The impact of storage temperature on the ability of meat products to hold water has been regularly studied since the 1980’s (O'Keeffe and Hood, 1980-1981; Offer and Knight, 1988; Hertog-Meischke et al., 1998; Jeremiah and Gibson, 2001). Previous research has shown that storage temperature impacts beef color stability and water holding capacity ultimately reducing product yield and consumer appeal (Hertog-Meischke et al., 1998; Jeremiah and Gibson, 2001). Mancini and Ramanathan (2014) evaluated the impact of storage temperature on color and reported that steaks from cuts aged at 41 °F had increased color intensity but less color stability compared to steaks aged at 32 °F. Differences in color intensity and stability are important factors that contribute to a consumer’s purchasing decisions. Beef consumers expect the beef they purchase at retail to be a bright, cherry-red color (Killinger et al., 2004). Products that are discolored or are darker in appearance will likely be passed over by consumers resulting in increased food waste and lost revenue. An estimated 15% of beef in retail stores is discounted due to discoloration resulting in approximately $1 billion in lost revenue for the beef industry annually (Smith et al., 2000). However, the length of time products can be subjected to elevated storage temperatures before meat color is impacted is unknown. Alternatively, Calpain-1, the endogenous enzyme largely thought to be responsible for proteolysis or the postmortem tenderization of meat, becomes more active with increased temperature resulting in improved tenderness (Geesink et al., 2000; Hwang et al., 2004). It is unclear whether the temperature differences during shipping would result in enough difference in product temperature to increase proteolysis. It was the goal of this research to examine these quality attributes to determine if the transportation temperatures of beef products should be more closely monitored to preserve product yield and quality attributes.
Cases of beef strip loins (n = 24) and center-cut sirloin top butts (n = 24) were chosen from a commercial packing facility from a single production day. The following day, the cases were equally divided between two pallets. Each pallet was loaded into pre-chilled refrigerated trucks at set temperatures of either 38 ℉ (38 °F First Transport) or 28 ℉ (28 °F First Transport). Each refrigerated truck was also loaded with seven pallets, each containing four 30-gallon plastic barrels containing approximately 27 gallons of water to simulate a fully loaded refrigerated truck.
The loaded trucks were driven 600 miles on Interstate roadways over the course of 12 hours to mimic transportation of subprimal products from a harvest plant to a case ready plant. Upon completion of the first transportation period, both pallets were placed in a holding cooler with an average temperature of 34.5 ± 2.5 ℉ until product reached nine days post fabrication to mimic aging requirements for a case ready plant. Products were subsampled by removing one piece from the approximate middle of each case for further analysis.
Purge loss was calculated on each subsampled primal. Sirloin top butts were fabricated into four 1-inch thick steaks. Each steak was cut in half to create two steaks per 1-inch slice. Strip loins were cut into eight 1-inch steaks. The steaks were assigned to a second transport temperature (38 ℉ Second Transport or 28 ℉ Second Transport), steak aging day group (day 0 or 5 of case life), and shear force storage method (immediately frozen upon reaching designated aging day [frozen] or analyzed for shear force immediately [fresh]). Steaks were then placed in trays with oxygen permeable overwrap. The overwrapped trays were then placed into vacuum seal bags (known as mother bags) and gas flushed. The mother bags were placed in industry standard steak transport trays and stacked on pallets with four trays per level and 12 levels per pallet, one pallet per truck.
Steaks were stored in their mother bags for five days prior to undergoing a second transportation. Similar to the first transport, one pallet was placed in each pre-chilled refrigerated truck and the remainder of the space in the truck was filled with pallets of water barrels. One truck was set to hold at 38 ℉ and the other was set at 28 ℉. The trucks travelled approximately 640 miles over the course of 12 hours to mimic transport from a case ready plant to a distribution center. Upon completion of the second transport, the pallets were again placed into a holding cooler with an average temperature of 34.5 ± 1.6 ℉ for 10 days.
Steaks were analyzed for purge loss, cook loss, and Warner-Bratzler shear force (WBSF) separately based on storage method (fresh vs frozen). Additionally, strip loin and sirloin steaks were analyzed separately to better evaluate the impacts of transport temperatures and case life day on each type of steak.
The steaks for case life analysis were placed under fluorescent lighting for 6 days. Two L* (lightness), a* (redness), and b* (yellowness) measurements were recorded on each steak daily.
Prior to cooking for WBSF, steaks were weighed for cook loss calculations. Steaks were cooked to a target internal temperature of 160 ℉ using an electric clam shell grill. Steaks were allowed to cool overnight. After steaks were warmed to room temperature, they were weighed again to determine cook loss. Five cores were removed. Peak force was recorded for each core, and shear force value was determined by averaging the peak force values for all five cores for each steak.
Data were analyzed using the Mixed procedure of SAS 9.4 with fixed effects of first transport temperature, second transport temperature, and day of case life (where applicable). For subprimal purge loss, subprimal piece was considered the experimental unit, for all other data, steak was considered the experimental unit. Cook loss, WBSF, and case life color measurements were analyzed as repeated measures. Peak internal temperature was used as a covariate for WBSF and cook loss using a Toeplitz covariance structure. Significance was declared at P < 0.05. First transport temperature, second transport temperature, and day of case life interactions were evaluated where appropriate and are reported when significant.
Sirloin subprimals transported at 38 °F had increased purge loss compared to subprimals transported at 28 °F. Strip steaks from subprimals transported at 28 °F were lighter and more yellow and had less purge loss than steaks from subprimals transported at 38 °F. Sirloin steaks from subprimals transported at 28 °F were darker but had less purge loss than steaks from subprimals transported at 38 °F. Freezing both types of steaks negated any previously observed differences in purge loss. Fresh strip steaks from subprimals transported at 38 °F were more tender than steaks from subprimals transported 28 °F at day 5 of case life.
These data highlight the importance of ambient temperature during the transport of meat products, especially the first time whole subprimals are transported. The increase in purge loss and subsequent yield of sirloins transported at elevated, yet still acceptable temperatures has the potential to be detrimental to the bottom line for any meat processor. However, these data indicate subprimal response to temperature variations is mixed. Thus, a universal recommendation for all meat products is not possible, and further investigation into the impacts of transportation temperatures on various meat products is vital to the optimization of the meat supply chain.