Although swine and most other livestock species begin synthesizing vitamin C early in life, researchers have reported promising benefits to health, performance and (or) meat quality with dietary vitamin C supplementation under various conditions. Now, a series of studies at Iowa State University (Kremer et al., 1999) has shown significantly better color and water retention of pork during retail display when pigs received a single feeding of vitamin C shortly before processing.
Poor color and water seepage in retail packages remain serious concerns for the swine industry, even though breeding companies have largely rid their lines of the halothane gene that predisposes pigs to produce pale, soft, exudative (PSE) pork. Other causes of these meat quality problems have not been fully identified, but at the cellular level they have long been associated with the reduction in muscle pH that follows slaughter.
More specifically, studies have linked seepage problems to postmortem glycolysis, or the conversion of glucose and other carbohydrates to lactic acid in the muscle. Kremer et al. (1999) and several previous researchers also linked postmortem glycolysis to poor meat color. Vitamin C supplementation is believed to limit these changes because the body converts excess vitamin C to oxalate, which inhibits the glycolytic enzyme pyruvate kinase.
Researchers have noted improvements in meat quality with vitamin C supplementation at least since Rajic (1971) reported an increase in the muscle color scores of pork from supplemented pigs. However, these earlier studies used relatively low levels of vitamin C in long-term supplementation regimens. Kremer et al. (1999) provided much higher vitamin C supplementation in a single feeding four hours before the pigs were sent to the packer. The researchers chose this timing to optimize oxalate concentrations and minimize glycolysis after processing.
Fortification levels in the Iowa State studies were 783 and 2,348 ppm. These levels provided average one-time vitamin C intake per animal of 290 and 704 mg, respectively. The supplemented pigs were estimated to have body-water concentrations of oxalate equivalent to two and six times the inhibitory constant for pyruvate kinase in the muscle at processing.
Muscle pH was then measured in the right longissimus (LM) muscle at 22, 45, 90 and 180 minutes postmortem. Researchers have associated PSE pork with an ultimate pH of 5.5 or below. In this work, none of the muscle declined to that level during the 180 minutes after slaughter. However, muscle from both supplemented groups had a significantly higher pH (P < 0.13) than muscle from the controls (Table 1).