78 Effects of extended aging, modified atmospheric packaging, and display time on metmyoglobin reducing activity and oxygen consumption of high-pH beef

Abstract

Abstract Metmyoglobin reducing activity (MRA) and oxygen consumption (OC) are two important biochemical processes that can influence beef color. Several studies have determined the effects of aging and modified atmospheric packaging (MAP) on biochemical properties of normal-pH beef (5.5–5.7 pH range). However, limited knowledge is currently available on the effects of aging and MAP on biochemical properties of high-pH beef (> 6.2). Therefore, the objective was to determine the effects of extended aging, MAP, and display time on MRA and OC of high-pH beef. Ten USDA Choice (pH = 5.6) and ten ‘No-Roll’ dark cutting (high-pH; pH > 6.4) strip loins were obtained from a commercial packing plant within 72 hours of harvest. Loins were vacuum packaged and aged for 0, 21, 42, and 62 days at 4 °C. Following aging, from each normal- and high-pH loin sections, 2.5cm thick steaks were cut and packaged in PVC, high oxygen- (HiOx-MAP), and carbon monoxide modified atmospheric (CO-MAP) packaging. The surface color, MRA, and OC were determined on day 0 and 6 of the respective aging period. The experiment was replicated ten times (n = 10). High-pH steaks in all packaging and aging times had more stable red color than normal-pH steaks. High-pH steaks packaged in PVC and HiOx-MAP had greater (P < 0.05) MRA than normal-pH steaks. There were no differences (P > 0.05) in MRA between normal- and high-pH steaks on day 21 when steaks were packaged in CO-MAP, but high-pH had greater (P < 0.05) MRA on day 62. At all aging periods, high-pH steaks had greater (P < 0.05) OC than normal-pH steaks. However, a decrease in OC was greater (P < 0.05) for high-pH than normal-pH steaks. The results suggest that normal- and high-pH beef have different trends for the changes in MRA and OC.