vitamin E and C on porcine meat quality

Nowadays aspects of meat quality are quite important issues, such as physical and sensory characteristics, nutritional value, and safety. Meat quality is affected by several factors i.e. genotype, nutritional and management conditions, and pre- and post slaughter conditions. Genotype unsuitable for the adequate processing aim, improper nutritional and management conditions and pre- and post slaughter conditions notably increase the water-holding capacity, as one of the important parameter of technological quality. Colour, taste and tenderness are important parameters for customer quality of meat.

The high quality of the pig herd is generally recommended, but the processor and the customer have different aspects. The higher amount of PUFA content of the meat is more desirable from customer's aspect, but it may decrease the oxidative stability of meat, and consequently decreases the shelf-life. In addition to this unlike trait higher PUFA content results in undesirable texture of meat which also real disadvantage for processors.

Antioxidant property of vitamin E is widely known and it protects polyunsaturated fatty acids from uncontrolled oxidation, called lipid peroxidation. Vitamin E supplementation can therefore increase the shelf-life, stabilize the colour and improve the water-holding capacity of the meat. Although feeding stuffs generally include vitamin E, it is, however, normally not enough to reach the above mentioned positive effects. Vitamin E content of the muscle needs to meet or exceed a threshold to show these meat quality improvements (Faustman et al., 1989, Arnold et al., 1993a). It is also reported that different tissues can store different amount of α-tocopherol, which is the biologically most efficient form of vitamin E (Morrissey et al., 1996). Muscle can store a lower amount of a-tocopherol as compared to liver, heart and subcutaneous fat. Faustamn et al. (1998) stated that in case of cattle the maximally storable level can be reached only by feeding 500 mg α-tocopherol per animal for 126 days.

Many experiments were conducted to describe the methodology how increased vitamin E supplementation effects on water-holding capacity, colour and oxidative stability. Supplementation rate and experiment duration influenced the results, not to mention the fact that even the muscle type has a great impact on the final consequences.

Vitamin E supplementation effect on water-holding capacity can be measured as drip loss. Both positive and neutral effects have already been stated. This variety of results could be caused by the difference in duration and the extent of investigations. High amount (500 mg vitamin E kg^-1 feed) supplementation that lasted for a short-term (3 weeks) and 45 days resulted in numerically lower drip loss (Rosenvold et al., 2002, Swigert et al., 2004). Cannon et al. (1996) reported controversial results, when moderate vitamin E supplementation complemented feed were given for swine for a long-term period.

Adequate colour shows the freshness of the meat to consumers, so it is very important to keep its desirable intense during the short and long-term storage too. However, fibre type is seemingly the major factor in meat colour and not the conditions of vitamin E supplementation. Trials with cattle and rabbit showed that vitamin E had a significant effect on the colour stability, especially a* (redness) (Faustman et al., 1998, Corino et al., 1999). Some experiments with pig also suggest improved colour attributes (a*, L*) (Lanari et al., 1995, Monahan et al., 1994) while some other researchers found no significant differences between control and treated groups, independent of the amount of the added vitamin E (Cannon et al., 1996, Rosenvold et al., 2002, Swigert et al., 2004).

As mentioned above, the shelf-life of meat can be described with the oxidative stability. Monahan et al. (1994) added 200 mg vitamin E kg^-1 feed for 2 weeks before slaughtering which resulted significantly improved oxidative stability. The same results occurred when long-term (84 days) lower dose (100 mg vitamin E kg^-1 feed) investigations were conducted (Cannon et al. 1996). Experiments with rabbit and cattle showed similar tendencies in case of shelf-life improvement affected by vitamin E (Corino et al., 1999, Faustman et al., 1998).

Ascorbic acid (vitamin C) is a water-soluble vitamin, and though its antioxidant capacity is widely know, only a few experiments were made to evaluate the effect of increased vitamin C on meat quality parameters. Gebert et al. (2005) concluded that low, moderate and high amount of vitamin C supplementation for growing pigs did not improve either water-holding capacity or colour stability.

The feeding trials were conducted in a standardized pig farm (Pig Farm Ltd., Békés, Hungary). A total of 120 growing-finishing pigs of the same genotype were investigated for 2 weeks before slaughtering.

Three dietary treatments were applied such as the control, vitamin E and vitamin C groups (40 pigs in each). Stunning, slaughtering and processing followed the EU requirements.

1. (control) group was fed with standard diet for growing-finishing pig, containing 24 mg vitamin E kg^-1 feed and no additional vitamin C.

2. (Vitamin E) group was given standard diet for growing-finishing pig, containing 90 mg vitamin E kg^-1 feed and no additional vitamin C.

3. (Vitamin C) group was fed with standard with standard diet for growing-finishing pig containing 24 mg vitamin E and 500 mg vitamin C kg^-1 feed.

Measured parameters in the loin after slaughter:

pH values were measured with pH-STAR meat pH meter (Firma Matthäus, Germany). Instrumental colour measurements were carried out using a chromameter (Minolta CR-330, Minolta Co., Japan). CIE values were expressed as lightness (L*), redness (a*), and yellowness (b*). Drip loss was measured in loin with the modified Honikel probe (Fischer etl al., 1980). Loin samples were frozen (-70 ^oC) till the oxidative stability analyses. Samples were thawed in room temperature and homogenized in phosphate-buffered saline before the analyses. Homogenates incubated in phosphate buffered iron(II)-sulphate solution at 37 ^oC with continous stirring (Huang and Miller, 1993). Samples were taken in 15 minutes intervals and further lipid oxidation stopped with cold (4 ^oC) BHT solution. Thiobarbituric acid reactive substances determined after protein precipitation with trichloroacetic acid using 2-thiobarbituric acid method (Mihara et al., 1980).

The statistical evaluation of the data was made by a two-sample t test (MS Excel 7.0 software).

The pH value of the loin from the group fed diet supplemented with vitamin E differed significantly (P<0.001) from that of the controls at the 45^th minute post-mortem, though there were no significant differences between control and vitamin C supplemented groups (Table 1). Concerning pH₁ high consistency is shown in all groups.

The pH values measured at the 4^th hour post-mortem were considerably similar to the values measured in the 24^th hour, in particular in loins of the pigs from the control and vitamin C supplemented groups. Concerning pH_4, significant difference (P<0.05) occurred between control and vitamin C groups. However, pH₄ in loin from pigs fed vitamin E supplemented diet did not differ significantly from the other measured pH₄ results.

In addition, 24 hour post-mortem mean pH in control group showed significant difference (P<0.001) from both treated (vitamin E and vitamin C) groups pH means. 

Table 1: pH means in loin in 45 minutes, 4 hours and 24 hours post-mortem

^ab P<0.01

^ac P<0.05

The results showed that CIE  L*, a* and b* values were considerably similar both 4 and 24 hours post-mortem in the control and vitamin C supplemented groups, except the a* values at 24 hours after slaughtering when significant difference (P<0.01) was found (Table 2). Considering vitamin E treated group, the differences were much remarkable. Every other occasions showed significant differences from control values, except the a*₄ and the b*₂₄ values.

Table 2: Colour values of loin at 4 and 24 hours post-mortem

Different superscipts of the same row means significant difference : ^ab P<0.001; ^ac P<0.01

Consumer quality of the meat can be evaluated based on the changes of the different CIE values. ΔE*_ab value needs to be defined according to CIE L*, a* and b* values to evaluate the customers' preference:

ΔE*_ab=√(ΔL*)²+(Δa*)²⁺(Δb*)²

With these categories results can be compared and visually perceived, thus differences between treated groups become more understandable (Table 3).

Table 3: Link between ΔE*_ab categories and visual perceptibility (Lukács, 1982)

The changes of loin colour at 4 and 24 hours post-mortem are different in treated groups. Loin from control groups had a clearly visible (5.53) change in colour. In addition, vitamin E and vitamin C supplemented groups had a distinctly visible change in the loin colour (7.00 and 6.56, respectively).

Changing in colour was considered not only within but between groups. Comparing the colour of loins from pigs of the control and vitamin E supplemented groups, remarkable difference was noticed. At 4 hours after slaughtering the difference was clearly visible, this moved towards to distinctly visible category 24 hours post-mortem. Contrarily, differences between control and vitamin C treated groups were just fell into visible category in the whole experimented time (Table 4).

Table 4: Differences in colour between groups 4 and 24 hours post-mortem

Drip loss of loin samples were measured 24 hours after slaughtering. Results showed that control (7.20±2.63%) and vitamin C groups (4.17±1.10%) showed significant differences (P<0.001). However, there was no significant difference between control (7.20±2.63%) and vitamin E supplemented groups (6.16±3.00%).

As it can be seen, vitamin E supplementation numerically improved the water-holding capacity, but the current experiment showed that high dose of vitamin C could produce much remarkable result.

Figure 1. Drip loss of loins of pigs fed diets supplemented with vitamin E or vitamin C

Oxidative stability, which give information about the shelf-life of the meat showed moderate changes. It was found that vitamin E supplementation decrease the malondialdehyde formation as compared to the control samples even at the 45^th minute of the incubation in the iron-induced free radical generation system (Figure 2). Vitamin C supplementation did not cause the same effect.

Figure 2: Changes of the malondialdehyde content of the loin of pigs fed diets supplemented with vitamin E or vitamin C in an iron-induced oxidative stability system

The results of present study showed that additional 500 mg vitamin C kg^-1 feed for finishing pigs for 2 weeks prior to slaughter significantly reduced the drip loss, therefore improved the water-holding capacity. The results from the present study indicate that high amount of vitamin C did not influence the oxidative stability of loin, although 50 mg additional vitamin E kg^-1 feed had a great effect on this trait. Visual perceptivity of loin colour was positively affected by vitamin E what can influence the consumer's appreciation related to meat quality.

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