Study On Film-forming Characterization Of Gelatin α-subunits From Tilapia Skins

Theα₁-subunit andα₂-subunit were separated from tilapia（Tilapia zillii）skin gelatin using ultrafiltration,and the physicochemical properties of obtained subunits were investigated in this study,then the film-forming mechanism of the subunits was investigated.In addition,effects of sodium alginate addition on the properties of gelatin films were investigated.In Chapter 2,alpha-chain subunits were separated from tilapia skin gelatin using ultrafiltration,and the physicochemical properties of separatedα₁-andα₂-subunit were investigated.The results show that theα₂-subunit was rejected by 100 kDa molecular weight cut-off（MWCO）regenerated cellulose（RC）membrane and cellulose（CE）membrane at pH 5.0,whileα₁-subunit was rejected somewhat by 100 kDa polyesulfone（PSF）membrane and 150 kDa MWCO polyethersulfone（PES）membrane.Moreover,α₁-subunit andα₂-subunit with higher purity could be obtained by filtrated the ultrafiltrate separated by single RC membrane and PES membrane with a sandwich configuration of paired RC membranes and PES membranes,respectively.Amino acid composition ofα₁-subunit andα₂-subunit showed that glycine was the most dominant amino acid.However,tyrosine content was higher inα₂-subunit than inα₁-subunit,resulting in a stronger UV absorption near 280 nm.Based on the DSC analysis,it was found that the glass transition temperatures of gelatin,α₁-subunit andα₂-subunit were 136.48 ^oC,126.77 ^oC and 119.43 ^oC,respectively.Moreover,the reduced viscosity and denaturation temperature ofα₁-subunit were higher than those ofα₂-subunit,and the reduced viscosity reached the highest whenα-subunits were mixed with aα₁/α₂ ratio of approximately 2,suggesting thatα₁-subunit seems to play a more important role thanα₂-subunit in the thermostability of gelatin.Then in Chapter 3,effects ofα₁/α₂ ratios and drying temperatures on the properties of tilapia skin gelatin films were investigated.Tensile strength（TS）ofα₁-subunit based films andα₂-subunit based films were 30.4 MPa and 12.8 MPa,respectively.When films were prepared fromα-subunits atα₁/α₂ ratio of 2/1,both TS and elongation at break（EAB）of films were the highest.The color ofα-subunit based composite films was similar to that ofα₂-subunit based films.However,no obvious changes in the SDS-PAGE patterns were observed between film-forming solutions and films.On the other hand,the TS and EAB ofα-subunit based composite films prepared at 10 ^oC or 15 ^oC were much higher than those of films prepared at 20^oC or 25 ^oC.Circular dichroism analysis revealed that triple helical structure was formed in the films containingα₁-subunit dried at 15 ^oC or below,thus forming strong strength films.Effects of sodium alginate addition on the properties of gelatin films were investigated in Chapter 4.The results showed that TS of the compositite films decreased after Maillard reaction（60oC,75%relative humidity relative）.Based on the color,free amino group content and fluorescence intensity of the films,it was suggested that gelatin could be cross-linked with sodium alginate.No obvious change of TS was found among the composite films after they were heated for 48 h.In conclusion,α₁-subunit andα₂-subunit were different in some physicochemical properties.The contribution ofα₁-subunit in the formation of gelatin films was higher than that ofα₂-subunit,and the solution prepared withα₁/α₂ at the ratio of 2/1 exhibited excellent film-forming ability.Gelatin could cross-link with sodium alginate during the Maillrad reaction,and the mixing ratios of gelatin and sodium alginate play no obvious impact on the strength of composite films after they were heated for 48h.