| In this paper, the edible packaging films were made from pullulan as main material and with polyethylene glycol as a plasticizer. In order to provide a theoretical basis for the development of pullulan based edible films, the drying characteristics of film forming solutions, the physical, barrier and microstructure properties, and the effects of storage on fresh olive oil wrapped by films were investigated. The main findings are as follows:1.The drying curves of pullulan-based films were divided into three stage:a rising rate period, a falling rate period, a constant rate period. Drying process of pure pullulan films was consisted with Wang and singh model, and pullulan-PEG blends films conformed to Modified Page equation-II model. As the drying temperature increased from 40℃ to 70 ℃, the effective moisture diffusion coefficient (Deff) of pullulan films rised from 0.0196 ×10-nm/s2 to 0.2557×10-11m/s2 and pullulan-PEG films rised from 2.400 ×10-11m/s2 to 11.388×10-nm/s2. As the drying temperature increased, Deff of pullulan based films increased, and the Deff of pure pullulan films was lower than pullulan-PEG blends films. Drying activation energy of pullulan films was 9114.8 kJ/mol(R2=0.9103), and pullulan-PEG’s was 2475.2 kJ/mol(R2=0.9927).2. Changes in the macroscopic properties and microscopic properties of pullulan films and pullulan-PEG blends films were examined after storaged 0 day,6 day, 15day and 30 day under the storage temperature of 30℃ and 50℃. The results showed that, effects of storage time on the thickness of films was not significant. When the storage temperature increased, transparency of the films decreased, even a small number of the films yellowing. The water solubility of the films reduced as the storaged time increased. Pullulan-PEG blends films had higher mechanical strength and better flexibility than pure pullulan films. Storaging temperature did not significantly change the mechanical of the films. Pullulan films little changed in elongation at break, while pullulan-PEG blends films significantly increased in the late period of storage. Water barrier and oxygen barrier properties of pure pullulan films were better than pullulan-PEG blends films. In the medium storaging period, the water barrier properties of the films had been improved. The increasing of storaging temperature lowered the oxygen barrier properties, but films’oxygen permeability did not change much as the storage time increasing. As the changing of storage temperature and time, the molecules’peaks of wave number had moved, peaks of shape also changed, this change was consistent with the macroscopic properties of the films.3. Use pullulan films and pullulan-PEG films storaged 0 to 30 days under 30℃ and 50℃, ordinary blank plastic film as control, to wrap the fresh olive oil and determined the saponification value, peroxide value and acid value after 30 days storagement. The results showed that, the saponification value of the oil reached the range of physical and chemical indicators of edible olive oil(185-196mg/g), and also higher than the blank plastic films’(177mg/g). It proved that the unsaturation of olive oil wrapped by pullulan based films can be maintained at a certain level.The peroxide value of olive oil wrapped by pure pullulan films and pullulan-PEG films was lower than by blank plastic films, and as the storage time expanding, the rate of oxidation of olive oil wrapped by storaged films increased firstly and then reduced. The acid value of olive oil wrapped by pullulan based films increased as the storage time expanding, but was lower than blank plastic films’. Generally speaking, the films storaged 0 to 30 days under 30℃or 50℃ still had excellent barrier properties to be used as a potential packaging material and meet packaging requirements of olive oil. |
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