CHAPTER 1: INTRODUCTION ………………………………………………...1
CHAPTER 2: LITERATURE REVIEW
2.1. Pawpaw …………………………...…………………………………….4
2.1.1. Pawpaw biology …………………………...…………………4
2.1.2. Pawpaw fruit as food ………………………………………...6
2.2. Food Browning …………………………………………………………7
2.2.1. Non-enzymatic browning …………………………………….7
2.2.1.1. Maillard reaction …………………………………….…7
2.2.1.2. Ascorbic acid oxidation ...……………….…………..….8
2.2.1.3. Caramelization …………………………………………....8
2.2.2. Enzymatic browning …………………………………….…....9
2.2.2.1. Polyphenol oxidase (PPO) ……………………….……9
2.2.2.2. Factors affecting PPO activity ………………………..12
2.2.2.2.1. Enzyme active site ……………………………..12
2.2.2.2.2. Prosthetic groups ………………………………12
2.2.2.2.3. pH dependence ………………………………...14
2.2.2.2.4. Temperature dependence …..………………….14
2.2.2.3. Inhibition of PPO ……………………………….…...15
2.2.2.4. Methods to characterize PPO ………………………...16
2.2.2.4.1. Colorimetry ………………………………...….16
2.2.2.4.2. Extraction …………………………………..….18
2.2.2.4.3. Assay for PPO activity .……………………....18
2.2.2.4.4. Gel filtration chromatography .……………....19
2.2.2.4.5. SDS-PAGE ……..……………………………….19
2.3. Lipid Oxidation ………………………………………………………….21
2.3.1. Mechanism of lipid oxidation ……………………………….21
2.3.2. Measurements of lipid oxidation ……...….……………….22