Managing intramuscular fat and tenderness to improve the consumer experience

David Pethick and Alex Ball – School of Veterinary and Biomedical Sciences, Murdoch University, South St., Western Australia, 6150 and Meat & Livestock Australia, North Sydney, NSW, 2059 and Sheep CRC, CJ Hawkins Homestead, University of New England, Armidale, NSW 2351.

Abstract

This paper discusses the new research and potential implementation phases associated with managing eating quality in Australian lamb. Firstly we discuss the need for electrical stimulation systems as part of lamb processing, especially for supply chains with a domestic focus. We then describe the new eating quality traits being developed in the Sheep CRC Information Nucleus program namely intramuscular fat, shear force tenderness and consumer evaluation using Meat Standards Australia taste panels. Finally we discuss future ways the Industry will underpin and guarantee eating quality of lamb cuts.

Introduction

The current recommendations for managing the eating quality of lamb meat are captured in the Meat Standards Australia (MSA) lamb system. The key elements of the recommended pathway for best practice are summarised in Figure 1 (MSA 2012). This requires meeting recommended growth rates, carcase and fat specifications, curfew and lairage times, pH x temperature windows (i.e. controlled with electrical stimulation) and meat aging. In addition there are cut x cook recommendations for commercial cuts of lamb. A key feature is that the pathways are not difficult to achieve and represent Industry best practice throughout the lamb production supplychain.

Lamb processing – it must be monitored

An important factor influencing lamb tenderness and consumer appeal is the processing conditions post slaughter, especially for domestic product undergoing relatively short aging periods. Optimal processing of lamb for the domestic market typically relies on electrical stimulation of the carcase to accelerate the pH decline and so meet the temperature @ pH6 targets described in Figure 1 (Pethick et al. 2005). To put this in context – poor processing would mean a lamb loin achieving good every day (3 star) rather better than every day or premium (4/5 star). This has resulted in the wide spread adoption of electrical stimulation units in most processing plants with a significant domestic market. However recent research by the Sheep CRC in collaboration with the Australian Meat Processors Corporation has clearly underpinned the need for processors to carefully monitor these stimulation units. Thus we measured the stimulator performance in 5 abattoirs as part of the Sheep CRC Information Nucleus project and found only 1 to be functioning effectively (Pearce et al. 2010). The reasons for poor electrical stimulation performance included changed chilling rates, electrical faults, increased chain speed and incorrect settings. The conclusion is to have an auditing procedure that is underpinned by regular checks on pH decline and the simplest way forward is for processors to utilise the MSA lamb systems to do this.

Incorporating measures of eating quality

The Sheep CRC Information Nucleus is a tool for both R&D and simultaneous adoption of many new traits including eating quality and lean meat yield. We have measured 3 aspects of eating quality namely intramuscular fat, shear force tenderness and consumer taste panel responses to lamb.

Shear force tenderness

This is a laboratory measure of tenderness and is based on the kg of force required to pass a blade through a cooked piece of lamb and a higher value means tougher meat. Animal factors influencing this phenotype include animal age (beyond lamb), level of intramuscular fat and sire. The trait has a moderate heritability in sheep and 2 genes effecting tenderness (calpain and calpistatin) have tough and tender variants (Knight et al. 2012) in a similar manner to beef cattle.

Intramuscular fat

Is the amount of fat within the meat and is called marbling in beef. Intramuscular fat effects tenderness, flavour and juiciness of lamb and ideally should be in the range of 4-6%. The current mean level in Australian lamb is 4.2%. This trait is highly heritable, has a large range (1.5-9.1%) and is favourably genetically correlated to shear force tenderness making it a key target trait for managing eating quality into the future.

Consumer taste panels

The MSA system for assessing the eating quality of lamb by untrained consumers is being used to quantify or calibrate the true effects of the laboratory measures (shear force tenderness, intramuscular fat) on eating quality. The average lamb loin grades as a 4 star but there are also loins that achieve 3 and 5 star grades. About 50% of the topsides are unsatisfactory (2 star) with the remainder as good every day (3 star) or higher. The taste panel work clearly shows the eating quality of the loin and topside is influenced by the level of intramuscular fat and shear force and also by the sire of the lamb. The overall size of the effects for intramuscular fat, shear force and sire are in the range of 8-15 consumer units (out of 100), more then enough to change the overall acceptability or star rating. Indeed these animal effects are comparable or larger than the effects of electrical stimulation and aging.

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