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Muscular characteristics and meat qualities of Limousine cattle.Variations with age and muscle.

Genetic variability of Beef Meat Quality. Special focus on marbling in relationship with the metabolism of Bovine muscle fibres and intramuscular adipocytes. 

Muscular characteristics and meat qualities of Limousine cattle

Variations with age and muscle

Presented at the International Limousin Conference, France 2000

Written by P. PICARD et al. - INRA/URH, Theix, France.

The very important and unforeseeable variability of beef meat sensorial qualities (in particular tenderness) is the main crticism made of beef by consumers. A part of this variability comes from slaughter, postmortem and cooking conditions. The knowledge on this topic is relatively important and should be put into practice.

Another part of this variability is due to the genotype, to the management of cattle (age at slaughter), physiological and metabolic properties of muscle factors modify the physical, biochemical and metabolic properties of muscle characteristics, the meat sensorial qualities.

As a matter of fact, muscles are constituted by myofibers arranged longitudinally into bundles and enveloped by a net work of connective tissue consisting predominantly of the fibrillar collagens. The contractile and metabolic properties of fibers affect the muscle ageing and contribute, with the collagen properties (proportion and solubility), to define the level of meat tenderness. These characteristics take place during the fetal life and depend on the genotype and muscle type. But after birth they can be modified by several factors such as hormonal status of the animal (entire or castrated male or female). Little knowledge on these topics is available on the Limousine breed in the French production systems.

So, a long term study was taken in place by INRA on the Limousine breed to analyse

1)

The effect of age at slaughter and type of muscle on muscle characteristics, postmortem muscle transformations and meat qualities of young bulls and suckling cows.

2)

The relative part of different muscle characteristics (myofibers type, collagen solubility and content, lipid content, enzymes activities) in determination of tenderness.

At the INRA/Theix research centre, a total of 21 young Limousine bulls were slaughtered at 15, 19 and 24 months of age and 21 suckling Limousine cows were slaughtered at three stages 4-5, 6-7 and 8-9 years) after a fattening period.

The whole empty body composition of each animal was measured and three muscles

(Longissimus Dorsi, Triceps Brachii and Semi Tendinosus) were analysed for:

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Biological characteristics : number and size of fibers, contractile and metabolic type, pH at 1h, 3h and 24h postmortem, collagen content and solubility, collagen isoforms I and III, texture of the connective tissue, proteoloic enzymes and inhibitors content.

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Evolution of ageing at day 2, day 7 and day 14 postmortem by physical measurements.

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Tenderness as assessed by test panel.

This study is in progress, it will permit to measure the relationship existing between muscle characteristics and meat quality. Data will be discussed in comparison with the literature and with other data obtained in INRA on other breeds. A similar experiment is conducting on the Charolais, Salers and Aubrac breeds.

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GENETIC VARIABILITY OF BEEF MEAT QUALITY:

SPECIAL FOCUS ON MARBLING IN RELATIONSHIP WITH THE METABOLISM OF BOVINE MUSCLE FIBERS AND INTRAMUSCULAR ADIPOCYTES.

Presented to the International Limousin Conference France September 2000

Written by Jean Franicois Hocquette, INRA

INRA, Herbivore Research Unit, Muscle Growth and Metabolism Group, 63122, Theix France (JF Hocquette)

Murdoch University, Division of Veterinary and Biomedical Sciences, Perth, Australia 6150 (DW Pethick)

UPRA France Limousin Se1ection, Lanaud, 87220 Boisseuil, France (JN Bonnet)

CSIRO, Molecular Animal Genetics Center, University of Queensland, St Lucia, Brisbane, 4067 Australia (G Harper)

BACKGROUND INFORMATION

The quality of the raw, initial product (i.e. muscles of the carcass which are then converted into meat) is essential to ensure consumer satisfaction. Intramuscular fat deposition (marbling) influences quality attributes of beef, such as flavour, juiciness and tenderness. Marbling continues to be the primary factor determining the quality grade of beef meat in North American and Asian markets. Currently the only way to achieve a reliable marbling response is to 'over fatten' steers from specific breeds (e.g. Angus, Japanese Black) in an expensive production system built around the lot feeding of steers for 12 months. Clearly, beef produced from French cattle breeds contains a low amount of fat. In addition, the selection of animals for increased protein retention has induced a reduction in fat content of muscles, and consequently, beef flavour may be reduced. French breeders or beef producers are thus seriously disadvantaged to export beef meat to North American and Asian markets.Marbling is controlled by genetics and nutrition and this project aims to investigate the fundamental mechanisms operating at these critical control points. De novo synthesis of fat in intramuscular adipocytes seems to occur primarily from glucose (and less from acetate as in bovine adipocytes from other fatty tissues). This suggests that it may be possible to increase fat accumulation within intramuscular adipocytes, independently to that in fatty tissues of the carcasses by using glucose only as the fat precursor. However, oxidation of plasma glucose and fat within muscle fibers competes with lipogenesis and fat accumulation between muscles fibres. The question is to identify the biological mechanisms to achieve preferential development of intramuscular fat.

OBJECTIVES

This project aims to get a better understanding of the determinants of marbling. It is likely that the metabolic activity of muscle fibers and intramuscular adipocytes differ between bovine breeds with different ability to develop marbling. Our purpose is to take advantage of this natural genetic variability to identify precisely these metabolic differences and, hence, the major genes which control fat accumulation within muscles.

EXPERIMENTAL DESIGN

The general objective is to compare energy, lipid and glucose metabolism in muscle fibers, intramuscular adipocytes and other fat depots between three groups of ten 24-30 month old steers from 3 genotypes: (i) pure bred Angus and (ii) crossbred Angus x Japanese Black steers with high marbling depots, which will originate from Australia, (iii) Limousin steers with low marbling depots, which will originate from France. Samples of fat depots and from two muscles (one oxidative and one glycolytic) will be taken. In case of marbling depots, intramuscular fat will be dissected away from muscle fibers and analysed separately.

Fats which accumulate within intramuscular adipocytes originate either (i) from uptake of circulating fats or (ii) from de novo synthesis by the lipogenic pathway, which requires uptake of glucose from plasma. The activities and expression of glucose transporters and lipogenic enzymes (including lipoprotein lipase, ATP citrate lyase, fatty acid synthase, glucose 6-phosphate dehydogenase, malic enzyme) will be determined in muscles and fat tissues, as well as the activities of enzymes involved in oxidation of fats and glucose within muscle fibers.

OUTCOMES AND PRINCIPAL BENEFITS

The biological markers (e.g. the key metabolic activities), which will be identified, may be used in cattle breeds, (i) to predict the ability of young calves to develop marbling when they will get older, (ii) to select cattle on their ability to develop marbling. Other objectives are the creation of new interactions between the research groups to allow efficient use of new information and its translation into new tools. A series of dissemination measures including presentations, publications such as scientific papers and, if possible, end-user orientated pamphlets to indicate how the results of this research can be used to optimise raw material production (i.e. muscles).

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Last updated: October 09, 2000 .