The Impact of Carcass Size, Chilling Conditions, and Electrical Stimulation on Beef Postmortem Temperature and pH Decline

Abstract

Variability in carcass size can influence carcass chilling rates, which could result in issues associated with beef tenderness and color. Moreover, the usage of electrical stimulation can affect postmortem metabolism and meat quality. However, few studies have looked at the combined impact of chilling and electrical stimulation on temperature decline, postmortem biochemistry, and color among the current population of US beef. Beef carcasses (N = 162, <30 mo) were randomly selected from 2 beef processing plants. One side of each carcass was electrically stimulated, while the opposing side was not electrically stimulated. Matched sides were subjected to either conventional spray chilling (CONV) or delayed spray chilling (DELAY). Deep tissue (10.5 cm under the pelvic bone) and surface temperature (1.5 cm under the loin fat) were continuously monitored during chilling in addition to temperature and pH measurements from the semimembranosus (SM), longissimus lumborum (LL), and psoas major (PM) muscles at an initial time (45 to 60 min), 6 h, 12 h, and after chilling (28 to 36 h) postmortem. Further, the instrumental (L*, a*, and b*) and visual color were evaluated on 14-d aged PM steaks. For data analysis, carcasses with hot carcass weights above or below the plant average were considered heavy or light, respectively. A nonlinear regression model was fitted to the continuous deep and surface temperatures, whereas other parameters were evaluated using a mixed model. Electrical stimulation improved L* (lightness; P < 0.05) of PM in lightweight carcasses but not (P > 0.05) in heavyweight carcasses. Temperature decline was faster (P < 0.05) and pH decline slower (P < 0.05) in the SM and LL of lightweight carcasses under CONV compared to lightweight carcasses under DELAY and heavyweight carcasses under CONV and DELAY. Exponential decay models for deep and surface temperatures indicated the rate of cooling differed (P < 0.05) due to the combination of treatment factors. Heavyweight carcasses in DELAY had slower rates of temperature decline (P < 0.05). Overall, the variability in carcass size affected temperature decline and postmortem metabolism. Therefore, postmortem management practices should consider carcass weights to optimize meat quality.