Residual triose phosphate isomerase activity and color measurements to determine adequate cooking of ground beef patties

The objectives were to (i) compare the use of triose phosphate isomerase (T PI) activity and internal color scores for determination of cooking adequac y of beef patties and (ii) determine the effect of frozen storage and fat c ontent on residual TPI activity in ground beef. Ground beef patties (24.4% fat) were cooked to five temperatures ranging from 60.0 to 82.2 degrees C. TPI activity decreased as beef patty cooking temperature was increased from 60.0 to 71.1 degrees C; however, no difference (P > 0.05) in activity (6.3 U/kg meat) was observed in patties cooked to 71.1 degrees C and above. Deg ree of doneness color scores, a* values and b* values, of ground beef patti es decreased as internal temperature was increased from 60.0 to 71.1 degree s C; however, temperature had no effect on L* values. TPI activity in raw g round beef after five freeze-thaw cycles did not differ from the control. T hree freeze-thaw cycles of raw ground beef resulted in a 57.2% decrease in TPI activity after cooking. TPI activity of cooked beef increased during 2 months of frozen storage, but TPI activity in ground beef stored for 3 mont hs or longer did not differ from the unfrozen control. While past research has shown color to be a poor indicator of adequate thermal processing, our results suggest that undercooked ground beef patties could be distinguished from those that had been adequately cooked following U.S. Department of Ag riculture guidelines using residual TPI activity as a marker.