Comparative proteomic analyses to investigate premature browning in high­oxygen modified atmosphere packaged beef patties.

This study compared the proteomics of beef patties under high­oxygen modified atmosphere packaging (HiOx-MAP) and vacuum packaging (VP) during heating. The color and oxidation stability of fresh patties, and myoglobin denaturation of cooked patties were also measured. The results suggested that HiOx-MAP patties contained more oxymyoglobin in fresh meat and had higher myoglobin denaturation during heating than VP patties, resulting in premature browning (PMB) during cooking. Proteomic analysis found that the overabundance of proteasome subunit beta type-2 (PSMB2) and peroxiredoxin-2 (PRDX2) in HiOx-55 °C, which can remove the damaged proteins and inhibit oxidation respectively, are of benefit to meat color stability during storage, however, this was still insufficient to inhibit the occurrence of PMB during cooking. The high abundance of lamin B1 (LMNB1) in VP-55 °C can maintain the stability of meat color. This research provides greater understanding, based on proteomic perspectives, of the molecular mechanism of PMB.

Effects of Metmyoglobin Reducing Activity and Thermal Stability of NADH-Dependent Reductase and Lactate Dehydrogenase on Premature Browning in Ground Beef.

Premature browning is a condition wherein ground beef exhibits a well-done appearance before reaching the USDA recommended internal cooked meat temperature of 71.1 °C; however, the mechanism is unclear. The objectives of this study were: (1) to determine the effects of packaging and temperature on metmyoglobin reducing activity (MRA) of cooked ground beef patties and (2) to assess the effects of temperature and pH on thermal stability of NADH-dependent reductase, lactate dehydrogenase (LDH), and oxymyoglobin (OxyMb) in-vitro. Beef patties (lean: fat = 85:15) were packaged in high-oxygen modified atmosphere (HiOX-MAP) or vacuum (VP) and cooked to either 65 or 71 °C. Internal meat color and MRA of both raw and cooked patties were determined. Purified NADH-dependent reductase and LDH were used to determine the effects of pH and temperature on enzyme activity. MRA of cooked patties was temperature and packaging dependent (P < 0.05). Vacuum packaged patties cooked to 71 °C had greater (P < 0.05) MRA than HiOX-MAP counterparts. Thermal stability of OxyMb, NADH-dependent reductase, and LDH were different and pH-dependent. LDH was able to generate NADH at 84 °C; whereas NADH-dependent reductase was least stable to heat. The results suggest that patties have MRA at cooking temperatures, which can influence cooked meat color.

Effect of oxygen concentration in modified atmosphere packaging on color and texture of beef patties cooked to different temperatures.

Patties were made from raw minced beef after storage for 6days in modified atmosphere (0, 20, 40, 60, and 80% oxygen) to study the combined effect of oxygen concentration and cooking temperature on hardness and color. Increased oxygen concentrations generally led to larger (P<0.01) thiobarbituric acid-reactive substances (TBARS) values, greater (P<0.01) loss of free thiols and more formation of cross-linked myosin heavy chain. Hardness of cooked patties was generally lower (P<0.01) without oxygen. Premature browning of cooked patties was observed already at a relative low oxygen concentration of 20%. The internal redness of cooked patties decreased (P<0.05) with increasing oxygen concentrations and increasing cooking temperatures. Mean particle size (D(3,2)) of homogenized cooked meat generally increased (P<0.05) with increasing cooking temperatures and increasing oxygen concentrations, and particle size was correlated (r=0.80) with hardness of cooked patties.

Factors influencing internal color of cooked meats.

This manuscript overviews the pertinent research on internal color of uncured cooked meats, biochemical processes involved in meat cookery, and fundamental mechanisms governing myoglobin thermal stability. Heat-induced denaturation of myoglobin, responsible for the characteristic dull-brown color of cooked meats, is influenced by a multitude of endogenous (i.e., pH, muscle source, species, redox state) and exogenous (i.e., packaging, ingredients, storage) factors. The interactions between these factors critically influence the internal cooked color and can confuse the consumers, who often perceive cooked color to be a reliable indicator for doneness and safety. While certain phenomena in cooked meat color are cosmetic in nature, others can mislead consumers and result in foodborne illnesses. Research in meat color suggests that processing technologies and cooking practices in industry as well as households influence the internal cooked color. Additionally, the guidelines of many international public health and regulatory authorities recommend using meat thermometers to determine safe cooking endpoint temperature and to ensure product safety.

Consumer preferences, internal color and reduction of shigatoxigenic Escherichia coli in cooked hamburgers.

The aim of this study was to relate consumer preferences and preparation of hamburgers to color change, internal temperature and reduction of shigatoxigenic Escherichia coli (STEC) serogroups O157 and the "Big Six" (O26, O45, O103, O111, O121, O145) under two ground beef packaging scenarios: 75% O2 MAP and vacuum. 75% O2 MAP hamburgers cooked to 60 °C core temperature appeared done and showed less internal red color (lower a*) than corresponding vacuum hamburgers. Similar STEC reduction (<4 log10) was found for both hamburgers at core temperatures ≤ 66 °C. In a representative survey (N=1046) most consumers reported to judge hamburger doneness by the color and many preferred undercooked hamburgers. Premature browning of 75% O2 MAP hamburgers represents a risk of foodborne illness, when considering consumers' food handling practices. The risk is even greater if such ground beef is prepared by consumers who prefer undercooked hamburgers and judge doneness by color.

Effect of Precooking Conditions on Color of Cooked Beef Patties ‡.

In three separate trials, the visually and instrumentally determined 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 71°C within 12 h of thawing at 7°C remained red-pink. Only after thawing for 18 h or longer did cooking to 71°C result in a well-done appearance. The color of patties thawed while vacuum packaged and then cooked was more red than the color of non-vacuum-packaged patties after cooking. Spectral analysis of the raw product indicated that the effects of thawing and packaging on cooked color were linked to the level of metmyoglobin (metMb); higher levels of metMb resulted in a less red patty color after cooking. In trials 2 and 3, the metMb level was varied by storage and/or processing conditions. Differences in the metMb level before freezing seemed to decrease during freezing and thawing. Differences in metMb before processing did not significantly (P > 0.05) affect cooked color. Patties cooked from the frozen state were less red than those cooked directly after processing. After 24 h of thawing, patties cooked to 71°C were brown, irrespective of metMb level. Premature browning, i.e., the appearance of patties being well-done at temperatures lower than 71°C, only occurred in thawed patties. After 24 h of thawing, patties appeared well-done at 65°C. It is concluded that handling, other than internal temperature, strongly influences cooked beef patty color. Therefore, the color of cooked beef patties should not be used as an indicator of internal temperature.