Biochemical study of rapid discolouration mechanisms in Bison meat

鲜肉的颜色是消费者用来衡量新鲜度和健康度的重要指标，任何偏离正常颜色（如樱桃红）都表明功能差和可能变质。肉的颜色稳定性是牛肉行业主要关注的问题之一，因为在有氧零售包装下，它比牛肉颜色更深，变色更快。因此，长期目标是通过监测客观和主观颜色变化，全面了解在不同包装下的储存和零售展示过程中，不同野牛肌肉中肌红蛋白氧化/还原的决定因素。短期目标是：1)研究4-羟基-2-壬烯醛（HNE）、蛋白质氧化、非血红素铁和肌浆蛋白质组对两种稳定性不同的野牛肌肉在储存期间颜色稳定性的影响；2)建立两种野牛肌肉贮存过程中生化成分、氧化稳定性和肌浆蛋白与肌红蛋白氧化的关系；3)测试近红外反射光谱（NIRS）区分颜色稳定与不稳定的野牛肌肉的能力；4)测定一氧化碳修饰气调包装（CO-MAP）对不同色稳定性、不同贮存期野牛肉排生化成分及零售陈列特性的影响。死后骨骼肌中肌红蛋白的氧化还原生化反应特别复杂，其中出现的小生物分子可导致色素快速氧化和表面变色；但是，它们的作用机制尚不清楚。野牛体内较高的多不饱和脂肪酸含量可促进氧化，生成HNE等活性二次氧化产物，加速肌红蛋白氧化。这一过程可能涉及到冷藏过程中的蛋白质氧化、血红素分子的分解以及随后卟啉环中非血红素铁的释放，这也可能增加肉类系统中的氧化不稳定性。此外，肌质中抗氧化/促氧化成分蛋白（如硫氧还蛋白）平衡的变化可诱导脂质氧化并导致肉变色。这些措施将与近红外光谱一起使用，以促进组织中颜色稳定性的发展，并应用肌肉特定的加工策略，如新型包装（例如CO-MAP），以提高零售颜色稳定性。当然，通过更好地了解决定颜色稳定性的因素，工业可以扩大鲜肉的销售，为消费者提供更一致、更可接受和更理想的产品。此外，我的项目还将培养3名本科生和2名硕士研究生。从野牛身上获得的经验可以适用于其他物种，并减轻它们的颜色问题

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.**