S. Moeller 1, D. Wulf, D. Meeker, M. Ndife, and N. Sundararajan
The Ohio State University Department of Animal Sciences
Paired boneless pork loins were obtained from 76 market hogs to evaluate the tenderness, meat quality characteristics, sensory attributes, and microbial content of pork loins exposed to the Hydrodyne® Process (HP). The Hydrodyne® Process uses a small explosion to generate a shock wave in water. The resulting shock wave, when administered to meat with similar acoustic properties as water, passes through the meat and creates substantial damage to muscle structure, resulting in improved tenderness. Research on the impact of this technology on pork is limited, and this study was designed to evaluate the impact of the Hydrodyne® Process on tenderness in pork.
Administration of the Hydrodyne® Process resulted in a 17% improvement in tenderness over the nontreated control (C) loin when comparing Warner-Bratzler shear-force values. The effect of the HP on tenderness was consistent when cooked to two end-point temperatures, and no differences in cooking loss were observed when comparing HP and C loins at both end-point temperatures. No differences between HP and C were observed for color score, firmness score, Hunter L color, Minolta reflectance, or drip loss on uncooked samples. HP loins were found to have significantly lower marbling scores and intra-muscular fat contents than the paired C loin from the same pig. A subset of 16 paired loins was randomly selected and tested for sensory attributes. The loin samples used in the taste panel did not exhibit a significant improvement in Warner-Bratzler shear tenderness as a result of the hydrodyne treatment, which is in contrast to the improvement observed in the analysis of the entire set of loins. Sensory panelists were also unable to differentiate treatment differences between HP and C loins for both initial or sustained tenderness scores. Sensory evaluation on the subset of 16 paired loins also showed no differences in HP or C loins for pork flavor, off-flavor, cohesiveness, or number of chews prior to swallowing, but HP loins had a significantly higher juiciness score and more cooking loss than C loins. Microbial analysis on the subset of 16 loins showed no differences in coliform bacteria counts or aerobic plate counts for HP or C loins and no detectable levels of E. coli bacteria in either HP or C loins.
The development and implementation of carcass merit payment systems in the U.S. swine industry has resulted in dramatic changes in the lean composition of the swine produced over the last five to 10 years. Changes in genetics, feeding programs, and management strategies have all played a role in producing leaner, more efficient swine. Unfortunately, the demand for increased lean has resulted in undesirable changes in muscle quality traits including reduced intra-muscular fat content, lower ultimate pH, and poor water-holding capacity. Changes in these and other muscle quality traits have been shown to be related to the tenderness and overall acceptability of pork products when compared by trained sensory panels and in consumer preference trials (NPPC 1995, Terminal Line Program Results). Because tenderness is an important criteria in determining consumer acceptability of pork, exploration of new technologies to improve tenderness of pork should be addressed.
The Hydrodyne® Process, a relatively new procedure designed to improve tenderness of meat, was reported by Solomon and Long, 1995. They reported the Hydrodyne® Process uses a small amount of explosive to generate a shock wave in water, creating a pressure front of 10,000 psi at the point of contact with an object. The shock wave occurs in fractions of a millisecond and passes through objects in the water that are acoustic matches with water. Since meat is a good acoustic match with water, the HP process has an effect on meat. As the shock wave passes through the meat, a compression occurs in advance of the wave front and negative pressure occurs after its passage. If the shock pressure is large enough, a tenderizing effect (Solomon et al., 1995) brought about by destruction of muscle structure results. The Hydrodyne® Process has been shown to significantly increase tenderness in beef (Solomon and Long, 1995) and sheep (Solomon et al., 1995) muscles and has been viewed as a revolutionary approach to improve meat tenderness requiring less space, energy, and labor costs (Solomon et al., 1995) than alternative approaches. Research efforts to characterize the impact of the Hydrodyne® Process on pork muscle are important as the U.S. industry attempts to improve the eating quality and consumer acceptability of pork and seeks to increase both domestic and foreign demand for U.S. pork products.
The purposes of this study were to:
Animals
Pork muscle used in this study originated from 76 market animals, randomly selected from the 1996 Iowa State University, Livestock Producers Assistance Program SEW Test conducted at the Northeast Iowa Swine Improvement Association swine-testing station in New Hampton, Iowa. Following slaughter and carcass data collection at Hormel Foods™, Austin, Minnesota, paired loins (longissimus muscle, 10th rib through sirloin end) from each pig were de-boned, trimmed of external fat, vacuum packaged in an oxygen impermeable bag, and frozen.
Hydrodyne® Process
Frozen loins were transported to the USDA Beltsville Agricultural Experiment Station where the Hydrodyne® Process was conducted. One loin from each pig was assigned to either a control (C) (n=76) or HP (n=76) treatment protocol. All loins were thawed prior to administration of the HP. The HP process was conducted using standard protocols outlined by Solomon and Long (1995). The HP was conducted using groups of individually vacuum-packaged loins placed into a single, large rubber bag. A subset (n =16 paired loins) of the C and HP loins was randomly selected to be used for sensory evaluation and microbial characterization. Loins designated for sensory and microbial evaluation were individually treated in the HP protocol to avoid any possible cross contamination of samples.
Muscle Quality Procedures
Upon completion of the HP procedure, all loins (n = 152) were refrozen and transported to The Ohio State University. Upon arrival at Ohio State, loins were thawed and samples collected for further testing. Muscle-quality tests conducted included subjective, visual assessment of color, marbling, and firmness; objective, Minolta reflectance and color scores; drip-loss estimation of uncooked samples; and total lipid extraction.
Tenderness Evaluation
Two loin samples from each C and HP-treated loin (total of four samples per pig) were cut to a standard thickness of one inch. One loin sample from each treatment (C or HP) was assigned to one of two designated cooking times (11 or 16 minutes) to determine the effect of internal temperature on Warner-Bratzler shear-force values. All loin samples were cooked in an impingement oven set at 375°F, with the samples placed on an adjustable speed conveyor to standardize cooking time. Loin samples were weighed prior to and following cooking to determine cooking loss. Internal temperature on the cooked loin samples was recorded for use in data analysis.
Warner-Bratzler shear-force values were recorded on cooked loin samples to determine the effect of treatment and cooking time on the tenderness of the loin samples. Shear-force values were collected from six individual core samples per cooked loin, with the average of the six values used in data analysis for measurement of tenderness by the Warner-Bratzler shear method.
Sensory Evaluation
The subset of paired loin samples from 16 pigs (n = 32 total loins) was used to evaluate sensory attributes in a blind taste test by a trained sensory panel. The taste panel consisted of eight individuals who were randomly assigned to taste the loin samples from two pigs. In the experimental design, four individual tasting sessions were held, and each panelist tasted C and HP loin samples from two specific pigs in replicate. In total, 128 observations (16 pigs *4 samples/pig * 2 replications/pig) were recorded and used in the analysis. The four observations per pig consisted of two replicates of C and HP loins. Sensory traits evaluated included pork flavor, off-flavor, initial tenderness, sustained tenderness, juiciness, cohesiveness, and the number of chews necessary to consume the sample.
Microbial Characterization
Paired loin samples representing the subset of 16 pigs (n = 32 total) were collected using sterilized equipment, bagged, and sent to an analytical lab for testing. Samples were tested for coliform bacteria (mpn/g), E. coli bacteria (mpn/g), and aerobic plate counts (25ºC, three days). Microbial counts were converted to logarithmic function for analysis.
The data collected in the study were analyzed using statistical procedures outlined in SAS (1994). All data were analyzed using mixed model procedures with pig considered to be a random effect in the testing of differences among treatments (C or HP). Shear-force and cooking-loss data were analyzed using a second fixed effect of cooking time (11 or 16 minutes) and the interaction of treatment and cooking time. Sensory evaluation data were analyzed using panelist as a second random variable when testing treatment differences. The microbial characterization data were converted to a log10 scale and analyzed using a model with random effects of pig in the analysis of treatment differences.
Table 1 summarizes the results of muscle quality traits measured on the HP and C loin muscle samples. No significant differences were observed between the HP- and C-treated loins for visual assessments by color score or machine-measured light reflectance (Minolta) and color (Hunter L and Hunter b*), indicating that the HP process did not affect the overall appearance of pork loins. Significant differences were found for Hunter a*, indicating that HP-treated loins had reflectance values that were less red than C loins. Loins treated with the HP protocol also had significantly lower marbling scores and intra-muscular fat content than C loins from the same pig. This finding is not easily explained from a biological or procedural standpoint and is an area that needs to be investigated in the future. The results of this study indicate no negative effects on commonly measured muscle- quality traits of pork, including color, firmness, and water-holding capacity when treated by the HP protocol. The observed drip loss values were extremely low for both C (0.81%) and HP (0.73%) loins.
Table 1. Least Squares Means and Standard Errors for Longissimus (Loin) Muscle Quality Traits for Hydrodyne® Treated and Control Samples of Loin from the Same Pig. |
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|---|---|---|---|---|
| Treatment | ||||
| Traita | N | Control | Hydrodyne® | Significanceb |
| Color | 76 | 2.84 ± 0.04 | 2.90 ± 0.04 | NS |
| Marbling | 76 | 763.02 ± 0.04 | 2.86 ± 0.04 | + |
| Firmness | 76 | 2.89 ± 0.04 | 2.74 ± 0.04 | NS |
| Intra-muscular fat, % | 69 | 2.69 ± 0.06 | 2.48 ± 0.06 | * |
| Minolta reflectance | 76 | 25.91 ± 0.24 | 26.00 ± 0.24 | NS |
| Hunter L color | 76 | 50.79 ± 0.23 | 50.88 ± 0.24 | NS |
| Hunter a* | 76 | 14.40 ± 0.09 | 14.85 ± 0.09 | ** |
| Hunter b* | 76 | 7.11 ± 0.06 | 7.15 ± 0.06 | NS |
| Drip loss, % | 76 | 0.81 ± 0.11 | 0.73 ± 0.11 | NS |
|
aColor, 1—5 scale, 1 = pale and 5 = dark; Marbling, 1—5 scale, 1 = devoid and 5 = excess; Firmness, 1—5 scale, 1 = soft and wet and 5 = firm and dry; Minolta reflectance, 0 = no reflectance, 100 = total reflectance; Hunter L color, 0 = black and 100 = white; Hunter a*, red/green hue, higher number = more red; Hunter b*, blue/yellow, higher number = more yellow; Drip loss = percentage of exudate from noncooked sample. bSignificance level: NS = no significant difference between Hydrodyne® and control: + P < 0.10, * P < 0.05, ** P < 0.01. |
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The effect of HP on tenderness and cooking loss of the loin muscle is described in Table 2. Loins treated by the HP had shear-force values of 2.69 kg compared to 3.24 kg for the control, resulting in a 17% improvement in tenderness. Tenderness differences between HP and C were consistent across cooking time (11 or 16 min.) with the HP- treated loins 15% and 18% more tender than controls at 11 and 16 minutes, respectively. The effect of HP on cooking loss was not significant in the study, indicating that cooking-loss differences were not observed when comparing HP and C loins. Time of cooking, as expected, had a significant effect on cooking loss with loins cooked for 16 minutes having 22.5% more cooking loss for both HP and C loins cooked for 11 minutes. Data analysis results also show no significant interaction exists between Treatment (C or HP) and Cooking Time (11 or 16 min.), which means the impact of HP on tenderness was consistent across cooking times. It should be noted that the loins utilized in the study were frozen and thawed prior to HP treatment and collection of shear-force data, which is different than other experiments evaluating HP on other species. The impact of the HP protocol on fresh, never frozen, pork cannot be determined in this study. However, the results on frozen pork indicate that the HP protocol is an effective method of improving tenderness as measured by Warner-Bratzler shear force, an objective method of measuring meat tenderness.
Table 2. Least Squares Means and Standard Errors of Longissimus (loin) Muscle Tenderness and Cooking Loss Traits for Hydrodyne® Treated and Control Samples of Loin Cooked to Two Endpoint Times. |
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|---|---|---|---|---|---|
| Treatment | |||||
| Traita | N | Control | Hydrodyne® | Sigb | % Difference |
| Warner-Bratzler shear | |||||
| Overall | 152 | 3.24 ± 0.04 | 2.69 ± 0.04 | *** | 17.0 |
| 11 minute cooking | 76 | 3.19 ± 0.05 | 2.71 ± 0.05 | *** | 15.0 |
| 16 minute cooking | 76 | 3.30 ± 0.05 | 2.68 ± 0.05 | *** | 18.8 |
| Cooking Time | |||||
| 11 minutes | 16 minutes | Sigb | % Difference | ||
| Cooking Loss, % | |||||
| Overall | 152 | 26.39 ± 0.27 | 34.04 ± 0.27 | *** | 22.5 |
| Control | 76 | 26.51 ± 0.37 | 34.22 ± 0.37 | *** | 22.5 |
| Hydrodyne | 76 | 26.25 ± 0.37 | 33.85 ± 0.37 | *** | 22.5 |
|
aWarner-Bratzler shear force = kg of pressure
required to shear a standard core of muscle; bStatistical significance level for means within a row: *** P < 0.001. |
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Sensory evaluation scores are presented in Table 3. Significant differences were found between HP and C treatments for juiciness, with Hydrodyne loins having lower juiciness scores (4.87 vs. 5.20 units) than the Control. However, no differences were reported for initial tenderness, sustained tenderness, cohesiveness, or the number of chews necessary to consume the sample. Warner-Bratzler shear-force values on the subset of 16 paired loins were not different, which explains the failure to detect sensory differences in initial and sustained tenderness of the HP and C loins. Differences in pork-flavor and off-flavor approached significance (P < 0.10) with the HP-treated loins having slightly less off-flavor and higher pork-flavor scores than the control loin samples. The sensory evaluation findings suggest that the HP protocol had no major effect on sensory characteristics other than juiciness. Conclusions on the effect of HP treatment upon sensory evaluation of tenderness can not be clearly made because the subset of loins designated for sensory evaluation did not respond in the same manner as the entire set of 76 paired loins where a 17% improvement in Warner-Bratzler shear force was observed. The reason a random set of 16 loins, chosen from a set of 76 loins, did not show a treatment effect may be due to chance and a small number of observations.
Table 3. Least Squares Means and Standard Errors for Sensory Panel Attributes of Hydrodyne® Treated and Control Loin Samples. |
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|---|---|---|---|---|
| Treatment | ||||
| Traita | N | Control | Hydrodyne® | Significanceb |
| Pork-flavor | 16 | 5.61 ± 0.18 | 6.06 ± 0.18 | + |
| Off-flavor | 16 | 1.18 ± 0.05 | 1.04 ± 0.05 | + |
| Initial tenderness | 16 | 5.73 ± 0.15 | 5.79 ± 0.15 | NS |
| Sustained tenderness | 16 | 6.17 ± 0.16 | 5.96 ± 0.16 | NS |
| Warner-Bratzler Shear | 16 | 2.77 ± 0.05 | 2.74 ± 0.04 | NS |
| Cook loss, % | 16 | 29.69 ± 0.59 | 31.65 ± 0.43 | * |
| Juiciness | 16 | 5.20 ± 0.17 | 4.87 ± 0.17 | * |
| Cohesiveness | 16 | 5.23 ± 0.15 | 5.14 ± 0.15 | NS |
| Number of Chews | 16 | 17.59 ± 0.31 | 17.42 ± 0.31 | NS |
|
aPork-flavor, 1-10 scale, 1 = none & 10 = intense; Off-flavor, 1—10 scale, 1 = none and 10 = intense; Initial tenderness, 1-10 scale, 1 = very tough & 10 = very tender; Sustained tenderness, 1—10 scale, 1 = very tough and 10 = very tender; Warner-Bratzler shear = kg of force to shear the sample, Cook loss = moisture loss during cooking, Juiciness, 1-10 scale, 1 = very dry and 10 = very juicy; Cohesiveness, 1—10 scale, 1 = very chewy and 10 = non-chewy ; Number of chews = number of chews necessary to completely eat the sample. bStatistical significance level: NS = no significant difference between HP and C loins, + P < 0.10, * P < 0.05. |
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The results of the microbial tests conducted on the paired loin samples (n = 16 pigs) used in the sensory evaluation are presented in Table 4. Plate counts were converted to a logarithmic scale in the analysis. No significant differences between C and HP treatments were observed for coliform bacteria or aerobic plate count. No detectable levels of E. coli were observed in any samples.
Table 4. Least Squares Means for Microbial Characteristics of Hydrodyne® Treated and Control Pork Loins. |
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|---|---|---|---|---|
| Treatment | ||||
| Traita | N | Control | Hydrodyne® | Significanceb |
| Coliform Bacteria Count | 16 | 0.80 ± 0.26 | 1.40 ± 0.26 | NS |
| E. coli Bacteria Count | 16 | ND | ND | |
| Aerobic Plate Count | 16 | 4.38 ± 0.17 | 4.50 ± 0.17 | NS |
|
aColiform Bacteria Count: level indicated is log10 the described plate count; E. coli Bacteria, Not detectable; Aerobic Plate Count, (25ºC for 3 days), level indicated is log10 the described plate count. bStatistical significance level: NS = no significant difference. |
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The results of the study indicate that use of the HP protocol is an effective method of improving tenderness of pork-loin muscle when measured by Warner-Bratzler shear force. However, the improvement in Warner-Bratzler shear force (17%) was not detectable in the subset of loins utilized for trained sensory evaluation, resulting in no observable differences in taste panel scores for initial or sustained tenderness of pork loin.
The observed improvement in Warner-Bratzler shear force resulting from the HP treatment was determined to have no detrimental effects on visual or objective measures of color, loin water-holding capacity measured by visual firmness/wetness scores, drip loss and cooking loss, or microbial growth and contamination. Sensory evaluation showed HP loins were less juicy than C loins, but no differences were found for pork flavor, off-flavor, initial or sustained tenderness, or cohesiveness of the loin. Pork loins treated with HP had significantly lower marbling scores and intra-muscular fat percentage than C loins and a higher cooking loss. This may explain why the sensory panel observed HP-treated loins were less juicy.
The overall importance of this research for the swine industry is that the Hydrodyne® Process, a process that requires little space, time, or energy, appears to improve tenderness of the pork loin without having major detrimental affects on muscle quality traits, sensory characteristics, or the safety and wholesomeness of pork. The observed differences in Warner-Bratzler shear force on the pork loin, one of the most tender cuts of pork, warrants further research on less tender cuts of pork and necessitates evaluation of the feasibility of using the Hydrodyne® Process in the packing industry. The use of the Hydrodyne® Process may be a tool that can be effectively utilized by the pork industry to improve overall tenderness of pork products produced, but it should not be considered a short cut to improving tenderness problems associated with major genes, genetic types, nutrition programs, or management styles that contribute to tough pork. Techniques such as the Hydrodyne® Process must be evaluated for their impact and place in the industry effort to improve pork products along the entire pork chain.
National Pork Producers Council. 1995. Genetic Evaluation: Terminal Line Program Results.
Solomon, M. B. and Long, J. B. 1995. The Hydrodyne® Process for tenderizing meat. J. Anim. Sci. Lopes, 73 (Suppl. 1): 159. Abstract.
Solomon, M. B., Long, J. B., Eastridge, J. S., and Carpenter, C. E. 1995. Tenderizing Callipyge lamb with the Hydrodyne® Process. 41st International Congress of Meat Science and Technology. 1995. San Antonio, Texas. pp 622—623.
1 For more information, contact at: The Ohio State University 122D Animal Science, 2029 Fyffe Road, Columbus, OH 43210, (614) 688-3686, Fax (614) 292-3513; email:moeller.29@osu.edu