Razor blade shear method for evaluating duck breast meat and tendon texture

2014 Poultry Science Association, Inc. Razor blade shear method for evaluating duck breast meat and tendon texture D. P. Smith,* 1 J. K. Northcutt, and M. A. Parisi * Prestage Department of Poultry Science, North Carolina State University, Raleigh 27695; and Department of Food, Nutrition and Packaging Sciences, Clemson University, Clemson, SC 29634 Primary Audience: Research and Development Personnel, Quality Assurance Personnel SUMMARY Ducks are a small but important portion of the US poultry industry, and are a much larger proportion of the poultry markets in other countries. More duck meat fillet products enter the further processing market, yet few studies have been conducted on meat quality characteristics. Therefore, this project was conducted to determine the effects of sex, bird size, and marination treatment on breast (pectoralis major) fillet weight, cook yield, and Warner-Bratzler (WB) shear values. Razor shear was also used to isolate connective tissue in the breast meat that is typically responsible for consumer complaints regarding toughness. Ducks were identified at 1 d of age for sex, processed at 35 d of age in a commercial facility, and carcasses were categorized as small (1.6 kg), medium (2.0 kg), or large (2.5 kg). Breast fillets (120, 20 each from 2 sexes and 3 sizes) were divided and 60 were marinated using vacuum tumbling whereas 60 were left unmarinated. All of the fillets were then weighed, cooked, and reweighed to determine cook yield. Razor shear was conducted on 2 areas within each fillet and another 2 razor shear measurements were taken on each fillet directly through the connective tissue near the wing insertion. A section of each fillet was then removed for a 2-slice WB shear. Carcass size from small to large corresponded to an increase in raw fillet weight. Fillets from males required more razor shear force than fillets from females. Marination improved cook yield and reduced both the WB shear values and the razor shear values for the meat and the tendon. The razor shear method was effective at measuring both duck meat texture and tendon toughness. Key words: duck breast meat, razor shear, Warner-Bratzler shear, tenderness 2014 J. Appl. Poult. Res. 23 :742 747 http://dx.doi.org/10.3382/japr.2013-00905 DESCRIPTION OF PROBLEM Duck fillets are a growing segment of the US further-processed poultry industry. In 2012, the USDA reported that more than 24 million head of duck were commercially processed into approximately 119 million pounds of chilled and frozen certified duck products [1]. These products are commonly sold to customers who are willing to pay more for deboned duck breast fillets in exchange for a convenient premium product. For all meat sold at the retail level, including duck meat, consumers base their purchase decision primarily on appearance (typically color) and then later evaluate the meat for quality based on texture [2, 3]. A common complaint 1 Corresponding author: dpsmith@ncsu.edu

Smith et al.: DUCK MEAT RAZOR SHEAR 743 by consumers of duck fillets is meat toughness. Appropriate aging before deboning is required to reduce toughness [4]. Further alleviation of toughness can be accomplished with marination, a common industry practice that has been found to improve cook yield and tenderness of duck fillets along with overall perceived juiciness, and flavor [5, 6]. However, very little research is available on commercial duck meat marination. Previous research on lactic acid marination of spent laying ducks in Taiwan showed that postmortem degradation of muscle fibers could be increased [7]. Although no texture testing was conducted in that study, theoretically this would produce more tender meat. A similar study reported that mule duck breast meat also exhibited accelerated postmortem degradation when marinated in red wine [8]. The same study was repeated on Muscovy duck breast marinated with ginger, with similar results [9]. The few available reports agree that marination of duck breast muscle may result in increased tenderness and cooked meat yields. In recent research (D. P. Smith, J. K. Northcutt, and R. I. Qudsieh, unpublished data, North Carolina State University, Raleigh), it was found that duck fillets were generally in the moderately tender range [3.6 to 6.1 kg for Warner-Bratzler (WB); 8.1 to 14.8 kg for Allo-Kramer (AK)] using a scale comparing texture panel and the WB and AK objective methods [10]. However, the connective tissue near the wing (humeral) insertion of the fillet occasionally interfered with the WB shear test and resulted in increased shear values for the second slice. Therefore, another method of shear evaluation was necessary to determine the tenderness of meat separately from the connective tissue or tendon. Due to the bluntness of the blades and relatively large surface areas sampled by AK and WB shear methods, an adaptation of the razor shear method was evaluated on duck fillets to determine the contribution of the tendon to overall meat texture. MATERIALS AND METHODS Approximately 4,000 Pekin ducks of the same strain were hatched, reared, processed, and marinated at facilities owned and operated by a commercial producer. Ducks were sexed at 1 d of age and raised in separate pens by sex in the same house. At 35 d of age, all ducks were processed in a commercial facility, with sexes identified and kept separate throughout the process. Ducks were transported to the processing facility, manually hung on shackles, then electrically stunned and exsanguinated. All carcasses were scalded, picked, waxed, and eviscerated. Carcasses were chilled using cold water immersion for 60 min. Pekin ducks, sorted by sex, were processed at 35 d of age in a commercial facility. Processing steps included stunning, exsanguination, scalding, picking, waxing, evisceration, and immersion chilling. After chilling, carcasses were stored sorted by size (small = 1.6 kg; medium = 2.0 kg; or large = 2.5 kg) then placed in a cooler at the plant for approximately 6 h before the front halves were manually harvested from carcasses. Front halves were manually deboned to produce boneless breast fillets (pectoralis major). Half of the fillets from each of the sex-size categories were held as fresh (unmarinated), and the other half of the fillets within each sex-size category were sent to the marination process. A total of 360 fillets were produced, with 30 fillets in each of 12 categories (see Table 1). Marination was conducted at the commercial facility using a vacuum tumbler and procedures typical of the commercial facility. The marinade solution (86% water, 8% salt, and 6% sodium tripolyphosphate, at a temperature of 13 C) was added at approximately 5% weight of the raw Table 1. Duck fillets categorized by sex, marination treatment, and carcass size in the current experiment (n = 10) Sex Marination 1 size 2 Carcass Female No (control) S Female No (control) M Female No (control) L Female Yes (treatment) S Female Yes (treatment) M Female Yes (treatment) L Male No (control) S Male No (control) M Male No (control) L Male Yes (treatment) S Male Yes (treatment) M Male Yes (treatment) L 1 No = control fillets not marinated; Yes = marinated treatment fillets. 2 S, M, L refers to small (1.6 kg), medium (2.0 kg), and large (2.5 kg) carcasses, respectively.

744 JAPR: Research Report fillets. The vacuum tumbler was operated for 8 min at 3.5 rpm with a vacuum of 25 mmhg. After marination, fillets were bagged in lots of 30 fillets per sex-size category. Fillets (n = 360) were shipped in insulated containers with cold packs for overnight delivery to the laboratory for evaluation. On the day of delivery, fillets were skinned, weighed, cooked in a convection oven to an endpoint temperature range of 77 to 80 C, and then cooled to room temperature (approximately 2 h). Fillets were held overnight at 4 C on aluminum trays overwrapped with aluminum foil for approximately 12 h, after which the covered fillets were allowed to warm to room temperature for 2 h and reweighed. Ten fillets from each of the 12 groups were randomly selected for razor shear evaluation to determine the effect of the tendon on meat texture (n = 120). Fillets were measured for tenderness using an adaptation of the razor blade shear method [11] equipped with a rectangular chiseltip blade mounted on a texture analyzer [12]. Shear force was calculated as the area under the force deformation curve from the beginning to the end of the test and reported as newtons. Two shear force measurements were conducted in the meat tissue, one cranial to the wing attachment (insertion) and the second caudal to the wing insertion (Figure 1). Both razor shear force measurements on the meat tissue were approximately 1 cm from wing tendon, in areas free from fat or connective tissue, and with the blade perpendicular to the surface fibers. Two additional razor shear force measurements were made directly through the tendon at the wing insertion. The 2 meat shear values (M) were averaged together, and the 2 meat and tendon values (M+T) were averaged together. An estimate of tendon shear value (T) was then calculated as the difference between meat and tendon shear value and meat tissue alone: (M+T) M = T. After the subgroups of fillets were tested with the razor shear, all of the fillets were sheared using the WB method [13]. Each strip was sheared twice perpendicular to the fiber direction and the shear values were averaged and reported in kilograms of shear force. Data were analyzed using the ANOVA option of the general linear model procedure of SAS [14]. The model tested the main effects of sex, bird size, and marination treatment. Residual error was used as the error term, unless significant interactions were observed, whereupon that interaction was used as the error term. Significance level was P < 0.05. RESULTS AND DISCUSSION Raw weight, cook yield (as a percent of cook weight divided by raw weight), and texture (razor and WB shear) of either unmarinated (fresh) or marinated duck breast fillets are shown in Table 2. Fillet weight was not affected (P > 0.05) Figure 1. Diagram of duck breast fillet (right side), connective tissue (tendon) area, and location of 2 razor shears of meat only (M Shear 1 and 2) and 2 razor shears of meat and tendon area (M+T Shear 1 and 2).

Smith et al.: DUCK MEAT RAZOR SHEAR 745 by sex or marination, but was significantly influenced by carcass size (data not shown in Table 2). Predictably, fillets from large birds were heavier than medium bird fillets, which were heavier than fillets from small birds (180.2 vs. 142.1 vs. 109.3 g, respectively). The overall average raw fillet weight was 143.9 g. Bird sex and size had no effect on cook yield, but marinated fillets had higher cook yield (73.1%) than fresh fillets without marination (68.0%). In previous studies, researchers measured duck breast cook yield with results including 59.5, 60.4, 62, 65.5, and 66% [4, 15, 16 18]. Marination has been previously shown to improve duck breast cook yield from 64.5 to 72.9% [5]. Phosphates present in the marinade solution hold water in the meat even during cooking. In another study, researchers focused on differences between male and female Pekin ducks and reported that cook yield of male Pekin duck breast meat (76.3%) was significantly higher than yield from female breast meat (70.2%) [19]. In the present study, we report that duck breast fillet WB shear values were not affected by bird sex or size, but were affected by marination treatment (Table 2). Fresh, unmarinated fillets had higher shear values than the shear values observed for marinated fillets (3.3 vs. 2.2 kg of force, or 32.3 to 21.6 N, respectively). In previous research on unmarinated duck breast meat, it was reported that WB shear force ranged from 4.2 to 3.7 kg of force (41.2 36.3 N) [15, 18]. Other researchers found that WB shear of unmarinated male duck breast meat was significantly more tender than breast meat from female ducks (2.6 vs. 3.4 kg, or 25.5 vs. 33.3 N, respectively); the lower WB values may have been due to the smaller core samples used in that study as compared with other studies [19]. A razor shear method has been developed and used to measure texture of cooked poultry meat [11]. In the present study the method was adapted to isolate the effect of tendon on duck meat texture by shearing breast meat only (M), meat with tendon (M+T), and using the difference in values as an estimate of tendon (T) toughness. The razor blade was wider than the actual tendon in the muscle and the tendon appeared to not be uniform throughout the intact fillet. Also, the razor shear method measured total force under the deformation curve. Because of these factors, the T toughness could only be measured as an estimate because of the surrounding meat force. Removal and isolation of the tendon from the fillet was not considered feasible for the number of samples tested. Fillets that were marinated had significantly lower razor shear values in M versus unmarinated meat, at 6.6 versus 7.4 N, respectively (Table 2). The M+T shear values were also lower in marinated meat as compared with unmarinated meat (15.1 vs. 18.8 N, respectively). The difference between M and M+T values is an estimate of the T shear value. Tendon shear value was also lower for marinated fillets as compared with unmarinated fillets (8.6 vs. 11.4 N, respectively). Sex (but not size) also affected both M+T and T shear force values. The M+T shear values were significantly higher (P < 0.05) for males as compared with females (18.4 vs. 15.4 N, respectively). The estimated T shear force for males (11.7 N) was higher than females (8.2 N). Overall, the force required to shear M+T was more Table 2. Means of duck breast fillet raw weight, cook yield, Warner-Bratzler shear force, and razor shear force (on meat, meat and tendon, and tendon only, as estimated by the overall difference between meat and tendon 1 ) by fresh or marinated treatment Razor shear (N) Treatment Number of fillets (N) Raw fillet weight (g) Cook yield (%) Warner-Bratzler shear (kg) Meat only (M) Meat + tendon (M+T) Difference (T) Fresh 60 142.5 68.0 3.3 7.4 18.8 11.4 Marinated 60 145.3 73.1 2.2 6.6 15.1 8.6 Pooled SEM 2.84 0.38 0.11 0.11 0.52 0.52 P-value 0.6131 <0.0001 <0.0001 <0.0001 0.0002 0.0062 1 Razor shear was measured on meat without connective tissue (M), on the tendon embedded in the meat (M+T) near the wing insertion, and the difference in the 2 values used as an estimate of tendon shear force (T).

746 JAPR: Research Report than 150% above the force required to shear M for unmarinated meat. Although marination decreased shear values, M+T shear force was still more than 125% greater than M values for marinated fillets. Data indicate the T connective tissue is contributing to a localized effect of meat toughness in the duck fillets. The toughness appears to be reduced by marination. However, the reduction in T values due to marination were likely an artifact of the method itself, as the meat surrounding the tendon that was sheared with the tendon tissue (and together were measured as total force) would have reduced toughness from the marination process. Tendon tissue itself, due to its composition, was likely unaffected by marination. Connective tissue seems to influence duck breast texture measures. Collagen, a component of connective tissue, has been reported as significantly higher in duck breast than chicken breast, and duck breasts required more force to shear than chicken after appropriate carcass aging [4, 20]. Muscovy duck breast required greater shear force than Pekin breast, and Muscovy was also scored higher by a taste panel for stringiness than Pekin meat [21]. The differences in tenderness values and stinginess scores in these prior reports could be related to levels of connective tissue. In the present study, collagen levels were not measured; however, differences in razor shear values were present between sexes. Further research could determine if correlations exist between levels (or solubility) of collagen and tenderness based on sex. The increase of carcass size from small to large increased raw fillet weight as expected. Sex affected meat texture as determined by the razor shear values, where more force was required to shear both the M+T and the T fillets from males as compared with females. Marination improved cook yield and reduced both WB and razor shear values as compared with unmarinated meat. The technique of using the razor shear showed that the fillet tendon is much tougher than meat alone, as much as 3 times tougher in some individual samples. Based on the results for the razor shear, the method appeared as a viable test to objectively determine the effect of sex, size, and marination on duck meat toughness, especially in the area of the fillet containing connective tissue. CONCLUSIONS AND APPLICATIONS 1. The tendon and connective tissue in duck breast associated with the wing insertion area is likely a cause of consumer complaints for duck breast meat toughness. 2. Breast meat razor shear values and estimated tendon shear values showed that male ducks were tougher than female ducks. 3. Razor shear is a valid method to determine meat and tendon toughness and may be used to objectively assess efforts by the duck industry to reduce toughness. REFERENCES AND NOTES 1. USDA, National Agricultural Statistics Service. 2013. Poultry Slaughter 2012 Summary. Accessed November 2014. http://usda.mannlib.cornell.edu/usda/nass/ PoulSlauSu/2010s/2013/PoulSlauSu-02-25-2013.pdf. 2. Acton, J. C., and R. L. Dick. 1986. Protecting color in fresh and processed meats. The National Provisioner 194:12 17. 3. Fletcher, D. L. 2002. Poultry meat quality. World s Poult. Sci. J. 58:131 145. 4. Smith, D. P., D. L. Fletcher, and C. M. Papa. 1992. Duckling and chicken processing yields and breast meat tenderness. Poult. Sci. 71:197 202. 5. Smith, D. P., D. L. Fletcher, and C. M. Papa. 1991. Evaluation of duckling breast meat subjected to different methods of further processing and cooking. J. Muscle Foods 2:305 310. 6. Smith, D. P., and J. C. Acton. 2010. Marination, cooking, and curing of poultry products. Pages 311 336 in Poultry Meat Processing, 2nd ed. C. Owens, C. Alvarado, and A. Sams, ed. CRC Press, Boca Raton, FL. 7. Chou, R.-G. R., T.-F. Tseng, and M.-T. S. Chen. 1997. Acceleration of post-mortem changes in Tsaiya duck breast muscle by lactic acid marination. Br. Poult. Sci. 38:78 83. 8. Lin, Y.-C., W.-T. Chen, and R.-G. R. Chou. 2000. Postmortem changes in mule duck muscle marinated in red wine. J. Food Sci. 65:906 908. 9. Tsai, L.-L., N.-J. Yen, and R.-G. R. Chou. 2012. Changes in Muscovy duck breast muscle marinated with ginger extract. Food Chem. 130:316 320. 10. Lyon, B. G., and C. E. Lyon. 1991. Shear value ranges by Instron Warner-Bratzler and single-blade Allo-Kramer devices that corresponded to sensory tenderness. Poult. Sci. 70:188 191. 11. Cavitt, L. C., G. W. Youm, J. F. Meullenet, C. M. Owens, and R. Xiong. 2004. Prediction of poultry meat tenderness using razor blade shear, Allo-Kramer shear, and sarcomere length. J. Food Sci. 69:11 15. http://dx.doi. org/10.1111/j.1365-2621.2004.tb17879.x. 12. Texture Analyzer (TA), Model TA-XTplus, Texture Technologies, Scarsdale, N.Y. The TA was fixed with a 50-kg load cell and a number 17 X-Acto carbon steel ra-

Smith et al.: DUCK MEAT RAZOR SHEAR 747 zor blade (height 24 mm, width 8 mm; Elmer s Products Inc., Westerville, OH) set to a penetration depth of 25 mm. The crosshead speed was set to 10 mm/s and the test was triggered by a 1 g of contact force. The blade, which has a straight 6.35-mm edge, was affixed in a #1 knife handle and attached to the TA using a TA-95 adjustable chuck with 3/8 shaft. 13. Warner-Bratzler shear device, G-R Electrical Mfg. Co., Manhattan, KS. A 1.9-cm wide section of cooked meat from each fillet that was parallel with the direction of the muscle fibers, roughly from the wing insertion area to the keel, was removed and sheared twice. The first shear slice was taken approximately 1.0 to 1.5 cm from the keel end of the strip; the second slice was taken approximately 3.0 to 3.5 cm from the keel end, which was closer to the wing insertion end of the strip. The shear values were averaged together and data are reported in kg shear. 14. SAS. 2008. SAS for Windows, ver. 9.2 ed. SAS Inst. Inc., Cary, NC. 15. Ali, M. S., H. S. Yang, J. Y. Jeong, S. H. Moon, Y. H. Hwang, G. B. Park, and S. T. Joo. 2008. Effect of chilling temperature of carcass on breast meat quality of duck. Poult. Sci. 87:1860 1867. 16. Alvarado, C. Z., and A. R. Sams. 2000. The influence of postmortem electrical stimulation on rigor mortis development, calpastatin activity, and tenderness in broiler and duck pectoralis. Poult. Sci. 79:1364 1368. 17. Ali, M. S., G. H. Kang, H. S. Yang, J. Y. Jeong, Y. H. Hwang, G. B. Park, and S. T. Joo. 2007. A comparison of meat characteristics between duck and chicken breast. Asian-Australas. J. Anim. Sci. 20:1002 1006. 18. Kim, H. W., S. H. Lee, J. H. Choi, Y. S. Choi, H. Y. Kim, K. E. Hwang, J. H. Park, D. H. Song, and C. J. Kim. 2012. Effects of rigor state thawing temperature, and processing on the physiochemical properties of frozen duck breast muscle. Poult. Sci. 91:2662 2667. 19. Omojola, A. B. 2007. Carcass and organoleptic characteristics of duck meat as influenced by breed and sex. Int. J. Poult. Sci. 6:329 334. 20. Smith, D. P., D. L. Fletcher, R. J. Buhr, and R. S. Beyer. 1993. Pekin duckling and chicken Pectoralis muscle structure and function. Poult. Sci. 72:202 208. 21. Chartrin, P., K. Meteau, H. Juin, M. D. Bernadet, G. Guy, C. Larzul, H. Remignon, J. Mourot, M. J. Duclos, and E. Baeza. 2006. Effects of intramuscular fat levels on sensory characteristics of duck breast meat. Poult. Sci. 85:914 922. Acknowledgments The authors thank Maple Leaf Farms (Leesburg, IN) for their generous support of this project. We especially appreciate the technical advice and assistance of Mike Turk, Rhonda Murdoch, Dan Shafer, and August Konie.