Study On Extraction And Properties Of Gelatin From American Eel (Anguilla Rostrata) Bone

Gelatin is the product of denaturation and hydrolysis of collagen.It has many excellent functional properties such as gelling properties,emulsification and water holding capacity.It has been widely used in food,cosmetics and medicine.Using fish scales to produce gelatin can not only improve the utilization rate,save resources and reduce environmental pollution,but also has higher safety and bio-compatibility.In this study,acid-soluble collagen(ASC)and pepsin-soluble collagen(PSC)were prepared from American eel(Anguilla rostrata)bone by acidic method and enzymatic method,and their physicochemical properties were investigated.The American eel bone was pretreated with acid or alkali,and the fish bone gelatin was extracted at 60°C water bath.The effects of pretreatment methods on the physicochemical properties and gel properties of fish bone gelatin were investigated.Fish bone gelatin was prepared by different extraction temperatures,and the effects of the physicochemical properties and functional properties of fish bone gelatin were studied.Moreover,fish bone gelatin with good emulsifying properties was selected and used in the preparation of chocolate.The effects of fish bone gelatin on the rheological properties of black chocolate were also investigated.Detailed results are as follows:(1)ASC and PSC were prepared from American eel bone and the differences in physicochemical properties were studied.The results of SDS-PAGE showed that the protein contained three?subunits,one?chain and a small amount of?chain.Both of the two collagens are mainly composed of type I collagen,which the contents of?and?in ASC were higher than those in PSC.The amino acid composition results showed that the sub-amino acid contents of ASC and PSC were 164 and 163 residues/1000 residues,respectively.The results of FTIR and CD showed that ASC and PSC retained complete triple helix structure.The denaturation temperature of ASC was slightly higher than that of PSC,30.4°C and 30.1°C,respectively.ASC could self-assemble to form a uniform and dense collagen fiber network in vitro.(2)Fish bone was pretreated by acid/alkali treatment.Acidic gelatin(AG60)and Alkali gelatin(BG60)were extracted at 60°C water bath.The effects of two pretreatment methods on the physicochemical properties and gel properties of fish bone gelatin were studied.As results,the yields of AG60 and BG60 was 13.6%and 6.9%,with the corresponding gel strength of 102.0 g and 78.7 g,respectively.The hydroxyproline contents of AG60 and BG60 were 3.4 g/100 g and2.8 g/100 g,respectively.Both gelatins contain?,?₁ and?₂ chains,and AG60 has higher?₁+?₂content than BG60.AG60 has higher gel temperatures and melting temperatures and shorter gelation time than BG60.The SEM results showed that AG60 had a denser and more uniform gel network structure.This study showed that compared with alkali pretreatment,the eel bone gelatin extracted by acidic pretreatment had higher yield and better gel properties.(3)The effects of extraction temperatures on the physicochemical properties and functional properties of eel bone gelatin were investigated.The results showed that with the increase of extraction temperature,the yields of bone gelatin increased while the contents of hydroxyproline decreased gradually.SDS-PAGE results showed that the?and?subunits of gelatin were degraded as the extraction temperature increased,and the gel strength gradually decreased.With the increase of extraction temperature,gelatin gelation temperature and melting temperature decrease,and the time needed to form gelatin gradually increases.Surface hydrophobicity and emulsifying properties of alkali treated gelatin were positively correlated with the extraction temperature,while acid treated gelatin exhibited the opposite correlation.The above results showed that the extraction temperature had significant influence on the fish bone gelatin,resulting in some variability in its physicochemical properties.(4)The effect of fishbone gelatin on the rheological properties of black chocolate were investigated using the type B gelatin,incorporating with cocoa fat emulsion as fat-based substitutes.The results showed that the stability of fishbone gelatin and cocoa butter emulsion increased with the increase of extraction temperature.The addition of gelatin could significantly improve the apparent viscosity of melted chocolate in the emulsion.Based on the frequency scanning results,all samples present viscous behavior with higher G??values than G?.Moreover,the addition of gelatin did not change the melting point and color difference of black chocolate.The above results indicated that the type B collagen could be the ideal substitute of cocoa butter for black chocolate.