Electrical stimulation or moisture infusion improves the eating quality attributes of loin and silverside cuts from female and immunocastrated male pigs
Introduction
A pathway based, non-prescriptive eating quality model is being developed by the Australian pork industry that, when implemented, will enable supply chains to choose various pathway interventions to deliver consistent, high quality pork to their domestic and export customers (Channon & Warner, 2011). In order to do this, a key industry focus has been to undertake research studies to address knowledge and data gaps identified from meta-analysis studies (Channon, D'Souza, & Dunshea, 2017; Channon, Hamilton, D'Souza, & Dunshea, 2016) to understand the effects of multiple pathway factors, including gender, final liveweight, ageing period, final internal temperature, cut type and cooking method on pork eating quality (Channon, D'Souza, & Dunshea, 2016; Channon, D'Souza, & Dunshea, 2018a; Moore, Mullan, & Dunshea, 2017).
Entire male pigs immunised against gonadotrophin releasing factor (GnRF) produce pork that is more acceptable (D'Souza & Mullan, 2003; Font i Furnols et al., 2008), with lower shear force values (Jeong, Choi, Han, Lee, & Hennessy, 2008; Moore, Dunshea, Mullan, Hennessy, & D'Souza, 2009; Pauly, Spring, O'Doherty, Kragten, & Bee, 2009) and has a lower fail rate (Moore et al., 2017) than entire males. Jones-Hamlow et al. (2015), in a study evaluating loins aged for 10 d post-slaughter from immunocastrated males (with or without added ractopamine at 5 ppm for 33–40 d prior to slaughter), entire males, physical castrates and females slaughtered at 130 kg liveweight, concluded that boar aroma of pork from immunologically castrated males was lower than entire males, while tenderness, juiciness and off-flavours of pork from immunocastrated males, physical castrates and females did not differ. However, no studies have directly compared the eating quality attributes of pork from immunocastrated males and female pigs, particularly for different cut x cooking method combinations. This is an important comparison since many Asian butchers in Australia demand carcases from female pigs to ensure high quality pork, or at least pork that is free from boar taint.
Ageing of pork for >2 d post-slaughter can improve pork eating quality (Channon, Taverner, D'Souza, & Warner, 2014; Moore, Mullan, & D'Souza, 2012; Wood et al., 1996), reduce shear force (Channon et al., 2014; Jin et al., 2016; Jones-Hamlow et al., 2015) and has been shown to be an additive factor in its effects on eating quality (Channon et al., 2014; Moore et al., 2012). More recently, Channon, D'Souza, and Dunshea (2016) identified that ageing of vacuum packaged Australian pork cuts for 7 d may not be resulting in eating quality improvements of the magnitude as previously observed. However, possible explanations for this remain unclear. Frenzel, Harp, Lambert, Sawyer, and Frenzel (2014), in a study conducted in the US, also reported that whilst ageing (0, 3, 6, 9 and 12 d post-slaughter) of loins increased initial juiciness, initial tenderness and flavour scores obtained from trained panelists, overall tenderness and palatability were not improved by ageing. This was despite lower shear force values being obtained as ageing period increased. This suggests that additional data is needed to understand whether ageing period may be effective in combination with other pathway interventions as well as quantify whether this issue extends to different supply chains, with pigs sourced from a different genetic base and environmental conditions, in order for this pathway intervention to be included as a variable into predictive models.
Similarly for ageing period, electrical stimulation (Channon, Baud, Kerr, & Walker, 2003; Taylor & Martoccia, 1995; Taylor, Perry, & Warkup, 1995) and moisture infusion (Moore et al., 2012; Sheard, Nute, Richardson, & Wood, 2005; Walker, Channon, Baud, & Warner, 2005) are each effective, as additive factors, in improving pork eating quality. Pork from carcases that were electrically stimulated using 150 mA of constant current for 30 s at 2 min post-exsanguination and aged for 2 d was shown to be comparable in eating quality to pork from non-stimulated carcases aged for 7 d (Channon et al., 2003) without adversely affecting colour or drip loss. This is in contrast to the use of constant voltage systems, where issues with drip loss, colour and the development of pale, soft and exudative pork have been reported (Bowker, Wynveen, Grant, & Gerrard, 1999; Taylor et al., 1995; Taylor & Martoccia, 1995). However, constant current electrical stimulation systems have not yet been commercially adopted by Australian pork processors as a means of improving pork eating quality consistency. Whilst this may reflect that pork processors are not yet being financially rewarded on the basis of eating quality, further data that validates its effectiveness in current pig genotypes is required. It is noteworthy that this intervention has been successfully incorporated into the Meat Standards Australia (MSA) for sheepmeat, together with ageing (Young, Hopkins, & Pethick, 2005).
This commercial validation study aimed to determine whether the combination(s) of key pathway interventions of gender, electrical stimulation, ageing period and moisture infusion can deliver pork of consistently high eating quality and achieve fail rates of <10% when evaluated at a cuts-based level by Australian consumers.
Section snippets
Methodology
All animals in this study were managed according to experimental protocol 13M073C approved by the Animal Ethics Committee of Rivalea (Australia) Pty Ltd.
Results
Average daily gain of immunocastrated males from weeks 17 to 21 were higher (P < 0.001) than females, resulting in a higher (P = 0.017) final live weight at week 21 (Table 2). Gender of the pig did not influence fat depth at the P2 site, hot or cold carcase weight. Higher (P < 0.001) dressing percentages of carcases from immunocastrated males, compared with females, appeared to offset the higher final live weight at slaughter observed for immunocastrated males.
Gender
Growth performance was influenced by gender, with higher average daily gain during the final four weeks prior to slaughter in immunocastrated males compared with females. These findings confirm those reported in previous studies (eg. Braña, Rojo-Gómez, Ellis, & Cuaron, 2013; Rikard-Bell et al., 2009) that evaluated the growth performance of immunocastrated males with females. However, pork eating quality attributes were not influenced by gender of the pig in this study, providing additional
Conclusion
Overall, the fail rate target of <10% was not consistently attained across all treatments imposed in this study. Only stir fry cuts met this requirement, but this was dependent upon the treatment imposed. Whilst moisture infusion reduced fail rates for both quality grade and re-purchase intention for all cut type x cooking method combinations investigated, consistent improvements in eating quality scores due to moisture infusion were not found across all cuts. Immunocastrated males produced
Acknowledgements
The High Integrity Australian Pork Co-operative Research Centre is gratefully acknowledged for providing funds to undertake this study (3A-109). The authors also sincerely thank and 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
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Aspects of this work has been previously published as: Channon, H. A., D'Souza, D. N., & Dunshea, F. R. (2015). Pork eating quality was not improved by extended ageing for 14 days. Animal Production Science, 55(12), 1468-1468.