Study On Preparation Of Chicken Bone Gelatin And Its Structure And Functional Properties

Gelatin, as a denaturalized product of collagen, comes from animal bone, tendon, cartilage, epimysium and hide. Gelatin has been widely utilized in food, medicine and Chemistry industry, which take the advantage of its unique properties such as viscosity, reversible gel to sol transition, film making and side-chain reactivity.Chicken bone is a main by-product of chicken processing, which contains large amount of collagen. Only little portion of chick bone is used as human foodstuff and it is a waste to discard the chicken leg bones, which easily become the pollutants. This thesis focused on using chicken leg bones to produce food gelatin, which not only reduces environment pollution but also develops some new foodstuff to satisfy Muslim people's need such as chicken gelatin. This thesis solves the problem of compositive utilization of poultry and enlarges the raw material of gelatin.Methods and conditions of extracting high purity collagen from chicken bone material were studied in this paper. Ether distillation at low temperature could remove most of the fat, leading to a fat residual rate of 0.99%. Decalcification of bone contained the following steps: soaking blocks in a 0.48mol/L HCl stirring at 100rpm, renewing the acid solution per 2h until mineral remain 0.90% (w/w, dry basic) in decalcified ossein. The collagen content was 63.54% in ossein and purity was 88.83%.Structure of chicken bone collagen was studied. Amino acid analysis showed that glycine accounted for 1/3 while proline and hydroproline accounted for 1/4 of the total amino acids. There were abundance of alanine and absence of tryptophan and cysteine. Chicken bone collagen remained tri-helix configuration by X-ray diffraction analysis. The shrinkage temperature of chicken bone collagen fibre was 65.9℃ by DSC analysis. The diameter of collagen fibre bundle was 20-25μm observed through optical microscope. Chicken bone collagen was type I collagen with depart optical character.Liming condition of chicken bone collagen and mechanism of alkali function were investigated. Collagen fibre was soaked in a 0.1% (w/v) Ca(OH)₂ solution at 10℃ for 6 days while the ratio of bone to solution was 1:6, renewing the alkali solution per 24h. After liming, non-collagen protein was dissolved and the collagen purity was increased to 93.78%. The collagen fibre swelled, became wide and the diameter increased to 40-50μm. The shrinkage temperature decreased to 60.24℃ by DSC. It was conferred that dissolution of cell matrix that wrapped collagen fibre resulted into the collapse of collagen fibre bundle. Native fibres of collagen that attracted by elactrostatic attraction between polar section and non-polar section were excluded from each other by the effect of alkali ion, which lead to the decline of density and breakage of crystal structure of collagen. Gelatin extracting ratio from the collagen fibrewas 19.65%, while the viscosity and gel strength were 6.22mPa.s and 2353.4g respectively.Extraction conditions and effect of H2O2 on the conversion from collagen to gelatin were studied. Gelatin was extracted twice. Firstly collagen was heated directly for 3h at pH 5 and 70 'C (solid to liquid was 1:6, size was lmm and stirring rate was lOOrpm) to get chicken bone gelatin 1. The residue collagen was soaked in a 0.2% (w/w) H2O2 solution for 12h, then extracted for 3h at pH 5 and 70*C to get chicken bone gelatin 2. The quality of chicken bone gelatin 1 and 2 were accorded with those of food gelatin of A and B quality index respectively. The total yield ratio was 63%. Clarification of gelatin solution contained the following steps: stirring for 30min at 60°C with diatomite as the sorbent and centrifuging for lOmin at 8000rpm. Gelatin solution was concentrated at 60 °C with the vacuum of 0.1 MPa. Gelatin was dried for 12h at 30-35"Cat first and then kept at 50°C for 8h. The amino acids that tended to be oxidized and unsaturated bond (covalent bond) were attacked directly by H2O2, which made collagen peptide chain break off rapidly and accelerated the conversion from collagen to gelatin.The amino acid composition and structure of chicken bone gelatin were studied. In chicken bone gelatin, there were large amount of glycine, proline, hydroproline, alanine and hydrolysine, but none tryptophan and cysteine. The content of imino acid in chicken bone gelatin was close to pigskin gelatin. Compared with gelatin 1, there were fewer histidine, tyrosine, methionine and phenylalanine in gelatin 2. SDS-PAGE electrophoresis and intrinsic viscosity determination showed that the molecular weight distribution of gelatin 1 was more centralized than gelatin 2. Total configuration content of ai and (X2 in gelatin 1 and gelatin 2 were 83.2% and 22.9% respectively. The average visco-molecular weight of gelatin 1 and 2 were 122,000 and 58,500 respectively, Surface hydrophobicity(So) of gelatin 1 and gelatin 2 were 2.21 and 1.855 respectively and the pi of gelatin 1 was about 9. Gelatin 1 is consisted of tri-helix and single- helix configuration, but gelatin 2 is merely contained of single-helix configuration by FT-IR and X-ray analysis. CD spectrum proved that chicken bone gelatin behaved as helix configuration in solution higher than Tm.Gelatin gelling properties and gelling mechanism were studied. Viscosity of gelatin solution increased with higher concentration and decreased with higher temperature. Viscosity of gelatin solution decreased with increasing of shear rate and behaved as Plastic liquid, when shear rate was higher than 20S"1, viscosity of gelatin solution kept constant and behaved as Newton liquid. Gel was formed when gelatin solution was cooled. Gelling concentration decreased with higher relative molecular weight. Gelling temperature and melting temperature increased with gelatin concentration. Gel strength increased with the enhancing of concentration, the approaching to pi, prolonging time or lowing temperature.Gelling included two steps of rapid formation of gel network and slow growth of gel network. In the first step, viscosity solution system was translated to rigidity gel systemrapidly. And during the second step, rigidity of gel system was strengthened. Configuration of junction zone of gelatin network was tri-helix configuration as collagen, which was confirmed by the change of CD spectrum from positive absorb in 222nm to negative absorb when gel to sol transition. Gelling was prevented in urea solution and restrained in SDS solution, acidic or alkaline solution. Hydrogen bonds was formed and the distance between different molecular chains was shorted when gelling by FT-IR spectrum. Fluorescence intensity increased highly when gelatin solution was cooled to its gelling temperature. Those result showed that hydrogen bond maintained gel network structure, while both electrostatic and hydrophobic interaction participated in the formation of gel network. The trend which gelatin molecules aggregated with each other automatically to form gel network was showed by atom force microscope. Gelling mechanism of gelatin was described as following: the gelatin molecule chains congregated to form a well-regulated structure region when gelatin solution was cooled down. When regulated structure region were distributed in all solution, the movement of molecule chain ceased and gel network was formed. If cooled down furtherly, the well regulated structure region extended, leading to increase gel strength. The configuration of junction zone was similar with tri-helix of collagen. Hydrogen bond maintained gel network structure, while both electrostatic and hydrophobic interaction participated in the formation of gel network.Filming properties of gelatin was studied.A transparent and bright film was formed with 8% gelatin and 1/6 glycerol, which had good mechanical properties, oxygen barrier properties and low vapor barrier properties. Gelatin and pullulan were incompatible with each other from the view point of thermodynamics. The properties of their blended film depended on the gelatin ratio in blends. When the ratio of gelatin to pullulan was 4:1, the oxygen barrier property of the blend film increased. Simulated capsule shell made from these blends had a similar quality as pigskin gelatin capsule shell. Simultaneously the phenomenon of retarded dissolution during the storage was improved.