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. 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. 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
Novel MAP applications for fresh-prepared produce 193 10.3 Testing novel MAP applications Two industrially funded research Clubs were set up at CCfRA to investigate in detail the interesting effects of novel MAP on fresh prepared produce. A High O2 MAP Club ran from April, 1995 to September, 1997 and as a follow-up, a Novel Gases MAP Club ran from January, 1998 to December, 1999. These Clubs were supported by a total of nine prepared produce suppliers, five gas companies, four ckaging film suppliers, three retailers, two suppliers of non-sulphite dips, two manufacturers of MAP machinery and two gas instrument companies In addition, further investigations were carried out during a three-year EU FAIR funded project, which started in September 1996. The overall objective of this project was to develop safe commercial applications of novel MAP for extending the quality shelf-life of a wide range of fresh prepared produce items Other aims included investigations of the effects of novel MAP on non-sulphite dipped prepared produce, labile nutritional components, and microbial and biochemical spoilage mechanisms. The major focus of this research was on high O2 MAP, followed by Ar MAP, and to a minor extent, N2O MAP In summary, the following major results and achievements were made during the course of CCfra's Club and eu-funded novel map research High O2 compatible MAP machines were used safely and successfully during the course of the projects experimental trial work. A non-confidential guidelines document on the safe use of high O, MAP was published(BCGa 1998) Enzymic discolorations of prepared non-sulphite dipped potatoes and apples were generally more effectively inhibited by anaerobic (<2% O2) MAP ombinations of N2, Ar and COz, compared with high O2 MAP. However, high O2 MAP was found to have certain odour and textural benefits for prepared potatoes and apples. Also, high O2 Ma packed non-sulphite dipped prepared potatoes and bananas were found to have longer achievable shelf- lives, in comparison with equivalent low O2(8%)MA packed control For most prepared produce items, under defined storage and packaging conditions, high O2 MAP was found to have beneficial effects on sensory uality in comparison with industry-standard air packing and low O2 MAP High O2 MAP was found to be effective for extending the achievable shelf- lives of prepared iceberg lettuce, sliced mushrooms, broccoli florets, Cos lettuce, baby-leaf spinach, raddichio lettuce, lollo rossa lettuce, flat-leaf parsley, cubed swede, coriander, raspberries, strawberries, grapes and Ar-containing and N2O-containing MAP treatments were found to have negligible, variable or only minor beneficial effects on the sensory quality of several prepared produce items, in comparison with equivalent N2-containing MAP treatments High O2 MAs were found to inhibit the growth of several generic groups of bacteria, yeasts and moulds, as well as a range of specific food pathogenic
10.3 Testing novel MAP applications Two industrially funded research Clubs were set up at CCFRA to investigate in detail the interesting effects of novel MAP on fresh prepared produce. A High O2 MAP Club ran from April, 1995 to September, 1997 and as a follow-up, a Novel Gases MAP Club ran from January, 1998 to December, 1999. These Clubs were supported by a total of nine prepared produce suppliers, five gas companies, four packaging film suppliers, three retailers, two suppliers of non-sulphite dips, two manufacturers of MAP machinery and two gas instrument companies. In addition, further investigations were carried out during a three-year EU FAIR funded project, which started in September 1996. The overall objective of this project was to develop safe commercial applications of novel MAP for extending the quality shelf-life of a wide range of fresh prepared produce items. Other aims included investigations of the effects of novel MAP on non-sulphite dipped prepared produce, labile nutritional components, and microbial and biochemical spoilage mechanisms. The major focus of this research was on high O2 MAP, followed by Ar MAP, and to a minor extent, N2O MAP. In summary, the following major results and achievements were made during the course of CCFRA’s Club and EU-funded novel MAP research: • High O2 compatible MAP machines were used safely and successfully during the course of the project’s experimental trial work. A non-confidential guidelines document on the safe use of high O2 MAP was published (BCGA, 1998). • Enzymic discolorations of prepared non-sulphite dipped potatoes and apples were generally more effectively inhibited by anaerobic (<2% O2) MAP combinations of N2, Ar and CO2, compared with high O2 MAP. However, high O2 MAP was found to have certain odour and textural benefits for prepared potatoes and apples. Also, high O2 MA packed non-sulphite dipped prepared potatoes and bananas were found to have longer achievable shelflives, in comparison with equivalent low O2 (8%) MA packed control samples. • For most prepared produce items, under defined storage and packaging conditions, high O2 MAP was found to have beneficial effects on sensory quality in comparison with industry-standard air packing and low O2 MAP. High O2 MAP was found to be effective for extending the achievable shelflives of prepared iceberg lettuce, sliced mushrooms, broccoli florets, Cos lettuce, baby-leaf spinach, raddichio lettuce, lollo rossa lettuce, flat-leaf parsley, cubed swede, coriander, raspberries, strawberries, grapes and oranges (Tables 10.1 and 10.2). • Ar-containing and N2O-containing MAP treatments were found to have negligible, variable or only minor beneficial effects on the sensory quality of several prepared produce items, in comparison with equivalent N2-containing MAP treatments. • High O2 MAs were found to inhibit the growth of several generic groups of bacteria, yeasts and moulds, as well as a range of specific food pathogenic Novel MAP applications for fresh-prepared produce 193
194 Novel food packaging techniques Table 10.1 Overall achievable shelf-life obtained from fresh prepared iceberg lettuce LAP Storage days at 8 C to drop to Shelf-life limiting Overall treatments uality attribute(s) achievable shelf-life Appearance Odour Texture 095 Appearance/texture 4 days CO285%N27 Appearance/odour 7 days 80%Oy 20%N2 11 11 Appearance/odour/ 11 days and spoilage microorganisms, namely Aeromonas hydrophila, salmonella enteritidis, Pseudomonas putida, Rhizopus stolonifer, Botrytis cinerea Penicillium roqueforti, Penicillium digitatum and Aspergillus niger (e.g Figs 10.3 and 10. 4). High O MAs alone were not found to inhibit or stimulate the growth of Pseudomonas fragi, Bacillus cereus, Lactobacillus sake, Yersinia enterocolitica and Listeria monocytogenes, but the addition of 10-30%CO2 inhibited the growth of all these bacteria. Ar-containing and N2O-containing MAs were found to have negligible antimicrobial effects on Table 10.2 Overall achievable shelf-life obtained from several fresh prepared produce Prepared produce items Overall achievable shelf-life(days)at &C Industry standard air/low High O2 MAP O, MAP 4-11 ananas 4 Cos lettuce Strawberries Baby leaf spinach Lolla rossa lettuce Radicchio lettuce Flat leaf parsley Coriander Cubed swede 3 9 Little gem lettuce 4-8 Dipped potate 3-6 Baton carrots Sliced mushrooms
and spoilage microorganisms, namely Aeromonas hydrophila, Salmonella enteritidis, Pseudomonas putida, Rhizopus stolonifer, Botrytis cinerea, Penicillium roqueforti, Penicillium digitatum and Aspergillus niger (e.g. Figs 10.3 and 10.4). High O2 MAs alone were not found to inhibit or stimulate the growth of Pseudomonas fragi, Bacillus cereus, Lactobacillus sake, Yersinia enterocolitica and Listeria monocytogenes, but the addition of 10–30% CO2 inhibited the growth of all these bacteria. Ar-containing and N2O-containing MAs were found to have negligible antimicrobial effects on Table 10.1 Overall achievable shelf-life obtained from fresh prepared iceberg lettuce trial MAP Storage days at 8ºC to drop to Shelf-life limiting Overall treatments quality grade C quality attribute(s) achievable shelf-life Appearance Odour Texture 5% O2/95% N2 4 7 4 Appearance/texture 4 days 5% O2/10% CO2/85% N2 7 7 8 Appearance/odour 7 days 80% O2/ 20% N2 11 11 11 Appearance/odour/ 11 days texture Table 10.2 Overall achievable shelf-life obtained from several fresh prepared produce trials Prepared produce items Overall achievable shelf-life (days) at 8ºC Industry standard air/low High O2 MAP O2 MAP Iceberg lettuce 2–4 4–11 Dipped sliced bananas 2 4 Broccoli florets 2 9 Cos lettuce 3 7 Strawberries 1–2 4 Baby leaf spinach 7 9 Lolla Rossa lettuce 4 7 Radicchio lettuce 3 4 Flat leaf parsley 4 9 Coriander 4 7 Cubed swede 3 10 Raspberries 5–7 9 Little Gem lettuce 4–8 6–8 Dipped potatoes 2–3 3–6 Baton carrots 3–4 4 Sliced mushrooms 2 6 194 Novel food packaging techniques
Novel MAP applications for fresh-prepared produce 195 40 Boirvis cinerea Mycelial □ Penicillium echinulatum diameter nm) AIR 5%O 15%CO215%CO220%CO2 Source: ATO-DLO Fig. 10.3 Inhibition of fungal growth by different MAs a range of microorganisms, when compared with equivalent N2-containing MAs Respiration rates of selected prepared produce items were not found to be significantly affected by high O2 or high Ar MAs, but were substantially reduced by the addition of 10% Co2 High O2 and high Ar MAP did not prevent the enzymic browning of non sulphite dipped apple slices, but no further browning took place after pack fungal area 20 o days at 18C 15 10 21%O221%O250%O250%O280%O280%O 0%CO20%CO30%CO120%CO20%CO20%CO Different gas atmospheres Source:AlO- DLo Fig. 10.4 Inhibition of fungal growth on Penicillium digitatum infected oranges under different MAs
a range of microorganisms, when compared with equivalent N2-containing MAs. • Respiration rates of selected prepared produce items were not found to be significantly affected by high O2 or high Ar MAs, but were substantially reduced by the addition of 10% CO2. • High O2 and high Ar MAP did not prevent the enzymic browning of nonsulphite dipped apple slices, but no further browning took place after pack opening. Fig. 10.3 Inhibition of fungal growth by different MAs. Fig. 10.4 Inhibition of fungal growth on Penicillium digitatum infected oranges under different MAs. Novel MAP applications for fresh-prepared produce 195
196 Novel food packaging techniques Ar-containing MAs were found to inhibit the activity of mushroom polyphenol oxidase(PPO), when compared with equivalent N2-containing MAs. In contrast, no significant inhibition of mushroom PPO activity was found under 80%O2/20% N2 when compared with 20%O2/80% N2 However, the incorporation of 20% CO2 into high O2 MAs may inhibi mushroom PPO as well as the activity of other prepared produce PPOs (Sapers, 1993) High O2 MAP increased membrane damage of apple slices, whereas high Ar MAP decreased membrane damage. However, apple slices stored under O2- free MAs suffered the most membrane damage, which adversely affected tissue integrity, cell leakage and texture. By comparison, high O2 and high Ar MAP were not found to affect adversely the cell permeability, tissue exudate or pH of prepared carrots High O, and high Ar MAP were found to have beneficial effects acid retention, indicators of lipid oxidation and inhibition of enzymic browning on prepared lettuce High O2 MAs increased the peroxidase activity of Botrytis cinerea, but the ddition of 10% CO2 substantially reduced this activity In comparison with air packing and low O2 MAP, high O2 MAP was not found to decrease preferentially single antioxidant(ascorbic acid, B-carotene and lutein) levels in prepared lettuce but did induce the loss of certain phenolic even though desirable total antioxidant capacity TRAP)values after chilled storage were increased Extracts from high O2 MA packed prepared lettuce and onions did not have any cytotoxic effects on human colon cells Ingestion of fresh lettuce resulted in an increase in human plasma TRAP values through the absorption of phenolic compounds and single antioxidant molecules. This increase in human plasma TRAP values was significantly higher than after ingestion of lettuce that had been chilled (5%C)stored for three days Ingestion of chilled stored lettuce packed under air and high O2 MAs resulted in measurable increases in human plasma TRAP values, whereas virtually no increases in TRAP values were measured after ingestion of equivalent lettuce packed under low O2 MAS A guidelines document was compiled which outlines good manufacturing and handling practices for fresh prepared produce using high O2 MAP and non- sulphite dipping treatments(Day, 2001a) 10.4 Applying high O2 MAP It should be appreciated that the potential applications of high O2 MAP technology are a recent innovation and new knowledge will evolve in the future Hence, the following guidance provided only reflects the current status of available knowledge and experience of high O2 MAP for fresh prepared
• Ar-containing MAs were found to inhibit the activity of mushroom polyphenol oxidase (PPO), when compared with equivalent N2-containing MAs. In contrast, no significant inhibition of mushroom PPO activity was found under 80% O2/20% N2 when compared with 20% O2/80% N2. However, the incorporation of 20% CO2 into high O2 MAs may inhibit mushroom PPO as well as the activity of other prepared produce PPOs (Sapers, 1993). • High O2 MAP increased membrane damage of apple slices, whereas high Ar MAP decreased membrane damage. However, apple slices stored under O2- free MAs suffered the most membrane damage, which adversely affected tissue integrity, cell leakage and texture. By comparison, high O2 and high Ar MAP were not found to affect adversely the cell permeability, tissue exudate or pH of prepared carrots. • High O2 and high Ar MAP were found to have beneficial effects on ascorbic acid retention, indicators of lipid oxidation and inhibition of enzymic browning on prepared lettuce. • High O2 MAs increased the peroxidase activity of Botrytis cinerea, but the addition of 10% CO2 substantially reduced this activity. • In comparison with air packing and low O2 MAP, high O2 MAP was not found to decrease preferentially single antioxidant (ascorbic acid, b-carotene and lutein) levels in prepared lettuce but did induce the loss of certain phenolic compounds, even though desirable total antioxidant capacity (TRAP) values after chilled storage were increased. • Extracts from high O2 MA packed prepared lettuce and onions did not have any cytotoxic effects on human colon cells. • Ingestion of fresh lettuce resulted in an increase in human plasma TRAP values through the absorption of phenolic compounds and single antioxidant molecules. This increase in human plasma TRAP values was significantly higher than after ingestion of lettuce that had been chilled (5ºC) stored for three days. • Ingestion of chilled stored lettuce packed under air and high O2 MAs resulted in measurable increases in human plasma TRAP values, whereas virtually no increases in TRAP values were measured after ingestion of equivalent lettuce packed under low O2 MAs. • A guidelines document was compiled which outlines good manufacturing and handling practices for fresh prepared produce using high O2 MAP and nonsulphite dipping treatments (Day, 2001a). 10.4 Applying high O2 MAP It should be appreciated that the potential applications of high O2 MAP technology are a recent innovation and new knowledge will evolve in the future. Hence, the following guidance provided only reflects the current status of available knowledge and experience of high O2 MAP for fresh prepared 196 Novel food packaging techniques
Novel MAP applications for fresh-prepared produce 197 produce. Potential applications of high O2 MAP to chilled combination food items(e.g. chilled ready meals, pizzas, kebabs, etc. )have been the subject of recent research(Day, 2001b), but are outside the scope of this chapter 10.4.1 Safety A specific guideline document on The safe application of oxygen enriched atmospheres when packaging food has been published an nd is publicly availa (BCGA, 1998). This document contains clear and concise advice and commendations on how to control safely the hazards of utilising O2-rich gas mixtures for the map of food Food companies and related industries (e.g. gas companies and MAP machinery manufacturers) are strongly encouraged to purchase this safety guidelines document and to follow closely the advice and recommendations given before undertaking any pre-commercial trials using high O2 MAP. Further advice and help on the safety aspects of high O2 MAP can be sought from qualified gas safety engineers and the bcga 10.4.2 Optimal gas levels Based on CCFRA's practical experimental trials, the recommended optimal headspace gas levels immediately after fresh prepared produce package sealing 80-95%O2/5-20%N After package sealing, headspace O2 levels will decline whereas CO2 levels will increase during chilled storage due to the intrinsic respiratory nature of fresh prepared produce. As previously explained, the levels of O2 and cO2 established within hermetically sealed packs of produce during chilled storage are influenced by numerous variables, i.e. the intrinsic produce respiration rate (which itself is affected by temperature; atmospheric composition; produce type variety, cultivar and maturity; and severity of preparation); packaging film permeability; pack volume, surface area and fill weight; produce volume/gas volume ratio and degree of illumination(Kader et al, 1989; Day, 1994; O Beirne, 1999) To maximise the benefits of high O MAP, it is desirable to maintain headspace levels of O2 >40% and CO2 in the range of 10-25% during the chilled shelf-life of the product. This can be achieved by lowering the temperature of storage, by selecting produce having a lower intrinsic respiration rate, by minimising cut surface tissue damage, by reducing the produce volume/ gas volume ratio by either decreasing the pack fill weight or increasing the pack headspace volume, by using a packaging film which can maintain high levels of O2 whilst selectively allowing excess CO2 to escape, or by incorporating an innovative active packaging sachet that can adsorb excess CO2 and emit an equal volume of O2(McGrath, 2000)
produce. Potential applications of high O2 MAP to chilled combination food items (e.g. chilled ready meals, pizzas, kebabs, etc.) have been the subject of recent research (Day, 2001b), but are outside the scope of this chapter. 10.4.1 Safety A specific guideline document on The safe application of oxygen enriched atmospheres when packaging food has been published and is publicly available (BCGA, 1998). This document contains clear and concise advice and recommendations on how to control safely the hazards of utilising O2-rich gas mixtures for the MAP of food. Food companies and related industries (e.g. gas companies and MAP machinery manufacturers) are strongly encouraged to purchase this safety guidelines document and to follow closely the advice and recommendations given before undertaking any pre-commercial trials using high O2 MAP. Further advice and help on the safety aspects of high O2 MAP can be sought from qualified gas safety engineers and the BCGA. 10.4.2 Optimal gas levels Based on CCFRA’s practical experimental trials, the recommended optimal headspace gas levels immediately after fresh prepared produce package sealing are: 80-95% O2/5–20% N2 After package sealing, headspace O2 levels will decline whereas CO2 levels will increase during chilled storage due to the intrinsic respiratory nature of fresh prepared produce. As previously explained, the levels of O2 and CO2 established within hermetically sealed packs of produce during chilled storage are influenced by numerous variables, i.e. the intrinsic produce respiration rate (which itself is affected by temperature; atmospheric composition; produce type, variety, cultivar and maturity; and severity of preparation); packaging film permeability; pack volume, surface area and fill weight; produce volume/gas volume ratio and degree of illumination (Kader et al., 1989; Day, 1994; O’Beirne, 1999). To maximise the benefits of high O2 MAP, it is desirable to maintain headspace levels of O2 > 40% and CO2 in the range of 10–25% during the chilled shelf-life of the product. This can be achieved by lowering the temperature of storage, by selecting produce having a lower intrinsic respiration rate, by minimising cut surface tissue damage, by reducing the produce volume/ gas volume ratio by either decreasing the pack fill weight or increasing the pack headspace volume, by using a packaging film which can maintain high levels of O2 whilst selectively allowing excess CO2 to escape, or by incorporating an innovative active packaging sachet that can adsorb excess CO2 and emit an equal volume of O2 (McGrath, 2000). Novel MAP applications for fresh-prepared produce 197
