Part II Developments in modified atmosphere packaging (MAP) 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 (O 2 ) 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 O 2 MAP. The results from an extensive European Commission and industry funded project have shown that high O 2 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 O 2 MAP and references to this research are listed. This chapter highlights how extended shelf-life can be achieved by using high O 2 MAP. Practical guidance 10 Novel MAP applications for fresh- prepared produce B.P.F. Day, Food Science Australia on issues such as safety, optimal high O 2 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 (N 2 O) 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 O 2 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 O 2 and enrichment of carbon dioxide (CO 2 ) 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 O 2 , CO 2 and nitrogen (N 2 ), a beneficial EMA may be established more rapidly than a passively generated EMA. For example, flushing packs with N 2 or a mixture of 5–10% O 2 , 5–10% CO 2 and 80–90% N 2 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 2 and 3–10% CO 2 . 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% O 2 and >20% CO 2 ). Recently developed, microperforated films, which have very high gas transmission rates, are now commercially used for maintaining aerobic EMAs (e.g. 5–15% O 2 and 5–15% CO 2 ) 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 10.2 Novel MAP gases 10.2.1 High O 2 MAP Information gathered by the author during 1993–1994 revealed that a few prepared produce companies had been experimenting with high O 2 (e.g. 70– 100%) MAP and had achieved some surprisingly beneficial results. High O 2 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 O 2 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 2 MAP could overcome the many disadvantages of low O 2 MAP. High O 2 MAP was found to be particularly effective at inhibiting enzymic discolorations, preventing anaerobic fermentation reactions and inhibiting microbial growth. In addition, the high O 2 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 O 2 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 O 2 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 O 2 (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 (N 2 O) 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, N 2 O. Air Liquide’s broad range of patents claim that in comparison with N 2 O, 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 and N 2 O 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 O 2 and its higher solubility in water and density compared with N 2 and O 2 . Hence, Ar is probably more effective at displacing O 2 from cellular sites and enzymic O 2 receptors with the consequence that oxidative deterioration reactions are likely to be inhibited. In addition, Ar and N 2 O 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 N 2 O (Day, 1998). Fig. 10.1 Hypothesised inhibition of microbial growth by high O 2 MAP. Fig. 10.2 Hypothesised inhibition of enzymic discoloration by high O 2 MAP. 192 Novel food packaging techniques 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 O 2 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 O 2 MAP, followed by Ar MAP, and to a minor extent, N 2 O 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 O 2 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 O 2 MAP was published (BCGA, 1998). ? Enzymic discolorations of prepared non-sulphite dipped potatoes and apples were generally more effectively inhibited by anaerobic (<2% O 2 ) MAP combinations of N 2 , Ar and CO 2 , compared with high O 2 MAP. However, high O 2 MAP was found to have certain odour and textural benefits for prepared potatoes and apples. Also, high O 2 MA packed non-sulphite dipped prepared potatoes and bananas were found to have longer achievable shelf- lives, in comparison with equivalent low O 2 (8%) MA packed control samples. ? For most prepared produce items, under defined storage and packaging conditions, high O 2 MAP was found to have beneficial effects on sensory quality in comparison with industry-standard air packing and low O 2 MAP. High O 2 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 oranges (Tables 10.1 and 10.2). ? Ar-containing and N 2 O-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 N 2 -containing MAP treatments. ? High O 2 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 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 2 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% CO 2 inhibited the growth of all these bacteria. Ar-containing and N 2 O-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% O 2 /95% N 2 4 7 4 Appearance/texture 4 days 5% O 2 /10% CO 2 /85% N 2 7 7 8 Appearance/odour 7 days 80% O 2 / 20% N 2 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 O 2 MAP O 2 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 a range of microorganisms, when compared with equivalent N 2 -containing MAs. ? Respiration rates of selected prepared produce items were not found to be significantly affected by high O 2 or high Ar MAs, but were substantially reduced by the addition of 10% CO 2 . ? High O 2 and high Ar MAP did not prevent the enzymic browning of non- sulphite 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 ? Ar-containing MAs were found to inhibit the activity of mushroom polyphenol oxidase (PPO), when compared with equivalent N 2 -containing MAs. In contrast, no significant inhibition of mushroom PPO activity was found under 80% O 2 /20% N 2 when compared with 20% O 2 /80% N 2 . However, the incorporation of 20% CO 2 into high O 2 MAs may inhibit mushroom PPO as well as the activity of other prepared produce PPOs (Sapers, 1993). ? High O 2 MAP increased membrane damage of apple slices, whereas high Ar MAP decreased membrane damage. However, apple slices stored under O 2 - free MAs suffered the most membrane damage, which adversely affected tissue integrity, cell leakage and texture. By comparison, high O 2 and high Ar MAP were not found to affect adversely the cell permeability, tissue exudate or pH of prepared carrots. ? High O 2 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 O 2 MAs increased the peroxidase activity of Botrytis cinerea, but the addition of 10% CO 2 substantially reduced this activity. ? In comparison with air packing and low O 2 MAP, high O 2 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 O 2 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 O 2 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 O 2 MAs. ? A guidelines document was compiled which outlines good manufacturing and handling practices for fresh prepared produce using high O 2 MAP and non- sulphite dipping treatments (Day, 2001a). 10.4 Applying high O 2 MAP It should be appreciated that the potential applications of high O 2 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 O 2 MAP for fresh prepared 196 Novel food packaging techniques produce. Potential applications of high O 2 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 O 2 -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 O 2 MAP. Further advice and help on the safety aspects of high O 2 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% O 2 /5–20% N 2 After package sealing, headspace O 2 levels will decline whereas CO 2 levels will increase during chilled storage due to the intrinsic respiratory nature of fresh prepared produce. As previously explained, the levels of O 2 and CO 2 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 2 MAP, it is desirable to maintain headspace levels of O 2 > 40% and CO 2 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 O 2 whilst selectively allowing excess CO 2 to escape, or by incorporating an innovative active packaging sachet that can adsorb excess CO 2 and emit an equal volume of O 2 (McGrath, 2000). Novel MAP applications for fresh-prepared produce 197 Also, in order to maintain levels of O 2 > 40% and CO 2 in the range 10–25% during the chilled shelf-life of the product, it is desirable to introduce the highest level of O 2 (balance, N 2 ) possible just prior to fresh prepared produce package sealing. Generally, it is not necessary to introduce any CO 2 in the initial gas mixture since levels of CO 2 will build up rapidly within sealed packages during chilled storage. However, for fresh prepared produce items that have low intrinsic respiration rates packaged in a format with a low produce volume/gas volume ratio, are stored at low chilled temperatures, or have an O 2 emitter/CO 2 adsorber sachet incorporated into the sealed package, then the incorporation of 5–10% CO 2 into the initial gas mixture may be desirable. Based on the results of controlled atmosphere storage experiments, the most effective high O 2 gas mixtures were found to be 80–85% O 2 /15–20% CO 2 . This had the most noticeable sensory quality and antimicrobial benefits on a range of fresh prepared produce items (Day, 2001a). The type of MAP machinery used will greatly influence the maximum achievable O 2 level that can be introduced just prior to fresh prepared produce package sealing. Most light prepared salad items are commercially MA packed on vertical form-fill-seal (VFFS) and horizontal form-fill-seal (HFFS) machines (Hartley, 2000). These machines use a gas flushing or air dilution technique to introduce gas in MA pillow-packs just prior to sealing. Since these machines do not use an evacuation step, then c.80% O 2 would be the highest practical level that could be achieved within sealed fresh prepared produce packs by initially flushing with 100% O 2 . Higher levels of in-pack O 2 could be achieved by substantially increasing the flow rate of O 2 through the gas flushing lance of these machines, but this is not recommended for economic and safety reasons (BCGA, 1998). In contrast to VFFS and HFFS machines, thermoform-fill-seal (TFFS), preformed tray and lidding film (PTLF), vacuum chamber (VC) and snorkel type (ST) machines use a compensated vacuum technique to evacuate air and then introduce gas into tray and lidding film and/or flexible MA packs (BCGA,1998). Since these machines use an evacuation step prior to gas (i.e. 100% O 2 ) introduction, much higher levels of headspace O 2 (85–95%) can be achieved within such sealed fresh prepared produce packs. Also, all compensated vacuum machines (except VC machines) are intrinsically safer for high O 2 MAP applications, compared with gas flushing VFFS and HFFS machines, since O 2 is introduced directly into the MA packs after air evacuation and prior to sealing, and consequently O 2 levels in the air surrounding these machines are not enriched (BCGA, 1998). 10.4.3 Produce volume/gas volume ratio In order to maintain headspace O 2 levels > 40% and CO 2 levels in the range 10– 25% during the chilled shelf-life of the product, it is desirable to minimise the produce volume/gas volume ratio of fresh prepared produce MA packs. This can be achieved by either decreasing the pack fill weight or increasing the pack 198 Novel food packaging techniques headspace volume. Decreasing the pack fill weight of fresh prepared produce will have the effect of reducing the overall respiratory load or activity within MA packs and hence the rate of O 2 depletion will be reduced. Increasing the pack headspace volume will have the effect of increasing the reservoir of O 2 for respiratory purposes and hence the rate of O 2 depletion will also be reduced. Consequently, low produce volume/gas volume ratios are conducive to maintaining headspace O 2 levels > 40% and CO 2 levels in the range 10–25%. The important influence of the produce volume/gas volume ratio, in addition to the intrinsic produce respiration rate and packaging film permeability, is well illustrated by the results from CCFRA’s bulk iceberg lettuce trial (Day, 2001a). Depletion of O 2 and elevation of CO 2 levels within the high O 2 MA bulk packs of this trial were very rapid because these packs contained 2kg of fresh prepared iceberg lettuce as opposed to only 200g for retail MA packs. Consequently, the produce volume/gas volume ratio and overall respiratory load were much higher in these MA bulk packs compared with MA retail packs. Also, the iceberg lettuce used for this bulk pack trial was shredded (10mm cut) and hence had a much higher intrinsic respiration rate compared with retail salad cut (40–70 mm) iceberg lettuce. In addition, the thicker (60 m compared with 30 m for retail) and less permeable bulk OPP/LDPE bags exacerbated the depletion of O 2 and elevation of CO 2 . Hence, it was not surprising that the achievable shelf-life at 8oC for high O 2 MA bulk packed fresh shredded iceberg lettuce was found to be only two days, even though the shelf-life of equivalent low O 2 MA bulk packed iceberg lettuce was even shorter (Day, 2001a). It should be appreciated that there are practical and commercial limits to the reduction of produce volume/gas volume ratios for fresh prepared produce MA packs. Obviously, retail consumers will not readily accept MA packs of fresh prepared produce that appear to be underfilled with too much headspace gas. Therefore it is recommended that potential users of high O 2 MAP technology should carry out pre-commercial trials with fresh prepared produce packs having different but practical produce volume/gas volume ratios. 10.4.4 Packaging materials Based on the results of CCFRA’s practical experimental trials, the recommended packaging material for high O 2 MA retail packs of fresh prepared produce is 30 m orientated polypropylene (OPP) with anti-mist coating. It should be noted that initial experimental trials carried out at CCFRA on high O 2 MAP of fresh prepared produce used an O 2 barrier film, i.e. 30 m poly- vinylidene chloride (PVDC) coated OPP with anti-mist coating, because it was considered at the time to be important to maintain the highest levels of O 2 within high O 2 MA packs. However, extensive experimental trials on high O 2 MAP of fresh prepared iceberg lettuce using 30 m PVDC coated OPP film clearly demonstrated that excess and potentially damaging levels of CO 2 (30–40%) could be generated within such O 2 barrier film packs, particularly at higher chilled storage temperatures (i.e. 6–8oC). Consequently, 30 m OPP film was Novel MAP applications for fresh-prepared produce 199 used for subsequent high O 2 MAP experimental trials, instead of 30 m PVDC coated OPP film, and for the majority of fresh prepared produce items, was found to have sufficient O 2 barrier properties to maintain high in-pack O 2 levels (>40%) and be sufficiently permeable to ensure that in-pack CO 2 levels did not rise above 25%, after 7–10 days storage at 5–8oC (Day, 2001a). It should be appreciated that other packaging materials, apart from 30 m OPP, may be suitable for high O 2 MAP of fresh prepared produce (Air Products, 1995; Day and Wiktorowicz, 1999). For example, laminations or extrusions of OPP with low density polyethylene (LDPE), ethylene-vinyl acetate (EVA) or polyvinyl chloride (PVC) or other medium to very high O 2 permeability films, may be more suitable for high O 2 MAP of fresh prepared produce items that have a higher respiration rate than iceberg lettuce. Also, the produce volume/gas volume ratio of different retail MA pack formats (e.g. pillow packs or tray and lidding film systems), the intrinsic fresh prepared produce respiration rate and chilled temperature of storage will influence the selection of the most suitable packaging film for high O 2 MAP applications (Day, 2001a). It is recommended that potential users of high O 2 MAP for fresh prepared produce should initially carry out pre-commercial shelf-life trials using 30 m OPP with anti-mist coating as the packaging film for flexible pillow packs or as a tray lidding film. Regular gas analyses of the in-pack atmospheres during chilled storage will reveal whether the packaging film is not permeable enough (resulting in build-up of excess levels of CO 2 to >25%) or too permeable (resulting in depletion of O 2 to < 40% and slow build-up of CO 2 to <10%). If the in-pack O 2 levels fall < 40% and CO 2 levels lie outside the range 10–25% by the end of the chilled shelf-life of the product, then adjustments to the produce volume/gas volume ratio, chilled temperature of storage, pack format and/or permeability of the package film will need to be made and further shelf-life trials carried out. It should also be noted that O 2 barrier films could be used for high O 2 (or low O 2 ) MAP of fresh prepared produce items if an O 2 emitter/CO 2 adsorber sachet is incorporated into sealed packages. Appropriate transparent O 2 barrier films (with anti-mist coatings) include PVDC coated OPP, and coextrusions or laminations containing ethylene-vinyl acetate (EVOH), polyester (PET), polyamide (nylon) and/or PVDC (Air Products, 1995; Day and Wiktorowicz, 1999). Whatever packaging material is used for high O 2 MAP applications, all of them must comply with statutory legal requirements. In the UK, these requirements include the Materials and Articles in Contact with Food Regu- lations 1987, Plastic Materials and Articles in Contact with Food Regulations 1998, Producer Responsibility Obligations (Packaging Waste) Regulations 1997 and Packaging (Essential Requirements) Regulations 1998. All packaging materials should be purchased to an agreed specification that includes details of technical properties and performance. Quality assurance on all incoming packaging materials should be subject to an agreement between the packaging supplier and user. Each delivery or batch should be given a reference 200 Novel food packaging techniques code to identify it in storage and use, and the documentation should allow any batch of packaged product to be correlated with deliveries of respective packaging materials. All packaging materials should be stored off the floor in separate and dry areas of the factory and should be inspected at regular intervals to ensure that they remain in acceptable condition. Authorised procedures and documentation should be established and followed for the issue of packaging materials from store (Day, 1992). Further advice on the technical requirements, properties, performance and handling of packaging materials should be sought from reliable suppliers. 10.4.5 Temperature control The importance of proper temperature control to retard quality deterioration and assure the microbial safety of fresh prepared produce cannot be overemphasised. For high O 2 MA packed fresh prepared produce, it is recommended that the temperature be maintained below 8oC, and ideally in the range 0–3oC, throughout the entire chill chain. The important influences of storage temperature and packaging film permeability on the quality of high O 2 MA packed fresh prepared produce can be illustrated by the results from CCFRA’s fresh prepared iceberg lettuce trials (Day, 2001a). The results from these trials clearly demonstrated that temperature and packaging film permeability are critical factors in determining the development of O 2 and CO 2 levels within high O 2 MA packs, during chilled storage. Higher temperatures of storage correlate to high respiratory rates and hence greater depletion of O 2 and elevation of CO 2 within sealed high O 2 MA barrier (i.e. 30 m PVCD coated OPP) pillow packs of fresh prepared iceberg lettuce. The most beneficial sensory effects of high O 2 MAP were obtained when the temperature of storage was 3–5oC and the O 2 levels dropped from 70% to 55% and the CO 2 levels reached only 15% after ten days’ storage. In contrast, largely negative sensory effects were obtained when an elevated chill temperature of storage regime (8oC) was employed. Under this elevated chilled temperature of storage regime, O 2 levels dropped from 80% to 35–40% whereas CO 2 levels reached 35–40% after ten days’ storage. These high levels of generated CO 2 within the high O 2 MA barrier pillow packs of fresh prepared iceberg lettuce were responsible for the undesirable ‘CO 2 damage’ discoloration observed. Later high O 2 MAP experimental trials used more permeable OPP film whereby high O 2 (> 40%) levels were generally maintained and CO 2 levels did not rise above 25% after 7–10 days’ storage at 5oC and 8oC. Under these high O 2 MAP conditions, beneficial sensory effects were observed for the majority of the fresh prepared produce items studied, in comparison with industry standard air and/or low O 2 MAP (Day, 2001a). 10.4.6 Fresh prepared produce applications High O 2 MAP has been found to have beneficial effects on the sensory quality of the vast majority of fresh prepared produce items studied. Under defined storage Novel MAP applications for fresh-prepared produce 201 and packaging conditions and in comparison with industry-standard air packing and/or low O 2 MAP, high O 2 MAP was found to be effective for extending the achievable shelf-lives of retail packs of fresh prepared iceberg lettuce, sliced mushrooms, potatoes, sliced bananas, little gem lettuce, cos lettuce, baby-leaf spinach, raddichio lettuce, lollo rosso lettuce, flat-leaf parsley, cubed swede, coriander, raspberries and strawberries. In addition, the results from trials carried out prior to September 1997, showed beneficial sensory effects of high O 2 MAP for fresh prepared tomato slices, baton carrots, pineapple cubes, broccoli florets, honeydew melon cubes, sliced mixed peppers and sliced leeks. Also, high O 2 controlled atmospheres were found to extend the shelf-life of table grapes and oranges (Day, 2001a). It should be noted that in comparison with industry-standard air and/or low O 2 MAP, high O 2 MAP was found not to have beneficial effects on the sensory quality of retail packs of fresh prepared apple slices, curly parsley, red oak leaf lettuce and Galia melon cubes, and bulk packs of shredded iceberg lettuce. However, it is probable that beneficial effects of high O 2 MAP on the above fresh prepared produce items would have been achieved if the chilled storage temperature, high O 2 gas level, packaging film permeability, produce volume/ gas volume ratio and/or preparation procedures had been optimised adequately. Consequently, it is recommended that potential users of high O 2 MAP for specific fresh prepared produce items or combinations, carry out pre-commercial optimisation trials by utilising the advice given previously. 10.5 Future trends High O 2 MAP has become a fertile area of research during the last three years. Partly as a result of the interest stimulated by CCFRA’s Club and EU funded novel MAP research, several research studies and reviews have recently appeared in the scientific literature (e.g. Amanatidou, 2001; Go¨zu¨kara, 2000; Kader and Ben-Yehoshua, 2001; Perez and Sanz, 2001; Wszelaki and Mitcham, 2001; and Jacxsens et al., 2002). These studies have shown some interesting and mainly beneficial effects of high O 2 MAP and pointed in the direction of future research needs. Novel MAP (particularly, high O 2 ) has the potential to maintain the quality and assure the microbial safety of fresh prepared produce. The commercial implementation and success of this new technology may encourage greater consumption of conveniently packed fresh prepared produce and help towards improving the health and well-being of consumers. The publication of practical guidance on high O 2 MAP and non-sulphite dipping has already facilitated commercial exploitation of this new technology (Day, 2001a). Arun Foods Limited (Littlehampton, West Sussex, UK) has produced a wide range of salads and stir-frys for the commercial retail market using high O 2 MAP technology (Day, 2002). These high O 2 MA packed products have been presented in a tray and lidding film format and were assigned a chilled shelf-life of 7–8 days in comparison with only 3–4 days in control air packs (Dr Steve 202 Novel food packaging techniques Yeo, Arun Foods Limited, personal communication, June 2002). A soft fruit supplier in Belgium is also using high O 2 MAP for extending the chilled shelf- life of its product range (Dr Frank Devlieghere, Universiteit Gent, Belgium, personal communication, June, 2002). In addition, the author is aware of several other companies who are actively trialling high O 2 MAP for fresh prepared produce and chilled ready meal applications. With specific regard to the high O 2 MAP of fresh prepared produce, the following future research directions are suggested: ? Further investigate the potential applications of an innovative dual-action O 2 emitter/CO 2 scavenger active packaging sachet that has been developed by Standa Industrie (Caen, France) and marketed by EMCO Packaging Systems (Worth, Kent, UK). Initial trials carried out by CCFRA and LinPac Plastics Limited (Pontefract, Yorkshire, UK) in association with several soft fruit suppliers have clearly demonstrated the shelf-life extending potential of this active packaging device (McGrath, 2000). This O 2 emitter/CO 2 scavenger sachet enables high O 2 levels to be maintained within high O 2 MA packs of respiring fresh prepared produce whilst simultaneously controlling CO 2 below levels that may cause physiological damage to produce. Also, the inclusion of this sachet within high O 2 MA packs of fresh prepared produce that have a high intrinsic respiration rate and/or produce volume/gas volume ratio will prevent excessive depletion of in-pack O 2 levels and build-up of in- pack CO 2 levels. In addition, this sachet could also be utilised in low O 2 MA packs of fresh prepared produce to prevent the development of undesirable anaerobic conditions during chilled storage. ? Thoroughly investigate the potential synergy of high O 2 MAP and other active packaging devices (e.g. moisture absorbers, ethylene scavengers and antimicrobial films) and suitable edible coatings and films (Day, 1994; Baldwin et al., 1995; Nussinovitch and Lurie, 1995; Rooney, 1999). Selection criteria of promising active packaging devices and edible coatings and films should be based on their technical efficacy, cost, regulatory status and consumer acceptability (Day, 2000). ? Carry out further underpinning research investigations on the effects of high O 2 MAP on the various spoilage and pathogenic microorganisms associated with fresh prepared produce items. Also, further research is merited on the effects of high O 2 MAP on the beneficial nutritional components present in fresh produce and on the complex biochemical reactions and physiological processes that occur during storage. ? Establish optimal high O 2 MAP applications for extending the quality shelf-life and assuring the microbial safety of further fresh prepared produce items and combination food products which consist of respiring produce and non-respiring food items (e.g. ready meals, pizzas, kebabs, etc.). Initial trials carried out by CCFRA have already clearly demonstrated that high O 2 MAP is capable of extending the achievable shelf-life of several chilled ready meals, in comparison with CO 2 /N 2 MAP and industry-standard air packing (Day, 2001b). Novel MAP applications for fresh-prepared produce 203 With regard to more general aspects of fresh prepared produce, the following knowledge gaps and suggested research directions are highlighted, in order to assist researchers in the future. ? Provision of packaging film permeability data on commercial laminations and coextrusions at realistic chilled temperatures (0–10oC) and relative humidities (85–95%). At the present time, virtually all gas permeability data is quoted for single films at unrealistic storage temperatures and relative humidities (e.g. 23oC and 0% RH). ? Provision of extensive respiration rate data on a wide variety of fresh prepared produce items at different chilled temperatures and under various gaseous storage conditions. At the present time, most respiration rate data available is for whole produce items stored in air. ? Provision of data on the physiological tolerance of fresh prepared produce items to low (and possibly high) O 2 levels and elevated CO 2 levels. Currently, extensive data is available on the tolerance of whole produce items to low O 2 and high CO 2 levels (Kader et al., 1989) but there is a dearth of information on the tolerance of fresh prepared produce items to varying gaseous levels. ? Provision of information on the residual effects of MAP on individual fresh prepared produce items after subsequent pack opening and storage in air. ? Thoroughly investigate an integrated approach to minimal processing techniques, which cover the entire chain ‘from farm to fork’, so as to maintain the quality and assure the microbial safety of fresh prepared produce (Ahvenainen, 1996). ? Carry out further investigations on new and innovative natural preservatives, such as those produced by lactic acid bacteria and those derived from herbs and spices (Kets, 1999). ? Devise improved washing and decontamination procedures for fresh prepared produce that are based on safe non-chlorine alternatives. ? Develop peeling and cutting machinery that can process fresh produce more gently and hence extend the quality shelf-life of fresh prepared produce. ? Devote more resources into refrigeration equipment, design and logistics so that optimal storage temperatures for fresh prepared produce can be maintained throughout the entire chill chain. 10.6 References AHVENAINEN, R. (1996) New approaches in improving the shelf-life of minimally processed fruit and vegetables. Trends in Food Science and Technology 7 (6), 179–87. AIR PRODUCTS (1995) The Freshline guide to modified atmosphere packaging (MAP). Air Products Plc, Basingstoke, Hants., UK, pp 1–66. AMANATIDOU, A. (2001) High oxygen as an additional factor in food 204 Novel food packaging techniques preservation. Ph.D. Thesis, Wageningen University, The Netherlands. BALDWIN, E.A., NISPEROS-CARRIEDO, M.O. and BAKER, R.A. (1995) Use of edible coatings to preserve quality of lightly (and slightly) processed products. Critical Reviews in Food Science and Nutrition 35, 509–24. BCGA (1998) The safe application of oxygen enriched atmospheres when packaging food. British Compressed Gases Association Guidance Note GD5, BCGA, Eastleigh, Hants., UK. BETTS, G.D. (1996) A code of practice for the manufacture of vacuum and modified atmosphere packaged chilled foods. Guideline No. 11, CCFRA, Chipping Campden, Glos., UK. BRODY, A.L. and THALER, M.C. (1996) Argon and other noble gases to enhance modified atmosphere food processing and packaging. Proceedings of IoPP conference on ‘Advanced technology of packaging’, Chicago, Illinois, USA, 17th November. DAY, B.P.F. (1992) Guidelines for the good manufacturing and handling of modified atmosphere packed food products. Technical Manual No. 34, CCFRA, Chipping Campden, Glos., UK. DAY, B.P.F. (1994) Modified atmosphere packaging and active packaging of fruits and vegetables. In: Minimal Processing of Foods, VTT Symposium Series 142, VTT, Espoo, Finland, pp 173–207. DAY, B.P.F. (1998) Novel MAP – a brand new approach. Food Manufacture 73 (11), 22–24. DAY, B.P.F. (2000) Consumer acceptability of active and intelligent packaging. Proceedings of the Conference on ‘Active and Intelligent Packaging: ideas for tomorrow or solutions for today’, TNO Nutrition and Food Research, Zeist, The Netherlands. DAY, B.P.F. (2001a) Fresh prepared produce: GMP for high oxygen MAP and non-sulphite dipping. Guideline No. 31, CCFRA, Chipping Campden, Glos., UK. DAY, B.P.F. (2001b) Novel high oxygen MAP for chilled combination food products. R&D Report No. 125, CCFRA, Chipping Campden, Glos., UK. DAY, B.P.F. (2002) Industry guidelines for high oxygen MAP of fresh prepared produce. Proceedings of the Postharvest Unlimited Conference, Universiteit Leuven, Belgium, 12–14 June. DAY, B.P.F. and WIKTOROWICZ, R. (1999) MAP goes on-line. Food Manufacture 74 (6), 40–1. FATH, D. and SOUDAIN, P. (1992) Method for the preservation of fresh vegetables. US Patent No. 5128160. GONZALEZ RONCERO, M.I. and DAY, B.P.F. (1998) The effects of novel MAP on fresh prepared produce microbial growth. Proceedings of the Cost 915 Conference, Ciudad Universitaria, Madrid, Spain, 15–16th October. GO ¨ ZU ¨ KARA, Y. (2000). The effect of oxygen and carbon dioxide atmospheres on the quality of packaged fresh-cut lettuce. MSc. thesis, University of Melbourne, Werribee, Victoria, Australia. HARTLEY, D.R. (2000) The product design perspective on fresh produce Novel MAP applications for fresh-prepared produce 205 packaging. Postharvest News and Information 11 (3), 35N–38N. JACXSENS, L, DEVLIEGHERE, F., VAN DER STEEN, C. and DEBEVERE, J. (2002). Effect of high oxygen modified atmosphere packaging on microbial growth and sensorial qualities of fresh-cut produce. International J. Food Micro. 71 (2), 197–210. KADER, A.A. and BEN-YEHOSHUA, S. (2001). Effects of superatmospheric oxygen levels on postharvest physiology and quality of fresh fruits and vegetables. Postharvest Biology and Technology 20 (1), 1–13. KADER, A.A., ZAGORY, D. and KERBEL, E.L. (1989) Modified atmosphere packaging of fruits and vegetables. Critical Reviews in Food Science and Nutrition 28 (1), 1–30. KETS, E.P.W. (1999) Applications of natural anti-microbial compounds. In: Proceedings of the International Conference on ‘Fresh-cut Produce’, Campden & Chorleywood Food Research Association, Chipping Campden, Glos., UK. MCEVILEY, A.J., IYENGAR, R. and OTWELL, W.S.(1992) Inhibition of enzymatic brewing in foods and beverages. Critical Reviews in Food Science and Nutrition 32 (3), 253–73. MCGRATH, P. (2000) Smart fruit packaging. Grower 133 (22), 15–16. NUSSINOVITCH, A. and LURIE, S. (1995) Edible coatings for fruits and vegetables. Postharvest News and Information 6(4), 53N–57N. O’BEIRNE, D. (1999) Modified atmosphere packed vegetables and fruit – an overview. In: Proceedings of the International Conference on ‘Fresh-cut Produce’, Campden & Chorleywood Food Research Association, Chipping Campden, Glos., UK. PEREZ, A.G. and SANZ, C. (2001). Effect of high oxygen and high carbon dioxide atmospheres on strawberry flavor and other quality traits. J. Agric. Fd. Chem. 49 (5), 2370–5. ROONEY, M. (1999) Active and intelligent packaging of fruit and vegetables. In: Proceedings of the International Conference on ‘Fresh-cut Produce’, Campden & Chorleywood Food Research Association, Chipping Campden, Glos., UK. SAPERS, G.M. (1993) Browning of foods: control by sulfites, oxidants and other means. Food Technology 47 (10), 75–84. SPENCER, K. (1999) Fresh-cut produce applications of noble gases. In: Proceedings of the International Conference on ‘Fresh-cut Produce’, Campden & Chorleywood Food Research Association, Chipping Campden, Glos., UK. THOM, S.R. and MARQUIS, R.E. (1984) Microbial growth modification by compressed gases and hydrostatic pressure. Applied Environmental Microbiology 47 (4), 780. WSZELAKI, A.L. and MITCHAM, E.J. (2001). Effects of superatmospheric oxygen on strawberry fruit quality and decay. Postharvest Biology and Technology 20 (2), 125–33. 206 Novel food packaging techniques 10.7 Acknowledgements CCFRA gratefully acknowledges the financial support of the EU FAIR Programme and industrial Club Members for the work described in this chapter. The research contributions of CCFRA’s EU FAIR partners (ATO-DLO, The Netherlands; SIK, Sweden; VTT, Finland; University of Limerick, Ireland; and INN, Italy) are also gratefully acknowledged. Novel MAP applications for fresh-prepared produce 207