Evaluation of the Further-Processing Quality of Ham Muscles from Hampshire Hogs
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In order to evaluate processing quality effects of the Napole gene and the feasibility of improving the functionality of pork from hogs possessing the Napole gene (RN-), paired hams from 40 hogs (selected from a Hampshire progeny test conducted at the Western Illinois Test Station) were obtained. Two processing scenarios were applied to the paired hams, one of which was intended to improve the functional quality of pork over a conventional processing method. The addition of 0.125% sodium hydroxide to a conventional injection solution increased cooking yields, cooked pH, 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 benefitted the normal hams, maintaining an advantage to not having the gene.
The Napole Gene (RN-, rn+) 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 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, as an asset to the U.S. pork industry, should not be discarded. 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 the glycolytic potential (GP). Hogs with GP values of 180 and below are considered low GP, and hogs with GP values of 250 and above are considered high GP. Paired hams from 40 hogs were obtained for processing and analysis, depending upon the GP values and characterization of the hogs. Obtaining paired hams allowed a comparison of two processing scenarios, one of which is intended to improve the functional quality of this pork over a second, conventional processing method.
After surface fat and connective tissue were removed, each RN- and rn+ inside (top) ham muscle was ground through a 9.5 mm plate. The outside (bottom) muscle of each ham was vacuum packaged and frozen to compare the same treatments using frozen muscles.
After grinding, pH was determined. Nonmeat 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., 30% 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 solution: 28% water, 2% sodium chloride, 0.5% sodium tripolyphosphate/hexametaphosphate mixture, and 0.125% sodium hydroxide.
After mixing, samples of each ham/treatment were stuffed into fibrous casings, fully cooked or smoked to an internal temperature of 155öF, chilled, and vacuum packaged. After cooking/smoking, cooking yields, cured internal color (Hunter L, a, and b), pH, and texture (Instron) 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.
Results and Discussion
The addition of 0.125% sodium hydroxide significantly increased (P < 0.01) cooking yield, cooked product pH, and Minolta L values over the control product (Table 1). The cooking yield effect is expected, because of the increase in pH associated with the addition of sodium hydroxide.
|Table 1. Effects of Sodium Hydroxide (NaOH) Addition on Processed Ham
Muscle Yield, pH, Color, and Purge Accumulation.
|Control||0.125% NaOH||Significance Level|
|Cooking yield (%)||87.2||90.0||0.0001|
|Minolta L value||64.5||63.2||0.0005|
|Minolta a value||10.8||10.4||0.629|
|Minolta b value||8.1||7.8||0.094|
|Package purge (g)||6.85||7.2||0.405|
Color results were somewhat expected, particularly with the L values. L values were significantly reduced by the addition of sodium hydroxide (Table 1). From experience with PSE pork, increased pH (or reduction in PSE severity) typically reduces L values (or darkens product color).
There was no significant difference between the purge quantities accumulated after eight weeks of vacuum-packaged storage from sodium-hydroxide-treated ham slices compared to the control product. This was surprising, as the sodium-hydroxide-treated ham slices have additional moisture to lose during vacuum storage compared to the control ham slices.
Covariant analysis shows that one unit increase in GP value decreased cooking yield of all hams by 0.037% and that adding sodium hydroxide increased cooking yields by 2.8%. What this also means is that adding 0.125% sodium hydroxide to ham is equivalent to reducing the GP value by 75.4 units. This 75 GP range barely bridges the limits established for the high and low GP classifications. Considering the average GP values of the high (> 250) and low (< 180) GP hams (Table 2), adding sodium hydroxide to high GP hams is not equivalent to using low GP hams, in terms of cooking yield (Table 3).
|Table 2. Glycolytic Potential (GP) Value Means for 34 Sets of Hams
in High and Low GP Groups.
|Low GP group||143.2||110.7-164.4|
|High GP group||270.8||249.5-318.2|
|Table 3. Predicted Values for pH, Cooking Yield, and Minolta L Value.|
|Control||Low GP (143.2)||90.25||5.85||63.29|
|High GP (270.8)||85.52||5.69||61.16|
|NaOH treated||Low GP (143.2)||93.04||6.19||64.5|
|High GP (270.8)||88.31||6.03||62.4|
Similarly, a one unit increase in GP value decreased pH by 0.0013 units and adding sodium hydroxide increased pH by 0.34 units, meaning that adding sodium hydroxide to pork is equivalent to reducing the GP value by 261.5 units. In other words, sodium hydroxide addition had more effect on pH than did GP value, but GP value had more effect on cooking yield than did the addition of sodium hydroxide. The predicted cooking yields (Table 3) for sodium-hydroxide-treated high GP hams are lower than that of the control, low GP hams, while the predicted pH is higher for the sodium-hydroxide-treated high GP hams.
As GP values increased, L and a values decreased and b values increased. These data suggest one difference between high GP hogs and PSS hogs, their effect on pork color values. With PSE pork, L values increase (become lighter) with increase in severity of PSE. Minolta b values increase as both GP values increase and PSE severity increases.
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