The objective of this study was to evaluate the effects of extended aging and modified atmospheric packaging on beef LM color. Using a randomized complete block design, each beef longissimus lumborum muscle ( = 10; USDA Choice, 3 d postmortem) was equally divided into 3 sections and randomly assigned to 1 of 3 aging periods (21, 42, or 62 d at 2°C). After respective aging, each loin section was cut into four 2.5-cm-thick steaks and randomly assigned to 1 of 3 packaging types (PVC, HiOx-MAP [80% oxygen and 20% carbon dioxide], or CO-MAP [0.4% carbon monoxide, 69.6% nitrogen, and 30% carbon dioxide]). The steaks were displayed under continuous fluorescent lighting for 6 d, and surface color was determined daily using a HunterLab Miniscan XE Plus spectrophotometer and a visual panel. The fourth steak was used to characterize oxygen consumption (OC), lipid oxidation, and metmyoglobin reducing activity (MRA) on 21, 42, and 62 d (before display). On d 6 display, MRA, OC, and lipid oxidation also were measured. An increase in aging time decreased ( < 0.0001) muscle pH. Loin sections aged for 42 and 62 d had a lower ( < 0.0002) pH compared with loin sections aged for 21 d. An aging period × packaging × display time interaction ( < 0.0001) resulted for a* values (redness), chroma, and visual color (muscle color and surface discoloration). As aging time increased, HiOx-MAP had the most discoloration ( < 0.0001) compared with other packaging types on d 6. At all aging periods, steaks packaged in CO-MAP had greater ( < 0.0001) MRA on d 6 than PVC and HiOx-MAP, whereas steaks packaged in HiOx-MAP had the least MRA ( < 0.0001). There were no differences ( = 0.34) in thiobarbituric acid reactive substances values between steaks aged for 21 and 42 d when steaks were packaged in CO-MAP and displayed for 6 d. However, steaks packaged in HiOx-MAP and displayed 6 d had greater ( < 0.0001) lipid oxidation than CO-MAP. Steaks packaged in HiOx-MAP had a lower ( < 0.0001) OC compared with PVC and CO-MAP when aged for 42 and 62 d. There were no differences ( = 0.49) in OC between steaks packaged in PVC and HiOx-MAP when aged for 21 d and displayed 6 d. The results indicate that extended aging is detrimental to color stability when packaged in PVC and HiOx-MAP. However, steaks in CO-MAP had stable red color during display. Decreased color stability in PVC and HiOx-MAP could be associated, in part, with decreased MRA and OC.

The objective of the current study was to evaluate the effects of aging on myoglobin chemistry of dark-cutting beef. Ten USDA Choice (mean pH = 5.6; normal pH beef) and 10 no-roll dark cutter (mean pH = 6.4) strip loins were obtained from a commercial packing plant within 3 d of harvest. Loins were cut into 4 sections, vacuum packaged, randomly assigned to 0-, 21-, 42-, and 62-d aging at 2°C in the dark. Following aging, loin sections were cut into 2.5-cm-thick steaks and were used to determine bloom development, oxygen consumption (OC), metmyoglobin reducing activity (MRA), and lipid oxidation. Surface color readings were measured using a HunterLab Miniscan XE Plus spectrophotometer. A significant muscle type × aging time interaction resulted for OC ( < 0.001). Normal pH steaks declined more ( < 0.001) in OC during aging than dark-cutting beef. On d 0, dark-cutting beef had a greater OC ( < 0.001) than normal pH beef. There was a significant muscle type × oxygenation time × aging period interaction for L* values, deoxymyoglobin (DeoxyMb), and oxymyoglobin (OxyMb). When dark-cutting sections were aged for 62 d, both 0 and 60 min bloom development L* values were greater ( < 0.0001) than 0 min dark-cutting sections aged for 21 or 42 d. At all aging periods, normal pH beef had greater OxyMb content and lower DeoxyMb ( < 0.0001) during bloom development than dark-cutting beef. An aging period × muscle type interaction was significant for % overall reflectance ( = 0.0017) and absorbance ( = 0.0038). Dark cutting and normal pH beef loin sections aged for 62 d had greater reflectance ( < 0.0001) than 21 d. On d 0, dark-cutting beef had greater ( < 0.0001) MRA than normal pH beef. There were no significant ( = 0.14) differences in MRA between 42 and 62 d between dark-cutting and normal pH beef. Dark cutting steaks had lower thiobarbituric acid reactive substances values ( < 0.0001) than normal pH steaks. The results indicate that characterizing the myoglobin chemistry during aging will help to design strategies to improve appearance of high pH beef.

The objective of current research was to determine the effects of extended aging, modified atmospheric packaging (MAP), and display time on metmyoglobin reducing activity (MRA) and oxygen consumption (OC) of high-pH beef using pH sensitive methodology for MRA and OC. Ten normal-pH (mean pH = 5.6) and 10 high-pH loins (mean pH = 6.4) were vacuum packaged on d 3 postmortem and aged for 0, 21, 42, and 62 d at 2°C. Following aging, 2.0-cm-thick steaks were cut from each of the normal- and high-pH loin sections and packaged in either PVC film, high-oxygen (HiOx-MAP), or carbon monoxide modified atmospheric (CO-MAP) packaging. Surface color, OC, and MRA were measured on d 0 and 6 of the respective aging periods. Steaks in HiOx-MAP and CO-MAP had similar (P > 0.05) L* values, which were greater (P < 0.05) than high-pH steaks packaged in PVC film. On 21-d of aging, steaks with at both pHs in CO-MAP and HiOx-MAP had greater (P < 0.05) a* values than steaks packaged in PVC. As aging time increased, MRA decreased (P < 0.05) for steaks with normal- and high-pH when packaged in PVC and HiOx-MAP. Steaks with a high-pH in CO-MAP had greater (P < 0.05) MRA than steaks with a normal-pH in CO-MAP at all aging periods. Steaks with a high-pH had greater (P < 0.05) OC on d 0 and 6 than normal-pH steaks. Steaks with a normal-pH aged for 21 d and packaged in PVC and HiOx-MAP had greater (P < 0.05) lipid oxidation than high-pH steaks aged for 21 d and packaged in PVC and HiOx-MAP. After 62 d of aging and 6 d of display, the greatest color stability chemistry (based on MRA and OC for all package types) were: high-pH meat > normal-pH meat; thus the MRA and OC methodology was useful in relative comparison of packaged meat color stability differences due to pH.

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Abstract:The objective was to determine the effects of modified atmosphere packaging (MAP) on the surface color of darkcutting beef that had been aged for 21 d. The USDA Choice (normal-pH; IMPS #180) strip loins (n = 10) and no-roll dark-cutter strip loins (n = 10) were obtained from a commercial packing plant within 72 h of harvest. Both normal-pH and dark-cutting beef were vacuum packaged and aged for 21 d. Steaks were cut from both normal and dark-cutting loins, assigned to 1 of 3 packaging treatments; PVC, HiOx-MAP, and CO-MAP, and stored in a simulated retail display under continuous fluorescent lighting at 2°C for 6 d. Instrumental and visual color were measured every 24 h. Thiobarbituric acid assay was used as an indicator for lipid oxidation. There was a packaging × muscle type × display time interaction (P < 0.0001) for instrumental and visual color. On d 1 of display, dark-cutting steaks packaged in HiOx-MAP had greater (P < 0.001) a* values and chroma than darkcutting PVC steaks. On d 6 of the display, dark-cutting steaks packaged in CO-MAP had 10 units greater a* values than darkcutting steaks packaged in PVC. The visual panel also noted less muscle darkening (P < 0.002) in HiOx-MAP and CO-MAP compared with steaks packaged in PVC on d 6 of the display. There was less surface discoloration (P < 0.001) in HiOx-MAP and CO-MAP dark-cutting steaks compared with PVC dark-cutting steaks by the end of the display. There was a packaging × muscle type interaction for instrumental L* values and lipid oxidation. Dark-cutting steaks packaged in HiOx-MAP and CO-MAP had greater (P < 0.05) L* values compared with dark-cutting steaks in PVC packaging. In conclusion, HiOx-MAP improved redness of dark-cutting beef during the initial phase of display, while CO-MAP resulted in a stable red color.