425 Effects of pre-mortem stress on protein expression, steak color, and myofibrillar fragmentation index in the longissimus lumborum following harvest

Abstract

Abstract Undesirable variation in beef tenderness and stability of flavor and color may be associated with the abundance of heat shock proteins (HSP). This study aimed to determine whether pre-mortem stress impacts HSP expression in the skeletal muscle following harvest. Forty Holstein steers were administered an i.v. bolus dose of adrenocorticotropic hormone (ACTH; 0.1 IU/Kg BW) to mimic an acute pre-mortem stress. Longissimus lumborum (LD) biopsy samples were taken prior to the ACTH challenge. Serum cortisol was measured every 0.5 h from -2 to 6 h relative to the ACTH challenge. Skeletal muscle and blood samples from 10 steers were collected at each harvest timepoint at (2, 12, 24 and 48 h post-challenge). Samples were collected from the LD immediately after harvest and after 14 d of aging. Protein expression of HSPβ1, P-HSPβ1, HSPβ5, and DJ-1 was analyzed in muscle samples taken prior to the ACTH challenge, at harvest, and after 14 d of post-mortem wet aging. In addition, steak color and myofibrillar fragmentation index (MFI) was analyzed in 14 d aged samples. Harvest time point following the ACTH challenge affected (P < 0.05) protein expression of HSPβ1 and P-HSPβ1. Protein expression of DJ-1 prior to the ACTH challenge was different (P < 0.05) among steers harvested at different timepoints. In addition, time of harvest had no effect on HSPβ5 expression (P > 0.05). Regarding steak color, time of harvest had an effect (P < 0.01) on a*, b*, hue, chroma, and ratio, but no effect (P > 0.05) on L*. Lastly, time of harvest had an effect (P < 0.05) on MFI. These data indicate that HSP expression, steak color, and MFI in the LD after harvest may be related to time of harvest following a stressful event pre-mortem.