Isolation And Structural Characterization Of Collagen And Rheological Properties Of Dispersions

Collagen has a wide range of applications in cosmetic,biomedical,food and pHarmaceutical fields,due to its biocompatibility,biodegradability and low immunogenicity properties.Lumpfish,which is commonly found in the iceberg area of arctic or north Atlantic,belongs to the circular fin species.They live in the 200 meters deep in the ocean,where no pollution is a factor.In addition,the fish contains a lot of unsaturated fatty acid and calcium.More important,their skins are very thick,accounting for about one third of their total body weight,which explains why lumpfishes have rapidly caught scientific attention these days.In the process of collagen products,collagen inevitably will be affected by all kinds of mechanical action,such as shear or extrusion.Therefore,there has a very important guiding significance in full understanding of the rheological properties of collagen solution for processing and application of collagen.Guanidine hydrochloride(GuHCl)is a kind of typical hydrogen bond breaker,containing two amino.hydrogen bonds were formed between the hydroxyl,carboxyl and amino of collagen molecules,replacing part of collagen intermolecular and intramolecular hydrogen bonds,making collagen conformation or the state of aggregation structure changes.For the study of rheology,thixotropy is one of the important content,but because of its complexity,so far the change rule and the understanding of the mechanism is still lack of unified.Therefore,this thesis focuses on guanidine hydrochloride/collagen thixotropic property of dispersion system.This thesis contains four chapters.(1)Collagen was successfully extracted from the outer skin of lumpfish and pig using the method of pepsin digestion.The acid-soluble collagen(ASC),pepsin-soluble collagen(PSC)and pig collagen(PPSC)were characterized with Sodium dodecyl sulfate-polyacrylamide gel electropHoresis(SDS-PAGE),Fourier transform infrared spectroscopy(FTIR)and Ultraviolet(UV).According to the electropHoretic pattern,the isolated pig skin collagen was classified as type I collagen.FTIR and UV results confirmed the presence of triple helical structure in collagen molecule.Moreover,the isoelectric points and the denaturation temperatures were studied.(2)Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were used to study changes of collagen structure and aggregation behavior with increasing guanidine hydrochloride concentration.It found that along with the increase of concentration of guanidine hydrochloride,the aggregation structure of collagen was destroyed and the network structure became loose.(3)The rheological properties of GuHCl/collagen dispersions were investigated as a function of guanidine hydrochloride(GuHCl)concentration and action time.The results of flow curves indicated that the pseudoplastic flow behavior of GuHCl/collagen dispersions gradually close to the Newtonian fluid with the increase of GuHCl concentration in the range of 0~6.0 mol/L and action time in the range of 6~48 h.The linear oscillatory shear experiment,steady shear experiment and thixotropic loop experiments were performed to investigate thixotropic behavior of the GuHCl/collagen dispersions.It was found that the thixotropic type of the GuHCl/collagen dispersions may be affected by GuHCl concentration and action time.With the increase of GuHCl concentration,the thixotropic type of GuHCl/collagen dispersions transformed from positive thixotropy to complex thixotropy and then negative thixotropy;and the thixotropic type of collagen dispersion with 1 M GuHCl transformed from complex thixotropy to negative thixotropy with the increase of GuHCl action time.The complex thixotropy in GuHCl/collagen dispersions has not been reported in similar systems so far.(4)Effect of collagen concentration,pH and temperature on rheological properties of GuHCl/collagen dispersions were studied.The results show that the thixotropic type of collagen dispersions was complex thixotropy at lower concentration of GuHCl(c<1.0 mol/L),when the collagen concentration is 0.2 mg/m L,1.0 mg/mL or pH is 11.0.When pH=5.0,GuHCl concentration c<1.0 mol/L,the dispersions was positive thixotropy.When pH=9.0,c=0.25 mol/L,the dispersions was positive thixotropy;c=0.75 mol/L,the dispersions was complex thixotropy.When c>=1.0 mol/L,the dispersions was negative thixotropy,despite the collagen concentration and pH how to change.When temperature was raised to 35 ? or 45 ?,GuHCl concentration c>=1.0 mol/L,the dispersions was negative thixotropy.