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3. ไอน้ำ permeability (WVP)An important function of edible films is to reduce exchangeof water between the wrapped product and environment, so thewater loss of product can be diminished (Du et al., 2011). Dete-rioration of food quality as a result of physic-chemical changes orchemical reactions is usually created by mass transfer phenomenonor between the food and its surrounding medium (Lacroix, 2009).Water, oxygen and flavor are compounds whose migrations need to be controlled, with the main concern being water. Utilization of a coating including hydrophobic elements (e.g., oils, fats, waxes,emulsifiers, essential oils, etc.) may be applied to isolate or maintain separation of constituents varying in water activity inside a composite food (Lacroix, 2009). The WVP of biocomposite films added with OEO at various amounts is shown in Table 1. In general, the incorporation of oregano oil into fish gelatin–chitosan films leads to an increase in WVP values from 0.41 to 0.76 g mm/kPa h m2.The similar trend has been found in fish gelatin films containing bergamot essential oil (Ahmad et al., 2012) and chitosan-based films incorporated with basil essential oil (Bonilla et al., 2012).According to Bonilla et al. (2012) this may be ascribed to the discontinuities caused in the polymer network by lipid droplets,in provoking a loss in film cohesion and consequently enhancement of transport phenomena through the film. Furthermore,the hydrophilic–hydrophobic ratio of the film constituents has adirect influence on the water vapor transfer process in the films(Hernandez, 1994). Perez-Gago and Krochta (2001) demonstrated that interactions of oil constituents with some hydrophilic protein domains may develop the decrease in the hydrophobic propertyof film matrix. However, other works on the addition of essen-tial oils have presented improvements in WVP (Benavides et al.,2012; Pelissari et al., 2009; Tongnuanchan et al., 2012). Therefore,it cannot be presumed that the WVP of edible films is reduced easily by incorporating a hydrophobic constituent into the film formulation, although the effect of the lipid incorporation on the emulsified film microstructure is a determining item in watervapor barrier ability (Atarés et al., 2010).
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