title: Effect of cyclic freeze-thawing process on the structure and properties of collagen.
abstract: The influence of freeze-thawing cycles (named 'N') on the rheological and thermal properties of bovine skin collagen solution was investigated using a rheometer and differential scanning calorimetry (DSC). The results of dynamic frequency sweep tests showed that the elasticity of collagen increased as N increased to 3, 5 and 7. Especially, after the freeze-thawing cycles of N=7, the recovery capacity of collagen remarkably increased (from 17.76% to 74.98%) and the hysteresis loop areas of collagen also became larger (from 95.53 to 218.24 Pa/s). Moreover, DSC and non-isothermal kinetic analysis revealed that although the freeze-thawing process had little impact on the thermal denaturation temperature, the endothermic enthalpy was increased by 73% when N=7, as estimated from the area under the endothermic peak and from the Friedman isoconversional method. In addition, as observed by atomic force microscopy (AFM), the fibers of collagen became thicker after the process of freeze-thawing cycles, indicating that the aggregation of collagen molecules was enhanced in the process of freeze-thawing. Meanwhile, the morphology of freeze-thawed collagen sponge examined by scanning electron microscopy (SEM) exhibited a porous network structure, and the pores became more regular with increasing N.
authors.affiliation: The Key Laboratory of Leather Chemistry and Engineering of Ministry of Education, Sichuan University, Chengdu 610065, PR China; College of Ecological Environment and Urban Construction, Fujian University of Technology, Fuzhou 350108, PR China.
authors.forename: Cuicui
authors.initials: C
authors.lastname: Ding
authors.affiliation: College of Materials Engineering, Fujian Agriculture and Forestry University, Fuzhou 350002, PR China.
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.affiliation: The Key Laboratory of Leather Chemistry and Engineering of Ministry of Education, Sichuan University, Chengdu 610065, PR China; National Engineering Laboratory for Clean Technology of Leather Manufacture, Sichuan University, Chengdu 610065, PR China. Electronic address: liguoyings@163.com.
authors.forename: Guoying
authors.initials: G
authors.lastname: Li
mesh_terms: D000818:Animals; D002417:Cattle; D003094:Collagen / Q000737:chemistry*; D005615:Freezing; D008422:Materials Testing; D055595:Mechanical Phenomena; D012212:Rheology; D013997:Time Factors
chemical_list: D003094:Collagen
keywords: Collagen; Freeze–thawing; Rheology; Thermal properties