15 Integrating MAP with new germicidal techniques J. Lucas, University of liverpool, UK 15.1 Introduction Modified Atmospheric Packaging(MAP)is a precise description of this shelf- ife extension technique(Bennett 1995). In the UK, MAP mainly involves the use of three gases- carbon dioxide, nitrogen and oxygen although other gases are used elsewhere. Products are packed in various combinations of these three gases depending on the physical and chemical properties of the food 15.1.1 MAP and food preservation, food spoilage and shelf-life )ver time, food spoilage inevitably sets in and the rate at which it occurs depends on the physical structure and properties of the food itself, the type of microorganisms present and the environment the food is kept in. By carefully matching individual modified atmospheres to specific food products, adopting appropriate manufacturing, handling and packaging methods and observing recommended storage and display conditions, a retailer can successfully extend the shelf-life of most foodstuffs. Fine tuning this process can result in substantial benefits. Selecting the correct mixture of gases for the modified atmosphere determined by looking at a combination of shelf-life and visual appearance. For the longest shelf-life red meat uses 100% carbon dioxide but the meat would not have the bright red colour desired by consumers. The redness of meat,an essential part of the consumer's decision to buy, can be maintained longer by using a MAP gas mixture between 60% and 80% oxygen. Once it has been accepted that it can, in certain cases, make economic sense to sacrifice some shelf-life to ensure visual appearance, then it has been established which mixture produces the best result for each product. The effect of the individual
15.1 Introduction Modified Atmospheric Packaging (MAP) is a precise description of this shelflife extension technique (Bennett 1995). In the UK, MAP mainly involves the use of three gases – carbon dioxide, nitrogen and oxygen although other gases are used elsewhere. Products are packed in various combinations of these three gases depending on the physical and chemical properties of the food. 15.1.1 MAP and food preservation, food spoilage and shelf-life Over time, food spoilage inevitably sets in and the rate at which it occurs depends on the physical structure and properties of the food itself, the type of microorganisms present and the environment the food is kept in. By carefully matching individual modified atmospheres to specific food products, adopting appropriate manufacturing, handling and packaging methods and observing recommended storage and display conditions, a retailer can successfully extend the shelf-life of most foodstuffs. Fine tuning this process can result in substantial benefits. Selecting the correct mixture of gases for the modified atmosphere is determined by looking at a combination of shelf-life and visual appearance. For the longest shelf-life red meat uses 100% carbon dioxide but the meat would not have the bright red colour desired by consumers. The redness of meat, an essential part of the consumer’s decision to buy, can be maintained longer by using a MAP gas mixture between 60% and 80% oxygen. Once it has been accepted that it can, in certain cases, make economic sense to sacrifice some shelf-life to ensure visual appearance, then it has been established which mixture produces the best result for each product. The effect of the individual gases on 15 Integrating MAP with new germicidal techniques J. Lucas, University of Liverpool, UK
Table 15.1 MAP gas mixtures for food items Food item Retail gas mix Storage temp.°C Shelf-life days CO N2 MAP gas In air Raw red meat 70 30 I to 5-8 days 24 days Raw offal I to 4-8 days 2-6 days Raw poultry and game I to 10-21 days 4-7 days Raw fish and seafood 0000000 2-3 days Cooked, cured and processed meat products 0to+3 Cooked, cured and processed fish and seafood 0to+3 5-10 days Cooked, cured and processed poultry and game 0to+3 7-21 days 5-10 days bird products Ready meals 0to+3 Fresh pasta products 00000 5-10 days 2-5 days 3-4 weeks 1-2 week Bakery products 0to+5 4-12 weeks 4-14 days Hard cheese 0to+5 2-12 weeks 1-4 weeks Soft cheese 0to+5 2-12 weeks 1-4 weeks Dried food products 1-2 4-8 months Cooked and dressed vegetable products 00 0to+3 7-21 days 3-14 days Liquid food and beverage products 0to+3 2-3 weeks Carbonated soft drinks 100 0to+3 I year 6 months
Table 15.1 MAP gas mixtures for food items Food item Retail gas mix Storage temp. oC Shelf-life days O2 CO2 N2 MAP gas In air Raw red meat 70 30 ÿ1 to + 2 5–8 days 2–4 days Raw offal 80 20 ÿ1 to + 2 4–8 days 2–6 days Raw poultry and game 30 70 ÿ1 to + 2 10–21 days 4–7 days Raw fish and seafood 30 40 30 ÿ1 to + 2 4–6 days 2–3 days Cooked, cured and processed meat products 30 70 0 to + 3 3–7 weeks 1–3 weeks Cooked, cured and processed fish and seafood 30 70 0 to + 3 7–21 days 5–10 days products Cooked, cured and processed poultry and game 30 70 0 to + 3 7–21 days 5–10 days bird products Ready meals 30 70 0 to + 3 5–10 days 2–5 days Fresh pasta products 50 50 0 to + 5 3–4 weeks 1–2 weeks Bakery products 50 50 0 to + 5 4–12 weeks 4–14 days Hard cheese 100 0 to + 5 2–12 weeks 1–4 weeks Soft cheese 30 70 0 to + 5 2–12 weeks 1–4 weeks Dried food products 100 Ambient 1–2 years 4–8 months Cooked and dressed vegetable products 30 70 0 to + 3 7–21 days 3–14 days Liquid food and beverage products 100 0 to + 3 2–3 weeks 1 week Carbonated soft drinks 100 0 to + 3 1 year 6 months
314 Novel food packaging techniques both food and microorganisms will now be outlined. Table 15. 1 gives summary ended gas mixtures, storage temperatures and achievable shelf-lives for 16 different foodstuffs There are sound commercial reasons why MA packed foods are in such emand in the extension of shelf-life by 50% to 500% minimisation of waste restocking and ordering can become more flexible quality, presentation and visual appeal -all improved reduction of need for artificial preservatives semi-centralised production is possibe ucts increased distribution distances of prod 15.1.2 New germicidal techniques No matter how effectively modified atmosphere technology is applied to food no product can remain on the supermarket shelf indefinitely. For each food there is a recommended gas mixture, storage temperature and achievable shelf-life as given in Table 15. 1. At the end of the shelf-life, a summary of the main sources of food spoilage and poisoning which have occurred under the MAP proc given in Table 15. 2. In all cases the principal spoilage mechanism is microbial and the main microorganisms responsible for food poisoning for that particular product have been identified Over time, food spoilage inevitably sets in but the rate at which it occurs can be slowed down by combining germicidal and MAP techniques. Both UV and Table 15.2 Sources of food spoilage and poisoning Food item Principal spoilage Some food poisoning hazards mechanism Raw red meat Colour change red to brown) S. aureus, Bacillus species, Listerpecies, monocyte poultry and Microbial Clostridium species, Salmonella species, Campylobacter species Raw fish and seafood Oxidative rancidity. Clostridium botulinum(non-proteolytic E, B and F)vibris parahaemolyticus Ready mea Microbial Clostridium species, Salmonella spec Listeria monocytogenes, Yer enterocolitica S. aureus, Bacillus species, Moisture Cheese Microbial, oxidative Clostridium species, Salmonella spec ancid S. aureus, Bacillus species, Listeria Physical separation monocytogenes, E coli
both food and microorganisms will now be outlined. Table 15.1 gives summary advice on recommended gas mixtures, storage temperatures and achievable shelf-lives for 16 different foodstuffs. There are sound commercial reasons why MA packed foods are in such demand in the UK. These are: • extension of shelf-life by 50% to 500% • minimisation of waste – restocking and ordering can become more flexible • quality, presentation and visual appeal – all improved • reduction of need for artificial preservatives • increased distribution distances of products • semi-centralised production is possible. 15.1.2 New germicidal techniques No matter how effectively modified atmosphere technology is applied to food, no product can remain on the supermarket shelf indefinitely. For each food there is a recommended gas mixture, storage temperature and achievable shelf-life as given in Table 15.1. At the end of the shelf-life, a summary of the main sources of food spoilage and poisoning which have occurred under the MAP process is given in Table 15.2. In all cases the principal spoilage mechanism is microbial and the main microorganisms responsible for food poisoning for that particular product have been identified. Over time, food spoilage inevitably sets in but the rate at which it occurs can be slowed down by combining germicidal and MAP techniques. Both UV and Table 15.2 Sources of food spoilage and poisoning Food item Principal spoilage mechanisms Some food poisoning hazards Raw red meat Colour change (red to brown). Microbial. Clostridium species, Salmonella species, S. aureus, Bacillus species, Listeria monocytogenes, E. coli. Raw poultry and game Microbial. Clostridium species, Salmonella species, S. aureus, Listeria monocytogenes, Campylobacter species. Raw fish and seafood Oxidative rancidity. Microbial. Clostridium botulinum (non-proteolytic E, B and F) Vibris parahaemolyticus. Ready meals Microbial. Clostridium species, Salmonella species, S. aureus, Bacillus species, Listeria monocytogenes, Yersinia enterocolitica Bakery products Microbial, staling. Physical separation. Moisture migration. S. aureus, Bacillus species, Cheese Microbial, oxidative rancidity. Physical separation Clostridium species, Salmonella species, S. aureus, Bacillus species, Listeria monocytogenes, E. coli. 314 Novel food packaging techniques
Integrating MAP with new germicidal techniques 315 Log s-Log, C 0 LOg,s-Log(C)-3 Fig. 15. 1 Fraction of living microorganisms (S) ozone are able to kill microorganisms therefore the combining of uv and ozone with modified atmospheric packaging(MAP)results in a safer product and an extended shelf-life. Compact germicidal systems can be incorporated within the MAP packaging process, resulting in a sustainable increase in shelf-life The survival (S) of microorganisms when exposed to either UV or ozone is epresented by two rates of decay(Wekhof 2000)as follows S=C exp(-kD) for D< Do S=C exp(-mD)for D< Do This relationship is illustrated in Fig. 15.1. The dosage D is the product of the UV or ozone intensity and duration(n)of exposure. There is an initial rapid rate of kill(k)to a level (1-C)and this is followed by a much slower kill rate(m) The value of C is of the order of 10. Figure 15.2 shows a comparison of the dosages(D)required for UV, ozone and chlorine required to achieve a 99.9% kill level when compared with the dosage for Escherichia coli(. coli) in water They show comparative responses with a range of microorganisms The most likely explanation for the tailing off of the survival curves is the clumping effect suggested by various investigators- the tendency of micron- sized particles to clump together naturally. The clumping of bacteria cells protects a small percentage of bacteria and causes them to behave as if they had much higher ce to both uv and ozone 15.2 Ultraviolet radiation Ultraviolet (UV) radiation is a form of energy that can be absorbed by and can bring about structural changes of systems(Koller 1965). The exposure of microbiological systems to UV radiation, within the wavelength range defined by Fig. 15.3, can dissociate the DNA, which are vital to metabolic and
ozone are able to kill microorganisms therefore the combining of UV and ozone with modified atmospheric packaging (MAP) results in a safer product and an extended shelf-life. Compact germicidal systems can be incorporated within the MAP packaging process, resulting in a sustainable increase in shelf-life. The survival (S) of microorganisms when exposed to either UV or ozone is represented by two rates of decay (Wekhof 2000) as follows S C exp ÿkD for D < Do S C exp ÿmD for D < Do This relationship is illustrated in Fig. 15.1. The dosage D is the product of the UV or ozone intensity and duration (t) of exposure. There is an initial rapid rate of kill (k) to a level (1 ÿ C) and this is followed by a much slower kill rate (m). The value of C is of the order of 10-3. Figure 15.2 shows a comparison of the dosages (Do) required for UV, ozone and chlorine required to achieve a 99.9% kill level when compared with the dosage for Escherichia coli (E. coli) in water. They show comparative responses with a range of microorganisms. The most likely explanation for the tailing off of the survival curves is the clumping effect suggested by various investigators – the tendency of micronsized particles to clump together naturally. The clumping of bacteria cells protects a small percentage of bacteria and causes them to behave as if they had much higher resistance to both UV and ozone. 15.2 Ultraviolet radiation Ultraviolet (UV) radiation is a form of energy that can be absorbed by and can bring about structural changes of systems (Koller 1965). The exposure of microbiological systems to UV radiation, within the wavelength range defined by Fig. 15.3, can dissociate the DNA, which are vital to metabolic and Fig. 15.1 Fraction of living microorganisms (S). Integrating MAP with new germicidal techniques 315
16 Novel food packaging techniques ∽>c ≌学> O O 2 Q-e∽w uy cl O, cl 2 Fig. 15.2 Mortalities of bacteria and pathogens in sterilisation of water 1849200 280300 400nm Ozone forming range Gcmicidc Ra Fig. 15.3 Ultraviolet radiation spectrum
Fig. 15.2 Mortalities of bacteria and pathogens in sterilisation of water. Fig. 15.3 Ultraviolet radiation spectrum. 316 Novel food packaging techniques