Antimicrobial food packaging J. H. Han, The University of Manitoba, Canada 4.1 Introduction Antimicrobial packaging is one of many applications of active packaging Floros et al., 1997). Active packaging is the packaging system which possesses attributes beyond basic barrier properties, which are achieved by adding active ingredients in the packaging system and/or using actively functional polymers (Han and rooney, 2002). Antimicrobial packaging is the packaging system that is able to kill or inhibit spoilage and pathogenic microorganisms that are contaminating foods. The new antimicrobial function can be achieved by adding antimicrobial agents in the packaging system and/or using antimicrobial polymers that satisfy conventional packaging requirements. When the packaging system acquires antimicrobial activity, the packaging system(or material) limits or prevents microbial growth by extending the lag period and reducing the growth rate or decreases live counts of microorganisms( Han, 2000) Compared to the goals of conventional food packaging such as(i) shelf-life extension,(ii) quality maintenance, and (iii)safety assurance which could be achieved by various methods, antimicrobial packaging is specifically designed to control microorganisms that generally affect the above three goals adversely Therefore some products, which are not sensitive to microbial spoilage or contamination, may not need the antimicrobial packaging system. However, most foods are perishable and most medical/sanitary devices are susceptible to contamination. Therefore, the primary goals of an antimicrobial packaging system are (i)safety assurance, (ii) quality maintenance, and (ii) shelf-life extension, which is the reversed order of the primary goals of conventional packaging systems. Nowadays food security is a big issue and antimicrobial packaging could play a role in food security assurance
4.1 Introduction Antimicrobial packaging is one of many applications of active packaging (Floros et al., 1997). Active packaging is the packaging system which possesses attributes beyond basic barrier properties, which are achieved by adding active ingredients in the packaging system and/or using actively functional polymers (Han and Rooney, 2002). Antimicrobial packaging is the packaging system that is able to kill or inhibit spoilage and pathogenic microorganisms that are contaminating foods. The new antimicrobial function can be achieved by adding antimicrobial agents in the packaging system and/or using antimicrobial polymers that satisfy conventional packaging requirements. When the packaging system acquires antimicrobial activity, the packaging system (or material) limits or prevents microbial growth by extending the lag period and reducing the growth rate or decreases live counts of microorganisms (Han, 2000). Compared to the goals of conventional food packaging such as (i) shelf-life extension, (ii) quality maintenance, and (iii) safety assurance which could be achieved by various methods, antimicrobial packaging is specifically designed to control microorganisms that generally affect the above three goals adversely. Therefore some products, which are not sensitive to microbial spoilage or contamination, may not need the antimicrobial packaging system. However, most foods are perishable and most medical/sanitary devices are susceptible to contamination. Therefore, the primary goals of an antimicrobial packaging system are (i) safety assurance, (ii) quality maintenance, and (iii) shelf-life extension, which is the reversed order of the primary goals of conventional packaging systems. Nowadays food security is a big issue and antimicrobial packaging could play a role in food security assurance. 4 Antimicrobial food packaging J. H. Han, The University of Manitoba, Canada
Antimicrobial food packaging 51 All antimicrobial agents have different activities which affect micro- organisms differently. There is no "Magic Bullet antimicrobial agent effectively orking against all spoilage and pathogenic microorganisms. This is due to the characteristic antimicrobial mechanisms and due to the various physiologies of the microorganisms. Simple categorisation of microorganisms may be very helpful to select specific antimicrobial agents. Such categories may consist of oxygen requirement(aerobes and anaerobes), cell wall composition(Gram positive and Gram negative), growth-stage(spores and vegetative cells), optimal growth temperature(thermophilic, mesophilic and psychotropic) and acid/ osmosis resistance. Besides the microbial characteristics. the characteristic antimicrobial function of the antimicrobial agent is also important to understand the efficacy as well as the limits of the activity. Some antimicrobial agents inhibit essential metabolic (or reproductive genetic) pathways of micro- organisms while some others alter cell membrane/wall structure. For example, lysozyme destroys cell walls without the inhibition of metabolic pathways and results in physical cleavages of cell wall, while lactoferrin and EDTA act as coupling agents of essential cationic ions and charged polymers. Two major functions of microbial inhibition are microbial-cidal and microbial-static effects In the case of microbial-static effects, the packaging system has to possess the active function of maintaining the concentration above the minimal inhibitory concentration during the entire storage period or shelf-life in order to prevent re- growth of target microorganisms Traditional preservation methods sometimes consist of antimicrobial packaging concepts, which include sausage casings of cured/salted/smoked meats, smoked pottery/oak barrels for fermentation, and bran-filled pickle jars. The basic principle of these traditional preservation methods and antimicrobial packaging is a hurdle technology(Fig. 4.1). The extra antimicrobial function of the packaging system is another hurdle to prevent the degradation of total quality of packaged foods while satisfying the conventional functions of moisture and oxygen barriers as well as physical protection. The microbial hurdle may not contribute to the protection function from physical damage. However, it provides tremendous protection against microorganisms, which has never been achieved by conventional moisture and oxygen barrier packaging materials Antimicrobial functions which are achieved by adding antimicrobial agents in the packaging system or using antimicrobial polymeric materials show generally three types of mode; (i) release; (ii) absorption; and (iii) immobilisation Release type allows the migration of antimicrobial agents into foods or headspace inside packages, and inhibits the growth of microorganisms The antimicrobial agents can be either a solute or a gas. However, solute antimicrobial agents cannot migrate through air gaps or over the space between the package and the food product, while the gaseous antimicrobial agents can penetrate through any space. Absorption mode of antimicrobial system removes essential factors of microbial growth from the food systems and inhibits the growth of microorganisms. For example, the oxygen-absorbing system can prevent the growth of moulds inside packages. Immobilisation system does not
All antimicrobial agents have different activities which affect microorganisms differently. There is no ‘Magic Bullet’ antimicrobial agent effectively working against all spoilage and pathogenic microorganisms. This is due to the characteristic antimicrobial mechanisms and due to the various physiologies of the microorganisms. Simple categorisation of microorganisms may be very helpful to select specific antimicrobial agents. Such categories may consist of oxygen requirement (aerobes and anaerobes), cell wall composition (Gram positive and Gram negative), growth-stage (spores and vegetative cells), optimal growth temperature (thermophilic, mesophilic and psychrotropic) and acid/ osmosis resistance. Besides the microbial characteristics, the characteristic antimicrobial function of the antimicrobial agent is also important to understand the efficacy as well as the limits of the activity. Some antimicrobial agents inhibit essential metabolic (or reproductive genetic) pathways of microorganisms while some others alter cell membrane/wall structure. For example, lysozyme destroys cell walls without the inhibition of metabolic pathways and results in physical cleavages of cell wall, while lactoferrin and EDTA act as coupling agents of essential cationic ions and charged polymers. Two major functions of microbial inhibition are microbial-cidal and microbial-static effects. In the case of microbial-static effects, the packaging system has to possess the active function of maintaining the concentration above the minimal inhibitory concentration during the entire storage period or shelf-life in order to prevent regrowth of target microorganisms. Traditional preservation methods sometimes consist of antimicrobial packaging concepts, which include sausage casings of cured/salted/smoked meats, smoked pottery/oak barrels for fermentation, and bran-filled pickle jars. The basic principle of these traditional preservation methods and antimicrobial packaging is a hurdle technology (Fig. 4.1). The extra antimicrobial function of the packaging system is another hurdle to prevent the degradation of total quality of packaged foods while satisfying the conventional functions of moisture and oxygen barriers as well as physical protection. The microbial hurdle may not contribute to the protection function from physical damage. However, it provides tremendous protection against microorganisms, which has never been achieved by conventional moisture and oxygen barrier packaging materials. Antimicrobial functions which are achieved by adding antimicrobial agents in the packaging system or using antimicrobial polymeric materials show generally three types of mode; (i) release; (ii) absorption; and (iii) immobilisation. Release type allows the migration of antimicrobial agents into foods or headspace inside packages, and inhibits the growth of microorganisms. The antimicrobial agents can be either a solute or a gas. However, solute antimicrobial agents cannot migrate through air gaps or over the space between the package and the food product, while the gaseous antimicrobial agents can penetrate through any space. Absorption mode of antimicrobial system removes essential factors of microbial growth from the food systems and inhibits the growth of microorganisms. For example, the oxygen-absorbing system can prevent the growth of moulds inside packages. Immobilisation system does not Antimicrobial food packaging 51
52 Novel food packaging techniques Moisture Oxygen Moisture Oxyge (LDPE) EVOH A)Conventional packaging system Moisture o Microbial barrier barrier (B)Antimicrobial packa Fig. 4.1 Hurdle technology in antimicrobial packaging system compared to the conventional packaging system release antimicrobial agents but suppresses the growth of microorganisms at the contact surface. Immobilisation systems may be less effective in the case of solid foods compared to the liquid foods because there is less possibility for contact between the antimicrobial package and the whole food product 4.2 Antimicrobial agents There are many antimicrobial agents that exist and are widely used. To be able to use antimicrobial agents in the foods, pharmaceuticals and cosmetic products the industry must follow the guidelines and regulations of the country that they se going to use them in, for example, FDA and/or EPA in the United States This implies that new antimicrobial packaging materials may be developed using only agents which are approved by the authorisation agencies as examples of FDA-approved or notified-to-use within the concentration limits for food safety enhancement or preservation. Various antimicrobial agents may be incorporated in the packaging system, which are chemical antimicrobial antioxidants, biotechnology products, antimicrobial polymers, natural antimicrobials and gas(Table 4.1) Chemical antimicrobial agents are the most common substances used in the industry. They include organic acids, fungicides, alcohols and antibiotics
release antimicrobial agents but suppresses the growth of microorganisms at the contact surface. Immobilisation systems may be less effective in the case of solid foods compared to the liquid foods because there is less possibility for contact between the antimicrobial package and the whole food products. 4.2 Antimicrobial agents There are many antimicrobial agents that exist and are widely used. To be able to use antimicrobial agents in the foods, pharmaceuticals and cosmetic products, the industry must follow the guidelines and regulations of the country that they are going to use them in, for example, FDA and/or EPA in the United States. This implies that new antimicrobial packaging materials may be developed using only agents which are approved by the authorisation agencies as examples of FDA-approved or notified-to-use within the concentration limits for food safety enhancement or preservation. Various antimicrobial agents may be incorporated in the packaging system, which are chemical antimicrobials, antioxidants, biotechnology products, antimicrobial polymers, natural antimicrobials and gas (Table 4.1). Chemical antimicrobial agents are the most common substances used in the industry. They include organic acids, fungicides, alcohols and antibiotics. Fig. 4.1 Hurdle technology in antimicrobial packaging system compared to the conventional packaging system. 52 Novel food packaging techniques
Table 4.1 Antimicrobial agents and packaging systems n Packaging materials Microorganisms References Tilapia fillets Total bacteria Huang et al, 1997 Pen. spp, Asp. nige g et al., 1997 Parabens LDPE Migration test g a Styrene-acrylates Benzoic sorbic acids PE-co-met-acry late Asp. niger, Pen. spp Weng et al, 1999 LDPE S. cerevisiae Han and Floros. 1997 PE, BOPP, PET Han and Flore LDPE Yeast, mould Devileghere et al., 2000a itic acid Rico-Pena and tor 1991 MC/HPMC/fatty acid Migration test Vojdana and Torres, 1990 MC/chitosan Culture Chen et al. 1996 Asp niger, Pen. roquefort Ghosh et al.. 1973. 1977 Sorbic anhydride Culture media S. cerevisiae. moulds Weng and Hotchkiss, 1993 PE Apples Irmness akovlleva et aL. 1999 m nisin. EDTA SPI. zein E. coli, Lb. plantarum adgett et al. 1998 WPI Culture media g EDTA, propyl paraben typhimurium, E. coli, B. Rodrigues et al., 2002
Table 4.1 Antimicrobial agents and packaging systems Antimicrobials Packaging materials Foods Microorganisms References Organic acids Benzoic acids PE Tilapia fillets Total bacteria Huang et al., 1997 Ionomer Culture media Pen. spp., Asp. nige Weng et al., 1997 Parabens LDPE Simulants Migration test Dobias et al., 2000 PE coating Simulants Migration test Chung et al., 2001a Styrene-acrylates Culture media S. cerevisiae Chung et al., 2001b Benzoic & sorbic acids PE-co-met-acrylates Culture media Asp. niger, Pen. spp. Weng et al., 1999 Sorbates LDPE Culture media S. cerevisiae Han and Floros, 1997 PE, BOPP, PET Water, cheese Migration test Han and Flores, 1998a; b LDPE Cheese Yeast, mould Devileghere et al., 2000a MC/palmitic acid Water Migration test Rico-Pena and Torres, 1991 MC/HPMC/fatty acid Water Migration test Vojdana and Torres, 1990 MC/chitosan Culture media Chen et al., 1996 Starch/glycerol Chicken breast Baron and Summer, 1993 WPI Culture media S. cerevisiae,. Ozdermir, 1999 Asp niger, Pen. roqueforti CMC/paper Cheese Ghosh et al., 1973, 1977 Sorbic anhydride PE Culture media S. cerevisiae, moulds Weng and Chen 1997; Weng and Hotchkiss, 1993 Sorbates & propionates PE/foil Apples Firmness test Yakovlleva et al., 1999 Acetic, propionic acid Chitosan Water Migration test Ouattara et al. 2000a Enzymes Lysozyme, nisin, EDTA SPI, zein Culture media E. coli, Lb. plantarum Padgett et al., 1998 Lysozyme, nisin, WPI Culture media L. monocytogenes, Sal. Rodrigues and Han, 2000; EDTA, propyl paraben typhimurium, E. coli, B. Rodrigues et al., 2002 thermosph., S. aureus
Table 4.1 Continued Antimicrobials Packaging materials Foods Microorganisms References PVOH, nylon, Culture media Lysozyme activity test Appendini and Hotchkiss, e ace Glucose oxidase Fields et al. 1986 bacteriocins Nisin B. thermosph Siragusa et al.. 1999 Coma et aL. 2001 S aureus Corn z Shrtdre d dese Total aerobes Cooksey et al, 2000 Nisin. lacticin Polyamide/LDPE M. favus An et al. 2000 L enes Nisin, lacticin, salts Polyamide/LDPE Culture media M flavus al.2000 Nisin. EDTA PE PE-CO-PEO Beef B thermosphacta al.,2001 Nisin, citrate, EDTA PVC, nylon, LLDPE Chicken Sal typhimurium and Sheldon 2000 Acrylics, PVA-Co-PE Water al,2001 Hoffman et al. 2001 Cellulose casing Turkey breast, enes Ming et al. 1997 Fungicides lonomer Culture media Halek and Garg, 1989 LDPE Bell pepper Miller et al. 1984 Weng and Hotchkiss. 1992
Table 4.1 Continued Antimicrobials Packaging materials Foods Microorganisms References Immobilised lysozyme PVOH, nylon, Culture media Lysozyme activity test Appendini and Hotchkiss, cellulose acetate 1996; 1997 Glucose oxidase Fish Fields et al., 1986 Bacteriocins Nisin PE Beef B. thermosph. Siragusa et al., 1999 HPMC Culture media L. monocytogenes, Coma et al., 2001 S. aureus Corn zein Shredded cheese Total aerobes Cooksey et al., 2000 Nisin, lacticins Polyamide/LDPE, Culture media M. favus, An et al., 2000 L. monocytogenes Nisin, lacticin, salts Polyamide/LDPE Culture media M. flavus Kim et al. 2000 Nisin, EDTA PE, PE-co-PEO Beef B. thermosphacta Cutter et al., 2001 Nisin, citrate, EDTA PVC, nylon, LLDPE Chicken Sal. typhimurium Tatrajan and Sheldon 2000 Nisin, organic Acrylics, PVA-co-PE Water Migration test Choi et al., 2001 acids mixture Nisin, lauric acid Zein Simulants Migration test Hoffman et al., 2001 Nisin, pediocin Cellulose casing Turkey breast, L. monocytogenes Ming et al. 1997 ham, beef Fungicides Benomyl Ionomer Culture media Halek and Garg, 1989 Imazalil LDPE Bell pepper Miller et al., 1984 PE Cheese Moulds Weng and Hotchkiss, 1992