Can Vitamin C Improve Pork Quality?

Several investigators have reported improvements in swine growth and meat quality when the animals' diet is supplemented with vitamin C. However, other studies have yielded inconsistent results, as some investigators have documented no effects or even negative effects of vitamin C supplements.

Vitamin C's effect on pork quality may be the result of changes in the metabolism of glucose and glycogen. One of the breakdown products of vitamin C is oxalic acid, which has been shown to slow the breakdown of glucose. This can result in a reduction of lactic acid production from glucose after slaughter and may prevent the rapid drop in pH associated with poor meat quality. Further, vitamin C has been reported to decrease the severity of pre-slaughter stress response, which further reduces the amount of glucose and glycogen available for lactic acid production.

Vitamin C is water soluble and can easily be supplemented through drinking water for short periods of time and at critical times pre-slaughter. Thus, adding vitamin C to pigs' water could be a practical method of supplying vitamin C and affecting pork quality. But vitamin C is rapidly excreted in the urine when high doses are supplied, and researchers need to understand how rapidly vitamin C is broken down and how soon after consumption it is excreted. With this knowledge, vitamin C can be supplemented more exactly to obtain a positive response in pork quality.

We at North Carolina State University conducted two experiments to investigate the effects of vitamin C supplementation through water on plasma vitamin C and oxalate concentrations and to gauge the effects on meat quality in swine.

Experiment 1 was conducted using 24 crossbred pigs that were fitted with jugular catheters (to allow for blood sampling multiple times) and housed in individual pens in order to properly determine the water and vitamin C intake of each animal. Pigs were given 0, 1,000, or 2,000 milligrams per liter (mg/L) of vitamin C in their drinking water, supplied through individual water systems. The supplemented drinking water was changed every 12 hours (h) during the 48-h supplementation period in order to minimize degradation of the vitamin during the treatment period. We had previously determined that vitamin C remains stable in water for at least 12 h (recovery after 14 h was 90 percent).

Water supplied to pigs was weighed and recorded in order to determine individual vitamin C intake from the quantity of water that disappeared. Individual water disappearance was measured at 0, 2, 4, 6, 12, 24, and 48 hours after supplementation began. In addition, blood samples were collected from all pigs at 0, 2, 4, 6, 12, 24, and 48 h after supplementation began and then again at 0, 2, 4, 6, 12, 24, and 48 h after supplementation ended. Vitamin C and oxalate concentrations were measured in all blood samples.

Experiment 2 used 30 finishing pigs that were housed in individual pens in order to determine individual water and vitamin C intake. Water was supplied through individual systems and was supplemented with 0, 500, or 1,000 mg/L of vitamin C. The supplementation, which started at 7 a.m., occurred over a 48-h period before slaughter. Individual water supplies for all pigs were weighed and recorded in order to determine individual vitamin C intake from the quantity of water consumed.

At the end of the 48-h period, the pigs were transported to a commercial slaughter plant, where they were randomly stunned and exsanguinated in groups of four. The slaughter occurred between 4 h and 5 h after the end of vitamin C supplementation. Carcass temperature was measured at 1 h post-slaughter; loin pH measurements were determined at both initial (1 h post-slaughter) and ultimate (24 h post-slaughter) times.

After chilling for 24 h, the carcasses were processed into primal cuts, and several pork quality measurements were made: degree of fluid loss, visual color scores, objective color scores (using a Minolta color measuring device), and oxidative stability (measure of development of rancidity). Then the pork chops were displayed in conditions similar to retail displays, and visual and Minolta color scores and oxidative stability were measured again.

In Experiment 1, supplementing finishing pigs with vitamin C at 1,000 mg/L or 2,000 mg/L increased the vitamin C concentration in the blood within 6 h of beginning supplementation and maintained greater levels through 48 h. Vitamin C concentrations rapidly declined and reverted to control levels within 2 h after supplementation ended (Figure 1).

As mentioned earlier, one of the breakdown products of vitamin C is oxalic acid. It seemed likely that by increasing vitamin C consumption, the amount of oxalic acid in the blood could be increased. However, supplementing vitamin C in the drinking water had no effect on plasma oxalate concentrations (Figure 2).

However, an injection of vitamin C seemed to make a difference. Following an injection of 22 mg of vitamin C per kilogram (kg) of body weight, pigs showed increased oxalic acid concentrations in the blood after 15 minutes (min) and up to 4 h later. The injection of vitamin C resulted in a much greater increase in the vitamin in the blood than did the water supplementation; therefore, there was more vitamin C that could be converted to oxalic acid.

In our studies, we supplemented vitamin C through the drinking water because this would provide an easy method of administration that could be implemented for a short time. Supplementing finishing pigs with 500 and 1,000 mg/L vitamin C in the drinking water (Experiment 2) did not affect pH values, visual color scores, or oxidative stability (Table1).

The failure of vitamin C to improve pork quality in this experiment may be related to the fact that vitamin C concentrations in blood and tissue or oxalic acid concentrations were not affected by supplementation at the time of slaughter. It has been speculated that oxalate influences pork quality by decreasing the breakdown of glucose and, therefore, reduces the formation of lactic acid in the muscle after slaughter. However, it is not known whether vitamin C or oxalic acid concentrations in the blood are indicators of pork quality or whether elevated concentrations are required to be able to positively affect pork quality (Table 1).

In Experiment 2, the negative effects of vitamin C supplementation on pork quality at 500 mg/L but not at 1,000 mg/L were unexpected. Supplementing finishing pigs with 500 mg/L of vitamin C through the drinking water resulted in higher, more undesirable Minolta L* values (paler meat) and increased fluid loss in loin chops from supplemented pigs when compared to the control group. In fact, the carcasses from pigs supplemented with 500 mg/L of vitamin C had a mean Minolta L* value of 54.4, which places those carcasses in the more undesirable PSE (pale, soft, exudative) category of pork quality.

Supplementation of water with vitamin C does not appear to be an effective method of improving pork quality. However, the timing of slaughter relative to vitamin C supplementation may be critical in order to achieve improvements in pork quality. Supplementation at the producer level may not be practical, but supplementation at the slaughter plant may be. More research is required to determine whether timing of supplementation relative to slaughter is important in obtaining a positive response to vitamin C.

By Eric van Heugten, Professor, Swine Husbandry
NCSU Department of Animal Science
Swine News (Volume 27, Number 08)
North Carolina State University Cooperative Extension Service

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Can Vitamin C Improve Pork Quality?