Impact of the Hydrodyne Process on Tenderness, Microbial Load, and Sensory Characteristics of Pork Longissimus Muscle 1,2

Transcription

1 Impact of the Hydrodyne Process on Tenderness, Microbial Load, and Sensory Characteristics of Pork Longissimus Muscle 1,2 S. Moeller*,3, D. Wulf*, D. Meeker*, M. Ndife*, N. Sundararajan*, and M. B. Solomon *Department of Animal Sciences, The Ohio State University Columbus and USDA, ARS, Meat Science Lab, Beltsville, MD ABSTRACT: Paired, boneless pork loin muscles and 83 C, respectively. No differences between H and were obtained from 76 market hogs to evaluate C were observed for color score, firmness score, tenderness, meat quality characteristics, sensory attributes, and microbial characterization of pork mus- samples. The H loins had lower marbling scores ( P < Minolta L*, Minolta Y, or drip loss on uncooked cle exposed to the Hydrodyne Process ( H ) compared.05) and intramuscular lipid ( P <.05) content than with untreated control ( C ) loin. A subset of 16 paired the paired C loin. Sensory evaluation on the randomly loins was randomly selected for use in sensory evaluation and microbial characterization. Loins were selected ( n = 16) paired loins samples showed no vacuum packaged and immersed in a heat shrink tank improvement in Warner-Bratzler shear force. Sensory prior to the H treatment. The Hydrodyne treatment panelists were also unable to detect a difference exposed the loin to the pressure equivalent of a between H and C loins for both initial and sustained 150-g explosive, generating a pressure distribution of tenderness scores. No differences between H and C approximately 703 kg/cm 2 at the surface of the loins were found for pork flavor, off-flavor, cohesiveness, or number of chews before swallowing, but H samples. Meat quality assessments taken following treatment included subjective color, firmness/wetness, loins had a significantly lower juiciness score and marbling scores (1 to 5 scale), Minolta reflectance and more cooking loss than C loins. Microbial analysis color readings, drip loss, and lipid content. The P- results showed no differences in coliform bacteria value for statistical significance for main effects and counts, aerobic plate counts, and no detectable levels interactions was set at <.05 in all analyses. Administration of H resulted in a 17% improvement in of Escherichia coli bacteria in any loins. The findings Warner-Bratzler shear force (2.69 vs 3.24 kg), with support the ability of the Hydrodyne procedure to the shear force similar at two end-point cooking times improve tenderness without impacting other muscle (11 and 16 min) corresponding to approximately 75 quality attributes of pork. Key Words: Pigmeat, Tenderness, Tenderizing 1999 American Society of Animal Science. All rights reserved. J. Anim. Sci : Introduction Payment under carcass merit systems in the United States swine industry has resulted in dramatic changes in the lean composition of swine produced. Changes in genetic background, feeding programs, and management strategies have all played a role in 1 Research support provided by the National Pork Producers Council. 2 Salaries and research support provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University. 3 To whom correspondence should be addressed. Present address: 122 Animal Science Building, 2029 Fyffe Road, Columbus, Ohio Received July 10, Accepted January 4, producing leaner, more efficient swine, but the rapid change in lean content has also resulted in undesirable changes in muscle quality traits, including reduced intramuscular fat, lower ultimate ph, and reduced water-holding capacity. Differences in muscle quality traits impact the acceptability of pork products in trained sensory panels and consumer preference trials (NPPC, 1995). Because tenderness is an important criteria in determining consumer acceptability of pork, exploration of emerging technologies to improve tenderness of pork should be addressed. The Hydrodyne Process, a new procedure designed to improve tenderness of meat, was reported by Solomon and Long (1995). The process uses a small amount of explosive in water to generate a shock wave that changes the structural properties of objects exposed to the process. The shock wave occurs in fractions of a millisecond and passes through objects 2119

2 2120 MOELLER ET immersed in water that are an acoustic match with water, like meat. Research has indicated an increase in tenderness of pork, beef, and lamb muscles exposed to the Hydrodyne treatment (Solomon et al., 1995, 1997a,b). The technology 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. The objectives of this study were 1) to determine the impact of the Hydrodyne process on tenderness, color, drip loss, and cooking loss of pork longissimus muscle, 2) to determine the effect of the Hydrodyne process on sensory attributes of the longissimus muscle, and 3) to determine the effect of the Hydrodyne process on microbial load of pork. Materials and Methods Animals. Pork muscle used in this study originated from 76 crossbred market hogs. Hogs were processed at Hormel Foods (Austin, MN), where carcass data were collected and paired loins (longissimus muscle, 10th rib through the last lumbar vertebra on the sirloin end) from each pig were deboned, trimmed to 3 mm of external fat, vacuum packaged in an oxygenimpermeable bag, and frozen within 48 h postmortem. Hydrodyne Process. Frozen, paired loins were transported to USDA, Agricultural Research Service, Meat Science Research Lab, Beltsville, MD. One loin from each hog was assigned to either a Hydrodyne ( H) or control ( C) treatment. All loins were thawed under refrigeration prior to packaging and administration of the H process. Loin samples were vacuum packaged (three to four loins per bag) and dipped in a heat shrink tank. A subset of H and C (n = 16 pairs) were randomly selected to be used for sensory evaluation and microbial characterization. The subset loins were individually packaged and encapsulated twice, first in a vacuum package bag followed by immersion in a heat shrink tank and then in a polymer isoprene (rubber) bag. Packaged meat samples, which were stored in 208-L containers containing ice packs, were transported to the Hydrodyne processing facility in Buena Vista, VA. Three bags containing meat samples were treated at one time in the Hydrodyne tank (1,060-L capacity and 122-cm diameter) filled with water. The explosive used was composed of a liquid (nitromethane) and a solid (ammonium nitrate). One hundred fifty grams of explosive were submerged in the water at a distance of 36 cm from the bottom wall of the tank, yielding an approximate front of 703 kg/ cm 2. A force of 704 kg/cm 2 has been shown to result in instantaneous and significant improvement in tenderness of beef (Solomon et al., 1997). Refrigerated H and C samples were transported to The Ohio State University Meat Research Laboratory for muscle quality, microbial characterization, and taste panel experimentation. AL. Muscle Quality Procedures. Upon arrival at The Ohio State University Meat Research Laboratory, the H and C loins were evaluated for meat quality. A 2.5-cm (length) section was cut from each loin at a location corresponding to approximately ribs 10 to 11 and allowed to bloom for 10 min prior to assessment of meat quality scores. Subjective scores for color, marbling, and firmness/wetness were taken on the cut surface following the procedures described by NPPC (1991). Color, marbling, and firmness/wetness were scored independently by two experienced meat scientists using a 5-point scale (1 = pale, soft, devoid of marbling; 5 = dark, very firm, and dry and moderately abundant marbling or greater) and averaged for analysis. Loin muscle reflectance and color were objectively measured (Y, L*, a*, and b* values) by using a CR-310 Minolta Chromometer (Minolta Camera Company, Ltd., Osaka, Japan). To measure drip loss, each chop was then weighed, suspended by a single fishhook, and refrigerated at 4 C in plastic bags. The samples were reweighed after 24 h to measure drip loss. For assessment of lipid content, a 2.5-cm section corresponding to approximately ribs 11 to 12 was homogenized using the procedures outlined by Bligh and Dyer (1959). Microbial Characterization. To evaluate the potential impact of the H treatment on bacterial population, H and C loins were evaluated for microbial load. The subset of 16 pairs of H and C loins was sampled for microbial analysis. Three 2.5-cm-diameter, 2-mmthick fat samples were collected from the dorsal surface of each loin (both ends and the middle) by aseptic techniques including flame sterilization of all equipment before and between sample collection. Samples were packaged and shipped to a commercial analytical laboratory (Silliker Laboratories, Columbus, OH) where they were evaluated for coliform (most probable number per gram [mpn/g]) (AOAC, 1995), E. coli bacteria (mpn/g) (Powers and Latt, 1977; AOAC, 1995), and aerobic plate counts (25 C, 3 d) (APHA, 1992). Shear Force and Sensory Evaluation. Two loin samples, taken near the 12th through the 14th ribs, from each H and C loin (total four samples per hog) were cut to a standard thickness of 2.5 cm. Paired H and C loin samples were cooked in a time-calibrated Lincoln impingement oven (Lincoln Food Service, Ft. Wayne, IN) at 190 C for 11 min and 16 min, which corresponded to desired end-point temperatures of 71 C (AMSA, 1995) and 81 C (representing overcooking), respectively. Samples were weighed before and after cooking to measure cooking loss and cooked internal temperature was recorded with a handheld thermocouple instrument. Cooked loin samples were cooled 1 to 4 h to 21 C, and six 1.3-cm diameter cores were removed parallel to the muscle fiber orientation. Shear force was measured using a Warner-Bratzler shear device. The subset of paired loin samples from 16 hogs (32 total loins) used for microbial characterization were also used to evaluate sensory attributes by a trained

3 TENDERNESS EVALUATION OF PORK MUSCLE 2121 sensory panel (AMSA, 1995). The taste panel consisted of eight individuals who were randomly assigned to taste the loin samples from two hogs. In the experimental design, four individual tasting sessions were held, and each panelist tasted H and C loin samples from two specific hogs in replicate. In total 128 observations (16 hogs 2 treatment loins 2 panelists 2 replications/hog) were recorded and used in the analysis. The four observations per hog consisted of two replicates of H and C loins. Sensory attributes evaluated included pork flavor, off-flavor, initial tenderness, sustained tenderness, juiciness, cohesiveness, and the chewiness of the sample. Statistical Analysis. All data were analyzed using mixed model procedures (SAS, 1994) with hog considered to be a random effect in the testing of differences among treatments ( H or C). Shear force and cooking loss data were analyzed using a second fixed effect of cooking time (11 or 16 min) 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 log 10 scale and analyzed using a model with random effects of hog in the analysis of treatment differences. Two- and three-factor interactions were included in initial models and removed when not significant ( P >.05). Model effects were considered significant for probability levels at <.05. Meat Quality Results and Discussion Traits Table 1 summarizes the results of muscle quality traits measured on the H and C loin muscle samples. No significant differences were observed between the H- and C-treated loins for visual assessments of color or machine-measured light reflectance Y and color ( L* and b*). Significant differences were found for a*, indicating that H-treated loins were less red on the red-green chromaticity coordinate than C loins. Loins treated with the H protocol had significantly lower marbling scores and chemically derived intramuscular fat (lipid) content than C loins from the same hog. The relatively small (.21%) difference in chemical lipid content is not easily explained from a biological or procedural standpoint, and it is an area that needs to be investigated in the future. The results do not indicate any effects on commonly measured muscle quality traits of pork, including color, firmness, and water-holding capacity when treated with the H protocol. The observed drip loss values were extremely low for both H (.73%) and C (.81%) and may be a result of the freezing and thawing that took place between collection, treatment, and measurement locations. Tenderness and Cooking Loss The effect of H on tenderness and cooking loss of the loin muscle is described in Table 2. Loins treated with the H had shear force values of 2.69 kg compared with 3.24 kg for the control, representing a 17% improvement in tenderness. Tenderness differences between H and C were consistent across cooking time (11 or 16 min). The H-treated loins were 15 and 18% more tender than controls at both 11 and 16 min (approximately 75 and 83 C, respectively). The H and C treatments had similar cooking losses in this experiment, and the loss is similar to the findings reported by O Rourke et al. (1998). Time of cooking, as expected, had a significant effect on cooking loss, with loins cooked for 16 min having 22.5% more cooking loss than loins cooked for 11 min, but time had no 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 Trait a N Control Hydrodyne Significance b Color ± ±.04 N.S. Marbling ± ±.04 * Firmness ± ±.04 N.S. Intramuscular fat % ± ±.06 * Y ± ±.24 N.S. L* ± ±.24 N.S. a* ± ±.09 ** b* ± ±.06 N.S. Drip loss % ± ±.11 N.S. a Color, 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; Y, 0 = no reflectance, 100 = total reflectance; L, 0 = black and 100 = white; a*, red/green hue, higher number = more red; b*, blue/yellow, higher number = more yellow; drip loss %, percent exudate from uncooked sample. b Significance level: N.S. = no significant difference; *P <.05; **P <.01.

4 2122 MOELLER ET 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 AL. % differ- Trait a N Control Hydrodyne Sig b ence Cooking loss, % Overall ± ±.28 N.S. 11 min 74.6 C (3.2) c ± ±.37 N.S. 16 min 83.4 C (3.1) ± ±.37 N.S. Warner-Bratzler shear, kg Overall ± ±.04 *** min 74.6 C (3.2) ± ±.05 *** min 83.4 C (3.1) ± ±.05 *** 18.8 a Cooking loss ( % ) = ((raw weight cooked weight)/raw weight) * 100; Warner-Bratzler shear force = kilograms of pressure required to shear a standard core of muscle. b Statistical significance level for means within a row: N.S., no significant difference. ***P <.001. c Standard deviation for cooking temperature. effect on Warner-Bratzler shear. Data analysis results also showed no significant interaction existed between treatments (H or C) and cooking time (11 or 16 min), indicating that the impact of H on tenderness was consistent across cooking times. The loins used in this study were frozen and thawed prior to H treatment, and the effect of H on fresh, never-frozen pork cannot be determined from this study. Other researchers have demonstrated that H treatment of frozen beef muscles resulted in a higher shear value and a smaller percentage improvement in tenderness compared with fresh muscle samples (Solomon et al., 1997), but the tenderness improvement of frozen product was still significant compared with an untreated control. The impact of freezing and thawing on the percentage improvement in tenderness cannot be answered in this study. Microbial Characterization The results of the microbial tests conducted on the paired loin samples ( n = 16) used in the sensory evaluation are presented in Table 3. Plate counts were converted to a logarithmic scale in the analysis. Plate counts were generally low for the tests performed, and no significant differences between H and C treatments were observed for coliform bacteria or aerobic plate count. No detectable levels of E. coli were observed in any samples. Sensory Evaluation Sensory evaluation scores are presented in Table 4. The H loins were found to have significantly lower juiciness scores (4.87 vs 5.20 units) and had a higher percent cooking loss than C loins. The correlation between cooking loss and juiciness was.24, indicating that as cooking loss went up juiciness scores went down. 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 (2.77 vs 2.74 kg), and this may explain the failure of the trained panel to detect sensory differences in initial and sustained tenderness of the loins. Differences in pork flavor and off-flavor approached significance ( P <.10), with the H-treated loins having slightly less off-flavor and higher pork flavor scores than the control loin samples. Sensory evaluation results suggest that the Table 3. Least squares means for microbial characteristics of Hydrodyne-treated and control pork loins Trait a N Control Hydrodyne Significance b Coliform bacteria count ± ±.26 N.S. E. coli bacteria count 16 N.D. c N.D. Aerobic plate count ± ±.17 N.S. a Coliform bacteria count: level indicated is log 10 of the described plate count; E. coli bacteria, not detectable; aerobic plate count, (25 C for 3 d), level indicated is log 10 of the described plate count. b Statistical significance level: N.S. = no significant difference. c N.D. = not detectable.

5 TENDERNESS EVALUATION OF PORK MUSCLE 2123 Table 4. Least squares means and standard errors for sensory panel and analytical attributes of Hydrodyne-treated and control loin samples Trait a N Control Hydrodyne Sig b Sensory Panel Pork flavor ± ±.18 N.S. Off-flavor ± ±.05 N.S. Initial tenderness ± ±.15 N.S. Sustained tenderness ± ±.16 N.S. Juiciness ± ±.17 * Cohesiveness ± ±.15 N.S. Number of Chews ± ±.31 N.S. Analytical Measures Warner-Bratzler shear ± ±.04 N.S. Cooking loss ± ±.43 * a Pork flavor, 1 10 scale: 1 = none and 10 = intense; off-flavor, 1 10 scale: 1 = none and 10 = intense; initial tenderness, 1 10 scale: 1 = very tough and 10 = very tender; sustained tenderness, 1 10 scale: 1 = very tough and 10 = very tender; 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; Warner-Bratzler shear = kilograms of force to shear the sample; cookloss = moisture loss during cooking. b Statistical Significance Level: N.S. = no significant difference between H and C loins; *P <.05. H protocol had no major effect on sensory characteristics other than juiciness. Conclusions about the effect of H treatment upon sensory evaluation of tenderness cannot 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, for which a 17% improvement in Warner-Bratzler shear force was observed. A possible explanation for the lack of tenderness improvement in the subset of 16 loins is that these 16 loins were individually placed in a second bag during H treatment, whereas the other 60 loins were not. However, in previous experiments (Solomon et al., 1997), a double bag system was used, and differences in tenderness were observed for H- treated meat. Other explanations may be random chance due to sampling (although standard errors were not large), or the small number of observations. Implications The Hydrodyne protocol improved shear force values of pork longissimus muscle by 17% without an observed change in subjective or objective meat quality measures, sensory characteristics, or aerobic and coliform bacterial populations. However, the failure to detect Hydrodyne treatment differences and sensory differences in a subset of loins warrants further investigation into the effect of packaging on treatment response. The reduced lipid content and marbling score for H loins needs to be further investigated to verify, explain, or refute the findings of this study. 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. Literature Cited AMSA Research guidelines for cookery, sensory evaluation and instrumental tenderness measurements of fresh meat. American Meat Science Assoc., Chicago, IL. AOAC FDA bacteriological analytical manual. Association of Official Analytical Chemists, Arlington, VA. APHA Compendium of methods for the microbiological examination of foods. American Public Health Association, Washington, DC. Bligh, E. G., and W. J. Dyer A rapid method of total lipid extraction and purification. Can. J. Biochem. Physiol. 37: NPPC Procedures to Evaluate Market Hogs (3rd Ed.). National Pork Producers Council, Des Moines, IA. NPPC Genetic evaluation: Terminal line program results. National Pork Producers Council, Des Moines, IA. O Rourke, B. M., C. R. Calkins, R. T. Rosario, J. S. Eastridge, M. B. Solomon, and J. B. Long Univ. Nebraska Cooperative Extension EC A, Lincoln. Powers, E. M., and T. G. Latt Simplified 48 hour IMViC test: An agar plate method. Appl. Environ. Microbiol. 34: SAS SAS/STAT Software: Changes and Enhancements. SAS Inst. Inc., Cary, NC. Solomon, M. B., and J. B. Long The Hydrodyne process for tenderizing meat. J. Anim. Sci. 73(Suppl.1):159(Abstr.). Solomon, M. B., J. B. Long, J. S. Eastridge, and C. E. Carpenter Tenderizing callipyge lamb with the Hydrodyne process. 41st Int. Cong. of Meat Sci. and Technol., San Antonio, TX. pp Solomon, M. B., J. S. Eastridge, and J. B. Long. 1997a. Shock waves tenderize pork. National Hog Farmer 42(13):18. Solomon, M. B., J. B. Long, and J. S. Eastridge. 1997b. The Hydrodyne: A new process to improve beef tenderness. J. Anim. Sci 75: