Differences in Spoilage Microflora Growth Kinetics Could Be Contributing to Beef Muscle-Specific Color Stability

The role of microbial communities on beef color stability during retail display is not fully understood. Therefore, this study aimed to characterize the physiochemical properties and microbial communities of color-stable (longissimus lumborum [LL]) and color-labile (psoas major PM]) beef muscles during aerobic retail display. Paired USDA Select beef LL and PM (n=5) were collected and aged (at 2°C) for 14 d. These were fabricated into 2.54-cm-thick steaks, packaged aerobically, and subjected to 7 d of retail display. Samples were evaluated daily for visual and instrumental color, percent-age discoloration, water activity, pH, metmyoglobin reducing activity (MRA), and bacterial population levels using conventional culture-based methodologies. Additionally, 16S ribosomal RNA (rRNA) amplicon sequencing was performed to characterize microbial communities associated with the LL and PM steaks throughout storage. The percentage discoloration was greater (P<0.05) in PM than LL after 2 d of retail display. Color stability, measured by MRA, was lower (P<0.05) for PM compared with LL each day. Culture-based microbiological analysis revealed that bacterial populations of PM steaks either exhibited no lag phase or had a shorter lag phase than the populations on LL samples. By the end of the retail display, bacterial levels on PM steaks were 1.3 to 1.6 log CFU/cm2 higher (P<0.05) than those recovered from LL samples. The 16S rRNA gene sequencing showed no differences (P≥0.05) in the alpha or beta diversities for the microbial communities of PM and LL on the same display day. The results confirmed that PM steaks had less color stability and a faster increase in bacterial numbers compared with LL during display. These results suggest that when initial bacterial communities are similar, the differential growth kinetics of bacteria present on these 2 muscles could contribute to the difference in their color stabilities.