Study On Film-forming Mechanism And The Improvement Of Protein Film Properties Based On Scale Gelatin

Gelatin from tilapia(Tilapia zillii)scales was used to prepare the gelatin film,and the effects of drying temperature and gelatin mass concentration on gelatin film-formation were investigated in this study.In addition,the properties of gelatin film were improved by thermal-treated soybean protein isolate(SPI)and konjac flour.In Chapter 2,the effects of drying temperature and mass concentration on properties of tilapia scale gelatin during sol-gel-film formation were investigated.Based on the rheological properties,the temperature of gelling point increased from 18.75℃ to 30.83℃ with increasing gelatin mass concentration from 5%to 30%.During the heating dry,there were good linear correlations between gelatin mass concentration and gelling point temperature in three segments of 25～30℃,33～55℃ and 55～70℃,and the linear slopes decreased with increasing temperature.Furthermore,helical structures were found in the gel with 5%gelatin prepared at 25℃,while random coil structures were involved in the gel formation at 35℃ and 55℃,respectively.The melting temperature of gelatin gel increased from 39.09℃ to 40.70℃,and to 48.40℃ with increasing gelatin concentration from 5%to 40%,and to 75%,respectively.Similar tendencies were observed in the enthalpy change of gelatin gels.The gelatin film strength decreased with the increase of drying temperature from 25℃ to 55℃.But strong gelatin films dried at 35℃ or 55℃ could be also obtained by evaporating to increase mass concentration at 25℃.The effects of thermal treatment temperature of SPI on the physicochemical properties of gelatin-SPI composite films were investigated in Chapter 3.As a result,both the tensile strength(TS)and elongation at break(EAB)of composite films first increased but decreased again with the increase of SPI thermal treatment temperature,and reached maximum values at 70℃,which were 33.12 MPa and 48.25%,respectively.While,the film solubility(FS)and water vapor permeability(WVP)showed opposite trends.Based on the results of associative forces involved in the formation of composite films,it was found that the composite films which SPI thermal-treated at 70℃ had the highest proportion of covalent bond compared with others samples.Moreover,the glass transition temperature(Tg)of composite films prepared by SPI with 70℃ thermal treatment was the highest.It was concluded that the water resistance,mechanical properties and thermal stability of the composite films prepared by SPI thermal-treated at 70℃were all best.In the next section of Chapter 4,the effects of thermal treatment temperature on the physicochemical properties of gelatin-konjac flour bi-layered composite films were investigated.As a result,the FS and protein solubility(PS)of the composite films in warm water at 30℃were 45.62%and 28.83%,respectively.When the thermal temperature of composite films was increased,both FS and PS were gradually decreased,the band intensities of a and β chain of protein dissolved in warm water of 30℃ were decreased.The contact angle in the gelatin side and the konjac flour side of composite films were 107.14° and 88.53°,respectively,both of which were increased after thermal treatment.The WVP of composite films was decreased,but both b*value and transparency value of films were increased with the increase of thermal temperature.Based on the results of scanning electron microscopy(SEM)and differential scanning calorimetry(DSC),it was found that the two layers of gelatin and konjac flour in the composite films were integrated gradually,and the thermal stability of films was increased as the thermal temperature increased.It was concluded that the water resistance,surface hydrophobic properties,moisture barrier properties and thermal stability of gelatin-konjac flour bi-layered composite films could be improved by increasing thermal treatment temperature.In conclusion,when the gelatin film was dried above the denaturation temperature,the gelatin mass concentration could be increased to enhance the strength of the film.The water resistance,mechanical properties and thermal stability of the gelatin film could be effectively improved by blending SPI which thermal-treated at 70℃ and TGase.The edible packaging film with excellent water resistance,moisture barrier properties and thermal stability could be obtained by thermal-treating bi-layered composite film prepared with gelatin and konjac flour at 100℃.