to the higher degree of cross linking that results from the formation of
quinones and free radicals which tend to promote the cross linking
[133]. However, the permeability of the ferulic acid incorporated film
at a concentration of 100 mg increased slightly in comparison to the
blend film containing 75 mg of ferulic acid, but was lower than that of
the control film indicating 75 mg of ferulic acid as the optimal concentration
of the cross-linking agent. Blend films with higher TS had lower
WVT rates probably owing to the better degree of organization of the
polysaccharide network up to the optimum concentration of ferulic
acid. They also studied oxygen transmission rates of chitosan/starch
films with different amount of ferulic acid. In general, polysaccharide
films are expected to be good oxygen barriers, due to their tightly
packed and ordered hydrogen-bonded network structure and lowsolubility.
The results showed that the oxygen transmission rate reduced
with the increase in the level of cross-linking agent. Kucuk and Caner
[134] have reported better stability and quality for sunflower oil
samples stored under packaging conditions free of air. High levels of oxygen
in food packages have been reported to cause the development of
off-flavors, off-odors and nutritional loss in food stuffs [135].
Since a main function of a food packaging is often to avoid or at least
to decreasemoisture transfer between the food and the surrounding atmosphere,
or between two components of a heterogeneous food product,
WVP should be as low as possible.
Shen et al. [52] showed that theWVP of sweet potato starch films decreased
significantly with the addition of over 10% chitosan. This was
also the case for tapioca-starch-based edible film examined by Chillo
et al. [47]. They explained the decreasing WVP transmission rate at
higher concentrations of chitosan as a result of reducing the available hydrophilic
group [31,47]. In addition the hydrogen bonding interaction
between chitosan and starch decreased the free sorption sites for
water, which is responsible for decreasing theWVP of the film [136].
WVP of chitosan films (CS) contain different concentrations of tea
tree essential oil (TTO) had been studied by Sanchez-Gonzalez et al.
[100]. The room temperature conditions used for measuring the WVP
(100/54.4) of the films were established to simulate the environmental
conditions when the films are applied as a coating for vegetables.WVP
values were in the range of those reported by other authors working
with films based on chitosan [29].
The WVP values showed a significant decrease in line with the increase
in TTO concentration, reaching a maximum WVP reduction of
about 40% with incorporation of 2% TTO in the film-forming dispersions.
This behavior is expected as an increase in the hydrophobic
compound fraction usually leads to an improvement in the water barrier
properties of films, as was previously reported for essential oils
addition in CS films [96].
Fig. 23. The change of antibacterial activities of starch/chitosan blend films with radiation
dose (80% starch, 20% chitosan) [155].
Fig. 24.