The overall objective of this project is to identify the microbial ecology and metabolic mechanisms underpinning muscle-specific responses to aging in terms of spoilage and pathogen growth for future development of a novel biomarker-based prediction system. Our central hypothesis is that characterizing key metabolic compounds in meat exudatewill provide crucial information to elucidate muscle-specific biochemical mechanisms. Our rationale is that successful completion of the proposed work will allow the development of biomarker-based, non-invasive/non-destructive spoilage and contamination prediction systems using simple, valueless and easy to obtain meat exudate. We will accomplish our overall objective by addressing the following two specific research objectives:Objective 1: Establish the temporal microbial changes that occur during muscle-specific aging under spoilage conditions and in response to Salmonella and E. coli O157:H7 proliferation.Objective 2: Identify key compounds present in beef exudate associated with microbial metabolism during aging.Collectively, the results will enable us to identify major metabolites and muscle-specific biochemical mechanisms that could be used as potential biomarkers for the future development of real-time detection systems to monitor and ensure safety of fresh meat products. We expect that completion of the work under these two objectives will provide scientific insight and practical implications of how key spoilage-related and pathogenic bacteria-related metabolites identified in beef exudates could: 1) advance our understanding of muscle-specific biochemical spoilage and microbial growth mechanisms; and 2) be used to develop biomarker-based prediction models to determine muscle-specific optimal aging practice to ensure meat freshness and safety.