Elsevier

Meat Science

Volume 135, January 2018, Pages 94-101
Meat Science

Diet composition and slaughter age up to 24 weeks have minimal impact on pork eating quality of loin steaks and silverside roasts from female pigs

https://doi.org/10.1016/j.meatsci.2017.09.005Get rights and content

Abstract

Female crossbred pigs were randomly allocated at 16 weeks of age to one of three dietary treatments (A: corn and soybean meal; B: wheat and canola meal; C: wheat and sorghum) matched for digestible energy (13.6 MJ DE/kg) and total lysine (0.93–0.95%) and fed for 4, 5 or 8 weeks, respectively, prior to slaughter. Loin (M. longissimus thoracis et lumborum) and silverside (M. biceps femoris) were obtained from 20 pigs per dietary treatment group and prepared into steaks and roasts, respectively, for consumer evaluation with ageing treatments of 7 and 28 days post-slaughter allocated within muscle. Neither dietary treatment/age at slaughter nor ageing treatment influenced sensory traits of either cut. Intramuscular fat levels were also not influenced by dietary treatment. Higher (P < 0.001) fail rates for silverside roasts compared with loin steaks indicate that different interventions are needed at a cut level to optimise pork eating quality consistency and consumer expectations.

Introduction

Delivering consistently high eating quality pork, across a range of cuts prepared using different cooking methods, to drive consumer demand and ensure ongoing industry sustainability and competitiveness is a key focus of the Australian pork industry (Anon, 2014). However, the ability of any supply chain to consistently produce high quality pork is both difficult and complex due to individualised responses of pigs to the various management practices and environmental factors experienced throughout their lives, coupled with additional pre- and post-slaughter factors that may interact to further influence pork eating quality. It is also recognised that even with the close management of those pathway parameters known to negatively influence pork eating quality (Channon & Warner, 2011; Dunshea, D'Souza, Pethick, Harper, & Warner, 2005; Rosenvold & Andersen, 2003), eating quality inconsistencies may still be experienced due to cooking methods used, final internal temperatures achieved, cooking abilities of consumers and consumer confidence in preparing pork meals (Ngapo & Gariepy, 2008).

Channon, Hamilton, D'Souza, and Dunshea (2016) described a statistical approach using published data to assist with developing a cuts-based eating quality predictive model for Australian pork and highlighted that additional data are needed to quantify effects of multiple pathway factors on eating quality attributes and to extend these findings to other cuts in addition to the loin muscle. In response to this, the effects of ageing period, cooking method, cut type and final internal temperature have been determined in entire male, female and surgical castrated pigs (Channon, D'Souza, & Dunshea, 2016) and entire male and immunocastrated males (Channon, D'Souza, Hamilton, & Dunshea, 2013) slaughtered at 90–100 kg liveweight from one current Australian genotype. Across those factors investigated, the largest differences in eating quality were due to the interaction between cut (shoulder, loin or silverside) and cooking method (roast and stir fry (all cuts) or steak (loin only)). Overall, it was shown that loin steaks and silverside roasts had lower overall liking scores than the other cuts evaluated – presenting significant implications if this is not addressed given that these cuts are strongly demanded at the retail level by consumers. Ageing of these pork cuts at 2 °C for 7 days, compared with 2 days, was also relatively ineffective in both reducing fail rates and in consistently improving eating quality traits of various pork cuts (Channon et al., 2016). From these outcomes, it was not clear whether an ageing period of > 7 days may be needed to optimise tenderness of loin steaks and silverside roasts. Furthermore, few studies have compared whether an extended ageing period of 28 days, as can be experienced by vacuum packaged chilled pork to meet supply arrangements both when exported and for domestic retailers, may deliver pork eating quality benefits compared to an ageing period of 7 days.

Intramuscular fat content of between 2.0 and 3.5% in the loin has been shown to positively influence pork eating quality (Alonso, Campo, Provincial, Roncalés, & Beltrán, 2010; Bejerholm & Barton-Gade, 1986; DeVol et al., 1988; Fernandez, Monin, Talmant, Mourot, & Lebret, 1999; Touraille, Monin, & Legault, 1989). However, levels of intramuscular fat levels in the loin, in the vicinity of 0.8–1.5%, have typically been found in Australian pork loin muscles (Jose, Trezona Murray, Channon, & D'Souza, 2013; Channon, Taverner, D'Souza, & Warner, 2014: D'Souza et al., 2015; Moore, Mullan, & Dunshea, 2017), with higher levels of 2.5–3.5% in the loin recently reported by Channon et al. (2016). Increased liveweight at slaughter can increase the deposition of subcutaneous (Wood et al., 2008) and intramuscular fat (Čandek-Potokar, Žlender, Lefaucheur, & Bonneau, 1998; Heyer & Lebret, 2007). Pigs produced in the United States of America, Canada and the European Union are generally slaughtered at heavier weights of 90–130 kg compared with Australian pigs where they are typically slaughtered at 85–100 kg liveweight to meet preferred carcase weight and fat depth specifications. It is also recognised that diet formulations differ between countries, with a corn-soybean meal diet primarily used in North America whilst in the EU, diets for pigs must be free from restricted animal materials (meat meal, fish meal, blood meal etc.; RAM). The influence of these different diet types fed to Australian pigs grown to heavier liveweights on pork eating quality attributes has not previously been reported. Slaughtering pigs at higher liveweights in combination with different diet formulations may therefore present another option for Australian producers to consider in order to reduce pork eating quality variability.

This study aimed to evaluate whether diet composition (using feed ingredients typically used in North America and northern Europe) and age/final liveweight at slaughter can increase intramuscular fat levels compared with pork from pigs slaughtered at 20 weeks of age, whether extended ageing for 28 days post-slaughter, rather than for 7 days post-slaughter, can improve the eating quality consistency of loin steaks and silverside roasts and whether these pathway interventions may be additive or multiplicative in their effects on eating quality.

Section snippets

Materials and methods

Experimental protocols used in this study were managed through CHM Alliance Pty. Ltd.'s Animal Ethics Committee (Protocol CHM PP 32/12).

A total of 75 crossbred female pigs (25 per dietary treatment/slaughter age group), from a piggery located in South East Queensland, Australia were randomly allocated at 16 weeks of age to one of three nutritional treatments matched for digestible energy (13.6 MJ DE/kg) and total lysine (0.93–0.95%) (Table 1). The dietary treatments were A: 77% corn and 16%

Results

Pigs allocated to Treatment A were heavier at slaughter (P < 0.001) and produced heavier (P < 0.001), fatter (P < 0.001) carcases with higher dressing percentages (P < 0.001) compared with pigs allocated to treatments B and C (Table 2). Carcases in treatment C had a higher estimated chill loss (P = 0.019) than carcases in treatments A and B.

Discussion

The importance of flavour to overall liking was again shown, with the coefficient for flavour found to be three times as large as for juiciness and tenderness, supporting previous studies (Channon et al., 2014; Channon et al., 2016; Jaworska, Przybylski, Kajak-Siemaszko, & Czarniecka-Skubina, 2009). Positive correlations between tenderness, juiciness and flavour observed in this study also concur with previous studies (including Huff-Lonergan et al., 2002; Jeremiah et al., 1999).

Conclusion

As few differences in pork sensory quality resulted from finishing female pigs of 20 to 24 weeks of age, our findings support the inclusion of heavier carcases in a pathway based eating quality system for Australian pork. Feeding isoenergetic and isonitrogenous diets, formulated using dietary ingredients typically used in North America and northern Europe, to finisher pigs of a major Australian commercial genotype also did not result in markedly different eating quality performance. Ageing for 28

Acknowledgements

The High Integrity Australian Pork Co-operative Research Centre is gratefully acknowledged for providing funds to undertake this study (3A-105). The authors also acknowledge the producer and processor involved for their co-operation, technical assistance and support. Dr. Cameron Jose from the Department of Agriculture and Food Western Australia is acknowledged for his assistance with carcase and meat quality measures. The biometrical support and advice provided by Richard Jarrett and Jessica

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    Aspects of this work has been previously published as: Channon et al. (2013). Diet and slaughter age have minimal impact on pork eating quality. In J. R. Pluske & J. Pluske (Eds.), Manipulating Pig Production XIV (p. 228) Australasian Pig Science Association Werribee, Australia.

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