Abstract: This study aimed to explore the effect of intramuscular connective tissue changes during freeze-thaw cycles on the quality of bovine rumen smooth muscle. The changes in the shear force, pH, thawing loss rate, collagen solubility, collagen-degrading enzyme activity, cross-linked pyridine content and microstructure of bovine rumen smooth muscle subjected to different freeze-thaw cycles were analyzed. The results showed that the activity of collagen-degrading enzymes including β-galactosidase (β-gal) and β-glucuronidase (β-GD), the contents of cross-linked lysine pyridinoline (LP) and hydroxylysine pyridinoline (HP), collagen solubility and thawing loss rate significantly increased with increasing freeze-thaw cycles (P < 0.05). Similarly, the degree of rupture of endomysium and perimysium as well as the gap between muscle fibers increased, so that the arrangement of muscle fibers became looser. The shear force and pH significantly decreased when the number of freeze-thaw cycles was greater than 1 (P < 0.05). The thawing loss had a significantly negative correlation with pH (P < 0.05), but a significantly positive correlation with the contents of cross-linked HP and LP (P < 0.01). The shear force a had significantly negative correlation with β-gal activity, β-GD activity, and collagen solubility (P < 0.01). In conclusion, the decrease in pH and the formation of crosslink can lead to an increase in thawing loss, and the decrease in shear force mainly depends on the damage of ice crystal to muscle and protein degradation. The rate of shear loss decreases slowly and the rate of thawing loss increases after 3 freeze-thaws. Therefore, controlling freeze-thaw cycles within three cycles can reduce the loss of enterprises while ensuring the quality of smooth muscle.

Key words: rumen; freeze-thaw cycles; collagen; degradation; cross-linking; quality