Research And Application Of Corn-wheat Starch Compound Edible Film

There is an inevitable tendency that the traditional packaging plastics would be replaced by green,edible films in the development of the food packaging industry.Starch edible film has ranked one of the most potential green packaging plastics considering its high transparency,biodegradability,easily obtaining,low cost and safety.Firstly,corn-wheat starch edible film was prepared,followed by comparison with commercial packaging materials to evaluate the edible film.Secondly,the storage assays of the naked film with or without storage samples were performed to study its storage stability and practical application.At last,industrial continuous production process was carried out to overcome the shortage of edible film regarding the mechanical properties and wettability,in order to obtain a better performance of convenience food packaging edible film.Valuable references for the research and development of corn-wheat starch composite edible film were conducted and suggested in this work to improve the production efficiency of starch composite edible film and open up a new way for the transformation from laboratory research to industrialized continuous production.Tape casting method was applied to form edible films based on corn and wheat starch.Then,the comparison was made between the edible film in this examine and commercial materials with respect to transparency,mechanical properties,barrier properties and microscopic morphology.The results showed that the transmittance of corn-wheat starch composite edible film was 89.7%,the haze 33.66%,which revealed the film transparency was good,next to the traditional PE film.The best oxygen barrier was purchased by corn-wheat starch film among the five film materials,for the peroxide value of packaged vegetable oil was only 182.42 mmol/kg after storage at 60 °C for 10 days.A certain gap between starch composite film and traditional packaging materials still existed in terms of mechanical properties.Nevertheless,the mechanical properties of the green edible film were better than Cron/PLA/PBTA and Cron/PE degradable plastics materials,implying a potential suitability of edible film on food packaging.The bags prepared by starch composite membranes were stored at 25 °C(relative humidity 40%,50%,60%),4 °C,-18 °C for 180 days,during which sampling was conducted every 30 days and the indexes,such as mechanical properties,water solubility,heat-sealing properties and appearance color of the composite film,of samples were detected to study the storage stability of starch composite membranes under different temperature and humidity conditions.It was indicated that the water solubility of the composite film bag increased first and then decreased,and the heat seal strength gradually decreased with the prolonged storage time.The tensile strength of the bare film stored in the composite film stored at 4 °C and-18 °C decreased gradually and tended to be gentle with the prolongation of storage time.Moreover,a significant decrease was found especially within 60 days.The tensile strength of bare bag maintained stable within 90 days at 40% humidity,followed by a slightly reducing with the expand of storage time.The tensile strength of bare bag showed a trend of rising first and then decreasing at both 50% and 60% humidity,with a maximum strength at 60 th day for 50% humidity and 30 th day for 60% humidity.In general,the tensile strength of the bare film tended to decrease with the extension of storage time under different storage conditions,while its appearance color and transparency showed a good stability.A certain amount of soybean milk powder packed in a starch composite film bag were stored at 25 °C(relative humidity 40%,50%,60%),4 °C,-18 °C for 120 days,during which sampling was carried out every 20 days and the performance of bare bag and soybean milk powder quality were measured to analyze the practicability and suitability of the developed starch composite film bag.It was demonstrated that the quality of soymilk powders stored at 4 °C,-18 °C and 40% humidity were relatively stable.However,the caking and precipitation after dissolution in hot water were observed for soymilk powders stored at 50% and 60% humidity.The tensile strength of the composite film bag with soy milk powder tended to decrease gradually and a moldy appearance occurred on the outer surface of the package at a humidity of 60%.Single-screw extrusion blow molding was conducted in this paper based on corn-wheat starch and antimicrobial polylactic acid as materials and glycerol as plasticizer to improve the mechanical properties and moisture resistance of composite membranes and to improve production efficiency and antibacterial activities,considering the disadvantages in practical applications showed through the above comparative study.The effects of glycerol additions on the film formation were studied and changes in the mechanical properties of edible film caused by different starch content were also explored in this work.The results manifested that 40% of glycerol addition contributed perfectly to the plasticizing facilitating the industrial application.Additionally,20% addition of starch was good at blowing molding,with longitudinal tensile strength 59.90 MPa and transverse tensile strength 38.05 MPa,respectively.