How Muscle Structure and Composition Influence Meat and Flesh Quality

Abstract

Skeletal muscle consists of several tissues, such as muscle fibers and connective and adipose tissues. This review aims to describe the features of these various muscle components and their relationships with the technological, nutritional, and sensory properties of meat/flesh from different livestock and fish species. Thus, the contractile and metabolic types, size and number of muscle fibers, the content, composition and distribution of the connective tissue, and the content and lipid composition of intramuscular fat play a role in the determination of meat/flesh appearance, color, tenderness, juiciness, flavor, and technological value. Interestingly, the biochemical and structural characteristics of muscle fibers, intramuscular connective tissue, and intramuscular fat appear to play independent role, which suggests that the properties of these various muscle components can be independently modulated by genetics or environmental factors to achieve production efficiency and improve meat/flesh quality.

Figure 1

General organization of the muscle [9]. Skeletal muscle predominantly consists of muscle fibers and connective tissue. The latter is distributed on three levels of scale in the muscle: the endomysium, which surrounds each muscle fiber, the perimysium, which compartmentalizes muscle in fiber bundles, and finally the epimysium, which is the external envelope of muscle. Within the fibers, the myofibrils occupy nearly the entire intracellular volume. The contractile unit of the muscle fiber is the sarcomere.

Figure 2

Diagram of a fish fillet (salmon) in longitudinal section, beneath the skin, to present the W-shape of myomere and the two muscle types.

Figure 3

Diagrammatic organization and distribution of muscle mass on a trout cutlet (cross section).

Figure 4

Histologic cross section of Sea Bass (Dicentrarchus labrax) white muscle stained with sirius red and fast green. Muscle consists of large and small fibers (approximately 100 and 10 microns in diameter, resp.).

Figure 5

The sarcomere, which is the smallest contractile unit of the muscle, is delimited by the Z disks. It consists of at least thirty different proteins, of which the most abundant are myosin and actin.

Figure 6

Semitendinosus muscle cross section from a Basque pig at 145 kg live weight. The intramuscular fat content (IMF) is approximately three times higher in the white glycolytic than in the red oxidative portion of the muscle (Lefaucheur, personal communication).

Figure 7

(a, b) Histological cross sections of bovine semitendinosus muscle taken at slaughter (a) and 12 days postmortem. (b) Observed by light microscopy. During storage (4°C in a cold room), cells shrink and extracellular spaces increase. (c, d) Histological longitudinal section of bovine semitendinosus muscle taken at slaughter (c) and 12 days postmortem (d) observed by transmission electron microscopy. At the ultrastructural scale, proteolytic action of enzymes causes breaking of myofibrils along the Z disks.