Influence of finishing systems on sensory characteristics and the mechanisms regulating tenderness formation in the longissimus lumborum of bison bulls.

The objective of this study was to characterize the influence of finishing system on the sensory characteristics and mechanisms of tenderness formation in the longissimus lumborum (striploin) of bison bulls. Bison bulls (n = 196) were randomly assigned to one of two finishing treatments at approximately 25 mo of age: 1) Grain-finished (n = 98; placed in an open lot with ad libitum access to prairie hay, alfalfa hay, and whole shell corn prior to slaughter) or 2) Grass-finished (n = 98; bulls allowed to graze native pasture until slaughter). Bulls were harvested at approximately 30 mo of age and striploins were collected. Ultimate pH was recorded, and striploins were fabricated into steaks for assessment of sensory characteristics by consumer and trained sensory panels (steaks aged 14 d), and analysis of Warner-Bratzler shear force (WBSF; steaks aged 4, 7, 14 or 21 d). Additional steaks were aged for 14 d for determination of collagen content and sarcomere length. Proteolysis of desmin and troponin-T was evaluated on samples aged for 4, 7, 14, or 21 d. Consumer panel results indicate that grain-finished steaks had higher ratings for overall liking (P = 0.04) and flavor liking (P < 0.01) whereas off-flavor intensity was increased (P < 0.01) for grass-finished steaks compared to grain-finished steaks. Trained panelists indicated that grass-finished bison steaks had increased (P < 0.01) aroma and flavor intensities compared to grain-finished bison steaks and "ammonia, metallic, and gamey flavors" were associated with the grass-finished treatment. Warner-Bratzler shear force was affected by the interaction of finishing treatment with aging period (P < 0.01). Steaks from the grain-finished bulls became more tender (P ≤ 0.02) as aging time increased from 4 d to 14 d, whereas WBSF of steaks from grass-finished bulls did not differ (P ≥ 0.10) during this period. Steaks from grass-finished bulls were more tender (P ≤ 0.01) than steaks from grain-finished bulls at 4 d and 7 d but treatments were similar (P ≥ 0.61) at 14 and 21 d. Samples from grass-finished bulls had less (P < 0.01) intact desmin compared to grain-finished bulls. This study demonstrates that finishing system influences sensory attributes of steaks from bison bulls and highlights the role of proteolysis as the primary mechanism regulating tenderization of bison.