Factors affecting premature browning in cooked ground beef Factors affecting premature browning in cooked ground beef

Some ground beef patties developed an internal, brown cooked color and looked well-done at tem peratures as low as 13 1 E F, whereas normal patties were re d to pink. The premature brown color was not relate d to percent fat; patty compaction; animal source and maturity;


Introduction
Internal color of cooked meat normally chang es from red to pink to tan as endpoint temperature s increase.These colors often are used to assess degree o f doneness.However, in some of our earlier studies, a well-done appearance has developed in ground beef at lower than expected temperat u res.Because this prematur e brown color could result in consumer s eating undercooked ground beef, concern s for food safety were raised.This researc h examined the chemical properties of ground beef that turned brown prematurely during cooking.

Experimental Procedures
Samples exhibiting normal and premature brow n cooked color were obtained from the quadricep s muscle of A-and E-maturity, British-bee f and dairy breeds and from frozen beef trimmings.All raw materials had pHs of 5.5 to 5.8 and fat contents from 3 to 18%.Quarter pound patties were forme d , crust frozen (-40EF), vacuum packaged, and stored at -4 EF for 2 to 11 months.
Oxidation-reductio n potential of raw sample s was measured usin g a platinum redox and a silver/silver chloride reference electrode.TBA values (a measure of oxidation) were determine d on raw patties using the perchloric acid extraction method .Total reducing activity, total pigment , and heme and nonheme iron also were determined.
Prior to coo king, external and internal patty colors were assessed visuall y to the nearest halfpoint using a 5-point descriptiv e scale (1=purple red, 2=dark reddish purple, 3=bright red, 4=brownish red, 5=very brown).Patties were cooked to 131, 149, or 16 7EF on an electric griddle (325EF).Internal temperature was monitored by intermittently inserting a needle thermo-prob e into the patty.Patties were cooled for 5 minutes and sliced for internal color evaluation to th e nearest half-point using a 5-point descriptive scale (1=very dark red to purple, 2=bright red, 3=very pink, 4=slightly pink, 5=tan, no evidence of pink).A Hunter Labscan 6000 was used to i nstrumentally evaluate color.Saturation index (color intensity) was calculated.
Data were analyzed as a completely randomized design where t reatments were a 2 × 3 factorial of cooked color group and endpoint temperature .SAS General Linear Models procedure s and least square means separation techniques were used.

Results and Discussion
An interaction (P<.05) was found for virtually all cooked color traits.As expected, patties from the normal group exhibited a typical color chang e during cooking from red to more tan as endpoint tempe r ature increased.At all three end point temperatures, patties that had premature browning were described as slightly pink to tan.Visually, the normal group at 131EF was the most red (P<.05), followed by normal at 149EF (Table 1).Normal patties at 167EF and prematurely brown patties at 131 and 149EF were similar (P>.05) in cooked color.Patties that were prematurely brown were visually similar at 131, 149, or 16 7 EF (P>.05) .Instrumental measurements (Table 1) supported visual scores, because normal patties at 131EF were the reddest (highest a*) and most intense in color (saturation index).For most instrumental color traits, the normal patties at 149EF were intermediate in redness (P<.05) , whereas normal at 16 7EF and prematurel y brown at 13 1EF were less red and not different (P>.05).For most instrumental traits, patties that were prematurely brown at 149 and 16 7EF did not differ (P>.05), and both exhibited the least (P<.05) redness.
Patties that had premature brown cooked color ha d higher (P<.05)TBA values (Table 2) than patties with normal color.They also had lower (P<.05)total reducing activity and oxidative-reductiv e potentials.No differences (P>.05 ) for heme, nonheme, or total pigment occur red in raw patties from the two cooked color groups (Table 2).After cooking, patties with normal color at 13 1EF retained higher concentrations of extr actable pigment and heme iron compar ed to patties with premature brown color at this temperature.Nonheme iron increased more in pat t ies with premature brown than normal color upon heating to 13 1 EF.Overall , patties with premature brown cooked color were more oxidized and exhibited less reducing ability than patties with normal color.

Table 2 . Means for Chemical Traits of Ground Beef Patties with Normal (NRM) and Prematurely Brown (PMB) Cooked Color Raw and Cooked to 131°F
Means for a trait with different superscript letters differ (P<.05).