Basic aspects of meat quality continue to challenge the pork industry. In a recent pork chain quality audit, for instance, retailers and consumers said their most common complaints about pork, after excessive fat, were inconsistent or inadequate color, excessive seepage and insufficient shelf life. Complicating the issue is the recognition that some of the genetic advances which the industry has made in lean growth potential have also brought a greater predisposition to pale, soft, exudative (PSE) pork.
Fortunately, research suggests that increased vitamin E supplementation during the finishing phase--and possibly before--may help with all but the problem of excessive fat.
A 1993 Australian study (Cheah) is typical in the results researchers have seen with increased vitamin E supplementation. That study found significant quality improvements in meat from both normal and PSE-prone Landrace X Large White pigs when the animals received daily vitamin E supplementation of 227 IU/lb (500 IU/kg) of complete feed for 46 days. Drip loss in the unfrozen longissimus thoracis (LT) muscle was reduced by 54 percent in the normal pigs, and by 45 percent in the PSE-prone pigs, compared to unsupplemented controls.
When daily vitamin E supplementation was doubled to 454 IU/lb (1,000 IU/kg) for PSE-prone pigs, the researchers found no occurrence of PSE carcasses. Biopsies taken from these pigs closely resembled those from pigs predicted to produce normal meat.
Cheah et al. also found that the water-holding capacity of LT samples taken from PSE-prone Pietrains approached that of normal British Landrace pigs after daily vitamin E supplementation of 91 IU/lb (200 IU/kg) of feed for 130 days.
Vitamin E concentrations in the muscle increased with higher dietary supplementation, and the researchers suggest that this produced the improvements in the cells' water-holding capacity by increasing cell membrane stability, as demonstrated by reduced erythrocyte fragility. They explain that stabilization of membrane integrity in the LT mitochondria was associated with the inhibition of phospholipase A2 activity, and thus reduced formation of free fatty acids in the cell membranes. In the PSE-prone pigs, the researchers also found a significant reduction in the release of excess Ca2+, which is due to phospholipase A2 activity and ultimately leads to PSE pork.
Other studies have shown that vitamin E concentrations also increase in fat tissue as the pigs' dietary vitamin E levels increase. Monahan et al. (1990) reported significantly improved oxidative stability in rendered fat as well as cell membranes with 91 IU/lb (200 IU/kg) of complete feed for two weeks before slaughter, compared with 13.6 IU/lb (30 IU/kg) for control pigs. The pork (both raw and cooked) was measured for oxidative stability after storage at 40°F (4°C) for up to eight days.
A study with PSE-prone pigs by Texas Tech University researchers (Ramsey et al., 1995) found similar improvements in meat quality with increased dietary vitamin E. The researchers fed 75 IU/lb (165 IU/kg) of vitamin E for four or eight weeks, along with increased levels of riboflavin, vitamin C, zinc, magnesium and selenium. The control group received 6.7 IU/kg of vitamin E, along with lower levels of the other vitamins and minerals.
Pigs receiving the higher level of supplementation had significantly less purge from the loins than controls: 0.5% for the eight-week group, compared to 0.8 percent for the four-week group and 1.5% for the controls. Supplemented pigs also had significantly higher (0.2 to 0.3 unit) muscle pH 24 hours after slaughter; PSE pork tends to have a lower muscle pH.
In addition, the supplemented pigs had more desirable carcass muscle color. The surface discoloration of the loin chops from supplemented pigs was less than those from control pigs during retail display for three days.
In a study that closely mirrored commercial storage and handling practices, Michigan State researchers (Asghar et al., 1991) assessed changes in meat quality when non-PSE pigs received 9.1, 91 or 182 TIU/ton (10, 100, or 200 IU/kg) of feed for approximately 14 weeks. Loin portions were removed from the carcasses, frozen at -4°F (-20°C) for three months and cut into pork chops. They were then placed on polystyrene trays with absorbent pads, wrapped with PVC meat stretch wrap and stored at 40°F (4°C) under fluorescent light for 10 days.
The researchers recorded drip loss, color changes and levels of thiobarbituric acid reactive substance (TBARS). The concentration of TBARS has been used to measure the amount of byproducts of the oxidation of fat in pork in various research studies. The oxidative byproducts are related to reduced pork quality, notably off-flavor and off-color. Decreased TBARS values are associated with good pork quality.
Ground pork was handled under the same conditions, and TBARS values were also taken for it at appropriate intervals.
