| The study of natural polymers prapare edible films has raised extensive attetion.Among the materials used to prepare edible films,gelatin has gradually been the focus because of its abundance source and excellent film-forming ability.In this study,effect of thermal treatment on the properties of collegen and the resulting films,and effect of drying method on the properties of gelatin films were investigated,and the last attempt to improve gelatin film properties.Firstly,effect of thermal treatment time on the physicochemical properties of acid-soluble collagen?ASC?from tilapia skins and thermal denaturation on the collegen protein films were investigated.No significant differences in the UV absorption,molecular weight distribution and FTIR absorption of collagen were observed during thermal treatment.With increasing thermal treatment time,the reduced viscosity value of ASC was decreased,and the denaturation temperature and thermal transition temperature were decreased from 32.6 °C to 27.0 °C and from 38.1 °C to 29.2 °C,respectively.When thermal treatment time was more than 10 min at 42 °C,the turbidity experiment indicated that the ASC did not possess fibril-forming ability.Furthermore,the fibril formation of natural collagen was also hindered by the therma l denatured collagen.O n the other hand,the tensile strength?TS?of collagen films was increased from 30.81 MPa to 41.33 MPa,the elongation at breaks?EAB?was increased from 8.95% to 11.59%,the transparency values was increased from 2.42 to 3.33,and the glass transition temperature was increased from 110.49 °C to 117.57 °C with increasing thermal treatment time.Based on the results of scanning electron microscopy,it was found that the fibrous structure of collagen films was gradually converted to wrinkle-like structure during thermal treatment.Then,effects of hot-air drying and infrared drying on the properties of gelatin films were investigated.With the increase of drying temperature from 40 °C to 80 °C,the drying rate of gelatin films was increased,and the maximum drying rates of films from hot-air drying and infrared drying at 80 °C were 0.199 g·min-1 and 0.228 g·min-1,respectively.With increaseing drying temperature,the TS of gelatin films prepared by hot-air drying and infrared drying were increased from 40.46 MPa to 48.05 MPa and 47.31 MPa,while the EAB were decreased from 44.29% to 32.04% and 31.63%,respectively.These results suggested that drying methods did not affect on the mechanical properties of gelatin films.On the other hand,no significant differences in color,light transmittance and protein patterns were noticed regardless drying method or drying temperature.Finally,effects of ferulic acid and laccase on the properties of gelatin were investigated.With the content of ferulic acid and laccase added,the strength of gelatin gel was increased from 188.25 g to 200.88 g;the TS of gelatin films was increased from 33.88 MPa to 39.87 MPa;the solubility of gelatin films was decreased from 91.90% to 81.95%;the color of gelatin films became yellow.Based on the results of SDS-PAGE,addition of ferulic acid and laccase promoted cross-linking in the gelatin film network by a quantity-effect relationship.When gelatin films were stored for 15 days at 25 °C and 50%?relative humidity?in an environmental chamber,the TS of films was increased from 39.87 MPa to 47.50 MPa,and the solubility of films was decreased from 81.95% to 59.16%.However,storage time did not affect the color and light transmittance of gelatin films.In conclusions,the fibril-forming ability of ASC from tilapia skins was decreased with deaturation,while the film-forming ability was increased.There were no obvious changes on the properties of fish gelatin films between hot-air drying and infrared drying.However,the effect of drying temperature on mechanical properties had a certain impact.The mechanical properties and water resistance of films were improved by cross-linking in proteins induced by ferulic acid and laccase. |
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