| It was obvious that,as regards to food packaging industry,the traditional plastic packaging will be replaced by the edible films packaging in the future.The starch edible films which were studied earliest occupied the extensive advantages,e.g.widely source,inexpensive,biodegradable.Therefore,this paper focused on the composite edible films composed of corn starch and wheat starch,and studied their preparation technology,the mechanism of edible packaging films combined natural antibacterial agent lemon essential oil with emulsifiers,the influence rules of citric acid and lemon essential oil in place of plasticizer and the heat sealing properties of composite edible film.This work would be valuable for the future research and application of the condiment packaging edible films.Firstly,the edible composite films were prepared from corn starch and wheat starch by casting films-solution on leved trays.Then,the effects of the radio of corn starch and wheat starch,sorbitol content,citric acid content,strengthening agent content,gelatinization temperature,gelatinization time on the mechanical properties were investigated separately.In addition,the four factors three levels orthogonal test was used to optimize the conditions of mechanical properties.The results showed that the order of tension strength was as follows:gelatinization time>citric acid content>sorbitol content>gelatinization temperature.The results showed that the order of elongation at break was as follows:sorbitol content>citric acid content>gelatinization time>gelatinization temperature.The optimum condition were as follows:solution concentration 60g/L,corn starch and wheat starch mass ratio 40:60,sorbitol content 0.6%,strengthening agent content 1.4%,citric acid content 2.5%,gelatinization temperature 85?,gelatinization time 40min.Under these conditions,the films tension strength was 14?15MPa,and the percentage elongation at break was 30?33%.Secondly,the lemon essential oils and emulsifiers Tween 80 and Span 80 were added to the composite films composed of corn starch and wheat starch,and then their physical,antibacterial effect and structural properties were investigated.The results showed that lemon oil changed the mechanical properties of the composite films,the tensile strength of 2%lemon essential oil composite films decreased 28.41%compared with the control,and the elongation at break increased 19.82%,significantly reduced moisture content and water vapor membrane permeability coefficient,decreased solubility and the light transmittance of the films,added color and haze of the films,and the solubility of 2%lemon oil dropped by 12.71%compared with the control membrane,while water vapor membrane permeability coefficient of 2%lemon oil dropped by 16.08%compared with the control film.After the Emulsifier Tween 80 and Span 80 were added,the tensile strength and light transmittance reduced,and the solubility and haze of the films improved.The inhibitory effect of Staphylococcus aureus was significantly higher than E.coli for the lemon essential oil liquid membrane.Scanning electron microscopy showed that adding lemon essential oil and emulsifier to the films promoted the density of the structure.Thirdly,the feasibility of films build with citric acid and lemon essential oil in stead of plasticizer were explored,regarding the complex films compose of corn starch and wheat starch.The composite films had the best performance by adding 5.0%of citric acid,which the tensile strength was 9.23MPa and elongation at break was 42.76%.Lemon oil affected the mechanical properties of the composite film,the tensile strength and elongation at break of 2%lemon essential oil composite films increased 16.61%and 8.04%compared with the control,significantly reduced the moisture content and the water vapor permeability coefficient of the film,decreased the solubility and the light transmittance and added color and haze of the film.The tensile strength was reduced after adding Emulsifier Span 80,and the haze of the film was improved.Moreover,the composite membrane water vapor permeation coefficient was reduced by 21.63%compared with the control film.With the increase of concentration of lemon essential oil,the antibacterial ability of liquid film could improve.The inhibitory effect of liquid film of Staphylococcus aureus was significantly higher than E.coli compared with the different concentrations of lemon essential oil antibacterial liquid film.Lastly,the sealing characteristic of corn starch and wheat starch composite edible films was studied.The effect of sealing temperature,time,and pressure on the sealing strength of the film was evaluated by single factors tests.Moreover,the sealing parameters were further optimized by the orthogonal test.The optimum parameters were the sealing temperature of 140?,sealing time of 1.5s,and sealing pressure of 0.4MPa,when the sealing strength of the film was 3.13N/15mm. |
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