Part I Developments in modified atmosphere packaging map)
Part II Developments in modified atmosphere packaging (MAP)
10 Novel MaP applications for fresh- prepared produce B P F. Day, Food Science australia 10.1 Introduction During recent years there has been an explosive growth in the market for fresh prepared fruit and vegetable(i.e. produce) products. The main driving force for this market growth is the increasing consumer demand for fresh, healthy, convenient and additive-free prepared product items. However, fresh prepared produce items are highly perishable and prone to the major spoilage mechanisms of enzymic discoloration, moisture loss and microbial growth. Good manufacturing and handling practices along with the appropriate use of modified atmosphere packaging (MAP) are relatively effective at inhibiting these spoilage mechanisms, thereby extending shelf-life. Shelf-life extension also results in the commercial benefits of less wastage in manufacturing and retail display, long distribution channels, improved product image and the ability to sell convenient, added-value, fresh prepared produce items to the consumer with reasonable remaining chilled storage life The application of novel high oxygen(O2) MAP is a new approach for the etailing of fresh prepared produce items and is capable of overcoming the many inherent shortcomings of current industry-standard air packaging or low O MAP. The results from an extensive European Commission and industry funded project have shown that high O2 MAP is particularly effective at inhibiting enzymic discolorations, preventing anaerobic fermentation reactions and moisture losses, and inhibiting aerobic and anaerobic microbial growth Independent research undertaken in the Netherlands, Belgium, Australia, USA and Spain has also shown many interesting and mainly beneficial effects of high O2 MAP and references to this research are listed. This chapter highlights how extended shelf-life can be achieved by using high O2 MAP. Practical guidance
10.1 Introduction During recent years there has been an explosive growth in the market for fresh prepared fruit and vegetable (i.e. produce) products. The main driving force for this market growth is the increasing consumer demand for fresh, healthy, convenient and additive-free prepared product items. However, fresh prepared produce items are highly perishable and prone to the major spoilage mechanisms of enzymic discoloration, moisture loss and microbial growth. Good manufacturing and handling practices along with the appropriate use of modified atmosphere packaging (MAP) are relatively effective at inhibiting these spoilage mechanisms, thereby extending shelf-life. Shelf-life extension also results in the commercial benefits of less wastage in manufacturing and retail display, long distribution channels, improved product image and the ability to sell convenient, added-value, fresh prepared produce items to the consumer with reasonable remaining chilled storage life. The application of novel high oxygen (O2) MAP is a new approach for the retailing of fresh prepared produce items and is capable of overcoming the many inherent shortcomings of current industry-standard air packaging or low O2 MAP. The results from an extensive European Commission and industry funded project have shown that high O2 MAP is particularly effective at inhibiting enzymic discolorations, preventing anaerobic fermentation reactions and moisture losses, and inhibiting aerobic and anaerobic microbial growth. Independent research undertaken in the Netherlands, Belgium, Australia, USA and Spain has also shown many interesting and mainly beneficial effects of high O2 MAP and references to this research are listed. This chapter highlights how extended shelf-life can be achieved by using high O2 MAP. Practical guidance 10 Novel MAP applications for freshprepared produce B.P.F. Day, Food Science Australia
190 Novel food packaging techniques on issues such as safety, optimal high O2 mixtures, produce volume/gas volume ratios, packaging materials and chilled storage temperatures will be outlined as to facilitate the commercial exploitation of this new technology. Brief reference in this chapter has been made with respect to novel argon(Ar) and nitrous oxide(,O)MAP, but in light of the variable results obtained for the novel MAP treatments, the majority of the text concentrates on the applications of novel high O2 MAP. Unlike other chilled perishable foods that are modified atmosphere(MA) packed, fresh produce continues to respire after harvesting, and any subsequent packaging must take into account this respiratory activity. The depletion of o2 and enrichment of carbon dioxide(CO2) are natural consequences of the progress of respiration when fresh produce is stored in hermetically sealed packs. Such modification of the atmosphere results in a respiratory rate decrease with a consequent extension of shelf-life(Kader et al, 1989). MAs can passively evolve within hermetically air-sealed packs as a consequence of produce respiration. If a produce items respiratory characteristics are properly matched to film permeability values, then a beneficial equilibrium MA(EMA) can be passively established. However, in the MAP of fresh produce, there is a limited ability to regulate passively established MAs within hermetically air-sealed packs. There are many circumstances when it is desirable to rapidly establish the tmosphere within produce packs. By replacing the pack atmosphere with a desired mixture of O2, CO2 and nitrogen (N2), a beneficial EMA may be established more rapidly than a passively generated EMA. For example, flushing packs with N2 or a mixture of 5-10%O2, 5-10% CO2 and 80-90%N2 is commercial practice for inhibiting undesirable browning and pinking on prepared leafy green salad vegetables(Day, 1998) The key to successful retail MAP of fresh prepared produce is currently to use packaging film of correct permeability so as to establish optimal EMAs of typically 3-10% O and 3-10% Co2. The EMAs attained are influenced by produce respiration rate(which itself is affected by temperature, produce type variety, size, maturity and severity of preparation); packaging film permeability pack volume, surface area and fill weight; and degree of illumination Consequently, establishment of an optimum EMA for individual produce items is very complex. Furthermore, in many commercial situations, produce is sealed in packaging film of insufficient permeability(Betts, 1996)resulting in development of undesirable anaerobic conditions (e.g. <2% O2 and >20% CO2). Recently developed, microperforated films, which have very high gas transmission rates, are now commercially used for maintaining aerobic EMAs (e.g. 5-15%O2 and 5-15%CO2)for highly respiring prepared produce items such as broccoli and cauliflower florets, baton carrots, beansprouts, mushrooms and spinach. However, microperforated films are relatively expensive, permit moisture and odour losses, and may allow for the ingress of microorganisms into sealed packs during wet handling situations(Day, 1998)
on issues such as safety, optimal high O2 mixtures, produce volume/gas volume ratios, packaging materials and chilled storage temperatures will be outlined so as to facilitate the commercial exploitation of this new technology. Brief reference in this chapter has been made with respect to novel argon (Ar) and nitrous oxide (N2O) MAP, but in light of the variable results obtained for these novel MAP treatments, the majority of the text concentrates on the applications of novel high O2 MAP. Unlike other chilled perishable foods that are modified atmosphere (MA) packed, fresh produce continues to respire after harvesting, and any subsequent packaging must take into account this respiratory activity. The depletion of O2 and enrichment of carbon dioxide (CO2) are natural consequences of the progress of respiration when fresh produce is stored in hermetically sealed packs. Such modification of the atmosphere results in a respiratory rate decrease with a consequent extension of shelf-life (Kader et al., 1989). MAs can passively evolve within hermetically air-sealed packs as a consequence of produce respiration. If a produce item’s respiratory characteristics are properly matched to film permeability values, then a beneficial equilibrium MA (EMA) can be passively established. However, in the MAP of fresh produce, there is a limited ability to regulate passively established MAs within hermetically air-sealed packs. There are many circumstances when it is desirable to rapidly establish the atmosphere within produce packs. By replacing the pack atmosphere with a desired mixture of O2, CO2 and nitrogen (N2), a beneficial EMA may be established more rapidly than a passively generated EMA. For example, flushing packs with N2 or a mixture of 5–10% O2, 5–10% CO2 and 80–90% N2 is commercial practice for inhibiting undesirable browning and pinking on prepared leafy green salad vegetables (Day, 1998). The key to successful retail MAP of fresh prepared produce is currently to use packaging film of correct permeability so as to establish optimal EMAs of typically 3–10% O2 and 3–10% CO2. The EMAs attained are influenced by produce respiration rate (which itself is affected by temperature, produce type, variety, size, maturity and severity of preparation); packaging film permeability; pack volume, surface area and fill weight; and degree of illumination. Consequently, establishment of an optimum EMA for individual produce items is very complex. Furthermore, in many commercial situations, produce is sealed in packaging film of insufficient permeability (Betts, 1996) resulting in development of undesirable anaerobic conditions (e.g. <2% O2 and >20% CO2). Recently developed, microperforated films, which have very high gas transmission rates, are now commercially used for maintaining aerobic EMAs (e.g. 5–15% O2 and 5–15% CO2) for highly respiring prepared produce items such as broccoli and cauliflower florets, baton carrots, beansprouts, mushrooms and spinach. However, microperforated films are relatively expensive, permit moisture and odour losses, and may allow for the ingress of microorganisms into sealed packs during wet handling situations (Day, 1998). 190 Novel food packaging techniques
Novel MAP applications for fresh-prepared produce 191 10.2 Novel map gases 10.2.1 High Oz MAP Information gathered by the author during 1993-1994 revealed that prepared produce companies had been experimenting with high O2(e 100%)MAP and had achieved some surprisingly beneficial results. Hi MAP of prepared produce was not exploited commercially during that period, probably because of the inconsistent results obtained, a lack of understanding of the basic biological mechanisms involved and concerns about possible safety implications. Intrigued by the concept of high O2 MAP, the Campden and Chorleywood Food Research Association(CCFRA)carried out limited experimental trials on prepared iceberg lettuce and tropical fruits, in early 1995. The results of these trials confirmed that high o, maP could overcome the many disadvantages of low O2 MAP. High O2 MAP was found to be particularly effective at inhibiting enzymic discolorations, preventing anaerobic fermentation reactions and inhibiting microbial growth. In addition, the high O MAP of prepared produce items within inexpensive hermetically sealed plastic films was found to be very effective at preventing undesirable moisture and odour losses and ingress of microorganisms during wet handling situations( Day, The experimental finding that high O2 MAP is capable of inhibiting aerobic and anaerobic microbial growth can be explained by the growth profiles of aerobes and anaerobes(Fig. 10.1). It is hypothesised that active oxygen radical species damage vital cellular macromolecules and thereby inhibit microbial growth when oxidative stresses overwhelm cellular protection systems Gonzalez Roncero and Day, 1998, Amanatidou, 2001). Also intuitively, high O2 MAP inhibits undesirable anaerobic fermentation reactions(Day, 1998) Polyphenol oxidase(PPO) is the enzyme primarily responsible for initiating discoloration on the cut surfaces of prepared produce. PPO catalyses the oxidation of natural phenolic substances to colourless quinones which subsequently polymerise to coloured melanin-type compounds (McEvily et al., 1992). It is hypothesised that high O2(and/or high Ar) levels may cause substrate inhibition of PPO or alternatively, high levels of colourless quinones lbsequently formed(Fig. 10.2)may cause feedback product inhibition of PPO 10.2.2 Argon and nitrous oxide mal Argon(Ar)and nitrous oxide(N20)are classified as miscellaneous additives and are permitted gases for food use in the European Union(EU). Air Liquide S.A.(Paris, France) has stimulated recent commercial interest in the potential MAP applications of using Ar and, to a lesser extent, N2O. Air Liquides broad range of patents claim that in comparison with N2O, Ar can more effectively inhibit enzymic activities, microbial growth and degradative chemical reactions in selected perishable foods(Brody and Thaler, 1996, Spencer, 1999). More specifically, an Air Liquide patent for fresh produce applications claims that Ar
10.2 Novel MAP gases 10.2.1 High O2 MAP Information gathered by the author during 1993–1994 revealed that a few prepared produce companies had been experimenting with high O2 (e.g. 70– 100%) MAP and had achieved some surprisingly beneficial results. High O2 MAP of prepared produce was not exploited commercially during that period, probably because of the inconsistent results obtained, a lack of understanding of the basic biological mechanisms involved and concerns about possible safety implications. Intrigued by the concept of high O2 MAP, the Campden and Chorleywood Food Research Association (CCFRA) carried out limited experimental trials on prepared iceberg lettuce and tropical fruits, in early 1995. The results of these trials confirmed that high O2 MAP could overcome the many disadvantages of low O2 MAP. High O2 MAP was found to be particularly effective at inhibiting enzymic discolorations, preventing anaerobic fermentation reactions and inhibiting microbial growth. In addition, the high O2 MAP of prepared produce items within inexpensive hermetically sealed plastic films was found to be very effective at preventing undesirable moisture and odour losses and ingress of microorganisms during wet handling situations (Day, 1998). The experimental finding that high O2 MAP is capable of inhibiting aerobic and anaerobic microbial growth can be explained by the growth profiles of aerobes and anaerobes (Fig. 10.1). It is hypothesised that active oxygen radical species damage vital cellular macromolecules and thereby inhibit microbial growth when oxidative stresses overwhelm cellular protection systems (Gonzalez Roncero and Day, 1998; Amanatidou, 2001). Also intuitively, high O2 MAP inhibits undesirable anaerobic fermentation reactions (Day, 1998). Polyphenol oxidase (PPO) is the enzyme primarily responsible for initiating discoloration on the cut surfaces of prepared produce. PPO catalyses the oxidation of natural phenolic substances to colourless quinones which subsequently polymerise to coloured melanin-type compounds (McEvily et al., 1992). It is hypothesised that high O2 (and/or high Ar) levels may cause substrate inhibition of PPO or alternatively, high levels of colourless quinones subsequently formed (Fig. 10.2) may cause feedback product inhibition of PPO. 10.2.2 Argon and nitrous oxide MAP Argon (Ar) and nitrous oxide (N2O) are classified as miscellaneous additives and are permitted gases for food use in the European Union (EU). Air Liquide S.A. (Paris, France) has stimulated recent commercial interest in the potential MAP applications of using Ar and, to a lesser extent, N2O. Air Liquide’s broad range of patents claim that in comparison with N2O, Ar can more effectively inhibit enzymic activities, microbial growth and degradative chemical reactions in selected perishable foods (Brody and Thaler, 1996; Spencer, 1999). More specifically, an Air Liquide patent for fresh produce applications claims that Ar Novel MAP applications for fresh-prepared produce 191
192 Novel food packaging techniques %o o Fig. 10.1 Hypothesised inhibition by high O2 MAP. and N2O are capable of extending shelf-life by inhibiting fungal growth, educing ethylene emissions and slowing down sensory quality deterioration (Fath and Soudan, 1992). Of particular relevance is the claim that Ar can reduce the respiration rates of fresh produce and hence have a direct effect on extension of shelf-life(Spencer, 1999) Although Ar is chemically inert, Air Liquide's research has indicated that it may have biochemical effects, probably due to its similar atomic size to molecular O2 and its higher solubility in water and density compared with N2 and Oz. Hence Ar is probably more effective at displacing O2 from cellular sites and enzymic O2 receptors with the consequence that oxidative deterioration reactions are likely to be inhibited. In addition, Ar and n,o are thought to sensitise microorganisms antimicrobial agents. This possible sensitisation is not well understood but may involve alteration of the membrane fluidity of microbial cell walls with a subsequent influence on cell function and performance(Thom and Marquis, 1984) Clearly, more independent research is needed to better understand the potential beneficial effects of Ar and N2O(Day, 1998) Product inhibition Phenols PPO+ O2 ▲ melanins Fig. 10.2 Hypothesised inhibition of enzymic discoloration by high O2 MAP
and N2O are capable of extending shelf-life by inhibiting fungal growth, reducing ethylene emissions and slowing down sensory quality deterioration (Fath and Soudain, 1992). Of particular relevance is the claim that Ar can reduce the respiration rates of fresh produce and hence have a direct effect on extension of shelf-life (Spencer, 1999). Although Ar is chemically inert, Air Liquide’s research has indicated that it may have biochemical effects, probably due to its similar atomic size to molecular O2 and its higher solubility in water and density compared with N2 and O2. Hence, Ar is probably more effective at displacing O2 from cellular sites and enzymic O2 receptors with the consequence that oxidative deterioration reactions are likely to be inhibited. In addition, Ar and N2O are thought to sensitise microorganisms to antimicrobial agents. This possible sensitisation is not well understood but may involve alteration of the membrane fluidity of microbial cell walls with a subsequent influence on cell function and performance (Thom and Marquis, 1984). Clearly, more independent research is needed to better understand the potential beneficial effects of Ar and N2O (Day, 1998). Fig. 10.1 Hypothesised inhibition of microbial growth by high O2 MAP. Fig. 10.2 Hypothesised inhibition of enzymic discoloration by high O2 MAP. 192 Novel food packaging techniques