Preparation of Biodegradable Poly(ε-caprolactone)-Based Films and Its Preservation Mechanism of Fruit and Vegetable
Author:Cheng Pei Fang
Supervisor:dong tong li ga dong tungalag
As well known,respiration is one of the key factors that influence the shelf-life and product quality of the fresh produce.Firstly,poly(ε-caprolactone)/poly(propylene carbonate)(PCL/PPC)blended film was used for garland chrysanthemum packaging.The effects of the PCL/PPC film on the shelf life of crowndaisy chrysanthemum were studied.Based on obove experiment,biodegradable poly(L-lactic acid)(PLLA),PCL,poly(butylene succinate)(PBS)were used to prepare heterogeneous blended system with different blendeding mass ratios by melt blendeding in order to obtain blended films with higher strength,good dimensional stability and suitable for presevation of fresh produce.The modify film was further used to grape packaing combined with cold storage,the effect of blended film on changes of the storage quality,disease resistance and volatile flavor compounds were investigated to explore the key factors of grape preservation.The main resultsare the following:(1).The PCL/PPC co-extrusion film was prepared and used for garland chrysanthemum packaging.The change of gas composition in package,physical and chemical quality and sensory quality of garland chrysanthemum during the storage were evaluated.The result showed that the package restrains a steady-state with 2.3～4.9%O2 and 2.9～7.3%CO2,which significantly reduce the respiratory rate and prevent the excessive consumption of nutrients.Compared with the low-density polyethylene package,the shelf life prolongs 6 days.This result indicated that the modified PCL can be a effective packaging film for fresh produce presevation.(2).With PLLA and PBS as modifier,PCL as the substrate material to prepare the PCL/PLLA(PBS)co-blended film and used for spontaneous atmospheric packaging.The effect of blending composition on phase morphology,compatibility,thermal properties,crystallization properties,mechanical properties and barrier properties of films was investigated.The result showed that different blending compositions has significant influence on the size,shape,uniformity of dispersed phase particles and the morphology of blended films.The different sea island phase separation structures were formed.When the content of PLLA(PBS)was less than 50%,PLLA(PBS)was kind of spherical granular and dispersed in PCL.However,the particle diameter incresed with incresing PLLA(PBS)content,indicating that homogeneity of the blended fims become worse.However,when the content of PLLA(PBS)as over than 50%,the extent of phase separation decreases and co-blended films with good mechanical properties and different permeability were obtained.This result indicated that controllable fresh-keeping packaging material can be prepared by controling the microphase separation structure.(3).Based on the co-blended film’s properties,several modified PCL-based films were used for grape packaging combined with cold storage.The result showed that the PCL/PLLA package restrains a steady-state with 2.2%O2 and 12%CO2.The grape in PCL/PLLA package kept good appearance and no mildew is observed during 40 days storage.Comapred with CK and pure PCL group,the shelf life of grape in PCL/PLLA package prolongs 16 day and 10 day,repectively.Besides,the consumption of soluble solid and titratable acid were significantly reduced with the PCL/PLLA film as package and the fruit kept a vitamin content about 65%.This is because the suitable atomosphere can effectively inhabit the respiration of grape and prevent the decrease of the sensory and biochemistry quality of fruit.(4).To further explore the fresh keeping mechanism of co-blended fims,PCL/PLLA blended film,which has good fresh keeping effect was used to grape packaging again with neat PCL and CK group as control group.The change of disease-resistance in each package was evaluated.The result showed that PCL/PLLA package can keep grape good cell wall structure,prevent the decrease of total phenols and malondialdehyde content and maintain higher activities of POD and CAT in grape.The obove result showed that PCL/PLLA package with suitable atmosphere can slow down the produce of reactive oxygen in respiration,thus increase the disease resistance and delay senescence of grapes.(5).The change of volatile chemicals during cold storage was investigated by combining high performance solid-phase microextraction(HS-SPME)with gas chromatography-mass spectrometry(GC-MS).The result showed that alcohols and aldehydes,the characteristic aroma of grapes,can be well kept in grape in PCL/PLLA package.The grape kept good original flavor and no ethyl alcohol was detected.