FACTORS AFFECTING THE FREE RADICAL SCAVENGING CAPACITY OF PANI

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Active Packaging

Active packaging refers to the incorporation of certain additives into the packaging systems with the aim of maintaining or extending product quality and shelf-life. The active additives can be either incorporated directly into the packaging matrix, attached to the interior of the packaging material or contained in separate containers such as sachets within the packaging system [6, 7], as demonstrated in Figure 1.1.
Active packaging provides dynamic, rather than the conventional passive, protection to the food it contains. It performs some desired role in food preservation other than just providing an inert barrier from external conditions [3, 6]. active packaging system release or absorb substances into or from the packaged food and the surrounding environment [4, 8, 9], thus promoting food preservation. Various active packaging systems, with attributes such as oxygen and carbon dioxide scavenging, antimicrobiology and antioxidant activity, have been developed.

Oxygen scavengers

Scavenging of oxygen from packaged foods is important as oxygen is deleterious to most food products. The presence of oxygen can trigger oxidative rancidity, discoloration, nutrient degradation and growth of aerobic bacteria, yeast and molds which cause food spoilage [3, 6, 10]. Most of the oxygen scavengers used commercially are based on the principal of iron oxidation [11, 12]

Carbon dioxide scavengers

Carbon dioxide, formed in some foods due to respiration reactions, also needs to be removed from the package to prevent it from bursting. Carbon dioxide absorbent sachets containing either calcium hydroxide, or calcium oxide and a dehydrating agent such as silica gel are commonly used for carbon dioxide removal [6, 16].

Antimicrobials

Antimicrobial active packaging materials help extend shelf-life and maintain product quality and safety by extending the lag phase and reducing the growth phase of microorganisms responsible for product spoilage [17]. The antimicrobial agents can be coated, incorporated or surface immobilized on the packaging materials to confer antimicrobial activity [18]. The antimicrobial effect is achieved by migration of active compounds from the active surface to the packaged product, as demonstrated in Figure 1.2.
PE and PE/ polyamide (PA) composite films, coated with sorbic acid, have exhibited significant inhibitory effect on Escherichia coli, when tested with Gouda cheese and pork loin inoculated with the test bacteria [20]. Extruded low density PE (LDPE) films containing linalool or methychaviol have been proposed as antimicrobial active packaging materials [21]. Melt processed PP films containing thymol and carvacrol have demonstrated antimicrobial activity against bacterial strains potentially present in food [22]. LDPE, polylactic acid (PLA) and polycaprolactone (PCL) films containing lemon extract, thymol or lysozyme also showed antimicrobial efficacy [23]. The antimicrobial activity was found to b temperature dependent and the PCL films had a superior antimicrobial efficiency as they were processed at a lower temperature. PP films coated with whey protein isolate combined with nisin have exhibited significant bacterial growth inhibition against Lactobacillus plantarum [5]. PP/ PE films coated with soy protein isolate containing allyl isothiocyanate, trans-cinnamaldehyde, garlic oil or rosemary oil have been instrumental in extending the shelf life of fresh sprouts by reducing the total microbial counts of alfalfa, broccoli and radish sprouts [24]. Furthermore, PE films loaded with zinc oxide nanoparticles have shown potency for antimicrobial active food packaging applications as they illustrated biocidal action against Escherichia coli [25].

READ PHYLOGENY OF PAPILLOMAVIRUSES OBTAINED IN SKIN LESIONS OF CAPE MOUNTAIN ZEBRA

Antioxidants

Antioxidants are incorporated in packaging materials or added to food stuffs to improve oxidation stability of lipids [16]. When incorporated within the packaging material, the antioxidants diffuse through the polymer bulk, towards the surface, to accomplish the antioxidant activity [26, 27]. Butylated hydrxoytoluene (BHT) and butylated hydroxyanisole (BHA) are commonly used synthetic antioxidants in food applications [27, 28]. The chemical structures of BHT and BHA are shown in Figure 1.3. However, due to consumer preference for natural food ingredients, the focus has shifted to natural antioxidants [3]. Natural antioxidants such as α-tocopherol, L-ascorbic acid, L-tyrosine, carvacrol and aromatic plant extracts have been utilized in antioxidant food applications [28-38].

CHAPTER ONE INTRODUCTION AND LITERATURE REVIEW
1.1 Introduction
1.2 Active Packaging
1.3 Principle of Lipid Oxidation
1.4 Intrinsically Conducting Polymers
1.5 PANI
1.6 Research Objectives
CHAPTER TWO FACTORS AFFECTING THE FREE RADICAL SCAVENGING CAPACITY OF PANI
2.1 Introduction
2.2 Experimental
2.3 Results and Discussions
2.4 Conclusions
CHAPTER THREE THE EFFECTS OF THERMAL TREATMENT ON THE ANTIOXIDANT ACTIVITY OF PANI
3.1 Introduction
3.2 Experimental
3.3 Results and Discussions
3.4 Conclusions
CHAPTER FOUR CHARACTERIZATIONS OF PET/ PANI COMPOSITES AS POTENTIAL ANTIOXIDANT MATERIALS
4.1 Introduction
4.2 Experimental
4.3 Results and Discussions
4.4 Conclusions
CHAPTER FIVE CHARACTERIZATION OF ANTIOXIDANT LDPE/ PANI COMPOSITES PREPARED VIA EXTRUSION
5.1 Introduction
5.3 Results and Discussions
5.4 Conclusions
CHAPTER SIX EVALUATION OF EXTRUDED LDPE/ PANI COMPOSITES FOR ACTIVE PACKAGING APPLICATIONS
6.1 Introduction
6.2 Experimental
6.3 Results and Discussions
6.4 Conclusions
CHAPTER SEVEN CONCLUSIONS
7.1 General Conclusions
7.2 Recommendations for Future Work
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