Phd Degree / Doktora

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Development of Functional Composite Edible Packaging Materials for Controlled Release of Bioactive Substances
(Izmir Institute of Technology, 2013) Arcan, İskender; Yemenicioğlu, Ahmet
The aim of this study was to control the release of bioactive agents by modification of hydrophobicity and morphology of zein films using composite and blend film making methods. The bioactive agents incorporated into zein based films were lysozyme and phenolic compounds. The incorporation of beeswax, carnauba or candelilla wax into films gave composite films containing amorphous wax particles, while the incorporation of oleic, lauric or linoleic acid into films caused formation of blend films containing many spherical zein capsules within their matrix. The release profiles of phenolic compounds from zein films were successfully altered by the development of composite and blend films. The composites and blends can show 2.5 to 17 fold lower lysozyme release rates than the controls. The lysozyme release rates of composites reduced as the melting point of waxes increased. The chain length and the concentration of fatty acid used in blend films could also have affected the release rates of lysozyme. The phenolic antioxidants, catechin, gallic acid, p-hydroxy benzoic acid and ferulic acid are effective plasticizers of zein films. These phenolic compounds eliminate the classical brittleness problem of zein films and increase their flexibility considerably (up to 196%). Furthermore, catechin contributed to controlled release properties of films by reducing the film porosity. The phenolic compounds also provided antioxidant activity to films (up to 86 μmol Trolox/cm2). The blends and composites of zein films containing phenolic compounds or lysozyme and phenolic compounds showed antimicrobial activity on critical food pathogenic bacteria or indicator microorganisms including Escherchia coli O157:H7, Listeria monocytogenes, Listeria innocua and Campylobacter jejuni. This work showed the possibility of obtaining advanced edible films having flexibility, antimicrobial and antioxidant activity and controlled release properties.
Development of Novel Bio-Based Methods for Inhibition of Plant Pathogens
(Izmir Institute of Technology, 2013) Alkan, Derya; Yemenicioğlu, Ahmet
In this thesis, to develop a post-harvest bio-based preservation method for spoilage of fresh fruits and vegetables, antimicrobial packaging commonly applied for inhibition of human pathogenic bacteria was adapted for inhibition of plant pathogenic bacteria including Pseudomonas syringae, Erwinia amylovora, Xanthomonas vesicatoria and Erwinia carotovora. The zein based films were developed by incorporation of pure phenolic acids such as gallic acid (GA), cinnamic acid (CA), vanillic acid (VA); essential oils such as carvacrol (CAR), thymol (THY), eugenol (EUG) and citral (CIT) and phenolic extracts obtained from clove, artichoke, oregano and walnut shells into film forming solutions. The films containing phenolic acids between 1 and 4 mg/cm2 were effective on all bacteria. Essential oils at concentrations between 2 and 4 mg/cm2 and clove extract at concentrations between 4 and 8 mg/cm2 were found effective against pathogens except P. syringae. The HPLC analysis showed that the clove extracts owe its inhibitory activity to high concentration of GA which is a potent antimicrobial. The incorporation of natural compounds and extracts into films caused significant changes in morphologies and mechanical properties of films. This thesis showed the good potential of antimicrobial films against plant pathogens for the first time in the literature.

Phd Degree / Doktora

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