Poultry Meat Quality: Pinking

Meat is still one of the main products of the food industry but it is slowly being overtaken by a rise in vegetarianism and veganism at the moment. Chicken and turkey are one of the leading meat foods owing to their versatility.

There are two issues that commonly affect poultry meat, pinking and red spot. The more serious issue is pinking because it gives the impression that the meat has been undercooked or worse, just raw. Both issues have been investigated for at least 50 years without satisfactory resolution. The discolouration is probably responsible for plenty of poultry meat to be discarded resulting in a significant economic loss to the industry i.e. producers of poultry, retailers and processors.

Pinking

The pink defect is usually known as pinking but it can be referred to as pink tinge and pinkness. It is a colour condition of cooked poultry meat where it retains a pink colour even though the meat has been thoroughly cooked, often beyond cooking specification. It is not a browning reaction as such but it is a cosmetic problem which affects consumer perception of the product. The pinking defect can also develop with storage of the meat so what may be seen as a high quality product following cooking may also then lose its perceived quality over time (King & Whyte, 2006). 

Consumers quite rightly would interpret the pink discolouration as an indicator of uncooked meat and thus unsafe to eat.  However inspections by the Food Safety and Inspection Services of the USA’s US Dept. of Agriculture for example have regularly checked the internal temperature of a bird being cooked and noted that whilst the meat is perfectly safe to eat there is still an ongoing issue.

Some of the best reviews on the phenomenon are by Maga (1994) and Froning (1995) who cover off between them the various factors in terms of biochemistry and processing that affect meat quality.

What Produces Pinking?

Most researchers believe that a number of different haemochrome complexes are involved which each have a pink colour. One of the most prevalent colours comes from a form of nitrosylhaemochrome (NITHEME). This is the heat-stable pink pigment that forms in all types of meat when it is cured using nitrates and nitrites. If it is added to chicken or turkey then a similar colour apparently forms too. Only 1 ppm of nitrite is needed to enhance red colour of any sort (Ahn & Maurer, 1987).

Other compounds that interact include nicotinamide.

What Factors Need To Be Considered? 

The factors that need to be considered include:-

  • reactions of various types of pigments including haemoglobin and cytochrome c.
  • preslaughter factors
  • stunning methods
  • levels of nitrite and nitrate contamination in the water supply and in post-processing
  • poultry diet
  • types of processing equipment
  • nonmeat ingredients
  • methods of cooking
  • levels of irradiation of precooked products

No one mechanism can be used to explain the situation because all these factors are complex in terms of how they interact with one another. There are methods available to reduce the pinking discolouration to limited extents.

Techniques To Limit Discolouration

  • Reduction in levels of nitrite and nitrate.
  • Addition of whey protein concentrate

References

Ahn, D.U., Maurer, A.J. (1987). Concentration of nitrate and nitrite in raw turkey breast meat and the microbial conversion of added nitrate to nitrite in tumbled turkey breast meat. Poultry Sci. 66 pp. 1957-1960.
Claus, J.R., Shaw, D.E., Marcy, J.A. (1994) Pink color development in turkey meat as affected by nicotinamide, cooking temperature, chilling rate and storage time. J. Food Sci. 59 pp. 1283-1285
Cornforth, D. P., Rabovitser, J. K., Ahuja, S., Wagner, J. C., Hanson, R., Cummings, B., & Chudnovsky, Y. (1998). Carbon monoxide, nitric oxide, and nitrogen dioxide levels in gas ovens related to surface pinking of cooked beef and turkey. Journal of Agricultural and Food Chemistry46(1), pp. 255-261.
Cornforth, D.P., Vahabzabeh, F., Carpenter, C.E., Bartholomew, D.T. (1986). Role of reduced hemochromes in pink color defect of cooked turkey rolls. J. Food Sci. 51 pp. 1132-1135

Froning, G.W. (1995). Color of poultry meat. Poultry Avian Biol. Rev. 6(1) pp. 83-93

Froning, G.W., Daddario, J., Hartung, T.E., Sullivan, T.W., Hill, R.M. (1969) Color of poultry meat as influenced by dietary nitrates and nitrites. Poultry Sci. 48 pp. 668-67
Holownia, K., Chinnan, M. S., & Reynolds, A. E. (2003). Pink color defect in poultry white meat as affected by endogenous conditions. Journal of Food Science, 68(3), pp. 742-747 (Article)

Kieffer, K. J., Claus, J. R., & Wang, H. (2000). Inhibition of pink color development in cooked, uncured ground turkey by the addition of citric acid. Journal of Muscle Foods11(3), pp.  235-243.

King, N.J., Whyte, R. (2006) Does it look cooked? A review of factors that influence cooked meat color. J Food Sci. 71:R31-R40 (Article)

Maga, J.A. (1994). Pink discoloration in cooked white meat. Food Rev. Int. 10(3) pp. 273-286
Schwarz SJ, Claus JR, Wang H, Marriott NG, Graham PP, Fernandes CF. (1997). Inhibition of pink color development in cooked, uncured ground turkey through the binding of non-pink generating ligands to the muscle pigments. Poultry Sci. 76 pp. 1450-1456.
Schwarz SJ,Claus JR, Wang H, Marriott NG, Graham PP. (1998). Quantification of nicotinamide hemochrome in cooked, uncured turkey by reflectance spectrophotometry. J. Muscle Foods 9 pp. 101-110.
Schwarz, S.J., Claus, J.R., Wang, H., Marriott, N.G., Graham, P.P., Fernandes, C.F. (1999) Inhibition of pink color development in cooked, uncured turkey breast through ingredient incorporation. Poultry Sci. 78 pp. 255-266
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