Troubleshooting

AMSA Exclusive: Practical applications to improve fresh meat color


By Guest Contributor on 4/20/2015

Editor's note: This is part of an occasional series of exclusive articles provided by authors commissioned by the American Meat Science Association in cooperation with Meatingplace. The article is taken from the AMSA 67th Reciprocal Meat Conference Proceedings.

Overall appearance of retail meat cuts is the primary factor that consumers consider when determining meat freshness and making purchasing decisions. In general, consumers prefer a bright red fresh meat color – and they have a definite bias against tan or brown discoloration.

Therefore, extending the shelf life of the fresh meat while maintaining bright red color that attracts consumers has been one of the primary goals of the meat industry. Numerous live-animal and post-harvest factors affecting meat color have been identified.

Diet

Different diets and particularly grass-finishing regimes greatly influence meat color. Pasture-raised cattle and sheep are darker in color than ruminants raised on grain concentrates primarily due to the tendency of having a higher ultimate pH, lower intramuscular fat contents and possibly a different growth rate.

Dietary supplementation with vitamin E for the final 100 to 125 days prior to cattle slaughter enhances meat color and color stability by suppressing lipid and myoglobin oxidation through elevated α-tocopherol. However, the antioxidant effect of α-tocopherol by the vitamin E supplementation varies depending upon the nutritional background.

Inclusion of dietary tannins in sheep diets improved the color stability of fresh lamb meat during extended refrigerated storage possibly through the positive influence of tannins on heme pigment concentration and reduced metmyoglobin formation. Further, dietary supplementation of creatine, magnesium and/or vitamin D3 has been shown to positively affect pork meat color characteristics by influencing glycolytic rate and/or shifting muscle metabolism to be more oxidative.

Breed

Superior color stability was reported for steaks from Charolais and Limousin carcasses compared to beef steaks from other breeds such as Angus, Hereford and Red Angus. Another study also found a breed difference in meat color in that Angus had significantly higher values for lightness, redness and yellow coloring than the Hereford-Friesian cross group, but the differences with the Jersey-Friesian cross steers were not significant for redness or yellow.

Variations in meat color between different pig breeds also have been observed. The muscles (longissimus dorsi and biceps femoris) from the Hampshire breed have been found to be more red and yellow and more saturated than the same muscles from the Swedish Landrace and the Swedish Yorkshire breeds.

Animal handling

Rough animal handling can cause bruises on carcasses and increase animal stress, which in turn negatively affects meat quality.

Further, the degree of pre-slaughter stress, and particularly its impact on elevating muscle temperature early post-mortem, has considerable influence on initial color development and color stability of pork. Pre-slaughter stress of animals can result in the muscle pH being either abnormally high or low pH.

In more extreme cases, stress-related quality defects such as DFD (dark, firm and dry - long term stress) and PSE (pale, soft and exudative – short term excitement) can occur.

Chilling

The rate of pH and temperature decline of pre-rigor muscle substantially affect meat color and color stability. A typical example of abnormal meat quality that is associated with rapid pH decline at higher than normal pre-rigor muscle temperature is PSE. Pale color and subsequent rapid discoloration during display of the PSE pork meat can be attributed to a significant denaturation of sarcoplasmic (myoglobin) and/or myofibrillar (myosin) proteins and/or altered myoglobin redox stability.

The PSE-like appearance also has been observed in muscles from other species such as beef, lamb and venison, when pre-rigor muscles were exposed to the protein denaturing conditions of high temperature combined with rapid pH decline.

Due to the size and thickness of the round muscles in the hind leg of beef carcasses, substantial variations in the rate of postmortem chilling regimes and pH decline can be found depending upon the location (depth) of the same muscle. The lighter color and reduced color stability have been observed in deep (inner) portions of the round muscles compared to the superficial (surface) portions of the muscles. These quality defects that are associated with location within the muscle are still problematic in the global meat industry.

For example, in Australia the incidence of high pre-rigor temperature of beef carcasses was 74.6 percent across seven beef processing plants (ranging from 56 percent to 94 percent). This may be attributed to the excessive use of electrical inputs (stunning, immobilisation and/or carcass stimulation) possibly coupled with heavier carcasses (exhibiting a faster glycolytic rate) resulting in protein denaturation of the beef muscle.

Storage and display temperature

Meat color and color stability can be influenced substantially by temperature during meat storage and display periods. The rate of autoxidation increases with the elevation of storage temperature resulting in the acceleration of metmyoglobin. In fact, an elevated temperature even for a short period of time can result in a substantial decrease in surface redness and consequently color stability.

A recent preliminary study found that a short-term temperature abuse for about 6 hours during display by increasing temperature from 3°C to 10°C resulted in about 17 percent reduction in a* (redness) values of beef muscles. Furthermore, an increase in aging temperature of vacuum packaged sub-primals resulted in a significant decrease in color stability during retail display period.

Enhancement and packaging

Improved fresh meat color stability through the addition of non-meat ingredients (particularly phosphate and/or lactate) has been well characterized. This stabilization may be attributed to an elevated pH from the phosphate/lactate enhancement and improved myoglobin redox stability through the replenishment of reducing substrates (e.g. NADH) in fresh meat.

A new vacuum packaging system has been developed and approved for use in the meat industry. It uses a small amount of sodium nitrite that is impregnated into the packaging film. The sodium nitrite then reacts with the meat to form nitrosylmyoglobin on the meat surface, making the meat appear bright red in color.

-- Yuan H. Brad Kim is an assistant professor of animal sciences at Purdue University


 
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