Fabrication And Characterization Of Gelatin Based Antimicrobial Films: Structure-function Relationship

Since the problems of microorganism breeding during food storage and theenvironmental pollution made by low-density polyethylene are growing, antimicrobialpackaging development has been focused by food industries. The aim of this thesis is todevelop a gelatin based antimicrobial packaging through oil input or crosslinking, to controlthe porosity of the film and the migration rate of antimicrobial from protein matrix. Inaddition, tensile and swelling properties, water vapor permeability (WVP) of antimicrobialfilms are also evaluated. The main research results are as follows:The microfluidizer provides the film-forming dispersions (FFD) with lower and narrowerparticle size distributions, promoting mechanical resistance, extensibility and transparency ofthe films. The physical properties of the emulsified films are improved with limits as themicrofluidization pressure or cycle enhanced. However, high process pressure or cyclesmakes dispersed lipid particles more susceptible to re-coalescence, giving rise to badmechanical properties. Lysozyme release kinetic studies show that olive oil-gelatin compositefilms efficiently retard the release of lysozyme, in a dose dependent manner, consistently withother properties.A naturally biochemical crosslinker (Genipin) is used to crosslink the gelatin films toachieve a controlled release of the antimicrobial lysozyme. Lysozyme release kinetic studiesare performed at acidic (pH3.8) or neutral (pH7.0) environment and some related propertiesare determined. Upon increasing Genipin concentration, thermal stability, mechanicalresistance and stiffness of gelatin films are enhanced, and the water stability is concomitantlyimproved by swelling decreased markedly. The release kinetic profile of lysozyme fromgelatin films can be described as a two-step biphasic process, an initial burst effect followedby subsequent slower release, and close linear relationship between released lysozymeactivities and incubating time is observed during burst release course. Genipin crosslinkingretards the release of lysozyme at neutral (pH7.0) environment, in a dose dependent manner,while lysozyme is rapidly released from the films with or without Genipin crosslinking atacidic environment. Concomitantly, antimicrobial activity of the films decreases gradually asGenipin concentration increases. The existing data shows that Genipin crosslinking is apromising way to extend antimicrobial effects during food storage and to enhance food safety,since gelatin films modified by Genipin crosslinking efficiently retard the release oflysozyme. Procyanidin has the peculiar capacity to react with proline accumulation area in gelatinmolecule. OPCs crosslinking is used to achieve a controlled microstructure of gelatin film anda controlled release of the antimicrobial lysozyme, antioxidant at the same time. The testindicates a retarded lysozyme release from gelatin films, especially at neutral (pH7.0)environment, in a dose dependent manner. More importantly, gelatin films crosslinked byOPCs have great reducing power and free radical scavenging capacity, the clearance ratereaches93.97%when OPCs is2.0%(w/w gelatin).In conclusion, gelatin based controlled-release antimicrobial films prepared bymicrofluidizer emulsification or crosslinking can efficiently delay the release rate of lysozymein neutral environment. Moreover, mechanical strength and water vapor barrier property areimproved to varying degrees. Modifying gelatin films are good carriers for active material,which will provide the direction and ideas for food preservation and antibacterial action.