Study On Properties And Film-forming Ability Of Tilapia Skin Gelatin By Hot-water Extraction

Usually,gelatin was obtained by hot-water extraction.However,gelatin was susceptive to be degraded during the hot-water extraction which would result in the decrease in the gel strength of gelatin and the tensile strength of gelatin films.Therefore,this study aimed at how to protect the protein patterns during hot-water extraction by controlling the acid pretreatment time and skin concentration,and then the properties and film-forming ability of the extracted gelatin were improved.In addition,the addition of thermal protectants on the protection of gelatin protein patterns were also investigated.Finally,the effect of storage time on the tilapia skin films was investigated.Firstly,the effect of acid pretreatment time on the properties and film-forming ability of gelatin from tilapia skin by hot-water extraction was investigated.The results of scanning electron micrograph(SEM)showed that the structure of tilapia skin became more loosen with increasing acid pretreatment time.When the acid pretreatment time was increased to 40 min,?-chain??-chain and ?-chain in tilapia skin collagen were more susceptive to be degraded during the hot-water extraction,and the hydroxyproline content of gelatin was decreased from 65 to 47 residues per 1000 amino acid residues.With increasing acid pretreatment time from 10 min to 80 min,the viscosity,gel strength and denatured temperature(Td)of gelatin,the tensile strength(TS)of gelatin films decreased from 14.88 cp?241.23 g?27.5oC?56.22 MPa to 8.93 cp,144.00 g,22.5 oC ? 34.18 MPa,respectively.The results of cricucal dichroism showed that gelatin films could form triple helical structure by renaturation below the denaturation temperature of gelatin..Nextly,the effect of skin concentration on properties and film-forming ability of gelatin from tilapia skin by hot-water extraction was investigated.The results showed that the viscosity and gel strength of the extracted gelatin both presented earlier increase and later decrease trend with the increasing skin concentration.The mechanical properties of films prepared from the extracted gelatin also presented the same trend.When skin concentration by hot-water extraction was 10.0%,the gel strength was 281.33 g and tensile strength(TS)of prepared films was 60.02 MPa.However,the amino acid composition and protein components were both found no significant differences.Based on the analysis of DSC(differential scanning calorimeter)and CD(Circular dichroism),random coil degree of the extracted gelatin was relatively small and the thermal stability of gelatin films was the highest when extraction skin concentration was10.0%.On the other hand,the addition of thermal protectants were investigated.The results showed that the glycine,trehalose and sorbitol had no obvious protection effect on the protein patterns.In addition,high contents of trehalose and sorbitol as plasticizers probably reduced the interactions between the gelatin molecules.TMAO had obvious effect on protecting the protein patterns during the hot-water extraction.The gel strength of gelatin and tensile strength of prepared gelatin films was increased with increasing TMAO.When TMAO was 7.0%,the gel strength was 224.68 g and tensile strength(TS)of prepared films was 55.27 MPa.Based on the results of SDS-PAGE,CD and FTILER,it was found that gelatin was dissloved out during the hot-water extraction,TMAO was probably excluded from the gelatin hydration layers.Therefore,gelatin proteins would tend to fold more compactly,and the interactions were enhanced.At last,the effects of storage time on the properties of tilapia skin gelatin films were investigated.25oC?0% RH storage had no obvious influences on the characteristic of gelatin films,and gelatin films could store in stable condition.In 25oC?50% RH storage as the storage time increased to 90 days,TSM of gelatin films decreased from 100% to 43.88%,and TS of gelatin films increased from 55.22 MPa,to 76.55 MPa.In addition,gelatin films became yellow gradually and the transparent values showed increasing trends.