Effect Of Environmental Conditions On The Properties Of Zein Films

Stability of zein films during storage was the main inhibiting factor for the applications.In this paper, the storage stabilities of zein film at different environmental conditions wereinvestigated, tensile strength (TS) and elongation at break (EB) were hired as evaluationindexes.Experiment results revealed that TS decreased and EB increased along with the filmthickness increase, but influence of thickness on mechanical properties of zein filmsreducedgradually, and thickness would have no significant effect on the mechanical propertieswhen the thickness was more than0.08mm. So films whose thickness more than0.08mmwere prepared at different conditions, and stored at room temperature Stability of the filmsduring storage was researched. From the results, the preparing conditions of the film withbetter steabilities were：protein concentration10%, film-forming temperature80°C, glycerolcontent0.3(g/g zein), PEG content0.2(g/g) zein. The EB of the films prepared with PEG asonly plasticizer changed greatly in the last storage period, and the amplitude of variationenlarged with increasing PEG content. The secondary structures of the proteins of the filmswere analyzed, the results showed that the content of β turn of the proteins in the filmsplasticized only by PEG-400increased, and α helixwas not detacted after24d. Furtherly, thestability of the films stored at different conditions was researched. Mechanical properties ofzein films were affected by storage temperature, humidity and air. Higher storage temperatureled to superior TS and inferior EB. Films stored at low temperature had better stability. Zeinfilms stored at34%RH,43%RH,54%RH,65%RH and80%RH. Stability of the filmstored at RH80%was the minimum. In early days of storage, TS decreased and EB increasedalong with the RH increase. But in the last period, the higher the humidity was, the moreobvious the EB decreased. TS of the films stored in natural indoor environment was muchhigher than that stored in controlled conditions. Stability of the films stored in differentseasons of Zhengzhou is: spring> winter> autumn> summer.Changes of mechanical properties of zein films were induced by the changes of theirconstituents and structure. Moisture content of zein films was affected by preparationconditions and storage conditions. Moisture in films increased with the increase of storageenvioronment humidity and plasticizers content. Instable films contained higher moisture. reesulfydryl content of the films increasing, TS decreased and EB increased respectively.