351 Effects of sorghum-based finishing diet on semitendinosus and infraspinatus objective and subjective color-stability.

Abstract Polyphenolic compounds within sorghum can affect oxidation status, behaving either as antioxidants or pro-oxidants. The objective of this study was to determine effects of a sorghum-based finishing diet on two beef muscles that are divergent in muscle fiber type, fat content, and color stability. Yearling cattle (N=300; initial BW 347±11.1 kg) were randomly allocated to 30 feedlot pens based on order of initial processing. Pens were randomly assigned to one of two dietary treatments (TRT) consisting of cattle fed a sorghum-(SG) or corn-based (CON) diet throughout a 182-day feeding period. Seventy-two hours postmortem, semitendinosus (ST) and infraspinatus (IF) muscles were collected, vacuum packaged and transported to the University of Georgia for 21 days of aging. After aging, steaks were fabricated and used for a 9-d stimulated retail display study where visual panel redness and surface discoloration percentage ratings and objective color measurements were collected. There was a Display Day (DD) × Treatment (TRT) × Muscle (MUS) interaction for panel redness color rating (P=0.02). There was no panel redness color rating difference between IF SG and CON steaks throughout the display period (P>0.13). In the ST, there were no differences between SG and CON steaks from display d 0 to 5 (P>0.33), but at d 7 and 9, CON steak redness rating was greater than SG steak redness rating (P< 0.01). There was no three-way interaction for panel surface discoloration rating (P=0.20), but all two-way interactions were significant (P<0.03). Over the entire display period, SG and CON steak discoloration ratings did not differ in the ST (P=0.74); however, IF SG-steak discoloration rating was greater (P<0.05) than CON-steak discoloration ratings. Across both steak types, CON and SG steak discoloration did not differ from d 0 to 5 (P>0.60), but SG steaks had greater (P< 0.01) discoloration ratings than CON steaks from d 7 to 9. There were no three- or two-way interactions for L*value (P >0.12). There tended to be a three-way interaction (P=0.07) for a*value. There was no difference between IF SG and CON steak a*value from display d 0 to 4 (P >0.06), but from d 5 to 9, CON steak a*value was greater (P< 0.01) than SG steak a*value. In the ST, there was no a*value difference between SG and CON steak throughout the display period (P >0.17), except d 5 ST CON steak a*value was greater (P< 0.01) than SG steak value. These results indicate SG steaks exhibited reduced color stability for both muscles during retail display, but differences were not apparent until the last three display days. These findings suggest sorghum feeding may adversely affect muscle antioxidant capacity, leading to muscle-dependent oxidative instability and shorter retail color shelf-life.