Characterization of Pigments Responsible for Red or Pink Discoloration in Cooked Pork

• Main Author: Ghorpade, Viswasrao M.
• Format: Others
• Published: DigitalCommons@USU 1992
• Subjects: Pigments; Red; Pink; Discoloration; Cooked Pork; Food Science
• Online Access: https://digitalcommons.usu.edu/etd/5388; https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=6444&context=etd

The pigments responsible for pink or red discoloration in cooked vacuum-packaged meat products {bratwurst (pork and beef), ground pork, and pork roasts} were investigated. In bratwurst, this study attempted to characterize the red pigment that appears upon refrigerated storage, and to determine the effect of pH, cooking and storage temperature, and sodium lactate on incidence of red discoloration. Myoglobin was identified in the exudate of samples with red discoloration. Myoglobin levels of cooked products were significantly lower in samples of low initial pH (5.5) or cooked to higher than normal internal temperature (74°C). Red discoloration was associated with microbial growth. Frozen samples had no red discoloration after 4 weeks storage. Microbial plate count and incidence of red discoloration were lower in samples of lower pH (5.5 vs 5.8 or 6.2), samples cooked to higher internal temperature (74° vs 68°C), and samples containing 3% sodium lactate. Further, the effects of microbial growth in raw materials (ground pork) on cooked pork color were investigated. In two trials with sow meat held aerobically at 2°C for 3 weeks, microbial load reached spoilage levels (107 cfu/g), pH increased to 6.46, and samples cooked to 71°C had red exudate, shown by absorption spectroscopy to contain myoglobin and cytochrome c. Samples cooked to 82°C received high panel ratings for red color, due to red, flocculent precipitate in exudate, but samples containing undenatured myoglobin levels received low panel ratings. In sow meat held frozen or vacuum packaged at 2°C, pH after 3 weeks was 6.03 and 6.18, and plate counts were 104 and 107, respectively, but exudates after cooking were much less red. In five trials with fresh U. S. #1 pork legs, plate counts also reached 107 cfu/g by 3 weeks storage, and pH increased from 5.99 to 6.37, but cooked samples were not red. Higher myoglobin levels in sow meat probably accounted for the red color and the high level of undenatured myoglobin remaining after cooking of high pH, spoiled samples. Finally, pink or red discoloration was investigated in the cooked U. S. #1 pork roasts. Myoglobin was the pigment responsible for pink color in pork roasts cooked to 65°C. Roasts cooked to 82°C had gray internal color after cooking, but developed pink internal color after refrigerated storage. Reflectance spectra of pink slices from roasts, cooked to 82°C, then stored for 12 days at 2°C, were charactetistic of denatured globin hemochromes or related non-nitrosyl hemochromes.