18.1 Introduction Fresh fish products are usually more perishable than most other foodstuffs due to their high a W , neutral pH, and presence of autolytic enzymes. The spoilage of fish and shellfish results from changes caused by oxidation of lipids, reactions due to activities of the fishes’ own enzymes, and the metabolic activities of microorganisms (Ashie et al., 1996). The rate of deterioration is highly temperature dependent and can be inhibited by the use of low storage temperature (e.g. fish stored on ice). The spoilage of fresh fish is usually dominated by microbial activities, however, in some cases chemical changes, such as autoxidation or enzymatic hydrolysis of the lipid fraction may result in off-odours and flavours and, in other cases, tissue enzyme activity can lead to unacceptable softening of the fish (Huss et al., 1997). The degree of processing and preservation together with product composition and storage temperature will decide whether fish undergoes microbial spoilage, biochemical spoilage, or a combination of both. These factors contributed to difficulties when using different technologies to extend the storage of fresh fish above that obtained by traditional ice storage. The term fish product covers a wide range, and includes fish that differ widely in composition, origin, shelf-life and applicability to novel packaging technologies. The range covers fish from temperate waters with a microbial flora adapted to psychrotrophic conditions to fish from tropical waters with different microflora, just as freshwater fish differ from seafish. There is also a wide distribution in the chemical composition of fish, for example, lean fish almost without fat, such as cod, and fatty fish, such as salmon; which often contains 20% fat. Some fish have a long natural shelf-life on ice (e.g. halibut) but others, 18 Active packaging in practice: fish M. Sivertsvik, NORCONSERV, Norway like the pelagic species (e.g. mackerel and herring) have a very short shelf-life. Fresh fish is very different from the various processed fish products that need packaging: heat-treated fish products (ready meals, fish pudding/balls), smoked, dried, or salted fish. We still have not taken into account the numerous different species of crustaceans and molluscs. This chapter will cover active packaging of fish products including the use of atmosphere modifiers such as oxygen scavengers and carbon dioxide emitters, packaging that controls water or with anti-microbial and anti-oxidative properties, and indicator mechanisms. Modified atmosphere packaging (MAP) is regarded by some as an active packaging technology. This is by now a well established method to extend the shelf-life of foods, including fish products, and will not be covered in this chapter except for the MA methods different from traditional MAP using gas flushing. Obviously, having such a broad spectrum of products, it is unlikely that one specific novel or active packaging technology will be a success for all, just as not all fishery products benefit from MAP when compared to vacuum packaging (Sivertsvik et al., 2002a). So, the potential for an active packaging technology to be successful for a product would depend on the technology’s ability to control and inhibit the shelf-life deteriorating spoilage reactions (e.g. bacterial growth of specific bacteria, oxidative rancidity, colour changes) in the specific product. 18.2 The microbiology of fish products As mentioned, the deterioration of fresh fish is usually microbial so controlling the microbial growth is usually the most important parameter for an active packaging technology to be successful. Fish normally have a particularly heavy microbial load owing to the method of capture and transport to shore, slaughtering method, evisceration and retention of skin in retail portions. The microorganisms associated with most seafood reflect the microbial population in their aquatic environment (Colby et al., 1993; Liston 1980; Gram and Huss 1996). Microorganisms are found on all the outer surfaces (skin and gills) and in the intestines of live and newly caught fish. The total numbers of organisms vary enormously and Liston (1980) states a normal range of 10 2 –10 7 cfu (colony forming units)/cm 2 on the skin surface. The gills and the intestines both contain between 10 3 and 10 9 cfu/g (Huss 1995). The fish muscle is sterile at the time of slaughtering/catch, but quickly becomes contaminated by surface and intestinal bacteria, equipment, and humans during handling and processing. The microflora of temperate-water fish is dominated by psychrotrophic, aerobic or facultative anaerobic Gram-negative, rod-shaped bacteria, but Gram-positive organisms can also be found in varying proportions. The flora on tropical fish often carries a slightly higher load of Gram-positive and enteric bacteria. The composition of fresh fish flesh makes it favourable to microbial growth. The muscle is composed of low collagen, low lipid, and high levels of soluble non-protein-nitrogen (NPN) compounds. Trimethylamine-oxide (TMAO), a part Active packaging in practice: fish 385 of the NPN compounds, can be broken down to trimethylamine (TMA) by endogenous enzymes. However, at chilled temperatures TMA is produced by the bacterial enzyme TMA oxidase. TMA is recognised as the characteristic ‘fishy’ odour of spoiled fish. When the oxygen level is depleted, many of the spoilage bacteria can utilise TMAO as a terminal hydrogen acceptor, thus allowing them to grow under anoxic conditions. Towards the end of shelf-life, various malodorous low molecular-weight sulphur-compounds such as H 2 S and CH 3 SH, together with volatile fatty acids and ammonia are produced because of bacterial growth. During chilled storage, there is a shift in bacterial types. The part of the microflora, which will ultimately grow on the products, is determined by the intrinsic (e.g. post mortem pH in the flesh, the poikilothermic nature of fish, and presence of TMAO and other NPN components) and extrinsic parameters (e.g. temperature, processing, and packaging atmosphere). When a product is microbial spoiled, the spoilage microflora will usually consist of a mixture of species, many of which can be completely harmless both in terms of health hazards and in terms of ability to produce off-odours and off-flavours. The bacterial group causing the important chemical changes during fish spoilage often consists of a single species; the specific spoilage organisms (SSO). Little is known of the SSOs of different fish from various aquatic environments under different packaging conditions. However, for many fish stored under aerobic conditions in ice, Shewanella putrefaciens has been identified as the main spoilage bacteria (Gram et al., 1987). S. putrefaciens produce very intense and unpleasant off-odours, reduce TMAO to TMA and produce H 2 S. Under anaerobic conditions (MAP, vacuum packaging, active packaging technologies) the spoilage bacteria differ from aerobic spoilage. The Gram- negative organism Photobacterium phosphoreum has been identified as the organism responsible for spoilage in VP and in MA packs (Dalgaard 1995). The growth rate of this organism is increased under anaerobic conditions and in contrast to S. putrefaciens, P. phosphoreum is shown to be highly resistant to CO 2 . It was also shown that the growth of this bacteria corresponds very well with the shelf-life of packed fresh cod. P. phosphoreum reduces TMAO to TMA at 10–100 times the amount per cell than S. putrefaciens probably due to the large size of the former (diameter 5 m) while very little H 2 S is produced during growth in fish substrates (Dalgaard et al., 1996). Spoiled MAP cod is characterised by high levels of TMA, but little or no development of the putrid or H 2 S odours typical for some aerobically stored spoiled fish. P. phosphoreum is widespread in the marine environment and it seems likely that this organism or other highly CO 2 resistant microorganisms are responsible for spoilage of packed seafood products. Lactic acid bacteria and Brochothrix thermosphacta have been identified as the typical SSOs of freshwater fish and fish from warmer waters. To obtain a longer shelf-life for fresh fish than obtained by ice or chilled MAP/vacuum, the approach is to inhibit the SSO limiting shelf-life for the technology chosen. For example P. phosphoreum is sensitive to freezing and is 386 Novel food packaging techniques totally inactivated in thawed chilled MAP cod fillets after frozen storage at 20oC and 30oC for 6–8 weeks. This approach has been used to further extend the shelf-life of MAP cod (Guldager et al., 1998) and salmon (Emborg et al., 2002) at 2oC, and should also be the approach for successful use of active packaging technologies to control microbial spoilage. 18.3 Active packaging: atmosphere modifiers Many of the most used active packaging technologies are closely related to modified atmosphere packaging. Together with anaerobic conditions, carbon dioxide is the active gas of MAP because it inhibits growth of many of the normal spoilage bacteria (Sivertsvik et al., 2002b). The effect of CO 2 on bacterial growth is complex and four activity mechanisms of CO 2 on microorganisms has been identified (Farber 1991; Daniels et al., 1985; Dixon and Kell 1989; Parkin and Brown 1982): Alteration of cell membrane function includes effects on nutrient uptake and absorption; direct inhibition of enzymes or decreases in the rate of enzyme reactions; penetration of bacterial membranes, leading to intracellular pH changes; and direct changes in the physico-chemical properties of proteins. Probably a combination of all these activities accounts for the bacteriostatic effect (Sivertsvik et al., 2002a). The CO 2 is usually introduced into the MA-package by evacuating the air and flushing the appropriate gas mixture into the package prior to sealing, typically using automatic form-fill- seal or flow-packaging machines. Two other approaches to create a modified atmosphere for a product are either to generate the CO 2 and/or remove O 2 inside the package after packaging or to dissolve the CO 2 into the product prior to packaging. Both methods can give appropriate packages with smaller gas/ product ratio, and thus decrease the package size that has been a disadvantage of MAP from the start. The first approach involves the most commercialised active packaging technology, namely oxygen scavengers, that by now are available from several manufacturers (Mitsubishi Gas Chemical Co., ATCO, Bioka, Sealed Air/ Cryovac, Multisorb a.o.), in different forms (sachets, packaging film, closures) with different active ingredients (iron, enzymes, dye). Some of the same companies have also developed CO 2 emitters, using the O 2 in the package headspace to produce CO 2 and to develop a CO 2 /N 2 atmosphere inside a package without the use of gas flushing. Other methods for generating the CO 2 gas inside the packages after closure include the use of dry ice (solid CO 2 ) (Sivertsvik et al., 1999) or carbonate possibly mixed with weak acids (Bjerkeng et al., 1995). The second approach is to dissolve the CO 2 into the product prior to packaging. Since the solubility increases at lower temperatures and at higher CO 2 pressures, a sufficient amount of CO 2 can be dissolved into the product during 1–2 hours prior to packaging using elevated pressures. This method is called soluble gas stabilisation (SGS) (Sivertsvik 2000). This is not an active packaging technology Active packaging in practice: fish 387 by definition, but it is a novel alternative to MA and it has been used successfully alone and in combination with O 2 scavengers (see below). The commercial use of atmosphere modifiers, and O 2 scavengers in particular, with fish products has been mostly limited to the Japanese market and to dried (seaweed, salmon jerky, sardines, shark’s fin, rose mackerel, cod, squid) or smoked (salmon) products (Ashie et al., 1996). These ambient stored products have low a W (<0.85) so the microbial deterioration is not shelf-life limiting, therefore the effect of the O 2 scavengers is to prevent oxidative reactions, discolouration, and mould growth. Other commercial products are fresh yellow- tail, salmon roe, and sea urchin all stored at superchilling conditions packaged with O 2 scavenger primarily to prevent oxidation and discolouration, but also to inhibit bacterial growth to a lesser degree (Ashie et al., 1996). Different O 2 scavengers are chosen dependent on the amount of O 2 to scavenge (pack size and material) and product a W . O 2 scavengers for high a W foods react faster compared to scavengers for dry foods but in general the absorption is slow and exothermic. Removal of oxygen from package interiors improves shelf-life by sub- optimising the environment for aerobic microbiological growth and for adverse oxidative reactions such as rancidity. Ferrous ironbased oxygen scavengers rely on the presence of moisture for activation, with a water activity of at least 0.7 required, and 0.85–0.9 being preferred (Brody 2001). Oxygen absorbers are designed to reduce oxygen levels to less than 100 ppm in package head-space. In iron-based oxygen scavengers the oxygen is removed by oxidation (rusting) of powdered iron forming non-toxic iron oxide (Ashie et al., 1996). Oxygen absorbers could be used to create oxygen-free conditions in head-space of packages of medium barrier properties. The sachet will absorb residual oxygen and oxygen permeated through the packaging material during storage. More inexpensive or environmentally ‘friendly’ packaging materials with lower oxygen barriers could be used in combination with an oxygen absorber instead of high-cost barrier materials (Sivertsvik, 1997). However, not all oxygen absorbers can be combined with MAP. Some of them, like the iron-based Ageless SS-type from Mitsubishi meant for use in high a W foods, will unintentionally absorb some of the carbon dioxide present, and decrease some of the inhibitory effects of CO 2 on bacterial growth. This is caused by a reaction of iron with CO 2 to form ferrous carbonate, and secondarily this ferrous carbonate reacts with O 2 . This reaction will also slow down the O 2 absorption (Sivertsvik, 1997 and 1999). The use of O 2 absorbers (Ageless SS-100) had only a marginal effect on microbial growth in packages of fishcakes, fish pudding and mackerel fillets, and far less than the significant effect obtained by MAP (Sivertsvik 1997). However, a signficant effect of the O 2 absorber was observed in packages with salmon fillets. The use of O 2 absorbers inhibited development of rancidity (TBARS) in both mackerel and salmon fillets (Sivertsvik, 1997), but in no higher degree than O 2 -free MAP. The effect of SGS treatment, different O 2 -absorbers/CO 2 -emitters and combinations of these on growth of psychrotrophic bacteria in salmon fillets is shown in Fig. 18.1 (Sivertsvik, 1999). The best microbial quality was 388 Novel food packaging techniques observed in packages combining SGS with the combined O 2 absorber and CO 2 emitter (Agelss G-100) i.e., the packages with most CO 2 inside the package. The fastest microbial growth was observed in salmon stored in air without absorbers and in air with Ageless SS-200 and ZPT-100 O 2 -absorbers. These samples were Fig. 18.1 Effects of different oxygen absorbers on the growth of psychotrophic bacteria in salmon fillets stored at 1oC a) packaged in air or b) SGS treatment with CO 2 prior to packaging a74 Ageless SS oxygen absorber for high a w foods; a73 Ageless ZPT oxygen absorber for dry foods; a72 Ageless G combined oxygen absorber and carbon dioxide emiiter; and a71 package without absorber (Sivertsvik et al. 1999) Active packaging in practice: fish 389 microbiologically spoiled after 13 days of storage. The effects of the absorbers and packaging method were not significant on the sensory evaluation scores but multiple comparisons confirmed the findings of the microbiological analyses. The SGS samples were evaluated as better compared to air samples on cooked flavour, cooked odour and texture, but got slightly lower scores on raw odour evaluation. Samples packaged with G-100 absorber/emitter gave the best cooked sensory scores, while samples without absorber got the lowest cooked sensory scores. On raw odour the samples packaged with G-100 and without absorbers were evaluated as better than samples with SS-200 and ZPT-100 absorbers. No differences were observed in the colour of the samples, in contrast to the reddish colour change observed when packaging perch and pike perch fillets with the Ageless G-100 CO 2 -emitters (Ahvenainen et al., 1997). They observed the same shelf-life for fresh perch and pike perch fillets packaged with G-100 as for traditional MAP using an anoxic high CO 2 atmosphere, and 2–4 days longer shelf-life when compared with over-wrap or vacuum packaging. However, colour change and a smell of raw liver in the raw fillets in the active packages was observed. This was not observed in the traditional MA-packages. No differences between the two packaging technologies were observed after cooking of the fish. The commercial CO 2 emitters usually contain ferrous carbonate and a metal halide catalyst although non-ferrous variants are available, absorbing the O 2 and producing equal volumes of CO 2 . Carbon dioxide could also be produced inside the packages after packaging by allowing the exudates from the product to react with a mixture of sodium carbonate and citric acid inside the drip pad, an approach used successfully for cod fillets (Bjerkeng et al. 1995) increasing shelf-life as compared to traditional MAP, even when using a low gas head- space in the package. The Verifrais package manufactured by Codimer, which has been used for extending the shelf-life of fresh meats and fish, is a similar concept (Day 1998). This package consists of a standard MAP tray but has a perforated false bottom under which a porous sachet containing sodium bicarbonate/ascorbate is positioned. When exudate from packed meat or fish drips onto the sachet, CO 2 is emitted and counteracts package collapse due to the CO 2 solubility in the food. 18.4 Active packaging: water control Excess moisture is a major cause of food spoilage and different humidity absorbers are used to protect dried products from humidity damage. However, these absorbers have a limited effect on fish products. Several companies manufacture moisture drip absorbent pads, sheets and blankets for liquid water control in watery foods such as meat, fish, poultry, fruit and vegetables. Moisture drip absorber pads or false-bottomed trays are commonly placed under packaged fresh meat, fish, poultry and prepared fruit to absorb unsightly tissue drip discharge. Larger sheets and blankets are used for absorption of melted ice 390 Novel food packaging techniques from chilled seafood during airfreight transportation (Day 1998). Commercial moisture absorber sheets, blankets and trays include Toppan Sheet (Toppan Printing, Japan), Thermarite (Thermarite, Australia) and Fresh-R-Pax (Maxwell Chase, US). An approach to extending shelf-life of chilled fresh fish is to decrease the water activity at the surface. The Showa Denko Co. (Tokyo, Japan) has developed a film (Pichit film), which is in the form of a pillow with entrapped propylene glycol between layers of polyvinyl alcohol (PVA). The PVA-film is very permeable to water but is a barrier to the glycol. When placed in contact for several hours with the surface of meat or fish by wrapping the film around, it absorbs water and causes injury to spoilage bacteria. This technique can increase the shelf-life of ocean fish by 2–4 days (Labuza 1993). The action is due to an a w difference between the fish (0.99) and the glycol (0.0); thus the water is rapidly drawn out of the fish surface. This surface dehydration not only inhibits some microbes but also may injure others without causing change in fish quality (Labuza and Breene 1989). It is most likely that some glycol also transfers to the food surface and slows microbial growth. The pichit film has been shown to maintain the colour of tuna, veal, pork and beef (Arakawa et al. 1990), since the colour in these products is related to the myoglobin content in the meat and a dehydration of the surface will lead to increased myoglobin concentration. The effect of the pichit film on the shelf-life of fish has been little exploited but for salmon fillets the effect of 2 and 4 hours of pichit pre-treatment on microbial growth and sensory spoilage was non-existent (Sivertsvik 2000). 18.5 Active packaging: anti-microbial and anti-oxidant applications Some commercial anti-microbial films and materials have been introduced, again primarily in Japan. For example, one widely reported product is a synthetic silver zeolite which has been directly incorporated into food contact packaging film. The major potential food applications for anti-microbial films include meat, fish, bread, cheese, fruit and vegetables. Several antimicrobial compounds might have potential to be incorporated into package structures to convert them into active packaging: chlorine dioxide, silver salts, bacteriocins, ozone, and natural spices such as rosemary and its derivatives (Brody 2001) but few have been investigated to be used in or on packaging material of fish products. One exception is benzoic acid anhydride on PE-film used on fish fillets (Han 2000). One anti-microbial packaging application used commercially for semi-moist and dried fish products in Japan uses ethanol emitters (e.g. Ethicap, Antimold 102 and Negamold (Freund Industrial), Oitech (Nippon Kayaku), ET Pack (Ueno Seiyaku) and Ageless type SE (Mitsubishi Gas Chemical)) (Day 1998). These films and sachets contain absorbed ethanol in a carrier material that allows the controlled release of ethanol vapour. Active packaging in practice: fish 391 Essential oils have anti-microbial effects and oils of oregano and cinnamon have the strongest antimicrobial activity, followed by lemongrass, thyme, clove, bay, marjoram, sage and basil oils (Mejlholm and Dalgaard 2002). Oregano oil (0.05% v/w) reduced growth of P. phosphoreum, the SSO in naturally contaminated MAP cod fillets and extended shelf-life from 11–12 days to 21– 26 days at 2oC (Mejlholm and Dalgaard 2002). Obviously, essential oils can extend the shelf-life of MAP seafood but because of the volatile nature of these components incorporating them into an active packaging could be a challenge. Another component with potential as an active packaging ingredient for fresh fish is acetate buffer that can extend the shelf-life of MAP packaged cod fillets by spraying it onto the fillets prior to packaging (Boskou and Debevere 2000). Production of total volatile bases and TMA was inhibited in treated fillets for ten days’ storage under modified atmospheres. Inhibition of TMA production could be attributed to growth inhibition of H 2 S-producing bacteria, inhibition of the TMAO-dependent metabolism of TMAO-reducing bacteria and the stable pH during storage. The shelf-life, at 7oC, of treated cod fillets, based on cooked flavour score, was almost 12 days, approximately 8 days more than the shelf-life of the control fillets (Boskou and Debevere 2000). Potassium sorbate is another preservative shown to increase shelf-life of fish products (Fey and Regenstein 1982; Drosinos et al., 1997) and could be an active ingredient in packaging materials for fishery products. Incorporating anti-oxidants, such as vitamin C and E, in packaging film may potentially reduce oxidative reactions such as the development of rancid flavour and odour in fatty fish products. The degradation of texture, flavour, and odour of stored seafood is attributed to the oxidation of unsaturated lipids. Processing operations such as salting, cooking, and mincing promote oxidation while smoking, dehydration, and freezing retard oxidation. The rate and degree of lipid degradation in frozen fish depends upon the fish species and muscle type, dark or white. Lipid oxidation proceeds in the following decreasing order: skin, dark muscle, and white muscle. Lipid oxidation within a given species will vary with season and location within the tissue. Metal ions affect oxidation in the following decreasing order: Fe2+, haemin, Cu2+, and Fe3+. Oxidation can be reduced through the use of single or combined antioxidants, however, vacuum packaging has a greater reduction on oxidation than the presence of additives (Flick et al., 1992). Lipid oxidation in fish fillets wrapped with butylated hydroxytoluene (BHT) anti-oxidant incorporated PE-film was inhibited as compared to non-wrapped fish fillets (Huang and Weng 1998). The BHT-incorporated PE film was able to inhibit lipid oxidation in both fish muscle and oil. 18.6 Active packaging: edible coatings and films Edible films can be looked upon as an active packaging technology, and many of the anti-microbials or anti-oxidants mentioned above incorporated in the 392 Novel food packaging techniques packaging material could as well be incorporated in an edible film meant to be eaten together with the product. An edible film might be a better approach to ensure good contact between the active component and the food. Different edible coatings have been developed to be used on fish products. Methyl cellulose and hydroxypropyl cellulose reduce uptake of fat during frying, important to the preparation of many seafood products. Alginates reduce moisture loss from fresh fish, while palmitates reduce moisture loss from frozen fish. Other edible films demonstrated to reduce moisture transfer, especially out of frozen fish, include whey protein isolates, coconut oil, and acetylated mono and diglycerides (Brody 2001). The chitosan coating of fresh fillets of cod (Gadus morhua) and herring (Clupea harengus) reduced moisture losses, lipid oxidation, headspace volatiles (total volatile basic nitrogen, TMA, and hypoxanthine), and growth of microorganisms as compared to uncoated samples. The preservative efficacy and the viscosity of chitosan were interrelated, the efficacy of chitosans with higher viscosities superior to that of lower viscosity. Thus, chitosan as an edible coating could enhance the quality of seafoods during storage (Jeon et al., 2002). Skinless tilapia (Dreochromis niloticus x D. aureus) fillets were covered with a gelatin coating containing benzoic acid as an antimicrobial agent. After seven days of storage under refrigeration, tilapia fillets coated with gelatin containing benzoic acid had acceptable VBN contents, increased moderately in microbial loads, and showed no significant sensory difference (P < 0.05) from fresh fillets. The results indicate that an antimicrobial gelatin coating is suitable for preservation of tilapia fillets (Ou et al., 2002). Glucose oxidase in a alginate coating extended shelf-life of winter flounder as compared to coating without enzyme (Field et al., 1986). 18.7 Active packaging: taint removal During storage of packaged fish microbial metabolites and protein breakdown products, such as amines and aldehydes, accumulate in the head-space of the package, leading to, for example, putrid (H 2 S) and fishy (TMA) odours. Removal of these components would therefore often enhance the initial perception of the products upon package opening, and also to some degree increase sensory shelf-life. The effectiveness of an innovative foam plastic tray provided with absorbers for volatile amines and liquids on the shelf- life of different fish products packed under a modified atmosphere (40%CO 2 :60%N 2 ), was evaluated in comparison with a standard tray (Franzetti et al., 2001). Fillets of sole (Solea solea), steaks of hake (Merluccius merluccius) and whole cuttlefish (Sepia fillouxi), placed in the two different kinds of tray, were kept at 3oC. The novel packaging associated with a rigorous control of storage temperature, increased the shelf-life up to ten days. In fact, the innovative tray sequestrated the greater part of TMA from the headspace, and led to delayed microbial growth, especially of Gram-negative Active packaging in practice: fish 393 and H 2 S- producing bacteria. In addition it favoured the growth of bacterial strains such as Moraxella phenylpiruvica which are not involved in off- flavouring production because of their lypolitic activity (Franzetti et al., 2001). A Japanese patent based on the interactions between acidic compounds (e.g. citric acid) incorporated in polymers and off-odours claims amine-removing capabilities (Vermeiren et al., 1999). Another approach to remove amine odours has been provided by the Anico Co. (Japan). The Anico bags made from a film containing ferrous salt and an organic acid such as citric or ascorbic acid are claimed to oxidise the amine or other oxidisable odour-causing compounds as they are absorbed by the polymer (Vermeiren et al., 1999). Some commercialised odour-absorbing sachets, e.g. MINIPAX1 and STRIPPAX1 (Multisorb technologies, USA) absorb the odours developing in certain packaged foods during distribution due to the formation of mercaptans and H 2 S (Vermeiren et al., 1999). 2-in-1, from United Desiccants (USA), is a combination of silica gel and activated carbon packaged together for use in controlling moisture, gas and odour within packaged products. Profresh1 is claimed to be a freshness keeping and malodour control masterbatch used in packaging materials (PE and PS). The active component ADI50 (composition not revealed) is claimed to absorb ethylene, ethyl alcohol, ethyl acetate and H 2 S. Whether these commercial odour absorbers are used and feasible for fish products is not known. 18.8 Intelligent packaging applications Smart packaging, such as Time Temperature Indicators (TTI) is a technology that appears to have a potential, especially with chill-stored products under anaerobic conditions where microbial safety is not otherwise ensured. Strict temperature control is necessary to ensure microbial safety, and temperature abuse should be avoided both because of safety issues and shortening of shelf- life. TTIs could be applied to monitor the temperature and to detect temperature abused packages (Labuza et al., 1992; Labuza 1993; Labuza 1996). Otwell (1997) evaluated the enzyme based Vitsab (Cox Technologies, Belmont, NC) TTI for use in MAP of seafood. Results demonstrated that the colour change from enzyme-based Vitsab labels correlated to spoilage of packaged salmon and other fish. The labels changed colour before formation of botulism toxin. Furthermore, the Vitsab indicator reflected the condition of the contents within the package. (Otwell 1997). Good correlation between colour change in different commercial TTIs on microbial growth/spoilage in smoked rainbow trout has also been found by Hurme and Smolander 2002. However, not such good correlation was found. , between colour change and sensory spoilage. A systematic approach for fish shelf-life modelling and TTI selection in order to plan and apply an effective quality monitoring scheme for the fish chill chain was developed by Taoukis et al., 1999, who modelled the growth of the SSOs of the Mediterranean fish boque (Boops boops). 394 Novel food packaging techniques Cox Technologies has also developed a spoilage indicator, FreshTag, meant to be affixed to the package surfaces. This indicator rapidly detects, measures and signals the presence of decomposition volatile bases such as ammonia, TMA, and dimethylamine in the headspace of the package (Kruijf et al., 2002). Results have been promising for shrimp, scallops, and coldwater fresh fish but not for fatty fish such as salmon or tuna (Brody 2001). The reason for the latter is probably because the shelf-life of fatty fish is not only limited by microbial growth alone, but also by oxidative reactions (Sivertsvik et al., 2002a). Related to the spoilage indicator is the Toxin Alert indicator (Toxin Alert, Mississauga, Canada). This indicator can possibly detect the growth of pathogenic microorganisms in real time without waiting (Brody 2001). 18.9 Future trends It is useful to distinguish between two categories of packaged fishery products. Those eaten without any heat treatment immediately prior to consumption, such as ready to eat products, sashimi/sushi, smoked salmon, cooked shellfish, and those products that will be subjected to heat treatment sufficient to kill all vegetative pathogens before serving (e.g. most fresh fish). Safety concerns regarding pathogenic microorganisms are of primary importance and deserve first priority during manufacture of fishery products, and the first category in particular. Fish and shellfish are vehicles for transmission of foodborne diseases (Huss et al., 1997). Pathogens found on fish are either naturally present in the fish from the aquatic environment (Clostridium botulinum type E and non-proteolytic types B and F; pathogenic Vibrio spp.; Aeromonas hydrophila; Plesiomonas shigelloides), or frequently present (Listeria monocytogenes, C. botulinum proteolytic types A, B; C. perfringens; Bacillus spp.), or originating from the animal/human reservoir (Salmonella, Shigella, Escherichia coli, Staphylococcus aureus). The pathogens of major concerns when packaging fish under anaerobic conditions have been and still are C. botulinum type E and non-proteolytic type B and Listeria monocytogenes i.e. those able to grow and multiply at chilled temperatures and that are more or less unaffected by CO 2 atmospheres (Sivertsvik et al., 2002a). Many of the above-mentioned active packaging technologies do not improve microbial safety of the products above that obtained by traditional MAP. O 2 scavengers and CO 2 emitters give little or no additional shelf-life to fresh fishery products compared to MAP and vacuum packaging, but the technologies could in some cases replace the traditional packaging technologies. Different anti- microbial components can extend shelf-life through inhibiting spoilage organisms. However, the inhibition of the spoilage bacteria reduces also bacterial competition that may permit growth and toxin production by non- proteolytic C. botulinum or growth of other pathogenic bacteria. The anti- microbial packaging should therefore also be able to inhibit growth of pathogens as well as the specific spoilage organisms to ensure microbial safe products. The Active packaging in practice: fish 395 risks from botulism in MAP fish have been widely reviewed (Sivertsvik et al., 2002a) and even if the results are not conclusive, there is a potential threat for a packaged fish product to become toxic prior to spoilage especially at storage temperature of 8oC or above. A mathematical model has been developed for prediction of lag time prior to C. botulinum toxigenesis (Baker and Genigeorgis 1990). The model revealed that about 75% of experimental variation was explained by storage temperature while the size of the C. botulinum spore inoculum explained 7.5%. Collectively factors such as MA compositions, type of fish and C. botulinum spore type attributed to only 2.3% of the variation. The data confirms the importance of temperature control. Under temperature abuse conditions most fish, independent of packaging method, can become toxic. TTIs and possibly toxin indicators are therefore maybe among the few methods that can be used to ensure the safety of fresh fishery products. For processed or prepared fish products changes in the a W , pH, salt, or heat-treatment is used to control the threat, and hopefully there will be active packaging technologies that could do the same without adversely changing the flavour, odour, colour and texture of a fresh fish product. Many of the active packaging technologies increase shelf-life of fish only marginally and usually not the initial prime quality. A better effect can be obtained by increasing the raw material quality, i.e. reducing the initial spoilage counts or lowering the storage temperature by one or two degrees. Combining active packaging with superchilling (sub-zero ( 1 to 2oC) storage) might reveal synergistic effects as observed for MAP combined with superchilling on the quality of salmon fillets (Sivertsvik et al., 2003). Superchilling is one of the few preservation technologies able to extend the prime quality phase of fresh fish (Haard 1992), a phase limited by autolytic enzyme activity and not microbial growth. A technology able to control and prolong this phase should be preferred. However, none of the existing active packaging technologies is able to do this today for fresh fish. Active packaging has therefore a greater potential to be a success for fish products with added value, for example, fish based ready meals. This is also possibly the segment with highest growth potential. Adding value to the raw material will drive increased seafood consumption. 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