Research and Reviews: Meat

Special Circular 172-99

Effects of Storage and NaOH Treatment on the Quality of Cured, Cooked Hams from Hampshire Hogs

B. D. Paxton, C. L. Knipe¹, D. L. Meeker, and N. R. St-Pierre
The Ohio State University Department of Animal Sciences

Abstract

In order to evaluate processing quality effects of the Napole gene (RN^-, rn⁺) and the feasibility of improving the functionality of pork from hogs possessing the unfavorable dominant allele (RN^-), paired hams from 40 hogs (selected from a Hampshire progeny test conducted at the Western Illinois Test Station) were obtained. One ham of each pair was stored non-frozen and the other frozen. Each ham was divided in half after storage and two processing scenarios were applied to each of the ham halves, one of which was intended to improve the functional quality of pork over a conventional processing method. The addition of 0.125% sodium hydroxide (NaOH) to a conventional injection solution increased cooked pH, cooking yields, and darkened product color over the control. No differences in purge quantities were found between the two treatments. These results showed that some of the detrimental effects of the Napole gene can be mitigated by altering processing techniques, but the scenarios tested here also benefited the normal (rn⁺) hams, maintaining an advantage to not having the gene. A sensory panel was also performed on these hams, and NaOH treatment was found to increase both tenderness and juiciness. A second, smaller study was also performed and supported the results of the first study.

Introduction

The Napole Gene is reported to be a major dominant gene influencing meat quality, particularly drip loss and cooking loss during processing of pork. The highest frequency of the gene is reported to be in the Hampshire breed.

Results of University of Illinois research indicate a significant economic loss to packer-processors due to increased drip and cooking loss of pork from pigs with the Napole gene. Some packers are requesting that commercial producers restrict their use of Hampshire boars, and some breeding companies are choosing to remove Hampshire genetics from their genetic lines. However, the superior leanness and carcass lean yield of the Hampshire is an asset the U.S. pork industry should not discard. In addition, the Hampshire breed is widely recognized as a genetic resource for the production of high-quality pork.

The Hampshire breed would benefit from increased understanding of the physiological mechanisms underlying the problem and possible alternate processing strategies that may mitigate the problem.

Materials and Methods

Paired hams, from hogs selected from a Hampshire progeny test conducted at the Western Illinois Test Station, were obtained from the Farmland plant in Monmouth, Illinois. Selection of hogs was based upon glycolytic potential (GP). Hogs with GP values of 180 and below were considered low GP, and hogs with GP values of 250 and above were considered high GP. Paired hams from 40 hogs were obtained for processing and analysis, depending upon the GP values and characterization of hogs. Only 33 pairs were included in the study due to product loss, loss of identification, or lack of GP value. Obtaining paired hams allowed for a blocked comparison of two storage conditions and two processing scenarios. One ham of each pair was stored non-frozen (30°F) and one was stored frozen (-10°F). Hams were divided in half, which allowed for two processing scenarios, one of which was intended to improve the functional quality of this pork over a second, conventional processing method.

After surface fat and connective tissue were removed, each ham muscle was vacuum packaged and stored for approximately one month unfrozen or frozen to compare the storage treatments. After storage, each ham was ground through a three-quarter-inch plate, and pH was determined. Non-meat ingredients were mixed with one ham of each pair, to simulate the levels of ingredients conventionally added to cured hams in the United States (e.g., 25% injection above green ham weight), with the identity of each ham mixture being maintained. To the other ham of each pair, a solution designed to maximize the pH and water-holding capacity of meat was added to the ground meat.

The solutions consisted of the following:

Conventional solution:
28% water, 2% sodium chloride, 0.5% sodium tripolyphosphate/hexametaphosphate mixture, 0.020% sodium nitrite, and 0.055% sodium erythorbate.

Test (NaOH) solution:
28% water, 2% sodium chloride, 0.5% sodium tripolyphosphate/hexametaphosphate mixture, 0.020% sodium nitrite, 0.055% sodium erythorbate, and 0.125% sodium hydroxide.

There was one difference in the curing solutions between storage treatments. Sodium nitrite and erythorbate were only present in the curing solutions of those hams that were frozen. Therefore, no nitrite or erythorbate (-NO₂) was a confounding variable with unfrozen hams in this project.

After mixing, samples of each ham/treatment were stuffed into pre-smoked, fibrous casings, fully cooked to an internal temperature of 155°F, chilled, and vacuum packaged. After cooking, pH, cooking yields, cured internal color (Minolta L*, a*, and b*), and package purge were determined for each ham/treatment. Vacuum-packaged ham slices were stored for four to six weeks, to determine the content of accumulated purge in packages over time.

A sensory panel study was also conducted on the frozen processed hams from both chemical treatments to evaluate sensory effects of ham from RN- pigs and the effects of using NaOH to improve RN- meat quality. Half of the ham samples were controls and the other half were samples with 0.125% NaOH. Each of the eight semi-trained members of the taste panel was served 66 samples of ham over four days. The panelists evaluated the sensory attributes of juiciness, tenderness, ham flavor intensity, and off-flavor intensity. An eight- number scoring scale was used, with one being the lowest score and eight being the highest.

A second study (phase 2) was also conducted on eight paired hams obtained from Herman Falter Packing Co., Columbus, Ohio. Glycolytic potential was measured at The Ohio State University; however, animals were not able to be classified in low and high GP groups due to the low number of hams selected for the study. Hams were processed in the same methods as the first study except all hams were processed at the same time, under the same conditions, and all hams contained nitrite and erythorbate. Package purge and pH were also measured after storage treatment.

Results and Discussion

Hams from high GP animals were found to have decreased pH, cooking yield, and Minolta L* (lightness) value compared with low GP animals. Hams from RN^- animals also had increased Minolta b* (yellowness) value and tenderness (conventional solution only). No differences in Minolta a* (redness) value, cured-product package purge, juiciness, ham-flavor intensity, and off-flavor intensity were found between GP groups.

The decrease in Minolta L* value of hams from RN^- pigs was in contrast to previous research where RN^- pigs were found to possess paler meat color (Enfalt et al., 1994; LeRoy et al., 1996; Lundstrom et al., 1996). However, most of this research studied fresh meat and Longissimus dorsi muscle. Ellis et al. (1997) reported lower Minolta L* values in the Gluteus Medius of the ham from RN^- compared to rn+ animals, supporting the results from this study.

Both the freezing treatment and NaOH treatment were found to significantly increase the pH, cooking yield, and decrease Minolta L* and b* values of cooked hams (Table 1). The significant increase in pH of hams treated with NaOH was expected, as NaOH is a strong base. The significant increase in cooking yield from NaOH addition supported previous research where higher cooking yields were observed with the addition of NaOH (Knipe et al., 1988; Anjaneyulu et al., 1990). Phase 2 results (Table 2) supported the increased cooking yield results of phase 1. The increase in cooking yield from both the frozen and NaOH treatments was found to be greater in hams from RN^- animals than rn⁺ animals (Figure 1 and 2). This is important if more comparable cooking yields between GP groups are desired. Sutton (1997) supported this research by reporting comparable cooking yields of pork from RN^- and rn⁺ animals, in buffered protein gels.

Figure 1. Two-way interaction (storage*genotype) on the cooking yield of cured, cooked ham.		Figure 2. Two-way interaction (chemical treatment * genotype) on the cooking yield of cured, cooked ham.

The decrease in Minolta L* from frozen storage was found to be greater in the lighter colored hams of rn+ animals (Figure 3). The lowest Minolta L* values were found in those hams treated with frozen storage and NaOH (Table 2). Frozen hams were also found to possess significantly less package purge after raw and cured product storage. The decrease in cured-product package purge from frozen storage was found to be greater in the hams of rn+ animals (Figure 4).

Figure 3. Two-way interaction (storage*genotype) on Minolta L* of cured, cooked ham.		Figure 4. Two-way interaction (storage * genotype) on package purge (pour) of cured, cooked ham.

No significant differences were seen between low and high GP groups for any of the four sensory characteristics. However, high GP animals showed trends towards higher juiciness and tenderness. Sensory results of NaOH-treated hams found significantly more tenderness and juiciness than controls (Table 3). Increased juiciness was also reported in NaOH-treated beef rolls, compared to controls, in previous research (Moiseev and Cornforth, 1997).

For those hams processed with the conventional solution, a significant increase in tenderness was observed for hams from RN- animals (Figure 5). However, when NaOH was added, an increased and more consistent tenderness was observed across GP. No significant difference was found between chemical treatments for ham-flavor intensity and off-flavor intensity, indicating panelists were unable to detect any off-flavor or loss of ham-flavor which may accompany the addition of NaOH.

Figure 5. Two-way interaction (chemical treatment * genotype) on the tenderness of cooked, cured ham (rn+ = normal ham and RN- = ham with Napole gene).

Conclusions

Hams from RN^- pigs showed advantages of darker cured color and increased tenderness. The increased pH, cooking yields, and decreased lightness observed after treatments of NaOH and frozen storage indicate that both are effective for improving the quality of meat from RN- animals, and to a smaller degree, rn+ animals. The tenderness and juiciness preferences reported by taste panelists for NaOH-treated hams supplement the improved cooking yields and color. The addition to hams of frozen storage and treatment with 0.125% NaOH would be very beneficial to pork processors. Not only do these treatments help to decrease the difference in the quality of meat between RN^- and rn⁺ pigs, they also slightly improve the quality of meat from rn⁺ pigs.

References

Anjaneyulu, A. S. R., Sharma, N., and Kondaiah, N. 1990. Specific effect of phosphate on the functional properties and yield of buffalo meat patties. Food Chemistry 36: 149-154.

Ellis, M., McKeith, F. K., and Sutton, D. S. 1997. Proceedings for the Pork Quality Summit. July 8 and 9. Des Moines, Iowa. p. 49—64.

Enfalt, A. C., Lundstrom, K., Lundkvist, L.,

Karisson, A., and Hansson, I. 1994. Technological meat quality and the frequency of the RN- gene in purebred Swedish Hampshire and Yorkshire pigs. 40th IcoMST.

Knipe, C. L., Olson, D. G., and Rust, R. E. 1988. Effects of inorganic phosphates and sodium hydroxide on the cooked cured color, pH and emulsion stability of reduced-sodium and conventional meat emulsions. J. Food Science. 53: 1305—1308.

Le Roy, P., Juin, H., Caritez, J. C., Billon, Y., Lagant, H., Elsen, J. M., and Sellier, P. 1996. Effet du genotype RN sur les qualites sensorielles de la viande de porc. Jounees Rech. Porcine en France. 28: 53—56.

Lundstrom, K., Andersson, A., and Hansson, I. 1996. Effect of the RN- gene on technological and sensory meat quality in crossbred pigs with Hampshire as terminal sire. Meat Science. 42: 145—153.

Moiseev, I. V. and Cornforth, D. P. 1997. Sodium hydroxide and sodium tripolyphosphate effects on bind strength and sensory characteristics of restructured beef rolls. Meat Science. 45(1): 53—60.

Acknowledgments

This project was made possible by support from:

National Pork Producers Council
Ohio Pork Producers Council
Hampshire Swine Registry
National Swine Registry

¹ For more information, contact at: The Ohio State University 122B Animal Science, 2029 Fyffe Road, Columbus, OH 43210, (614) 292-4877, Fax (614) 292-3513; email:knipe.1@osu.edu