Agriculture and Food Systems - Theses
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ItemPredicting the eating quality of porkChannon, Heather Anne ( 2017)Reducing the variability in eating quality of Australian fresh pork remains a significant issue that needs to be addressed to improve consumer demand and satisfaction and drive increased consumption frequency. The differentiation of Australian pork as a niche, high quality product within a largely global commodity pork market will be supported through the implementation of an eating quality system by industry to manage, and carefully control, key production, processing, post-slaughter and cooking factors that can influence pork eating quality. Unlike the red meat sector, the Australian pork industry has not yet developed a non-prescriptive, pathway based eating quality model that can be accurately applied to different cut and cooking method combinations to improve its acceptability and consistency. Extensive knowledge of individual factors that influence both the meat and eating quality of pork has been generated over many years, both in Australia and overseas. These have primarily involved sensory evaluations of loin (M. longissimus thoracis et lumborum) cooked as a steak, either grilled or roasted. This information has been utilised and incorporated into industry quality assurance programs with standards in place to enable good agricultural practices or good manufacturing practices to be followed, rather than being used to inform the development of integrated predictive models for eating quality. Where eating quality guidelines and checklists have been developed, these have been used to support individual company brands. An objective of this thesis was to determine whether data compiled from mainly published studies fitting selection criteria could be used to estimate the size and effect of various pathway factors and their interactions on pork eating quality of different cuts and use this information to develop an eating quality predictive model for pork. Both Monte Carlo simulation techniques (Chapter 3) and random effects meta-regression analyses (Chapter 4) were applied to the constructed datasets that included data for the loin muscle due to lack of data for other cuts. From this, positive effects of moisture infusion, ageing for more than 2 days post-slaughter and hanging from the aitchbone on tenderness were found, whilst cooking to an endpoint temperature of greater than 80˚C negatively affected tenderness and juiciness. Due to a lack of eligible studies (including those presenting eating quality data for treatment interactions) as well as differences in study designs and methodologies used, it was not possible to establish algorithms to reliably estimate the effects of multiple factors on pork eating quality. For immunocastrated males, estimated means for tenderness, juiciness and flavour were determined on limited studies compared with those for pork from females, physical castrate and entire male pigs. Further studies were needed to generate datasets for different cut type and cooking method combinations, in addition to the loin, so that the system will truly be cuts-based. A series of multifactorial studies were designed and conducted involving consumer evaluations of pork to address these knowledge gaps. These datasets are to be used to inform statistical approaches associated with the development of algorithms to predict consumer eating quality scores of different cut type and cooking method combinations. The effects of ageing period (2 or 7 days), endpoint temperature (70 or 75˚C), cut type (loin, silverside, shoulder) and cooking method (roast and stir fry (all cuts) and steak (loin only)) on the eating quality of pork from female, physical castrate and entire male pigs (Chapter 5) and entire male and immunocastrated males (Chapter 6) from major supply chain were investigated. Across both studies, neither endpoint temperature nor ageing period, as main effects, influenced the eating quality of the seven cut type x cooking method treatments evaluated. Cooking loin steaks and stir fry cuts to an endpoint temperature of 75°C lowered juiciness scores and increased cooking losses compared to cooking to 70°C, whilst endpoint temperature did not influence sensory scores for roasts. As the boar taint prevalence of 15% and 10% in entire males were identified in studies reported in Chapters 5 and 6, respectively, the inclusion of entire males in any eating quality program for pork was questioned due to risks of poor eating experience by consumers. The effect size on eating quality scores due to cut type x cooking method were larger than those of the other pathway interventions investigated; only the shoulder stir fry and roast cuts met the fail rate target of <10% (defined as the percentage of pork rated as either unsatisfactory or below average by consumers) and were also more preferred by consumers than those from the loin and silverside. Alternate interventions to optimise the eating quality performance of different cuts prepared from the loin and silverside muscles, when cooked using different methods need to be identified and trialled. Further investigation to determine why ageing for 7 days post-slaughter was not an effective intervention was also recommended; longer ageing periods were investigated in Chapters 7 and 8. A simulation study to investigate the effects of age at slaughter from 20 to 24 weeks, (combined with dietary composition) and ageing period (7 or 28 days) on the eating quality of loin steaks and silverside roasts from female pigs cooked to 70 and 75˚C, respectively, was then conducted (Chapter 7). Finishing female pigs on a corn/soy diet and slaughtering at 24 weeks of age did not increase intramuscular fat concentrations in either loin steaks or silverside roasts compared with those fed a wheat/sorghum diet and slaughtered at 20 weeks of age. Based on these findings, pigs grown to 24 weeks of age could be eligible for inclusion in an eating quality system for pork. Proteolysis plateaued before 7 days post-slaughter as no differences in mean sensory scores were found for cuts aged for 7 and 28 days post-slaughter. Continuing efforts to improve sensory attributes of both cuts, particularly the silverside, are required as the fail rate target of <10% was not achieved for either cut. Further work to validate additional processing interventions, ascertained from Chapters 3 and 4, to improve eating quality performance of cuts from the loin and silverside muscles was then conducted (Chapters 8 and 9) to address the observed lack of shift in eating quality means of treatments already imposed. Two commercial validation studies involving immunocastrated and female pigs aimed to evaluate whether ageing period, moisture infusion and either hanging method or electrical stimulation and their interactions were effective in improving mean sensory scores and reducing fail rates to <10% of five different pork cuts produced from the loin and silverside. Pork cuts from immunocastrated males and females were comparable in eating quality across both supply chains. Ageing for either 7 or 14 days post-slaughter did not influence eating quality or lower fail rates for quality grade and re-purchase intention compared with pork aged for 2 days. Treatments imposed did not enable fail rates of <10% to be consistently achieved across all cut type x cooking method combinations. Moisture infusion was effective in reducing the fail rate of pork to <10%, particularly for stir fry and roast from the loin. A fail rate for quality grade of 9% was achieved for loin stir fry through aitchbone hanging compared with 21% for Achilles hung carcases. Chapter 10 presents a review of eating quality research conducted over the past sixteen years in Australia, including work presented in this thesis, to support the development of an eating quality system for pork. Chapter 11 presents the main conclusions obtained from the studies presented in this thesis, provides recommendations for future work to gain industry support and involvement commercial implementation and opportunities for further studies to refine the system over time. Overall, additional mechanistic understanding of factors influencing the ageing potential of Australian pork is needed to determine why it was not effective as a main effect across any of the studies conducted as part of this thesis. This is needed to utilise ageing as a reliable intervention to improve pork eating quality consistency; ageing period is a critical control point in the sheepmeat and beef MSA systems. Different processing interventions imposed to improve pork eating quality consistency also varied between supply chains and between cuts. This highlights that the eating quality models that will be developed for the Australian pork industry utilising data generated in this thesis must be non-prescriptive and include multiple factors to enable individual supply chains to use different interventions to deliver high quality pork to their customers. It is envisioned that the adoption of a cost-effective industry system to guarantee eating quality consistency of Australian pork, on a cut type x cooking method basis, will be used to underpin differentiation and integrity claims made by the commercial owners of branded Australian pork products.