Carcass weight-dependent chilling rate modulates early postmortem metabolism and lean color development in beef

Smaller carcasses are routinely subjected to the same chilling protocols, potentially altering postmortem temperature decline and the metabolic processes that regulate pH decline and lean color development, perhaps predisposing them to quality defects such as atypical dark-cutting (ATDC). Because previous ATDC research has largely relied on limited sampling time points, interactions between chilling rate and early postmortem metabolism may be overlooked. Therefore, this study evaluated whether carcass weight-dependent differences in chilling rate alter early postmortem metabolism and contribute to darker lean color development associated with ATDC. Forty-four beef carcass sides were classified as heavy weight (HW; 231.4 ± 2.1 kg) or light weight (LW; 181.1 ± 2.1 kg). Longissimus lumborum temperature, pH, and metabolites were assessed from 0 to 24 h postmortem, as well as protein abundance, color, and tenderness were evaluated. Light-weight carcasses chilled more rapidly than HW carcasses, resulting in an approximately 3 °C lower muscle temperature between 3 and 24 h postmortem (P < 0.05). This accelerated chilling coincided with darker lean color, evidenced by lower L* values (P < 0.05). While ultimate pH did not differ between groups, LW carcasses retained greater glycogen and glucose-6-phosphate concentrations early postmortem despite similar initial substrate availability. Additionally, LW carcasses exhibited greater shear force at 1 d postmortem (P < 0.05) but tenderness differences resolved with aging. These findings demonstrate that relatively modest differences in carcass weight (∼ 50 kg/side) can alter chilling rate thus altering early postmortem metabolic progression and provide one potential mechanistic explanation for the development of ATDC-like phenotypes.