Intramuscular fat content has little influence on the eating quality of fresh pork loin chops 1

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1 Published December 5, 2014 Intramuscular fat content has little influence on the eating quality of fresh pork loin chops 1 P. J. Rincker,* J. Killefer,* M. Ellis,* M. S. Brewer, and F. K. McKeith* 2 *Department of Animal Science, and Department of Food Science and Human Nutrition, University of Illinois, Urbana ABSTRACT: Fresh pork loins (n = 290) were selected from a commercial packing facility based on subjective marbling of the intact loin and 24-h ph to determine the influence of marbling on sensory attributes. The study was designed using pigs from a similar genetic background, raised in similar production facilities, and slaughtered on a single kill day to minimize the effects of genetics, management, environment, and slaughter day. Loins were vacuum-packaged, transported to the University of Illinois Meat Science Laboratory, and aged for 7 d, after which a chop was removed from the area of the tenth rib for proximate analysis. Quality measurements, including National Pork Producers Council color, marbling, and firmness, ultimate ph, Minolta L*, a*, and b*, and drip loss, were determined after aging. After the proximate composition was completed, 150 loins were selected to provide a continuous and uniform distribution of extractable lipid, ranging from 1 to 8%, and a ph range from 5.5 to 5.8. Trained sensory panel analyses (end point cooking temperatures of 62, 71, or 80 C) as well as measurement of Warner-Bratzler shear force (cooked to 71 C) were per- formed on chops from the 150 loins. Consumer evaluation was also conducted on a subset (n = 40) of these loins, which were broken down into 5 discrete levels of intramuscular lipid, with averages of 1.6, 2.5, 3.6, 4.5, and 5.7% extractable lipid. Consumers were also asked to select the chops they would most prefer from a retail display case based on the amount of marbling present. Results from the consumer portion of the study indicated that intramuscular fat content had limited effects on perceived tenderness, juiciness, pork flavor, and oiliness; some significant differences (P < 0.05) were detectable, but they were numerically small. Most consumers also selected lean chops from the retail case, with nearly 50% selecting chops with less than 1.7% extractable lipid. Warner-Bratzler shear force was negatively related (P < ) to extractable lipid, with an R 2 value of Results from the trained panel sensory analysis indicate that the percentage of extractable lipid did not correlate strongly with perceived tenderness, juiciness, or pork flavor for this group of pork loins that was controlled for genetics, ph, management, and day of slaughter. Key words: consumer, lipid, marbling, pork, quality, sensory 2008 American Society of Animal Science. All rights reserved. J. Anim. Sci : doi: /jas INTRODUCTION There has been a long-running debate regarding the importance of marbling, or intramuscular fat (IMF), and the palatability or consumer acceptability of pork. Efforts have recently been made to increase the IMF level in some pigs because there is concern that pork from modern lean lines of pigs may have poorer eating quality than that from fatter genotypes, and that this 1 This material is based on work supported by the National Pork Board under award no Corresponding author: mckeith@uiuc.edu Received August 2, Accepted November 28, is resulting in reduced consumer satisfaction. This effort has been partially due to the increased demand for highly marbled pork for the export market, food service establishments, and branded retail sales. Many of the studies yielding positive results between IMF and palatability have used mixed-genotype populations in which the Duroc breed was probably present. Relatively speaking, the Duroc produces meat that is highly marbled and has good eating quality (Ellis et al., 1996) but that also differs from other breeds concerning muscle fiber type (Chang et al., 2003) and the incidence of PSE (Meat and Livestock Commission, 1992). Consequently, any study including this breed along with other genotypes is likely to find a favorable relationship between IMF and palatability. Studies involving mixed-breed populations risk confounding the effects of marbling 730

2 Marbling does not influence pork palatability 731 with a number of other factors that may influence sensory properties. At the same time, published data indicate that visible fat content is a major determinant of purchase intent, with consumers preferring leaner pork (Levy and Hanna, 1994; Brewer et al., 2001). The objective of our study was to establish the relationship between IMF and sensory properties (tenderness, juiciness, flavor), as well as Warner-Bratzler shear force, of loins of similar ph displaying a wide range of marbling, from pigs of a single genotype, raised under similar production settings, and slaughtered on a single day, by using both trained and consumer sensory panels. Additionally, we evaluated whether high IMF levels could protect pork from overcooking at different degrees of doneness. MATERIALS AND METHODS Animal Care and Use Committee approval was not obtained for this study because the samples were obtained from a federally inspected slaughter facility. Raw Materials A total of 290 fresh, boneless pork loins were selected from a commercial slaughter facility based on the ph at 24 h postmortem and visible marbling on the ventral side of the loin. A proprietary, commercial genetic line of pigs that displayed a high propensity to marble was selected and used for this study. The animals were all from a single genotype, raised under similar production settings, and slaughtered on the same date. The ph range was initially between 5.55 and 5.95, and the estimated visible marbling was selected to range from 1 to 7%. The loins were vacuum-packaged and transported to the University of Illinois Meat Science Laboratory, where they were aged until 7 d postmortem. After the aging was complete, vacuum bags were opened and the blade end of the loin was removed at the caudal end of the spinalis dorsi near the area of the tenth rib. Quality measurements, including National Pork Producers Council (NPPC) color (1999), firmness (1991), and marbling (1999); ultimate ph (ph STAR, SFK Technologies); and Minolta L*, a*, and b* values (8-mm aperture, D65 light source, and 0 observer, Minolta Camera Company, Osaka, Japan), were collected. Three chops were cut from the cranial end of the loin for determination of proximate composition, shear force, and drip loss, respectively. Drip loss after 7 d of cold storage was calculated by cutting and weighing a 1.3-cm chop, suspending it from a fishhook in a plastic bag, and reweighing the chop 24 h later. Loins were again vacuum-packaged and held in frozen storage at 30 C until determination of proximate composition could be completed for further sorting into a reduced population. Proximate Composition Proximate composition was determined following the procedures outlined by Novakofski et al. (1989). Chops were completely trimmed of all external fat and connective tissue before being homogenized in a Cuisinart (Cuisinart, East Windsor, NJ) food processor. Samples were weighed in duplicate and placed into a drying oven at 110 C for a minimum of 24 h. After drying, the lipids were extracted by using a solution of 4:1 chloroform:methanol, and the samples were then returned to the drying oven. Percentages of moisture and extractable lipids were determined by the difference. The NPPC (1999) Marbling Standards are visual estimates of extractable lipid; thus, marbling scores were used solely as the initial selection parameters. Because extractable lipid is precise and accurate, this, rather than visual marbling, was used for subsequent analysis. Shear Force The Warner-Bratzler shear force was determined on 2.5-cm-thick chops cooked to an end point temperature of 71 C on an open-hearth Farberware grill (Model 455N, Walter Kidde, Bronx, NY). The internal temperature was monitored with copper-constantan thermocouples (Type T, Omega Engineering, Stamford, CT) and a Barnant scanning digital thermometer (Model , Barnant Co., Barrington, IL). The chops were cooled to 25 C, and 1.3-cm-diameter cores were removed parallel to the orientation of the muscle fibers. The cores were sheared by using an Instron universal testing machine (model 112) set with a 10-kg load scale and a 200-mm/min chart drive and crosshead speed. A total of 4 cores per chop were sheared, and the values were averaged. Trained Panel Sensory Analysis A subpopulation was selected from the initial 290 pork loins to create a continuous variable of extractable lipid for use with the regression analysis. Further sorting of the population was completed by using the following guidelines. Objective color and firmness scores of 1 and 5 were discarded from the population. Ultimate ph was further limited to the range from 5.48 to A summary of the quality characteristics for this population can be seen in Table 1. The extractable lipid levels of the final population ranged from 0.76 to 8.09% and contained 150 loins. Thirty loins were selected to represent each of the following extractable lipid categories as uniformly as possible: 1 (0.76 to 1.99%), 2 (2.00 to 2.99%), 3 (3.00 to 3.99%), 4 (4.00 to 4.99%), and 5 (5.00% and above). Three chops were cut to 1.9 cm each for use in taste panels at 3 degrees of doneness (62, 71, and 80 C) and cooked on an open-hearth Farberware grill. Taste panel sessions were designed so that 1 chop from each of the previously mentioned marbling categories was consumed at each degree of doneness on each day. This resulted in 3 sessions (62, 71, and 80 C) of 5 chops each, for a total of 15 chops on any given day. All 3 sessions consumed in 1 d contained chops from the same 5 loins. A trained sensory panel consisting of

3 732 Table 1. Summary of loin quality (n = 150) Rincker et al. Consumer Chop Selection from a Display Case Item 1 Mean SD Minimum Maximum NPPC color, 1 to NPPC marbling, % NPPC firmness, 1 to Ultimate ph Minolta L* Minolta a* Minolta b* Drip loss, % Cook loss, % Shear force, kg Moisture, % Extractable lipid, % National Pork Producers Council (NPPC) color and marbling using the 1999 standards, and firmness using the 5-point scale (1991). 6 members evaluated tenderness, juiciness, and pork flavor by using a 15-cm, unstructured line scale anchored at both ends and at the center (0 = extremely tough, extremely dry, and no pork flavor; 15 = extremely tender, extremely juicy, and very intense pork flavor.) Results from all 6 panelists were averaged for use in data analyses. Consumer Panel Sensory Analysis Loins for the consumer panel were selected to fit into discrete levels of extractable lipid rather than being continuous, as described above. This population was selected from the center of each of the ranges described for the trained panel population. Table 2 summarizes the extractable lipid and ph ranges of the population used for evaluation by the consumer panel. Marbling categories of 1, 2, 3, 4, and 5 yielded average extractable lipid values of 1.58, 2.54, 3.56, 4.53, and 5.73%, respectively. Eight sessions of consumer panels were conducted, using 15 to 20 consumers per session, for a total of 148 consumers. As with the trained sensory panels, all consumers in any 1 session consumed chops from the same 5 loins. Chops were cut 1.9-cm thick and cooked to 71 C on an open-hearth Farberware grill. Demographic data were collected, and consumers then evaluated the samples for tenderness, juiciness, pork flavor, and oiliness by using a 5-point scale. After evaluation of the samples, consumers were directed to a coffin-style display case containing multiple packages of 2 chops per package from each marbling category used during the consumer panel. Chops were packaged immediately before display and changed throughout the day to control for other factors such as light fading and drip loss. The display case contained 3 packages from each marbling category, each of which had been assigned a coded number and placed randomly in the case, for a total of 15 packages in the display case. Chops were trimmed to the same level of subcutaneous fat, and the consumers were asked on their instruction sheet to ignore any differences in chop size. They were then asked to identify the package of chops they would be most likely to purchase and to indicate why by answering questions pertaining to the color of the lean tissue and the amount of marbling. The consumers were filtered in so that no more than 2 consumers were at the display case at any given time. Statistical Analysis This trial was designed for regression analysis of sensory attributes and shear force against a continuous variable (extractable lipid). The data were analyzed by using SAS (SAS Inst. Inc., Cary, NC). Summary tables for descriptive statistics were generated by using the MEANS procedure, regression analysis was performed by using the REG procedure, and the effects of end point cooking temperature and all consumer sensory data were analyzed by using the MIXED procedure with a Bonferroni adjustment. Significance was determined at P < 0.05 for all analyses. Loin Quality RESULTS AND DISCUSSION Loins selected for this study were from a commercial genetic line selected for its propensity to marble. In an effort to isolate the effect of marbling, we intentionally controlled for ultimate ph, color, and firmness during selection. Additionally, diet, management practices, slaughter facility, and slaughter date were all con- Table 2. Regression equations and R 2 values for trained sensory panel tenderness, juiciness, and pork flavor at 62, 71, and 80 C and shear force at 71 C 62 C 71 C 80 C Item 1 Slope Intercept R 2 Slope Intercept R 2 Slope Intercept R 2 Tenderness Juiciness Pork flavor Shear force Sensory properties were evaluated by using a 15-cm line scale, where 0 = extremely tough, extremely dry, no pork flavor and 15 = extremely tender, extremely juicy, intense pork flavor.

4 Marbling does not influence pork palatability 733 Figure 1. Histogram displaying the frequency distribution of percentage of extractable lipid from the reduced population (n = 150) of pork loins. trolled. Table 1 displays a summary of quality characteristics for the 150 loins used in the regression analysis of this research, and indicates that the range of ultimate ph values was 0.31 ph units (range: 5.48 to 5.79) and that NPPC subjective color (1999) and firmness (1991) values of 2, 3, and 4 were required for use in this study. Table 1 also indicates that we were able to identify a range of extractable lipid from 0.76 to 8.09%. The distribution of these values can be viewed in Figure 1, which demonstrates that this was a fairly uniform distribution, ranging up to 8%. Although the animals used for this study were chosen for their ability to deposit marbling, not all animals from this line deposited marbling equally, as indicated by the ranges present. Understanding the impact of variation in this trait, whether within or between genetic lines, was the rationale for conducting this research. Several authors have reported the possibility that a threshold level of marbling is needed to ensure a satisfactory eating experience (Kauffman et al., 1963; DeVol et al., 1988; Fortin et al., 2005). Although the minimum level reported varies by study, it is generally in the range of 2 to 3% lipid. The distribution obtained for the current study should allow us to determine whether a minimum level of marbling is needed in this population of pigs to ensure a positive eating experience. Trained Sensory Panel and Shear Force Response types for all regression analyses were found to be either linear or nonsignificant (nonlinear P-values not shown). Additionally, using ph as a covariate had no effect on analyses; thus, this was not included in the model. Regression analysis results from the trained sensory panel traits of tenderness, juiciness, and pork flavor at 71 C are shown in Figures 2, 3, and 4, respectively. It is visually apparent by the distribution of the samples around the regression lines that the relationship between extractable lipid and sensory properties is not strong. Additionally, the relatively flat slopes of all regression lines indicate that a substantial increase in marbling from 1 to 8% may improve the palatability measurements by only 1 taste panel unit. The slopes, intercepts, and R 2 values for all regression equations are shown in Table 2. Overall, as end point cooking temperature increased to 80 C, tenderness and juiciness decreased while the slopes of the regression lines remained relatively constant. At an end point temperature of 62 C, samples were more tender and juicy, but once again, the slopes of the regression lines remained unchanged. It is evident from the low R 2 values in Table 2 (maximum of 0.10) that the variation in marbling did not account for much of the variation in sensory panel tenderness and juiciness at any degree of doneness. Pork flavor (Figure 4 and Table 2) had the strongest relationship with marbling; however, the maximum R 2 achieved for this parameter was still only Although some studies have demonstrated very strong correlations between marbling and palatability (Batcher and Dawson, 1960), others have found very weak associations (Judge et al., 1960; Wood et al., 1979; Lentsch et al., 1991). Nevertheless, many investigations have yielded positive, favorable relationships between marbling and sensory characteristics (Kauffman et al., 1963; Davis et al., 1975; Fortin et al., 2005). Although the data from the current project do show a positive relationship between marbling and sensory properties, it is a weak relationship that explains, at most, 13% of the variation in any parameter measured. Our original hypothesis was that as the end point temperature increased, the more highly marbled chops would remain more juicy and tender than the chops with less marbling. This hypothesis did not hold true

5 734 Rincker et al. Figure 2. Linear regression of trained sensory panel tenderness at an end point cooking temperature of 71 C as related to percentage of extractable lipid. Sensory panel tenderness was evaluated by using a 15-cm line scale, where 0 = extremely tough and 15 = extremely tender. because the slopes of the lines were similar at all degrees of doneness for tenderness and juiciness (Table 2). The effect that degree of doneness has on sensory properties of pork chops (regardless of marbling level) is shown in Table 3. It is clearly visible that as end point cooking temperature increased, tenderness and juiciness both decreased while pork flavor remained relatively constant. Warner-Bratzler shear force values were also regressed against extractable lipid, and these results are shown in Figure 5. Although there is a statistically significant effect for shear force to decrease as lipid increases, it is still a weak relationship, with an R 2 value of only 0.10 (Table 2). These results indicate that end point cooking temperature had a much greater effect on palatability than did extractable lipid. Additionally, no threshold level of marbling appeared to be necessary to ensure a positive eating experience in this population of pigs. A consumer would have the same Figure 3. Linear regression of trained sensory panel juiciness at an end point cooking temperature of 71 C as related to percentage of extractable lipid. Sensory panel juiciness was evaluated by using a 15-cm line scale, where 0 = extremely dry and 15 = extremely juicy.

6 Marbling does not influence pork palatability 735 Figure 4. Linear regression of trained sensory panel pork flavor at an end point cooking temperature of 71 C as related to percentage of extractable lipid. Sensory panel pork flavor was evaluated by using a 15-cm line scale, where 0 = no pork flavor and 15 = intense pork flavor. chance of a pleasurable eating experience on either end of the marbling spectrum. Consumer Sensory Panel Briefly, the population representing our consumer panel was 60% female and 40% male, composed of 22% Asian, 9% Hispanic, 3% African American, 64% white (non-hispanic), and 2% other. The age ranged from 18 to 59 yr old, and 53% of the group were classified as students. The panelists consumed pork an average of 2 times per week. The loins used for the consumer portion of this study were selected based on extractable lipid and ultimate ph from the same group used for regression analysis. Table 4 shows the average, minimum, and maximum values of the 5 groups of loins. We were able to classify 40 loins into 5 discrete marbling levels and hold ph constant. Results from the consumer study are shown in Table 5 and indicate a slight increase in tenderness Table 3. Effect of end point cooking temperature on trained panel sensory evaluation Item 1 62 C 71 C 80 C SEM Tenderness 8.56 a 7.76 b 6.81 c 0.11 Juiciness 9.85 a 8.51 b 6.29 c 0.08 Flavor 4.66 a 4.75 a 4.56 a 0.07 a c Means within a row with different superscripts are different at P < Sensory properties evaluated by using a 15-cm line scale, where 0 = extremely tough, extremely dry, no pork flavor and 15 = extremely tender, extremely juicy, intense pork flavor. and juiciness values as chops approached 3.5 to 4.5% extractable lipid. There was, however, an unexplainable decline in these values for the chops with the highest level of marbling. Gransson et al. (1992) indicated that a maximum threshold for marbling might exist, beyond which tenderness may deteriorate. Our consumer panel data showed similar effects, but the overall magnitude of the differences was probably inconsequential. Consumer panel results also indicated absolutely no differences in pork flavor intensity and only a slight increase in oiliness for the chops near 4.5% lipid (Table 5). When consumers were asked to select chops that had been randomly placed in a display case, nearly 50% of consumers chose the chops with the least amount of marbling, even though all chops were trimmed to the same external fat level. Brewer et al. (2001) evaluated Table 4. Consumer sensory panel pork loin summary statistics 1 Marbling category Item Loins, n Minimum % lipid Maximum % lipid Average % lipid Minimum ph Maximum ph Average ph A total of 40 loins (n = 8 per marbling category) were selected from the 150 loins used for previous analyses.

7 736 Rincker et al. Figure 5. Linear regression of Warner-Bratzler shear force at an end point cooking temperature of 71 C as related to percentage of extractable lipid. whether consumers would visually differentiate among pork loin chops with low, medium, and high marbling fat contents (1.05, 2.33, and 3.46% IMF, respectively). The highly marbled chops were judged to be lighter in color, less lean, less acceptable in appearance, and less likely to be purchased than the chops with low or medium IMF levels. However, the consumers also judged that the highly marbled chops were more juicy, tender, and flavorful than the leaner chops when they were consumed under controlled conditions (Brewer et al., 2001). All chops in the case from the current study were NPPC color score 3, so differences in lean color should not have influenced chop selection. The selection of the leaner chops was most likely a reflection of the current trend toward health consciousness. Our results agree with Brewer et al. (2001) because consumers selected the least marbled chops much more frequently than any other chops. Table 5. Consumer sensory panel results 1 Marbling category Item SEM Tenderness 3.08 a 3.57 ab 3.92 bb 3.85 b 3.67 ab 0.17 Juiciness 3.19 a 3.52 ab 3.85 ab 4.15 b 3.64 ab 0.19 Flavor 3.48 a 3.43 aa 3.45 aa 3.39 a 3.55 aa 0.10 Oiliness 2.10 a 2.30 ab 2.47 ab 2.69 b 2.57 ab 0.12 a,b Means within a row with different superscripts are different at P < A total of 40 loins (n = 8 per marbling category) were selected from the 150 loins used for previous analyses. 2 Evaluated on a 5-point scale, where 1 = not tender, not juicy, no flavor, not oily and 5 = very tender, very juicy, very flavorful, and very oily. Results from this study indicate that marbling does not influence eating quality or shear force within a single genetic line, even when cooked to a well-done degree of doneness. Although there is demand for highly marbled pork by export markets (i.e., Japan and Korea) and food service establishments, selection of pork based solely on marbling may not ensure a pleasant eating experience. Additionally, consumers appear to select less marbled pork in the retail case, indicating that they prefer to purchase leaner cuts of pork. LITERATURE CITED Batcher, O. M., and E. H. Dawson Consumer quality of selected muscles of raw and cooked pork. Food Technol. 14: Brewer, M. S., L. G. Zhu, and F. K. McKeith Marbling effects on quality characteristics of pork loin chops: Consumer purchase intent, visual and sensory characteristics. Meat Sci. 59: Chang, K., N. da Costa, R. Blackley, O. Southwood, G. Evans, G. Plastow, J. D. Wood, and R. I. Richardson Relationships of myosin heavy chain fibre types to meat quality traits in traditional and modern pigs. Meat Sci. 64: Davis, G. W., G. C. Smith, Z. L. Carpenter, and H. R. Cross Relationships of quality indicators to palatability attributes of pork loins. J. Anim. Sci. 41: DeVol, D. L., F. K. McKeith, P. J. Bechtel, J. Novakofski, R. D. Shanks, and T. R. Carr Variation in composition and palatability traits and relationships between muscle characteristics and palatability in a random sample of pork carcasses. J. Anim. Sci. 66: Ellis, M., A. Webb, P. Avery, and I. Brown The influence of terminal sire genotype, sex, slaughter weight, feeding regime and slaughter-house on growth performance and carcass and meat quality in pigs and on the organoleptic properties of fresh pork. Anim. Sci. 62: Fortin, A., W. M. Robertson, and A. K. W. Tong The eating quality of Canadian pork and its relationship with intramuscular fat. Meat Sci. 69:

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