58 Novel food packaging been added to packaging systems to demonstrate effective antimicrobial activity against spoilage and pathogenic bacteria. More use of natural extracts expected because of the easier regulation process and consumer preference when compared to the chemical antimicrobial agents Gaseous antimicrobials have some benefit compared to the solid or solute types of chemical antimicrobial agents. They can be vaporised and penetrated into any air space inside packages that cannot be reached by non-gaseous antimicrobial agents. An ethanol sachet is one example of a gaseous antimicrobial system. Headspace ethanol vapour can inhibit the growth of moulds and bacteria. The use of chlorine dioxide has been permitted with no objection notification from FDa recently and can be incorporated into packaging material. Chlorine dioxide shows effective antimicrobial activity and some bleaching effect. Allyl isothiocyanate, hinokitiol and ozone have been incorporated into packages and demonstrated effective antimicrobial activity. However, the use of these reactive gaseous agents has to be considered after careful studies of their reactivity and permeability through packaging materials Since most antimicrobial agents have different antimicrobial mechanisms the mixture of antimicrobial agents can increase antimicrobial activity through synergic mechanisms when they do not have any interference mechanisms Therefore, the optimisation study on the combination of various antimicrobials will extend the antimicrobial activity of the mixture and maximise the efficacy and the safety of the antimicrobial packaging system 4.3 Constructing an antimicrobial packaging system Antimicrobial agents can be incorporated into a packaging system through simple blending with packaging materials, immobilisation or coating differently depending on the characteristics of packaging system, antimicrobial agent and food. The blended antimicrobial agents can migrate from packaging materials to foods, while the immobilised agent cannot migrate. Fig. 4.2 explains the antimicrobial systems and their releasing profiles Systems(A)and (B)release antimicrobial agents through diffusion, while systems ( C)and(D)release volatile antimicrobial agents by evaporation. Fig. 4.2 presents(A)One-layer system: the antimicrobial agent is incorporated into the packaging material or hemically bound on the packaging material by immobilisation. (B)Two-layer system: the antimicrobial agent (outer layer)is coated on the packaging material (inner layer), or the antimicrobial matrix layer(outer layer) is laminated with the control layer(inner layer) to control the release rate specifically. ( C)Headspace system: the volatile antimicrobial agent initially incorporated into the matrix layer releases into the headspace. Headspace antimicrobial agent is partitioned with the food product by equilibrium sorption/isotherm (D)Headspace system with control layer: the control layer specifically controls the permeation of the volatile antimicrobial agent and maintains specific headspace concentrationbeen added to packaging systems to demonstrate effective antimicrobial activity against spoilage and pathogenic bacteria. More use of natural extracts is expected because of the easier regulation process and consumer preference when compared to the chemical antimicrobial agents. Gaseous antimicrobials have some benefit compared to the solid or solute types of chemical antimicrobial agents. They can be vaporised and penetrated into any air space inside packages that cannot be reached by non-gaseous antimicrobial agents. An ethanol sachet is one example of a gaseous antimicrobial system. Headspace ethanol vapour can inhibit the growth of moulds and bacteria. The use of chlorine dioxide has been permitted with no objection notification from FDA recently and can be incorporated into packaging material. Chlorine dioxide shows effective antimicrobial activity and some bleaching effect. Allyl isothiocyanate, hinokithiol and ozone have been incorporated into packages and demonstrated effective antimicrobial activity. However, the use of these reactive gaseous agents has to be considered after careful studies of their reactivity and permeability through packaging materials. Since most antimicrobial agents have different antimicrobial mechanisms, the mixture of antimicrobial agents can increase antimicrobial activity through synergic mechanisms when they do not have any interference mechanisms. Therefore, the optimisation study on the combination of various antimicrobials will extend the antimicrobial activity of the mixture and maximise the efficacy and the safety of the antimicrobial packaging system. 4.3 Constructing an antimicrobial packaging system Antimicrobial agents can be incorporated into a packaging system through simple blending with packaging materials, immobilisation or coating differently depending on the characteristics of packaging system, antimicrobial agent and food. The blended antimicrobial agents can migrate from packaging materials to foods, while the immobilised agent cannot migrate. Fig. 4.2 explains the antimicrobial systems and their releasing profiles. Systems (A) and (B) release antimicrobial agents through diffusion, while systems (C) and (D) release volatile antimicrobial agents by evaporation. Fig. 4.2 presents (A) One-layer system: the antimicrobial agent is incorporated into the packaging material or chemically bound on the packaging material by immobilisation. (B) Two-layer system: the antimicrobial agent (outer layer) is coated on the packaging material (inner layer), or the antimicrobial matrix layer (outer layer) is laminated with the control layer (inner layer) to control the release rate specifically. (C) Headspace system: the volatile antimicrobial agent initially incorporated into the matrix layer releases into the headspace. Headspace antimicrobial agent is partitioned with the food product by equilibrium sorption/isotherm. (D) Headspace system with control layer: the control layer specifically controls the permeation of the volatile antimicrobial agent and maintains specific headspace concentration. 58 Novel food packaging techniques