Behavior Of Self-assembled And Simulated Digestion Of Isolated Collagen From The Chicken Feet Skin

Collagen has irreplaceable advantages as medicine and food materials,so there are increasing demand for it in recent years.Nowdays,China has become the second largest country in poultry industry after passed EU,but the low utilization of the by-product in chicken processing causeed the huge waste of resource.It is urgent to study the development and usage of chicken feet collagen due to its high content of collagen.However,collagen has poor mechanical properties,poor thermal stability and other disadvantages.In order to solve this problem,it is necessary to study the preparation and properties of collagen materials to improve its application performance.The research of their digestibility is improtant because no matter collagen or collagen material most would be intaken by people.In this paper,chicken feet skin was used as raw material to study the separation and extraction of collagen by salt,acid and enzymatic methods.The collagens were puried by salting-out,characterized and contrasted in their digestibility.The effects of ultrasound on the self-assembly process of collagen and the digest behavior of the different treatment products of collagen in the Biomimetic Dynamic Rat Stomach Digestive System(BD-RSDS)were studied,in order to provide theoretical foundation for the production,material applicaton,digestion and absorption of collagen from chicken feet.(1)Impure protein and fat in the chicken feet skin can be removed by buffered saline solution.Collagen was extrated by different solution,then characterized and its gastrointestinal digestibility was studied.The yeilds of sodium chloride-soluble collagen(SSC),acetic acid-soluble collagen(ASC)and pepsin-soluble collagen(PSC)were 1.13±0.31%,14.49±0.90% and 49.10±1.95%,respectively.PSC,ASC and SSC have the same secondary structure and maintained their intact triple helical structure,were characterized as type I collagen by the results of Fourier transform infrared spectroscopy,Sodium dodecyl sulphate polyacrylamide gel electrophoresis and circular dichroism.Amino acid analysis showed that the degree of hydroxylation of the collagens were 45.8%,45.2% and 37.5%,respectively.The highest degree of proline hydroxylation of PSC means the highest denaturation temperature,which was also consistent with the result of dynamic temperature scan of rheology test.Scanning electron microscopy and atomic force microscopy microstructure of collagens showed that they all have the unique network fiber structure.The degree of hydrolysis of collagen was demonstrated to be 21.00%(SSC),22.49%(ASC)and 24.00%(PSC),respectively,after 10 h hydrolysis experiments.The results showed that the reducing power was 0.34(SSC),0.35(ASC)and 0.40(PSC),and they might be related to the degree of hydrolysis and negatively correlated with the relative molecular mass.There was no obvious difference in ·OH scavening rate.Experiments showed that PSC has a higher extraction rate,better thermal stability,and easier to be digested,so the following tests were conducted by PSC.(2)The effects of ultrasonic frequency on collagen self-assembly were studied by using PSC as raw material.Samples were prepared by using different ultrasonic frequency :0,20 kHz/270 w,40 kHz/270 w,60 kHz/270 w,(20/40/60 kHz)/ 90 w during the first 5 min and non-ultrasonic solution were used as control,which called C0H0 m,C20H5m,C40H5 m,C60H5m and CtH5 m respectively.Turbidity and viscoelasticity test showed that the process of self-assembly was divided into three stages: nucleation stage,growth stage and equilibrium stage.Since the turbidity test only reflected the effect of collagen fiber aggregation on the absorbance value,the viscoelasticity test is more accurate.The Increasing frequency of the ultrasound will speed up the self-assembly,but the frequency of 60 kHz is better than the tri-band.Atomic force microscopy and transmission electron microscopy showed that the ultrasonic treatment made the self-assembled collagen fiber structure more loose and regular.The fiber diameter size of collagen gel C60H5m(65-89 nm)is bigger than C0H0m(80-161 nm)which measured by atomic force microscope.The result showed that the ultrasonic treatment could decrease the degree of self-assembly and the mechanical properties.The creep recovery rate are as follows: 81.54%(C0H0m),78.36%(C20H5m),76.26%(C40H5m),63.67%(C60H5m)and 72.66%(CtH5m).And the simulated gastrointestinal digestion test showed ultrasonic treatment makes collagen gel easier to be digested.(3)PSC,PSCU?PSCUN and PSCH were digested by the Biomimetic Dynamic Rat Stomach Digestive System(BD-RSDS).The determination of soluble amino groups showed that the hydrolysis rate of PSCH was the fastest,and the hydrolysis resistance of PSCUN was the best.Atomic force microscopy and inverted fluorescence microscopy results showed that the PSCH hydrolyzate was more evenly distributed in the field of view and therefore more conducive to digestion.Gel filtration chromatography(GPC)determination of relative molecular mass distribution and free amino acid analysis of the enzymatic hydrolysis product showed that the contents of aspartic acid,leucine,tyrosine and phenylalanine in the three samples varied greatly,the content of oligopeptides was the highest in the final digestion products.