Rheological Characterization Of Fish Bone Gelatin From Large Yellow Croaker(Larimichthys Crocea) And Its Composite System With Polysaccharides

Collagen is an important structural protein widely distributed in animal skins,muscles bonds and connective tissues,which is denatured and converted into gelatin.Due to its good biodegradability,hypoallergenicity and emulsification properties,gelatin is widely used in food,pharmaceutical and industrial applications.In recent years,with the outbreak of zoonotic diseases and religious restrictions,aquatic animal processing by-products have gradually replaced skin and bone of terrestrial animals as the ideal raw material for gelatin production.In this thesis,the acid-soluble collagen from different tissue sources was prepared and its physicochemical properties were comparatively analyzed using the major economic fish in China,Large yellow fish（Larimichthys crocea）,as the research object.Fish bone gelatin was prepared by hot water extraction method using fish bone as the main raw material,and the effects of different extraction temperatures on the physicochemical,gelation and rheological properties of gelatin were investigated.On this basis,the gelatin/carrageenan complexes were prepared by compounding the gelatin extracted at different temperatures with carrageenan,and the effects of different temperature extraction on the gelatin/carrageenan complexes were investigated on the gel properties and rheological properties of the gelatin/carrageenan complexes.The main experimental results are as follows.Acid-soluble collagens（ASCs）were extracted from different tissues of large yellow fish and their physicochemical properties were analyzed comparatively.The results showed that the yields of ASCs in bones,skins,scales and mucles were 3.22±0.47%,42.30±1.15%,2.82±0.31%and 0.89±0.12%,respectively.SDS-PAGE and FTIR analysis showed that ASCs consisted ofα_1（3）chain,α₂ chain,βchain andγchain,which were type I collagen and had a complete three-stranded helix structure.Quantitative analysis of SDS-PAGE showed that the proportion ofβ-chains in fish scales ASCs was lower than that of other tissues.The content of imino acids（proline and hydroxyproline）of ASCs in bones,skins,scales and mucles were 169,167,162 and 173 residues/1000 residues,respectively.The T_m=30.15℃of scale ASCs was lower than that of bone,skin and mucles.The percentage ofβ-chain content showed a high correlation with T_m determined by DSC（R²=0.984）,which was similar to the correlation between imino acid content and T_m（R²=0.994）,and the results indicated that theβ-chain content had an effect on the thermal stability of collagen.The effects of different extraction temperatures on the gelatin yield and its physicochemical properties were investigated using large yellow fish bones.The gelatin was extracted from 30℃to 90℃,and the lowest gelatin yield of 7.21±0.34%was obtained at30℃,and the highest gelatin yield of 23.32±0.32%was obtained at 80℃.Degradation of gelatin.Combined with the above experimental results,the gelatin extracted at 60℃,70℃and 80℃（G60,G70,G80）was selected for subsequent experiments.The gel strength results showed that G60 had the highest gel strength of 86.39±1.43 g,while G80 could not form a gel.FTIR analysis showed that the fish bone gelatin extracted at different temperatures had gelatin characteristic absorption peaks in the amide region,and the hydrogen bonds between gelatin molecules were broken at high temperatures.The rheological analysis showed that the gelation temperatures（T_g）of G60,G70 and G80 were 14.32℃,3.88℃and 2.18℃,respectively,and the melting temperatures（T_m）were 19.31℃,15.94℃and 14.05℃,respectively.The above results showed that the extraction temperature significantly affected the gelatin yield and molecular weight distribution,resulting in some variability in its physicochemical properties.Based on the above experimental results,G60,G70 and G80 gelatin samples were selected for compounding with carrageenan（G60K,G70K and G80K）.The results showed that the gel strength of the gelatin/carrageenan composite system increased significantly（p<0.05）with the decrease of the molecular weight of fish bone gelatin at the same carrageenan addition.In the rheological analysis,the viscosity of the formed composite system decreased with increasing shear rate,showing shear thinning phenomenon.The results of temperature scan showed that the T_g and T_m of G80K were significantly increased to 20.43℃and 43.39°C,respectively.The SEM observation shows that the microstructure of the composite system is dense and the pores disappear.The above results indicated that the composite systems of gelatin with different molecular weights and carrageenan were similar to mammalian gelatin and were expected to be used as a substitute for mammalian gelatin.