| Edible films prepared only with starch as the main film-forming matrix show poor mechanical properties and water resistance,which severely restricts its application as food packaging.In order to improve the water resistance and mechanical properties of the composite film,blending gelatin with starch as the main film-forming matrix,and added natural wax as the hydrophobic agent,and uses the extrusion blow molding film-forming process to make the film.Effects of gelatin's Bloom values,content and type of natural wax(beeswax(BW),candelilla wax(CL),and carnauba wax(CB),respectively)and processing temperature on the physicochemical properties and film-forming mechanism of starch/gelatin(S/G)was study.This study will provide a theoretical basis for the commercial application of bio-based edible membranes.The main findings are as follows:(1)The gelatin's Bloom value was significantly affected the properties of S/G films.The S/230G-BW blend exhibited the highest storage modulus and complex viscosity determined by rheological analysis.The results of dynamic mechanical analysis and scanning electron microscopy images demonstrated that starch granules could be more effectively melted and fractured in the composite films with higher Bloom values.Attenuated total reflectance-Fourier transform infrared(ATR-FTIR)and X-ray(XRD)diffraction spectra revealed that gelatin Bloom values strongly affected the migration and crystalline properties of beeswax in the film matrix,while the S/230G-BW film had more triple helical structures,as shown by the results of circular dichroism(CD)analysis.In addition,lower water solubility and higher thermal stability of the produced films was obtained from the gelatins with higher Bloom values.The highest water contact angle(WCA)(87°)of the outer film surface and lowest water vapor permeability(WVP)(0.88×10-10?g m-1?s-1?Pa-1)were obtained for the S/200G-BW sample.The S/230G-BW film had the maximum values of tensile strength(TS),elongation at break(EAB),and Young's modulus(YM)that exceeded those of the S/120G-BW film by 90.9%,96.8%,and 102.4%,respectively.Finally,the extremely high Bloom values enhanced the interfacial interactions between the starch and gelatin components in the films,which negatively affected their performance.(2)The performance of the composite films was significantly affected by the the addition of natural wax.S/G-natural wax blends showed decreased storage modulus and complex viscosity determined by rheological analysis.ATR-FTIR indicated that the molecular interaction in films was weakened by BW and CL,but not by CB.CB exhibited the strongest crystalline behavior in film matrix obtained by XRD.SEM images showed that the more irregular and rough surface structures were obtained after adding waxes.The presence of waxes increased the water resistance,water vapor barrier properties and surface hydrophobicity of S/G films.S/G-BW film exhibited the highest water contact angle(102.6°),strongest thermal stability,and lowest water vapor permeability.(3)The performance of the composite films was significantly affected by the the content of beeswax and processing temperature.ATR-FTIR showed that the increase in the content of beeswax and processing temperature weakened the intermolecular hydrogen bonding force of the film.XRD indicated that the increase of beeswax content and processing temperature promoted the crystallization of wax in the film matrix.DSC showed that the increase in the content of beeswax and processing temperature promoted the plasticization of starch.SEM showed that the shape and quantity of crystalline particles formed by beeswax on the film's surface are affected by the content of beeswax and procsssing temperature.The increase in the content of beeswax decreased the mechanical properties of the composite film.When the added content of beeswax was increased to 9%,the water resistance,water vapor barrier,and hydrophobic properties of the composite film were improved,but extremely high addition of beeswax was not conducive to the improvement of performance.The increase in processing temperature improves the mechanical,water barrier,hydrophobic and water resistance properties of the composite film. |
PDF Full Text Request