Investigating the impact of the microbiome on beef steak color stability
Date
2022
Authors
Smith, Colton Levi, author
Nair, Mahesh N., advisor
Morgan, J. Brad, committee member
Geornaras, Ifigenia, committee member
Weir, Tiffany, committee member
Metcalf, Jessica L., committee member
Clark, Daniel L., committee member
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Abstract
Meat color is the most influential characteristic for consumer purchasing decisions. In fact, consumer discrimination of discolored beef results in approximately $3.73 billion/year lost in revenue in the US. Interestingly, most often these products are not yet microbially spoiled, leading to unnecessary food waste. Complicating matters, different muscles originating from the same carcass discolor at different rates. Several studies have investigated the physiochemical, enzymatic, and intrinsic muscle properties of muscles with differing color stabilities such as color stabile beef longissimus lumborum (LL) and color labile psoas major (PM). However, the impact of microbial growth on the meat color stability has not been investigated yet. Therefore, the objective of this study was to characterize the microbial populations and their biochemical parameters of color labile and color stabile beef muscle cuts during aerobic retail display. Paired USDA Select LL and PM (n = 5) were collected from a local abattoir and aged for 14 days in darkness under vacuum at 3°C. After aging, the muscles were fabricated into 2.54-cm thick steaks and packaged aerobically in a foam tray wrapped with polyvinyl chloride film. Steaks were then placed into an open faced multi-decked retail display case for 7 days at 4°C ± 1°C. Each day, beginning day of fabrication, steaks were evaluated for visual color, percentage discoloration, instrumental color, water activity, pH, metmyoglobin reducing activity, microbial levels as determined by using culture-dependent methods (aerobic plate counts, lactic acid bacteria plate counts, Pseudomonas spp. plate counts and Enterobacteriaceae plate counts), and 16S rRNA bacterial gene sequencing (microbiome). Visual color was darker (P < 0.05) for PM than LL for all days, and percentage discoloration was greater (P < 0.05) for PM than LL from the second daif retail display. Color stability (determined by MRA) was greater (P > 0.05) in LL compared to PM for all days. The pH was greater (P < 0.05) for PM for the first 5 days of display compared to LL. However, water activity was the same (P > 0.05) for both muscles across all display days. Microbiological analyses revealed that aerobic plate counts, and lactic acid bacteria plate count were greater (P < 0.05) for PM starting on day 1 of display compared to LL. The Pseudomonas spp. plate counts were similar (P > 0.05) until day 2, after which PM was greater (P < 0.05) than LL and remained greater for the remaining days. Moreover, the 16S rRNA gene sequencing showed no differences (P > 0.05) in the alpha or beta diversities of the microbial communities between muscles. The results indicated that PM has less color stability and a greater amount of microbial growth than LL during retail display. Despite the increased number of bacteria on PM earlier during display, the microbiome analyses showed no major differences in the microbial communities between the muscles on the same display day. These data may suggest that microbial metabolic pathways, evidenced by faster microbial growth on PM compared to LL, may be a bigger contributor to color stability differences than the microbial community composition. Further work establishing these metabolic differences is needed to understand the biochemical interaction between the microbiota and the beef steaks.
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Subject
color stability
beef color
microbiome