Relationship between development of intramuscular connective tissue and toughness of pork during growth of pigs.

We investigated changes in structures and properties of the endomysium and perimysium during development of semitendinosus muscle in relation to the increase in toughness of pork using samples from neonates to 55-mo-old pigs. The shear force value of pork increased linearly until 6 mo of age, and the rate of increase slowed down thereafter. The secondary perimysium thickened owing to an increase in the number and thickness of perimysial sheets consisting of collagen fibers, which became thicker and wavy with the growth of the pigs. This increase in thickness of the secondary perimysium was correlated significantly with the increase in the shear force value (r = .98). The endomysial sheaths became thicker and denser in the muscle of 6-mo-old pigs. Maturation of the endomysium was accompanied by hypertrophy of muscle fibers. The amount of heat-soluble collagen decreased almost linearly, indicating that nonreducible cross-links between collagen molecules were formed throughout chronological aging. We conclude that thickening of the perimysium is closely related to an increase in the toughness of pork during growth of pigs.