TIMING OF MAGNESIUM SUPPLEMENTATION THROUGH

DRINKING WATER TO IMPROVE FRESH PORK QUALITY

 

B. Frederick, E. van Heugten, and M.T. See

 

Summary

Water supplementation with 900 ppm Mg for either 0, 2, 4, or 6 d prior to slaughter was evaluated as a means to improve pork quality. Hot carcass weights and carcass temperature and pH (45 min and 24 hr) were determined after slaughter. Chops from the Longissimus dorsi and the Semimembranosus were displayed for 2, 4, 6, and 8 days and color and retail fluid loss were determined. Magnesium supplementation for 2 and 6 d decreased retail fluid loss of fresh pork. Although magnesium supplementation for 6 d decreased loin fluid loss during retail storage, the effect was not evident during the initial storage period (0 to 4 d of storage). However, magnesium supplementation for 2 d prior to slaughter improved fluid retention in hams throughout the entire retail storage period.

 

Introduction

Short-term supplemental dietary Mg decreases water loss (D’Souza et al. 1998 1999, 2000; Hemann et al., 2000) and improves color (D’Souza et al., 1998, 2000) in pork. Furthermore, dietary Mg potentially decreases lipid oxidation of stored pork (Apple et al., 2001). Possible modes of action of Mg on pork quality include: 1) decreasing acute stress response resulting from handling prior to harvesting (Kietzmann, and Jablonski, 1985), 2) inhibiting severe muscle contraction by directly controlling intracellular calcium (Laver et al., 1997), and/or 3) delaying the initiation of glycolysis by maintaining high energy phosphates post-mortem (Moesgaard et al., 1993). Although many studies have concentrated on supplemental dietary Mg in feed, supplementation through drinking water has not been investigated.

 

Materials and Methods

Sixteen castrated males and sixteen gilts weighing 119 ± 4 kg were placed into 2.03 m by 0.74 m individual pens and provided with free access to water via a nipple waterer. Pigs were fed 2.7 kg of feed (Table 1, 0.12% Mg) per day for a 5 d adjustment period. After the adjustment period, pigs were allotted by sex and weight to water supplemented with 900 ppm Mg for either 0, 2, 4, or 6 d prior to slaughter. Plastic water containers (23 L capacity) were filled daily with 15 L of water containing Mg. Water containers were suspended from the ceiling and gravimetrically (approximately 600 ml/min) emptied into a galvanized pipe leading to an Aratoâ nipple. Daily water disappearance volumes were determined by weight.

 

Table 1. Composition of experimental diets (% of total)^a.

 

 

On the seventh day (08:00) all pigs were transported 110 km to a commercial abattoir. After approximately 45 min of lairage, pigs were electrically stunned and blood was immediately collected from the site of sticking to determine plasma Mg concentrations. Hot carcass weights were collected prior to refrigeration to determine carcass yield. The temperature and pH of the loin were measured between the 10^th and 11^th rib at 45 min post-mortem using a Sentron® pH meter.

 

At 24 h post-mortem the entire right loin and ham were removed and transported 60 km to a commercial meat fabrication facility. Minolta L*, a*, and b* color measurements were taken at four positions on the surface of the Longissimus dorsi at 45 min after the initial cut.  This chop and three others chops were deboned and closely trimmed of fat to obtain the Longissimus dorsi. Additionally, the Semimembranosus was removed from the ham and cut into four equal chops. One chop from each muscle was vacuumed packed and frozen until TBARS analysis could be performed. A second chop was used to determine retail fluid loss and color at 2, 4, 6, and 8 d and TBARS at 8 d of storage. Dry matter, 24 h pH, tissue Mg concentration, and drip loss were determined on another chop. The final chop was used for TBARS analysis after 4 d of retail storage.

 

Drip loss was determined by suspending a muscle sample (approximately 70 g) on a fishhook (barb removed) and fishing line in a covered plastic container for 48 h at 4°C. The percent drip loss was calculated by the percent difference in initial and final weight.

 

Chops designated for retail storage were placed individually on an absorbent pad in a commercial Styrofoam® tray and wrapped with an oxygen permeable film. Chops were stored under fluorescent lighting at 4°C for the appropriate time. After 2, 4, 6, and 8 d of storage the retail muscle samples were removed from their package, placed on a paper towel, and reweighed for calculation of retail fluid loss. Chops were then returned into their original tray. After Minolta color measurements were obtained, the chops were rewrapped and returned to refrigeration for further storage and measurements. Muscle samples designated for lipid oxidation determination after 4 and 8 d of storage were vacuumed packed and stored at -20°C until TBAR analysis could be performed.

 

Data were analyzed by split-plot design with sex as the main plot and magnesium supplementation as the subplot. No sex by treatment interaction was observed. Therefore, sex was removed from the model, which resulted in a randomized complete block design including Mg supplementation and weight block.

 

Results and Discussion

Carcass yield, muscle pH, temperature: Dressing percentage was higher after 6 d of supplementation versus 2 d of supplementation. The laxative effect of magnesium sulfate may decrease the amount of digesta in the gastrointestinal tract resulting in an increased dressing percentage. Given the short time period of supplementation it is unlikely that magnesium significantly increases protein or lipid deposition and thus does not affect carcass yield, although this was not directly determined. Magnesium supplementation did not affect temperature or pH of the loin at 45 min or 24 h post-mortem (Table 2). However, the hams from pigs offered Mg supplemented water for 2 d tended to have a greater pH at 24 h than those without Mg supplementation, 5.71 vs. 5.62 ± 0.03, respectively (P = 0.08). The pH of meat has often been used as a preliminary indicator of pork quality. Typically meat with a pH within the range of 5.6 to 5.9 is considered superior. Higher pH values usually correlate to less fluid loss and thus is more desirable. Therefore, meat from pigs provided supplemental Mg for 2 d prior to slaughter tended to have a more desirable pH than pigs without Mg supplementation.

 

Table 2. Effect of magnesium supplementation on fresh pork quality.¹

 

 

Fluid loss: Magnesium supplementation for 0, 2, 4, or 6 did not affect (P > 0.05) loin (3.29, 2.46, 3.16, and 3.55 ± 0.42%, respectively) or ham (3.33, 3.26, 3.83, and 3.36 ± 0.30%, respectively) drip loss. However, retail ham fluid loss was lower (P < 0.05) at 2, 4, 6, and 8 d of storage for pigs fed Mg supplementation for 2 d prior to slaughter compared to no Mg supplementation. This effect resulted in approximately 1.5 to 2.0% reduction in fluid loss for the duration of retail storage. Furthermore, retail loin fluid loss from pigs supplemented with magnesium was lower at 6 (P < 0.08) and 8 d (P < 0.05) of storage.

 

Although Mg supplementation did not affect drip loss, retail fluid retention of the ham and loin during storage was improved by Mg supplementation. Magnesium supplementation for 6 d prior to slaughter improved fluid retention of the loin during the end of the retail storage period. Thus, loins from pigs supplemented with Mg for 6 d had a lower fluid loss than the controls. However, magnesium supplementation for 2 d prior to slaughter improved fluid retention in hams throughout the entire retail storage period. 

 

Color: Magnesium supplementation did not affect Minolta L* or a* of the loin or ham compared to the control. However, magnesium supplementation for 2 d decreased initial yellowness (b*) of the ham compared to the control and lowered lightness (L*) after 2 d of retail storage compared to 6 d of Mg supplementation, 6.85 vs. 8.95 for b* and 48.7 vs. 52.6 for L*, respectively. However, the magnitude of the effects was not apparent throughout retail storage. Thus, in the present study there was only a slight and transient effect of Mg supplementation on pork color.

 

Table 3. Effect of magnesium supplementation on fresh pork color.¹

 

 

Implications

Magnesium supplementation for 2 and 6 d decreased retail fluid loss of fresh pork. Although magnesium supplementation for 6 d decreased loin fluid loss during retail storage, the effect was not evident during the initial storage period (0 to 4 d of storage). However, magnesium supplementation for 2 d prior to slaughter improved fluid retention in hams throughout the entire retail storage period.

 

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