Packaging-flavour interactions 149 8.2.7 Temperature Temperature is probably the most important environmental variable affecting transport processes. The permeability of gases and liquids in polymers increases with increasing temperature according to the Arrhenius relationship. Possible reasons for increased flavour absorption at higher temperatures are( Greml increased mobility of the flavour molecules hange in polymer configuration, such as swelling or decrease of crystallinity change in the volatile solubility in the aqueous phase 8.2.8 Relative humidity For some polymers, exposure to moisture has a strong influence on their barrie properties. The presence of water vapour often accelerates the diffusion of gases and vapours in polymers with an affinity for water. The water diffuses into the film and acts like a plasticiser. Generally, the plasticising effect of water on a hydrophilic film, such as ethylene-vinyl alcohol(EVOH) and most polyamides yould increase the permeability by increasing the diffusivity because of the higher mobility acquired by the polymer network (Johansson, 1993). Absorbed water does not affect the permeabilities of polyolefins and a few polymers, such as PET and amorphous nylon, show a slight decrease in oxygen permeability with increasing humidity. Since humidity is inescapable in many packaging situations, this effect cannot be overlooked. The humidity in the environment is often above 50%RH, and the humidity inside a food package can be nearly assus, 1997) 8.3 The role of the food matrix quality and the shelf-life of the packaged food depend strongly on physical chemical properties of the polymeric film and the interactions between food Con ponents and package during storage. Several investigations have shown that iderable amounts of aroma compounds can be absorbed by plastic kaging materials, which can cause loss of aroma intensity or an unbalanced flavour profile(Hotchkiss, 1997; Arora et al, 1991; Lebosse et al., 1997 Linssen et al., 1991a; Nielsen et al., 1992; Paik, 1992) factors,see Fig. 8.3)in determining the amount of flavour absorptions The composition of a food matrix is of great importance(besides ot plastic packaging materials. There is only limited information available in literature about the influence of the food matrix on flavour absorption by polymers. Linssen et al.(1991b)and Yamada et al.(1992) showed that the presence of juice pulp in orange juice decreased absorption of volatile compounds into polymeric packaging materials. They suggested that pulp particles hold flavour compounds(e.g, limonene) in equilibrium with the8.2.7 Temperature Temperature is probably the most important environmental variable affecting transport processes. The permeability of gases and liquids in polymers increases with increasing temperature according to the Arrhenius relationship. Possible reasons for increased flavour absorption at higher temperatures are (Gremli, 1996): • increased mobility of the flavour molecules • change in polymer configuration, such as swelling or decrease of crystallinity • change in the volatile solubility in the aqueous phase. 8.2.8 Relative humidity For some polymers, exposure to moisture has a strong influence on their barrier properties. The presence of water vapour often accelerates the diffusion of gases and vapours in polymers with an affinity for water. The water diffuses into the film and acts like a plasticiser. Generally, the plasticising effect of water on a hydrophilic film, such as ethylene-vinyl alcohol (EVOH) and most polyamides, would increase the permeability by increasing the diffusivity because of the higher mobility acquired by the polymer network (Johansson, 1993). Absorbed water does not affect the permeabilities of polyolefins and a few polymers, such as PET and amorphous nylon, show a slight decrease in oxygen permeability with increasing humidity. Since humidity is inescapable in many packaging situations, this effect cannot be overlooked. The humidity in the environment is often above 50%RH, and the humidity inside a food package can be nearly 100%RH (Delassus, 1997). 8.3 The role of the food matrix The quality and the shelf-life of the packaged food depend strongly on physical and chemical properties of the polymeric film and the interactions between food components and package during storage. Several investigations have shown that considerable amounts of aroma compounds can be absorbed by plastic packaging materials, which can cause loss of aroma intensity or an unbalanced flavour profile (Hotchkiss, 1997; Arora et al., 1991; Lebosse´ et al., 1997; Linssen et al., 1991a; Nielsen et al., 1992; Paik, 1992). The composition of a food matrix is of great importance (besides other factors, see Fig. 8.3) in determining the amount of flavour absorption by plastic packaging materials. There is only limited information available in literature about the influence of the food matrix on flavour absorption by polymers. Linssen et al. (1991b) and Yamada et al. (1992) showed that the presence of juice pulp in orange juice decreased absorption of volatile compounds into polymeric packaging materials. They suggested that pulp particles hold flavour compounds (e.g., limonene) in equilibrium with the Packaging-flavour interactions 149