156 Novel food packaging techniques and oxygen compete for the same sites, reducing the solubility of oxygen since many sites are already occupied and (ii) the flavour compounds swell the polymer, opening the structure and increasing polymer free volume, i.e. oxygen transport. The presence of holes is assumed for rubbery polymers as well as for glassy polymers. Hole filling is suggested as an important sorption mode above as well as below Tg, with one crucial difference between the sorption mechanisms in the rubbery and glassy regions, hole saturation does not occur in the rubbery state because new holes are formed to replace those filled with penetrant molecules( Stern and Trohalaki, 1990). Landois-Garza and Hotchkiss (1988) reported that the presence of water molecules in the polymer matrix occupied that otherwise would be available for the diffusion of permeant molecules, effectively increased the length of the viable diffusion paths, and diminished the permeant diffusivity The linear decrease of the oxygen diffusivity of PC due to flavour absorption suggests that hole filling,, resulting in an increased oxygen diffusion pathway, was also found in this study. However, the oxygen permeability of PET, which is also in its glassy state at 25C, was not significantly affected by absorption of flavour compounds. Because of the low oxygen permeability of PET, which was close to the detection limit of the oxygen analyser, a significant effect of flavour absorption on oxygen permeability cannot be ruled out. A more sensitive oxygen analyser or a smaller permeation cell should be used in order to investigate the influence of absorption of flavour absorption on the oxygen permeability of PET. Van Willige et al(2002b)concluded that flavour absorption increased oxygen permeability of Pp and LdPE by 130% and 21% after 8 hours of exposure to various flavour compounds Because of the higher oxygen permeability a reduction in the shelf-life of oxygen sensitive products, which are packed in LDPE or PP and contain the tested flavour compounds(such as orange juice and apple juice) expected. Furthermore, flavour absorption has probably a positive effect on the shelf-life of oxygen-sensitive products packed in PC, because of the reduction oxygen permeability of 11% after 21 days of exposure to various flavour pounds. Oxygen permeability of PET was not influenced by the presence of flavour compounds, meaning that PET remained a good oxygen barrier. One should realise that the concentrations of flavour compounds in real food products are usually substantially lower, with the exception of limonene, than the concentrations used in this study. Therefore, the observed effects may be less or even not significant in foods and beverage 8.5 Flavour modification and sensory quality One of the main aspects of flavour scalping is how this ph enomenon is able to affect the quality of foods. In this field a lot of research has been carried out fruit juices. During the last decades the quality of juices, aseptically packed in laminated cartons, has been investigated extensively. Loss of organolepticand oxygen compete for the same sites, reducing the solubility of oxygen since many sites are already occupied and (ii) the flavour compounds swell the polymer, opening the structure and increasing polymer free volume, i.e. oxygen transport. The presence of holes is assumed for rubbery polymers as well as for glassy polymers. ‘Hole filling’ is suggested as an important sorption mode above as well as below Tg, with one crucial difference between the sorption mechanisms in the rubbery and glassy regions; hole saturation does not occur in the rubbery state because new holes are formed to replace those filled with penetrant molecules (Stern and Trohalaki, 1990). Landois-Garza and Hotchkiss (1988) reported that the presence of water molecules in the polymer matrix occupied ‘holes’ that otherwise would be available for the diffusion of permeant molecules, effectively increased the length of the viable diffusion paths, and diminished the permeant diffusivity. The linear decrease of the oxygen diffusivity of PC due to flavour absorption suggests that ‘hole filling’, resulting in an increased oxygen diffusion pathway, was also found in this study. However, the oxygen permeability of PET, which is also in its glassy state at 25ºC, was not significantly affected by absorption of flavour compounds. Because of the low oxygen permeability of PET, which was close to the detection limit of the oxygen analyser, a significant effect of flavour absorption on oxygen permeability cannot be ruled out. A more sensitive oxygen analyser or a smaller permeation cell should be used in order to investigate the influence of absorption of flavour absorption on the oxygen permeability of PET. Van Willige et al. (2002b) concluded that flavour absorption increased oxygen permeability of PP and LDPE by 130% and 21% after 8 hours of exposure to various flavour compounds. Because of the higher oxygen permeability a reduction in the shelf-life of oxygen sensitive products, which are packed in LDPE or PP and contain the tested flavour compounds (such as orange juice and apple juice) can be expected. Furthermore, flavour absorption has probably a positive effect on the shelf-life of oxygen-sensitive products packed in PC, because of the reduction in oxygen permeability of 11% after 21 days of exposure to various flavour compounds. Oxygen permeability of PET was not influenced by the presence of flavour compounds, meaning that PET remained a good oxygen barrier. One should realise that the concentrations of flavour compounds in real food products are usually substantially lower, with the exception of limonene, than the concentrations used in this study. Therefore, the observed effects may be less or even not significant in foods and beverages. 8.5 Flavour modification and sensory quality One of the main aspects of flavour scalping is how this phenomenon is able to affect the quality of foods. In this field a lot of research has been carried out on fruit juices. During the last decades the quality of juices, aseptically packed in laminated cartons, has been investigated extensively. Loss of organoleptic 156 Novel food packaging techniques