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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 needto be controlled, with the main concern being water. Utilizationof a coating including hydrophobic elements (e.g., oils, fats, waxes,emulsifiers, essential oils, etc.) may be applied to isolate or maintainseparation of constituents varying in water activity inside a com-posite food (Lacroix, 2009). The WVP of biocomposite films addedwith OEO at various amounts is shown in Table 1. In general, theincorporation of oregano oil into fish gelatin–chitosan films leadsto 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 containingbergamot essential oil (Ahmad et al., 2012) and chitosan-basedfilms incorporated with basil essential oil (Bonilla et al., 2012).According to Bonilla et al. (2012) this may be ascribed to thediscontinuities caused in the polymer network by lipid droplets,in provoking a loss in film cohesion and consequently enhance-ment 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) demonstratedthat interactions of oil constituents with some hydrophilic proteindomains 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 reducedeasily by incorporating a hydrophobic constituent into the filmformulation, although the effect of the lipid incorporation on theemulsified film microstructure is a determining item in watervapor barrier ability (Atarés et al., 2010).
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