| The?1-subunit and?2-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 separated?1-and?2-subunit were investigated.The results show that the?2-subunit was rejected by 100 kDa molecular weight cut-off?MWCO?regenerated cellulose?RC?membrane and cellulose?CE?membrane at pH 5.0,while?1-subunit was rejected somewhat by 100 kDa polyesulfone?PSF?membrane and 150 kDa MWCO polyethersulfone?PES?membrane.Moreover,?1-subunit and?2-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 of?1-subunit and?2-subunit showed that glycine was the most dominant amino acid.However,tyrosine content was higher in?2-subunit than in?1-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,?1-subunit and?2-subunit were 136.48 oC,126.77 oC and 119.43 oC,respectively.Moreover,the reduced viscosity and denaturation temperature of?1-subunit were higher than those of?2-subunit,and the reduced viscosity reached the highest when?-subunits were mixed with a?1/?2 ratio of approximately 2,suggesting that?1-subunit seems to play a more important role than?2-subunit in the thermostability of gelatin.Then in Chapter 3,effects of?1/?2 ratios and drying temperatures on the properties of tilapia skin gelatin films were investigated.Tensile strength?TS?of?1-subunit based films and?2-subunit based films were 30.4 MPa and 12.8 MPa,respectively.When films were prepared from?-subunits at?1/?2 ratio of 2/1,both TS and elongation at break?EAB?of films were the highest.The color of?-subunit based composite films was similar to that of?2-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 of?-subunit based composite films prepared at 10 oC or 15 oC were much higher than those of films prepared at 20oC or 25 oC.Circular dichroism analysis revealed that triple helical structure was formed in the films containing?1-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,?1-subunit and?2-subunit were different in some physicochemical properties.The contribution of?1-subunit in the formation of gelatin films was higher than that of?2-subunit,and the solution prepared with?1/?2 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. |
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