Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 19, 1996
Publication Date: N/A
Interpretive Summary: Foodborne illnesses associated with the bacteria E. coli 0157:H7 and inadequately cooked beef patties have highlighted the need for an indicator of thorough cooking. Consumers have been advised to use the absence of pink color as an indicator of thorough cooking (internal temperature = 160 deg F. We evaluated the color of patties cooked from the fresh, frozen or thawed state. The internal color of patties cooked from the frozen state to 160 deg F remained red/pink. Only after thawing for more than 18 h, did cooking to 160 deg F result in a well-done color. When patties were vacuum- packaged during thawing, cooked color was more red than when patties were non-vacuum packaged. The effect of thawing and packaging on cooked color seemed linked to the state of the meat pigment myoglobin (Mb). Higher levels of metMb, the oxidized form of Mb, resulted in a less red cooked color. In a subsequent experiment, we prepared patties with different levels of metMb. Difference in metMb level of meat after processing decreased during freezing and thawing. Patties cooked from the frozen state were less red than those cooked directly after processing. After 24 h thawing, patties cooked to 160 deg F were brown, irrespective of metMb level. In thawed patties, premature browning (PMB), the phenomenon where the product appears well-done at internal temperatures lower than 160 deg F, occurred at 149 deg F. Conditions other than internal temperature strongly influence cooked beef patty color. Cooked color is not recommended as an indicator of internal temperature.
In three separate trials, the cooked color of patties cooked either fresh, frozen or after thawing was evaluated. In trial 1, the effects of thawing and packaging were evaluated. The internal color of patties cooked to 71øC within 12 h thawing at 7øC remained red/pink. Only after thawing for 18 h or longer, did cooking to 71øC result in a well-done appearance. Cooked color of patties thawed while vacuum packaged was more red than cooked color of non- vacuum packaged patties. Spectral analysis of the raw product indicated that the effects of thawing and packaging on cooked color were linked to level of metmyoglobin (metMb); higher levels of metMb resulting in a less red cooked color. In trial 2 and 3, we varied the metMb level by using different storage/processing conditions. Differences in metMb level before freezing seemed to become smaller after freezing and thawing. Differences in metMb before processing did not significantly affect cooked color. Patties cooked from the frozen state were less red than those cooked directly after processing. After 24 h thawing, patties cooked to 71øC were brown, irrespective of metMb level. Premature browning, the phenomenon where the product appears well-done at temperatures lower than 71øC, only occurred in thawed patties. After 24 h thawing, patties appeared well-done at 65øC. It is concluded that experimental conditions other than internal temperature strongly influence cooked beef patty color. Therefore, cooked color should not be used as an indicator of internal temperature.