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 the
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 (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
150 Novel food packaging techniques TEMPERATURE STORAGE TIME FOOD MATRIX POLYMER FLAVOUR RYSTALLINITY MOLECULAR SIZE ABSORPTION POLARITY POLARITY AFFINITY Fig8.3 Factors influencing flavour absorption by plastic polymers (Van Willige watery phase, which could be responsible for the decrease of absorption of these compounds by the plastics Fukamachi et al. (1996) studied the absorption behaviour of flavour compounds from an ethanolic solution as a model of alcoholic beverages. The absorption of a mixture of homologous volatile compounds(esters, aldehydes and alcohols with carbon chain length 4-12)into LDPE film first increased with a maximal absorption at 5-10%(/v)aqueous ethanol and then decreased remarkably with increasing ethanol concentration. EVOH film showed similar absorption behaviour, with maximal absorption at 10-20%(v/v) aqueous ethanol. Nielsen et al. (1992) investigated the effects of olive oil on flavour absorption into LDPE. Olive oil and, thereby, the flavours dissolved in the oil were absorbed in large amounts by the plastic. The partition coefficients for alcohols and short-chained esters in an oil/polymer system were higher than in a water/polymer system, while the partition coefficients for aldehydes and long- ined esters were lower in an oil/polymer system than in a water/polymer rstem. Not only the type of plastic used is of importance for the uptake of aroma compounds, but also possible interactions between flavour and food components. Flavour components may be dissolved, adsorbed, bound entrapped, encapsulated or retarded in their diffusion through the matrix by food components. The relative importance of each of these mechanisms varies with the properties of the flavour chemical(functional groups, molecular size shape, volatility, etc )and the physical and chemical properties of the components in the food(Kinsella, 1989, Le Thanh et al. 1992) Knowledge of the binding behaviour of flavour components to non-volatile food components and their partitioning between different phases(food omponent/water and water/polymer) is of great importance in estimating the rate and amount of absorption by polymers. Because many food products are emulsions of fat and water, such as milk and milk products, the fat content is an important variable in the food matrix. Fat/oil content is often reduced in order to
watery phase, which could be responsible for the decrease of absorption of these compounds by the plastics. Fukamachi et al. (1996) studied the absorption behaviour of flavour compounds from an ethanolic solution as a model of alcoholic beverages. The absorption of a mixture of homologous volatile compounds (esters, aldehydes and alcohols with carbon chain length 4-12) into LDPE film first increased with a maximal absorption at 5–10% (v/v) aqueous ethanol and then decreased remarkably with increasing ethanol concentration. EVOH film showed similar absorption behaviour, with maximal absorption at 10–20% (v/v) aqueous ethanol. Nielsen et al. (1992) investigated the effects of olive oil on flavour absorption into LDPE. Olive oil and, thereby, the flavours dissolved in the oil, were absorbed in large amounts by the plastic. The partition coefficients for alcohols and short-chained esters in an oil/polymer system were higher than in a water/polymer system, while the partition coefficients for aldehydes and longchained esters were lower in an oil/polymer system than in a water/polymer system. Not only the type of plastic used is of importance for the uptake of aroma compounds, but also possible interactions between flavour and food components. Flavour components may be dissolved, adsorbed, bound, entrapped, encapsulated or retarded in their diffusion through the matrix by food components. The relative importance of each of these mechanisms varies with the properties of the flavour chemical (functional groups, molecular size, shape, volatility, etc.) and the physical and chemical properties of the components in the food (Kinsella, 1989; Le Thanh et al. 1992). Knowledge of the binding behaviour of flavour components to non-volatile food components and their partitioning between different phases (food component/water and water/polymer) is of great importance in estimating the rate and amount of absorption by polymers. Because many food products are emulsions of fat and water, such as milk and milk products, the fat content is an important variable in the food matrix. Fat/oil content is often reduced in order to Fig. 8.3 Factors influencing flavour absorption by plastic polymers (Van Willige, 2002c). 150 Novel food packaging techniques
Packaging-flavour interactions 151 decrease caloric intake to make food healthier. Removal or reduction of lipids can lead to an imbalanced flavour, often with a much higher intensity than the original full fat food (Widder and Fischer, 1996, Ingham et al, 1996) De roos(1997) reported that in products containing aqueous and lipid phases, a flavour compound is distributed over three phases: fat(or oil),water and air. Flavour release from the oil/fat phase of a food proceeded at a lower rate than from the aqueous phase. This was attributed, first to the higher resistance to mass transfer in fat and oil than in water and second to the fact that in oil/water emulsions flavour compounds had initially to be released from the fat into the aqueous phase before they could be released from the aqueous headspace. Kinsella(1989)reported that several mechanisms might be involved in the interaction of flavour compounds with food components. In lipid systems, solubilisation and rates of partitioning control the rates of release Polysaccharides can interact with flavour compounds mostly by non-specifi adsorption and formation of inclusion compounds. In protein systems adsorption, specific binding, entrapment, encapsulation and covalent binding count for the retention of flavour Oil and fatty acids can also be absorbed by polymers(Arora and Halek, 1994 Riquet et al, 1998)resulting in increased oxygen permeability (Johansson and Leufven, 1994)and delamination of laminated packaging material(Olaffson and Hildingson, 1995; Olaffson et al., 1995) However, the availability of data about the influence of oil on the absorption of flavour compounds by plastic packaging materials is limited. Nielsen et al.(1992) found that some apple aroma compounds added to and stored in pure olive oil were lost to a greater extent to LDPE than from an aqueous solution, probably due to differences in polarity of the aromas, polymer and solutions. Thus, oil/fat has a major influence on flavour compounds (perception, intensity, volatility, etc. ) and on the properties of ackaging material Van Willige et al (2000a, b)did a more detailed study on the influence of the composition of the matrix on food products. These authors used a model system consisting of limonene, decanal, linalol and ethyl 2-methylbutyrate to study flavour scalping in LLDPE from different models representing differences in food matrices. The proteins, B-lactoglobuline (B-1g) and caseine were able to suppress absorption of decanal and limonene, because B-lg interacted irreversibly with decanal and caseine was capable of binding limonene and decanal by hydrophobic and covalent interactions. Dufour and Haertle(1990) and Charles et al. (1996)reported that B-lg does not bind terpenes as limonene and linalol. The behaviour of ethyl 2-methylbutyrate could not be fully The presence of carbohydrates also affected the absorption of flavour compounds by LLDPE. Absorption rates of limonene and to a lesser extent of decanal were decreased in the presence of pectine and carboxymethylcellulose lowed down diffu f fla ds from th matrix to LLDPE. Roberts et al.(1996) also reported that thickened solutions of similar viscosity did not show the same flavour release. Their results showed an
decrease caloric intake to make food healthier. Removal or reduction of lipids can lead to an imbalanced flavour, often with a much higher intensity than the original full fat food (Widder and Fischer, 1996; Ingham et al., 1996). De Roos (1997) reported that in products containing aqueous and lipid phases, a flavour compound is distributed over three phases: fat (or oil), water, and air. Flavour release from the oil/fat phase of a food proceeded at a lower rate than from the aqueous phase. This was attributed, first to the higher resistance to mass transfer in fat and oil than in water and, second to the fact that in oil/water emulsions flavour compounds had initially to be released from the fat into the aqueous phase before they could be released from the aqueous phase to the headspace. Kinsella (1989) reported that several mechanisms might be involved in the interaction of flavour compounds with food components. In lipid systems, solubilisation and rates of partitioning control the rates of release. Polysaccharides can interact with flavour compounds mostly by non-specific adsorption and formation of inclusion compounds. In protein systems, adsorption, specific binding, entrapment, encapsulation and covalent binding may account for the retention of flavours. Oil and fatty acids can also be absorbed by polymers (Arora and Halek, 1994; Riquet et al., 1998) resulting in increased oxygen permeability (Johansson and Leufve´n, 1994) and delamination of laminated packaging material (Olaffson and Hildingson, 1995; Olaffson et al., 1995) However, the availability of data about the influence of oil on the absorption of flavour compounds by plastic packaging materials is limited. Nielsen et al. (1992) found that some apple aroma compounds added to and stored in pure olive oil were lost to a greater extent to LDPE than from an aqueous solution, probably due to differences in polarity of the aromas, polymer and solutions. Thus, oil/fat has a major influence on flavour compounds (perception, intensity, volatility, etc.) and on the properties of packaging material. Van Willige et al. (2000a, b) did a more detailed study on the influence of the composition of the matrix on food products. These authors used a model system, consisting of limonene, decanal, linalol and ethyl 2-methylbutyrate to study flavour scalping in LLDPE from different models representing differences in food matrices. The proteins, -lactoglobuline ( -lg) and caseine were able to suppress absorption of decanal and limonene, because -lg interacted irreversibly with decanal and caseine was capable of binding limonene and decanal by hydrophobic and covalent interactions. Dufour and Haertle´ (1990) and Charles et al. (1996) reported that -lg does not bind terpenes as limonene and linalol. The behaviour of ethyl 2-methylbutyrate could not be fully explained and needs further investigation. The presence of carbohydrates also affected the absorption of flavour compounds by LLDPE. Absorption rates of limonene and to a lesser extent of decanal were decreased in the presence of pectine and carboxymethylcellulose. Increasing viscosity slowed down diffusion of flavour compounds from the matrix to LLDPE. Roberts et al. (1996) also reported that thickened solutions of similar viscosity did not show the same flavour release. Their results showed an Packaging-flavour interactions 151
152 Novel food packaging techniques influence of both viscosity and binding interactions with the thickener on the elease of flavour. Binding interactions with carbohydrate-based thickeners are often due to adsorption, entrapment in microregions, complexation, encapsulation and hydrogen bonding between appropriate functional groups Kinsella, 1989, Damodaran, 1996). The presence of disaccharides, lactose and saccharose was able to bind water and cause a salting out effect of the lesser polar flavour compounds, linalol and ethyl 2-methylbutyrate, resulting in an increased absorption in the polymer. Also Godshall (1997)reported that disaccharides can lower the amount of bulk water due to hydration, which increases the effective concentration of flavour compounds and therefore can enhance their absorption into polymers The main effect of the influence of the food matrix on flavour scalping, owever, is the presence of oil or fat. Even a small amount of oil (50g/f)had a major effect on the amount of flavour absorption. Absorption of limonene and decanal is reduced to approximately 5%. A quantity of oil as low as 2 g/l results in a decrease of about 50% of absorption, meaning that the presence of oil very strongly influences the level of absorption of flavour compounds in polymeric packaging material(Fig. 8.4) The composition of the food matrix plays a major role in the absorption of flavour compounds by LLDPE. Several studies have already revealed that flavour compounds interact with oil, carbohydrates and proteins, but the Limonene Linalool 2MB E08 Concentration oil (g/l) Fig. 8.4 Influence of oil on the relative absorption of limonene, decanal, linalool and ethyl-2-methylbutyrate(E2MB) by LLDPE after one day of exposure at 4(Van Willige et al., 2000a)
influence of both viscosity and binding interactions with the thickener on the release of flavour. Binding interactions with carbohydrate-based thickeners are often due to adsorption, entrapment in microregions, complexation, encapsulation and hydrogen bonding between appropriate functional groups (Kinsella, 1989; Damodaran, 1996). The presence of disaccharides, lactose and saccharose was able to bind water and cause a salting out effect of the lesser polar flavour compounds, linalol and ethyl 2-methylbutyrate, resulting in an increased absorption in the polymer. Also Godshall (1997) reported that disaccharides can lower the amount of bulk water due to hydration, which increases the effective concentration of flavour compounds and therefore can enhance their absorption into polymers. The main effect of the influence of the food matrix on flavour scalping, however, is the presence of oil or fat. Even a small amount of oil (50g/l) had a major effect on the amount of flavour absorption. Absorption of limonene and decanal is reduced to approximately 5%. A quantity of oil as low as 2 g/l results in a decrease of about 50% of absorption, meaning that the presence of oil very strongly influences the level of absorption of flavour compounds in polymeric packaging material (Fig. 8.4). The composition of the food matrix plays a major role in the absorption of flavour compounds by LLDPE. Several studies have already revealed that flavour compounds interact with oil, carbohydrates and proteins, but the Fig. 8.4 Influence of oil on the relative absorption of limonene, decanal, linalool and ethyl-2-methylbutyrate (E2MB) by LLDPE after one day of exposure at 4º (Van Willige et al., 2000a) 152 Novel food packaging techniques
Packaging-flavour interactions 153 influence on flavour absorption by plastic packaging materials in different food matrices has been unclear for a long time. Van Willige et al(2000a, b) showed that food components can affect the quantity of absorbed flavour compounds by LLDPE in the following order: oil or fat > polysaccharides and proteins disaccharides. Because of the lipophilic character of many flavour compounds food products with a high oil or fat content will lose less flavour by absorption into LLDPE packaging than food products containing no or a small quantity of 8.4 The role of differing packaging materials An important requirement in selecting food-packaging systems is the barrier properties of the packaging material. Barrier properties include permeability of gases(such as O2, CO2, N2 and ethylene), water vapour, aroma compounds and light. These are vital factors for maintaining the quality of foods. a good barrier to moisture and oxygen keeps a product crisp and fresh, and reduces oxidation of food constituents. Plastics are widely used for food packaging due to their flexibility, variability in size and shape, thermal stability, and barrier properties PE and PP have been used for many years because of their good heat sealability low costs and low water vapour permeability. However, poor gas permeability makes laminating of PE with aluminium foil and paper necessary. During the last decades, PET and, to a lesser extent, PC have found increased use for food packaging. PET has good mechanical properties, excellent transparency and relatively low permeability to gases. PC is tough, stiff, hard and transparent, but has poor gas permeability properties and is still quite expensive &s Unlike glass, plastics are not inert allowing mass transport of compounds such water, gases, flavours, monomers and fatty acids between a food product, package and the environment due to permeation, migration and absorption. The quality and shelf-life of plastic-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 showed that considerable amounts of aroma compounds can be absorbed by plastic packaging materials, resulting in loss of aroma intensity or an unbalanced flavour profile(van Willige et al., 2000a, b, Arora et al., 1991; Lebosse et al, 1997, Linssen et al. 1991b, Nielsen et al., 1992; Paik, 1992) Absorption may also indirectly affect the food quality by causing delamination of multilayer packages (Olafsson and Hildingsson, 1995: Olafsson et al., 1995)or by altering the barrier and mechanical properties of plastic packaging materials (Tawfik et al., 1998). Oxygen permeability through the packaging is an important factor for the shelf-life of many packed foods. Little information is available in literature about the influence of absorbed compounds on the oxygen permeability of packaging materials. Hirose et al.(1988)reported that the oxygen permeability of LDPE and two types of ionomer increased due to the presence of absorbed d-limonene. Johansson and Leufven(1994) studied the effect of rapeseed oil on the oxygen barrier properties
influence on flavour absorption by plastic packaging materials in different food matrices has been unclear for a long time. Van Willige et al. (2000a,b) showed that food components can affect the quantity of absorbed flavour compounds by LLDPE in the following order: oil or fat >> polysaccharides and proteins > disaccharides. Because of the lipophilic character of many flavour compounds, food products with a high oil or fat content will lose less flavour by absorption into LLDPE packaging than food products containing no or a small quantity of oil. 8.4 The role of differing packaging materials An important requirement in selecting food-packaging systems is the barrier properties of the packaging material. Barrier properties include permeability of gases (such as O2, CO2, N2 and ethylene), water vapour, aroma compounds and light. These are vital factors for maintaining the quality of foods. A good barrier to moisture and oxygen keeps a product crisp and fresh, and reduces oxidation of food constituents. Plastics are widely used for food packaging due to their flexibility, variability in size and shape, thermal stability, and barrier properties. PE and PP have been used for many years because of their good heat sealability, low costs and low water vapour permeability. However, poor gas permeability makes laminating of PE with aluminium foil and paper necessary. During the last decades, PET and, to a lesser extent, PC have found increased use for food packaging. PET has good mechanical properties, excellent transparency and relatively low permeability to gases. PC is tough, stiff, hard and transparent, but has poor gas permeability properties and is still quite expensive. Unlike glass, plastics are not inert allowing mass transport of compounds such as water, gases, flavours, monomers and fatty acids between a food product, package and the environment due to permeation, migration and absorption. The quality and shelf-life of plastic-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 showed that considerable amounts of aroma compounds can be absorbed by plastic packaging materials, resulting in loss of aroma intensity or an unbalanced flavour profile (Van Willige et al., 2000a,b; Arora et al., 1991; Lebosse´ et al., 1997; Linssen et al., 1991b; Nielsen et al., 1992; Paik, 1992) Absorption may also indirectly affect the food quality by causing delamination of multilayer packages (Olafsson and Hildingsson, 1995; Olafsson et al., 1995) or by altering the barrier and mechanical properties of plastic packaging materials (Tawfik et al., 1998). Oxygen permeability through the packaging is an important factor for the shelf-life of many packed foods. Little information is available in literature about the influence of absorbed compounds on the oxygen permeability of packaging materials. Hirose et al. (1988) reported that the oxygen permeability of LDPE and two types of ionomer increased due to the presence of absorbed d-limonene. Johansson and Leufve´n (1994) studied the effect of rapeseed oil on the oxygen barrier properties Packaging-flavour interactions 153