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Browsing by Author "Morgan, J. Brad, committee member"

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    Investigating the impact of the microbiome on beef steak color stability
    (Colorado State University. Libraries, 2022) 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
    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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    Processes to improve storage shelf-life and palatability of beef
    (Colorado State University. Libraries, 2023) González Sánchez, Sara Victoria, author; Nair, Mahesh N., advisor; Geornaras, Ifigenia, advisor; Morgan, J. Brad, committee member; Gutierrez-Rodriguez, Eduardo, committee member
    Three studies were conducted to evaluate processes to improve the storage shelf-life and palatability of beef. The first two studies evaluated the effects on retail shelf-life and palatability characteristics of beef following Suspended Fresh® storage. Suspended Fresh® (SF) is a patented, proprietary, trademarked process that allows the storage of beef muscles at temperatures at or slightly above their freezing point to slow down microbiological spoilage while maintaining the product's fresh status. These studies evaluated the impact of 60, 75, or 90 d of storage in SF (-2.7±0.3°C) on the retail shelf-life and palatability characteristics of steaks derived from inside rounds (IR), bone-in ribeyes (RE), and striploins (SL) from 10 (n=10) upper two-thirds Choice beef carcasses. Two steaks fabricated from each subprimal were vacuum-packaged, wet-aged for 21 d (3°C), and frozen (-20°C) for Warner-Bratzler shear force (WBSF) and sensory analyses. These steaks served as the control with regard to storage condition and time. The remainder of each subprimal was fabricated into three portions, and after vacuum packaging, were randomly allocated to an SF storage time of 60, 75, or 90 d. After each storage time, five steaks were fabricated from the subprimal pieces, overwrapped, and placed in a retail display case (3°C) under continuous fluorescent light for 7 d. Another two steaks were vacuum-packaged and stored at -20°C until WBSF and consumer sensory evaluations. Consumers (N=238) evaluated each sample for juiciness, tenderness, flavor liking, and overall liking. Instrumental and trained visual color were evaluated daily during retail display, and aerobic bacterial populations (APC), lactic acid bacteria, and Pseudomonas spp. were enumerated on days 0, 2, 4, and 7. Data were analyzed in R using a factorial design for the microbial counts or a split-plot for the rest of the analyses. Least-squares means were separated using a significance level of α=0.05. For all cuts, initial redness (a* values) of SF60 steaks were lower (P < 0.05) than SF75 and SF90 steaks. In general, irrespective of SF storage time or retail display day, trained panelists did not detect differences in lean color and discoloration of steaks. For all cuts, the APC of SF60 steaks on days 0, 2, and 4 of retail display were lower (P < 0.05) than those of SF75 and SF90 samples. The WBSF values decreased (P < 0.05) with increased storage time for all the cuts. Similarly, the consumer tenderness rating scores of IR and SL generally increased with the SF storage time. However, storage time did not influence (P ≥ 0.05) the juiciness, flavor, and overall liking of any cuts. The results of this study suggest it would be feasible to extend the storage time of beef while preserving or improving the sensory quality when held at optimal conditions above the freezing temperature. The third study was conducted to evaluate the effects of different temperature and time treatment combinations (1A: 56.1°C and 71 min; 1B: 56.1°C and 150 min; 1C: 56.1°C and 240 min; 2A: 61.7°C and 8 min; 2B: 61.7°C and 150 min; 2C: 61.7°C and 240 min) of sous vide cooking on the palatability of beef biceps femoris. Beef biceps femoris were sliced into 1.6-cm steaks, vacuum packaged as 4.5 kg bags, and randomly assigned to one of the six treatments with 16 packages (n=16) per treatment. Cooked and chilled packages were weighed, and then the weight of the meat was taken to measure cooking loss. Weighed samples were divided into two halves: one was left non-marinated, and the other was assigned to marination. Two 1.6-cm non-marinated steaks were randomly selected and cut in half to measure the internal cooked color. Additionally, non-marinated and marinated steaks were randomly selected for WBSF and sensory analysis by a trained panel. Data were analyzed using a complete randomized design in R with a significance level of α=0.05. The cooking loss of samples increased as the temperature and dwell time combinations increased (P < 0.05). Internal redness of steaks decreased (P < 0.05) with increased temperature and dwell time. The only major difference in WBSF and the trained sensory panel results was between treatment 1C (56.1°C and 240 min) and 2A (61.7°C and 8 min), where 1C samples had lower WBSF values and higher perceived tenderness scores than 2A samples. These results suggest that biceps femoris samples can be cooked at conditions examined in this study with minimal impact on palatability, allowing producers more flexibility with cooking time to optimize production time and energy while reducing cooking loss. Overall, the findings of these studies should be useful to the beef industry as they consider strategies for improving the storage shelf-life and palatability of beef.