Modern Problems with Meat Quality

Meat consumers are becoming more discerning about the appearance of fresh meat quality and their buying patterns are affecting demand further up the supply chain. For example, in European markets there is good demand presently for double muscling in cattle because it provides large cuts of lean meat. Similarly in pigs, leanness fetches a premium. In general, leanness is associated with lower levels of marbling fat within the muscle (intramuscular fat) as well as smaller amounts of subcutaneous and intermuscular fat. Marbling fat can, however, enhance the flavour and juiciness of the meat. Meat with limited marbling is likely to have a dry texture, and this has been one of the primary eating quality faults with pork in recent years. It has arisen from selection against fat deposition during growth, resulting in excessively lean meat (Fernandez et al ., 1999a). This has been managed by incorporating the Duroc breed in sire lines, which imparts superior marbling and succulence whilst producing acceptably lean carcasses. Meat consumers are reluctant to buy chops with a high level of marbling based on their appearance in a retail display cabinet, but this behaviour is susceptible to change once a consumer realizes the benefits that marbling has for eating quality (Fernandez et al ., 1999b).

Retail displays aim at minimizing differences between cuts and portions of meat. Otherwise, the purchaser may think that something is abnormal or wrong with a particular cut. Two-toning is becoming a more common problem in this respect. It can be due to differences in muscle fibre type within the same cut and to fat accumulation in a muscle masking the normal muscle pigment. These are natural effects, which cannot be avoided, but in pigs the colour contrasts are sometimes very obvious. In fish, two-toning occurs in the form of stripes where fat accumulates when the fish reach sexual maturity. Patches of pale muscle also occur in breeder fish where pigments have been mobilized for deposition in the skin and eggs. Both conditions lead to downgrading of breeder fish from the aquaculture industry.

Young fish do not have these problems but they can produce fillets that have poor cohesion. This becomes a problem when the meat is sliced thinly. The fillets show gaping between muscle blocks, and the fillet may break up and fall apart during cooking. This condition is exaggerated if there has been excessive contraction during rigor, causing the myotomes to separate from each other. Stress during catching, inadequate temperature control during processing and autolysis also contribute to this problem.

Blood splash, blood speckle, blood spots and ecchymoses are problems when the residual blood is visible at the surface of a meat cut. They are connected with the way the animal is stunned and bled, and are common causes of downgrading in both red and white meat species. In salmon, blood spots can occur where blood vessels branch from the aorta. The problem arises from engorged blood vessels, which rupture during evisceration and filleting. This is often worst during the summer when water temperatures are high.

Rearing Conditions

There are conflicting views about the effect growth rate has on subsequent meat tenderness. Theoretically, situations that enhance muscle catabolism through elevated calpain or reduced calpastatin activities could improve meat tenderization post mortem. Alternatively, if the animals are very slow-growing, or even losing weight, background toughness may be raised because connective tissue and collagen will be a larger component in the muscle. Overall, the majority of the evidence suggests that there is little or no effect of pre-slaughter growth rate on meat tenderness if the meat is aged (Perry and Thompson, 2005). The relationship may, however, depend on the cooking method that is used (Listrat et al ., 1999). When beef was cooked very lightly (to 55–60 ° C internal temperature), meat from fast-growing cattle was tougher.

Theoretically, if an animal is slaughtered during a period of compensatory growth, its meat could be more tender. If it is fed generously after a period of weight loss and growth rapidly compensates, the meat could have superior background tenderness to meat from animals grown throughout the rearing period at a more constant rate, provided calpain activity is still elevated. However, there is limited evidence that has tested whether this is a real effect.

In general, feedlot beef can have a less ‘grassy’ flavour than pasture-fed beef. This distinction is sometimes quite subtle and may not always be detected. Feedlot beef can also have a slightly paler red colour than grass-fed beef, but there is no difference in the tendency to develop surface discoloration when left in retail display cabinets. Meat from spayed feedlot heifers has the same tenderness as beef from maiden heifers, but meat from once-bred heifers can have more variable tenderness without, on average, being more or less tender (Field et al ., 1996).

In lambs, regular exercise during the rearing period is conducive to a leaner carcass with more tender meat in the hindleg (Garrett et al ., 1999). In steers, regular exercise during the finishing period can enhance redness in the meat (Dunne et al ., 2005b), but it may also increase two-toning (Dunne et al ., 2005a).

It has been suggested that it should be feasible to produce pigs outdoors in colder climates using a once-bred gilt system. The gilts would produce a litter in the spring with the piglets reared to slaughter weight outdoors. Replacement gilts would be retained over winter for farrowing the following spring. When this system was tested in Sweden, it was found that overall growth performance and instrumental meat quality were similar in comparison with conventional indoor finishing systems (Stern et al ., 2003).

Meat from red deer has poor colour stability compared with beef. It is prone to metmyoglobin formation during retail display, and this limits its retail life. This has been particularly noticeable in deer raised indoors and fed a pelleted ration. Pasture-raised venison has better colour stability, presumably because of the potentially higher concentrations of vitamin E in the meat (Wiklund et al ., 2006).

Turkeys reared in hot conditions might be prone to producing breast meat with a higher than normal pH ult , but it is not usually serious enough to affect overall quality (Owens et al ., 2000a).