| Konjac glucomannan(KGM)is a kind of abundant natural polysaccharide polymer,a small amount of its hydrosol can be made into edible membrane with high transparency.The hydrosol of KGM coated on the surface of fruits and vegetables can create a thin membrane which has a certain effect on keeping fresh.The membrane has many advantages,such as pollution-free,edible,easily degradable and so on,which is one of the ideal green environmental protection packing material and has widely development and application foreground.However,the membrane with single KGM is easily solubled in water,which limits its development.Beeswax(BW)is a kind of natural animal wax with good hydrophobic,safety and non-permeable,and it's an ideal material for food packaging.At present,there is no report about composite membrane made of KGM and BW,and lack of the research about both composite membrane preparation and its hydrophobicity.In this thesis,KGM and BW were utilized as the raw material,to research KGM/BW composite membrane preparation,performance characterization and its application on the fresh pomelo cut.The research results were as follows:(1)konjac gluconmannan(KGM)and beeswax(BW)were selected as membrane to make composite membrane,and its mechanical properties was analsized.Through the single-factor test,the central composite design with influence factors including the ratio of KGM/BW,glycerinum content and drying temperature was screened and determined in order to obtain the most suitable theoretical conditions.Then response surface method was used to optimize the process conditions.The results demonstrate that the KGM/BW ratio,content of glycerin and drying-temperature have the significant influence on the tensile strength of the composite membrane respectively.The results demonstrate that the KGM/BW ratio,content of glycerin and drying-temperature have the significant influence on the tensile strength of the composite membrane respectively.The optimal method of preparing the compound membrane was as follows:KGM/BW ratio 6.14:1,concentration of glycerol 0.42%,drying-temperature 70.71 C.The predicted value for tensile strength of the composite membrane 42.1560 MPa,and verified value 41.78 MPa.(2)Composite membranes were prepared with different ratio of KGM and BW,the structure and performance of the composite membrane was tested by SEM,ATR-FTIR,DSC and membrane material property test methods.The results shows that compared with KGM membranes,the elongation at break of KB2(KGM:BW=1:2)membranes or KB4(KGM:BW=6:4)membranes was improved,and the water vapor transmittance and solubility in water were both reduced,which demonstrates that adding a little BW can improve the mechanical and hydrophobic performance of KGM membranes.SEM analysis showes that the surface of KB2,KB4 membrane is relatively smooth,while other membrane is either coarse or appearing layer.This demonstrates that a small amount of BW can be well dispersed in KGM membrane system.ATR-FTIR analysis shows that the infrared spectrum of composite membranes with different ratio almost have no change,which states that both of them are mainly physical function.Thermal analysis shows that the thermal stability of the composite membrane system is reduced.Rheological analysis showed that rather than presenting Newtonian fluid characteristics of KB8(KGM:BW=2:8),pure KGM and its composite membrane liquid both presenting pseudoplastic characteristics.With the reduces of KGM proportion,the shear rate decreases correspondingly.(3)The effects of KGM/BW coating,KGM coating and the control group under the room temperature(20?)on the sensory quality and physicochemical property of the fresh-cut honey pomelo(Guanxi)during postharvest storage were researched.The result shows that KGM coating,especially KGM/BW coating,could protect the flesh-cut fruit best during storage from water loss and inhibit respiration as well as preserve the nutritious quality of the honey pomelo fruit. |
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