Thermal properties are an important parameter of connective tissue. Compared to NB, more IMCT was extracted from WB, not only at day 1 but also at day 3 post mortem (
Figure 4). Furthermore, DSC results showed no significant differences at the beginning and peak temperatures, however, the enthalpy of denaturation (ΔH) was significantly lower for WB compared to NB (
Table 1) and the endset tempature of WB was significantly lower compared to NB on 3 days postmortem. It should be mentioned that there was a slight downward trend in ΔH for WB and a subtle downward trend in end temperature from day 1 to day 3. According to Kopp, et al., (1990), collagen in IMCT showed a decrease in ΔH with increasing collagen cross-linking in dried samples of corrugated muscle, suggesting that the result of hydrophobic action corresponds to a change in stable cross-linked collagen fibers [
25]. We speculate that an alteration involving cross-linkages in the structure of the intramuscular connective tissue of WB may explain the lower ΔH, in addition, an increased amount of attributed to decorin, a proteoglycan that mediates collagen crosslinking, growth factor signaling, and cell growth in WB connective tissue [
26] could be another reason.. SDS-PAGE patterns showed that the protein profiles of intramuscular connective tissue extracted from WB and NB muscles differed (data not shown). The thermal and mechanical stability of intramuscular connective tissue is primarily related to the chemical nature of covalent intermolecular cross-linking of collagen [
27]. Velleman and Clark [
7] used real-time quantitative PCR analysis of WB muscle and found that the expression levels of decorin, a regulator of collagen cross-linking, correlated with differences in collagen organization. Differences in connective tissue composition may result in different thermal properties. Increased muscle stiffness affected by WB is not only associated with increased collagen content, but also with the degree of fibrillated collagen and structural features such as fiber diameter, cross-linking, fiber density, and other structural features [
28]. According to Sanden et al. [
29], wooden breast had more diffuse and broader connective tissues with more gaps, showing a thin and thick mixture of collagen fibers, and IMCT denaturation studied by DSC showed the presence of different endothermic peaks in the range of 50 - 80°C [
30]. As for the surface of the
pectoralis major muscle, the total enthalpy of protein denaturation was found to be significantly lower (
p < 0.05) in the WB group if compared to the NB group (3.2 vs 3.92 J/g) [
31,
32]. Collagen biosynthesis and intermolecular crosslinking is a complex biological process mediated by a series of key regulators [
33]. More collagen cross-linking decreases the elasticity of collagen fibers, leading to increased tissue stiffness and reduced meat quality. Although an increase in the amount of connective tissue components was found in the WB case mentioned above, thermally inert cross-linking could be responsible for a similar evolution of compression and shear force values measured on WB and NB cooked samples [
31]. It is well known that in skeletal muscle there are three layers of connective tissue containing extracellular matrix macromolecules, including epimysium, perimysium and endomysium The predominant extracellular matrix proteins in these layers are fibrillar collagens, particularly type I and III [
34]. Although different SDS-PAGE patterns were found, it is not very clear how these collagen types are affected by WB, if both type I and type III collagens were affected in the current study. This warrants more research in the future.