it is darker and discolours more rapidly than beef under aerobic retail packaging. Consequently, the long-term objective is to gain comprehensive understanding of factors determining myoglobin oxidation/reduction in different bison muscles during storage and retail display under diverse packaging, by monitoring objective and subjective colour changes. The short-term objectives are: 1) to examine the effect of 4-hydroxy-2-nonenal (HNE), protein oxidation, non-heme iron, and the sarcoplasmic proteome on the colour stability of two bison muscles of diverse stability during storage; 2) to establish the relationship among biochemical components, oxidative stability and sarcoplasmic proteins to the oxidation of myoglobin during storage of two bison muscles; 3) to test the ability of near infrared reflectance spectroscopy (NIRS) to segregate bison muscles with stable vs. unstable colour; 4) to determine the effects of carbon monoxide modified atmosphere packaging (CO-MAP) on biochemical components and retail display characteristics of bison steaks from with different colour stability using different storage periods. The redox biochemistry of myoglobin in post-mortem skeletal muscles is particularly complex, where small biomolecules occur that can cause rapid pigment oxidation and surface discolouration; but, their mechanisms of action are not well understood. The higher polyunsaturated fatty acid content in bison could promote oxidation and generate reactive secondary oxidation products such as HNE, and accelerate myoglobin oxidation. This process could involve protein oxidation during refrigerated storage, breakdown of the heme molecule and the subsequent release of non-heme iron from the porphyrin ring, which might also increase oxidative instability in the meat system. Also, variations in the balance between antioxidant/pro-oxidant component proteins (e.g. thioredoxin) in the sarcoplasm could induce lipid oxidation and cause meat discoloration. These measures will be used along with NIRS in order to enable development of colour stability in tissue and apply muscle-specific processing strategies such as novel packaging (e.g. CO-MAP) for improving retail colour stability. Certainly, with better understanding of the factors that determine colour stability, industry can expand fresh meat sales, offering a more consistent, acceptable and desirable product to consumers. In addition, three undergraduate and two M.Sc. students will be trained under my program. The experiences gained with bison could be applicable to other species and mitigate their colour issues.**