Dietary nutrient supplements improve meat quality

Food safety, price, nutritive value, meal convenience and appearance play an important role in determining whether consumers purchase meat, as well as the type and cut of meat. However, it is the eating experience or the quality of the meat product purchased that influences the consumer to repurchase that particular meat product. Hence consumer behaviours, attitudes and perceptions toward the quality of meat is an area that at present is commanding increased interest from all sectors of the meat industry.

A complex interaction of animal, pre-slaughter and post-slaughter factors can have a significant influence on meat quality. Meat quality defects such as pale, soft, exudative (PSE) meat in pigs and poultry, and dark, firm, dry (DFD) meat or ‘dark cutting’ meat in pigs, cattle and sheep still remain a major problem and have a major economic impact on meat industries in many countries.

As a consequence, considerable research has been directed toward establishing the ‘best practices’ for optimising meat quality. Often these ‘best practices’, such as remodelling of raceways and lairage yards at the abattoir, are difficult and expensive to implement in a commercial situation. Hence innovative approaches to improving meat quality attributes such as colour, drip loss, flavour, tenderness and shelf life are needed. The role of pre-slaughter dietary nutrient supplementation is one such approach that has proven to have a major impact in improving meat quality. The adoption, however, of such strategies remains low. This perhaps can be attributed to the fact that in many countries meat producers are still paid on carcass quality traits such as lean meat yield and weight rather than a combination of carcass and meat quality traits. It is only recently that a few meat processors have included meat quality traits into the carcass price matrix and this has led to the use of dietary nutrient supplements such as vitamin E, selenium and magnesium. The use of a range of dietary minerals and vitamins to improve meat quality will be discussed in this paper.


Minerals

SELENIUM

The beneficial effects of selenium supplementation on growth and carcass quality traits in pigs, poultry and cattle are significant and have been reviewed extensively by Close (1998; 1999) and Mahan (1999). Although the use of inorganic selenium (sodium selenite) in livestock feeds has resulted in tremendous productivity gains, recent research has shown that the use of organic selenium (Sel-Plex, Alltech Biotechnology Pty Ltd) has additional benefits that surpass that of selenite. Results from an experiment evaluating the efficacy of Sel-Plex and selenite at 0.1 and 0.3 ppm selenium in pigs indicate that Sel-Plex supplementation resulted in higher selenium levels in the loin muscle at both 0.1 and 0.3 ppm levels compared to pigs fed the inorganic selenite (Mahan and Kim, 1996).




Figure 1. Effect of selenium source and level on pig loin selenium levels (Mahan and Kim, 1996).


Selenium, an essential constituent of the antioxidant enzyme glutathione peroxidase (Rotruck et al., 1973), has also been shown to significantly improve meat quality by decreasing cell membrane oxidation leading to reduced muscle drip loss. Edens (1996) evaluated the use of selenite and Sel-Plex in broilers and demonstrated that mortality and drip loss were lower when organic selenium was fed to the birds (Table 1).

The influence of selenium supplementation on reducing drip loss in pigs is somewhat less clear compared to the reduced drip loss observed in broilers. Studies by Muñoz and his co-workers (cited by Lyons, 1997) have shown that dietary Sel-Plex supplementation in conjunction with other antioxidants such as vitamins E and C reduced drip loss from the loin muscle of pigs compared to pigs fed a control diet (Table 2). A recent study by Mahan et al. (1999) has shown that dietary selenite supplementation resulted in higher drip loss levels and paler meat for the loin muscle compared to pigs fed the control or Sel-Plex diets.


Table 1. Effect of selenium source on mortality and meat quality of broilers¹.



¹Edens (1996)


Table 2. Effect of dietary antioxidant* supplementation on drip loss % of the longissimus dorsi muscle¹.



¹Muñoz et al., 1997;
*0.1 ppm Sel-Plex 50, 20-100 kg body weight; 50 ppm vitamin E, 20-100 kg body weight; 670 ppm vitamin C, 80-100 kg body weight.


Selenium deficiency has also been linked with human heart and cellular diseases. Some researchers go as far as suggesting that selenium supplementation in humans may prevent some forms of cancer and may also boost the immune status. Hence selenium enriched foods are well placed as functional foods. Korean pork producers have recently capitalised on this and are currently incorporating Sel-Plex in pig diets and market-ing the selenium-enriched pork (SelenPork) as a functional food benefiting human health and nutrition. Consumer feedback also indicates that Koreans regard SelenPork as being juicier and having better appearance.


MAGNESIUM

Magnesium (Mg) is the second most abundant cation in intracellular fluid and is an important cofactor of numerous enzyme systems (Stryer, 1988). In addition magnesium also has a relaxant effect on skeletal muscle (Hubbard, 1973). Magnesium directly depresses skeletal muscle activity by antagonising calcium (required for neurotransmitter release) and reducing the secretion of neurotransmitters by motor-nerve impulses, which in turn reduces neuromuscular stimulation (Hubbard, 1973; Hagiwara et al., 1974). Studies have since shown that dietary magnesium supplementation alleviates the effects of stress by reducing plasma cortisol, norepinephrine, epinephrine and dopamine concentrations (Niemack et al., 1979; Kietzman and Jablonski, 1985). Consequently, studies have been conducted to investigate the influence of dietary magnesium supplementation on reducing the effects of stress and improving meat quality.

Numerous studies have shown that dietary magnesium supplementation in pigs results in improved meat quality. Otten et al. (1992) examined the use of long-term dietary magnesium supplementation and reported slight improvements in colour and initial pH, whereas Schaefer et al. (1993) studied short term dietary magnesium supplementation and reported reduced initial pH and % drip loss. D’Souza et al. (1998) have shown that dietary magnesium aspartate (3.2 g elemental Mg for 5 days pre-slaughter) supplementation significantly improved pork quality in pigs by reducing drip loss and improving pork colour and muscle pH, as well as reducing catecholamine levels (Table 3). Such were the benefits that there were no PSE carcasses in the magnesium supplementation treatment groups, irrespective of handling pre-slaughter (D’Souza et al., 1998).


Table 3. The effect of dietary magnesium aspartate (MgAsp) supplementation and preslaughter handling on meat quality indicators of the longissimus thoracis muscle 24hrs postslaughter.



¹D’Souza et al. (1998); *P<0.05; **P<0.01; ***P<0.001


The use of Bioplex Magnesium (Alltech Biotechnology) at 1.6 g elemental Mg for two days pre-slaughter (Table 4) similarly resulted in reduced drip loss and a lower incidence of PSE (D’Souza and Mullan, 1999). Dietary supplementation using inorganic magnesium sources such as magnesium sulphate and magnesium chloride (D’Souza et al., 1999) and magnesium mica (Apple et al., 2000) has also been shown to improve meat quality. Studies comparing the influence of organic and inorganic magnesium compounds on meat quality indicate that the improvements in muscle colour, drip loss, and the reductions in the incidence of PSE were greater with organic magnesium compounds such as magnesium aspartate and Bioplex Magnesium (Figure 2). The greater influence of organic magnesium compounds on meat quality is related to the increased bioavailability of elemental magnesium when organic magnesium compounds are used compared with inorganic magnesium supplements such as magnesium sulphate and magnesium chloride.


Table 4. The effect of dietary Bioplex Magnesium supplementation on meat quality indicators in the Longissimus thoracis muscle at 24 hrs post-slaughter¹.



¹D’Souza and Mullan, 1999; NS not significant; *P<0.05; **P<0.01; ***P<0.001





Figure 2. Effect of magnesium aspartate (organic Mg) and magnesium sulphate (inorganic Mg) diets on the incidence of pale, soft and exudative (PSE) pork in the longissimus thoracis (LT) muscle (D’Souza et al., 2000).


The use of dietary organic magnesium supplementation as a viable method to improve meat quality in pigs was also validated under commercial conditions in Victoria, Australia (Hofmeyr et al., 1999). Dietary magnesium supplementation was shown to significantly reduce the incidence of soft, exudative (SE) pork in all three replicates of the commercial validation study (Figure 3). The unusually high incidence of PSE pork in Replicate 1 was due to a high number of halothane gene carrier pigs used in Replicate 1.





Figure 3. Effect of organic magnesium supplementation on the incidence of soft and exudative (SE) pork in the longissimus thoracis (LT) muscle (Hofmeyr et al., 1999).


Dietary magnesium supplementation has also been used to reduce the effects of stress in cattle (Gardner personal communication) and sheep (Gardner and Pethick, 1998). Gardner and Pethrick (1998) found dietary magnesium supplementation reduced glycogen loss and increased the rate of glycogen repletion in the skeletal muscle pre-slaughter and reduced incidence of ‘dark cutting’ in sheep and cattle following slaughter.


CHROMIUM

Chromium is another important mineral in livestock through its role in the ‘glucose tolerance factor’ in insulin action and sensitivity and its reduction of stress (Close, 1999). Chromium supplementation in pig diets was found to improve feed efficiency and lean meat yield and reduce backfat thickness (Page et al., 1993). However, limited research has been conducted on the effects of chromium supplementation on meat quality. In a recent study by Matthews et al. (1999), dietary chromium proprionate supplementation in finisher pigs increased the level of marbling and reduced purge loss in the loin muscle. In contrast, Boleman et al. (1995) and O’Quinn et al. (1998) reported that the use of chromium picolinate supplementation had a detrimental effect on meat quality in pigs. It is possible that the source of chromium may be responsible for the different effects of chromium supplementation on meat quality and this warrants further investigation.


Vitamins

VITAMIN E

Dietary vitamin E supplementation (all-rac-α-tocopheryl acetate) in meat animals is perhaps the best known method of improving meat quality by reducing lipid oxidation in fresh meat and meat products. Fresh meat is stored for a very short duration and hence requires a relatively short shelf life. Processed meat products on the other hand require frozen storage for extended periods, hence making lipid oxidation one of the major quality concerns affecting the shelf life of the meat product. There are a range of factors that contribute to the deterioration in quality and loss of shelf life as a consequence of lipid oxidation occurring in meat and meat products. These factors include the state and content of prooxidants (iron, myoglobin), level of antioxidants present in muscle (α-tocopherol and enzymes such as glutathione peroxidase, superoxide dismutase and catalase), composition and amount of muscle lipids and the storage conditions of meat and meat products.

Porcine longissimus dorsi is the most frequently studied muscle with respect to the use of vitamin E supplementation to improve meat quality (Jensen et al., 1998). Vitamin E supplementation to pig diets to enhance meat quality has been incorporated at levels ranging from 40-700 mg allrac-α- tocopheryl acetate/kg feed. The improvements in meat quality include reduction of thiobarbituric acid reactive substances (TBARS - markers for rancidity and off-flavours) to scores below 0.50 mg malondialdehyde equivalents (MDA eq.), which is the borderline level for detection of rancidity and off-flavours by trained sensory panellists. Results from a few recent studies using vitamin E supplementation in pigs to improve meat quality are outlined in Table 5. Generally, vitamin E supplementation at doses of 200 mg all-rac-α-tocopheryl acetate/kg of feed for periods ranging from 84- 130 days pre-slaughter resulted in significantly reduced muscle oxidation levels, improved colour and reduced drip loss of fresh pork and pork products. Vitamin E supplementation at doses of 700-800 mg all-rac-α-tocopheryl acetate/kg of feed for shorter periods (7 days prior to slaughter) reduced lipid oxidation in the meat but had limited success in improving the colour and drip loss of pork and pork products.

As in the case of pork, dietary vitamin E supplementation has also been effectively used to improve the quality of poultry and poultry products (Table 6). Vitamin E supplementation at a dose of 100 mg all-rac-α-tocopheryl acetate/kg of feed significantly reduced lipid oxidation levels in both fresh poultry meat and poultry products. The effect of vitamin E supplementation on muscle colour is perhaps more evident in species that have higher levels of myoglobin (Jensen et al., 1998). Hence the influence of vitamin E supplementation on colour stability is minimal in pork and poultry products while having a significant effect in beef (Chan et al., 1996) and lamb (Guidera et al., 1997).


Table 5. The influence of vitamin E supplementation on pork quality traits of the longissimus muscle.



^Aall-rac-α-tocopheryl acetate ^BDecrease in TBARS numbers in supplemented group relative to control group
^CIncrease in a-values (red colour) in supplemented group relative to control group
^DDecrease in drip loss % in supplemented group relative to control group.


Table 6. The influence of dietary vitamin E supplementation on poultry meat and poultry meat product quality traits.



^Aall-rac-α-tocopheryl acetate ^BDecrease in TBARS numbers in supplemented group relative to control group


VITAMIN D

Davey and Gilbert (1969) first reported the involvement of calcium ions in the post-slaughter aging process of meat. Since then considerable research has established the influence of calcium ions on meat tenderness by the activation of the calpains in meat (Koohmaraie, 1992, review). Koohmaraie et al. (1989) reported improved tenderness of ovine meat infused with calcium chloride solution after only one day of post-mortem aging. The use of vitamin D supplementation in dairy cows was found to significantly increase serum calcium levels (Hibbs et al., 1951). This led to the hypothesis that the use of vitamin D₃ supplementation could improve the tenderness of meat by increasing meat calcium levels thereby activating the calpain systems during the aging process (Swanek et al., 1999). Swanek et al. (1999) conducted three experiments using beef steers and reported increased plasma and muscle calcium levels following vitamin D₃ supplementation for 7 and 10 days pre-slaughter, respectively. Objective and sensory evaluation of the beef indicated that the vitamin D₃ supplementation (5 x 10⁶ IU Vit D for 7 days pre-slaughter) in beef steers improved the tenderness of meat compared to their unsupplemented counterparts (Table 7). The use of vitamin D₃ supplementation to improve the tenderness of beef is very encouraging and the influence of vitamin D₃ supplementation on other meats certainly warrants further investigation.


Table 7. The effect of dietary vitamin D₃ supplementation in beef steers for 7 days preslaughter on muscle calcium content, Warner-Bratzler shear force and sensory traits of the longissimus muscle aged for 7 days post-slaughter¹.


¹Swanek et al., 1999 * 8 = extremely juicy, tender, none detected, intense to 1 = extremely dry, tough, abundant amount, bland.


Conclusion

The increasing use of specific diets and feed formulations has helped to better meet the animal’s nutritional requirements to maximise meat production efficiencies. The use of dietary supplements, in addition to improving meat production efficiencies, also has considerable potential to improve meat quality. Dietary supplementation of organic sources of selenium and magnesium and vitamins E and D in a range of species has resulted in reduced drip loss, improved colour and shelf-life, and improved eating quality attributes such as tenderness. However, to date, the above vitamins and minerals have been used independently of each other, targeting particular factors that influence meat quality. While there is some overlap, the modes of action of the different dietary supplements and their influence on meat quality are quite different. For example magnesium supplementation improves meat quality by reducing the effects of stress as a result of negative handling or transport, while selenium supplementation improves meat quality by reducing lipid oxidation. Hence there is a need for the development of a mineral-vitamin premix that targets the key factors that affect meat quality. The availability of such a mineral-vitamin premix will enable producers and processors to consistently produce high quality meat and meat products.


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