Antimicrobial food packaging 57 Organic acids such as benzoic acids, parabens, sorbates, sorbic acid, propionic acid, acetic acid, lactic acid, medium-size fatty acids and their mixture possess strong antimicrobial activity and have been used as food preservatives, food contact substances and food contact material sanitisers. Benomyl and imazalil had been incorporated in plastic films and demonstrated antifungal activity Ethanol has strong antibacterial and antifungal activity, however, it is not sufficient to prevent the growth of yeast. Ethanol may enhance some volatile flavour compounds but also causes a strong undesirable chemical odour in most food products. Some antibiotics can be incorporated into animal feedstuffs for the purpose of disease treatment, disease prevention or growth enhancement as well as human disease curing. The use of antibiotics as package additives is not approved for the purpose of antimicrobial functions and is also controversial due to the development of resistant microorganisms. However, antibiotics may be incorporated for short-term use in medical devices and other non-food products Antioxidants are effective antifungal agents due to the restrictive oxygen requirement of moulds. Food grade chemical antioxidants could be incorporated into packaging materials to create an anaerobic atmosphere inside packages, and eventually protect the food against aerobic spoilage(Smith et al, 1990 ). Since the package did not contain oxygen, the partial pressure difference of oxygen formed between the outside and inside of packaging materials. Therefore, in order to maintain the low concentration of oxygen inside the package, the packaging system requires high oxygen barrier materials such as EVOH, PVDC or aluminum foil that prevent the permeation of oxygen. Besides the antioxidants, a multi-ingredient oxygen scavenging system, such as commercial oxygen-absorbing sachets, can be used to reduce oxygen concentration inside the package Various bacteriocins that are produced by microorganisms also inhibit the growth of spoilage and pathogenic microorganisms. These fermentation products include nisin, lacticins, pediocin, diolococcin, and propionicins (Daeschul, 1989; Han, 2002). These biologically active peptides possess strong antimicrobial properties against various bacteria. Other non-peptide fermentation products such as reuterin also demonstrate antimicrobial activity Besides the above food grade bacteriocins other bacteriocins would be utilised for the development of antimicrobial packaging systems Some synthetic or natural polymers also possess antimicrobial activity Ultraviolet or excimer laser irradiation can excite the structure of nylon and create antimicrobial activity. Among natural polymers, chitosan(chitin derivative)exhibits antimicrobial activity. Short or medium size chitosan possesses quite good antimicrobial activity, while long change chitosan is not effective. Chitosan has been approved as a food ingredient from FDA recently therefore, the use of chitosan for new product development as well as a natural antimicrobial agent would become more popular. The use of natural plant extracts is desirable for the development of new food products and nutraceuticals, as well as new active packaging systems. Some plant extracts such as grapefruit seed, cinnamon, horseradish and clove haveOrganic acids such as benzoic acids, parabens, sorbates, sorbic acid, propionic acid, acetic acid, lactic acid, medium-size fatty acids and their mixture possess strong antimicrobial activity and have been used as food preservatives, food contact substances and food contact material sanitisers. Benomyl and imazalil had been incorporated in plastic films and demonstrated antifungal activity. Ethanol has strong antibacterial and antifungal activity, however, it is not sufficient to prevent the growth of yeast. Ethanol may enhance some volatile flavour compounds but also causes a strong undesirable chemical odour in most food products. Some antibiotics can be incorporated into animal feedstuffs for the purpose of disease treatment, disease prevention or growth enhancement as well as human disease curing. The use of antibiotics as package additives is not approved for the purpose of antimicrobial functions and is also controversial due to the development of resistant microorganisms. However, antibiotics may be incorporated for short-term use in medical devices and other non-food products. Antioxidants are effective antifungal agents due to the restrictive oxygen requirement of moulds. Food grade chemical antioxidants could be incorporated into packaging materials to create an anaerobic atmosphere inside packages, and eventually protect the food against aerobic spoilage (Smith et al., 1990). Since the package did not contain oxygen, the partial pressure difference of oxygen is formed between the outside and inside of packaging materials. Therefore, in order to maintain the low concentration of oxygen inside the package, the packaging system requires high oxygen barrier materials such as EVOH, PVDC or aluminum foil that prevent the permeation of oxygen. Besides the antioxidants, a multi-ingredient oxygen scavenging system, such as commercial oxygen-absorbing sachets, can be used to reduce oxygen concentration inside the package. Various bacteriocins that are produced by microorganisms also inhibit the growth of spoilage and pathogenic microorganisms. These fermentation products include nisin, lacticins, pediocin, diolococcin, and propionicins (Daeschul, 1989; Han, 2002). These biologically active peptides possess strong antimicrobial properties against various bacteria. Other non-peptide fermentation products such as reuterin also demonstrate antimicrobial activity. Besides the above food grade bacteriocins, other bacteriocins would be utilised for the development of antimicrobial packaging systems. Some synthetic or natural polymers also possess antimicrobial activity. Ultraviolet or excimer laser irradiation can excite the structure of nylon and create antimicrobial activity. Among natural polymers, chitosan (chitin derivative) exhibits antimicrobial activity. Short or medium size chitosan possesses quite good antimicrobial activity, while long change chitosan is not effective. Chitosan has been approved as a food ingredient from FDA recently; therefore, the use of chitosan for new product development as well as a natural antimicrobial agent would become more popular. The use of natural plant extracts is desirable for the development of new food products and nutraceuticals, as well as new active packaging systems. Some plant extracts such as grapefruit seed, cinnamon, horseradish and clove have Antimicrobial food packaging 57