ABSTRACT

Microorganisms associated with Deteriorated dioscorea rotundata L. (white yam) was studied. Discorea rotundata (white yam) with no symptoms of infection were procured locally from different yam sellers in Umuahia main market, Ubani, Abia state. The yam samples were stored using different methods which include; Ambient temperature, Polyethylene bag at 40oC, Unprotected from rain, Unprotected from rodent attack (27oC), dark cupboard (30oC) and Ambient temperature at 27oC and were labeled samples A, B, C, D and E respectively. The yam samples were stored for four (4) weeks in which the spoilage progress was monitored after which bacteria and fungi were isolated and identified using standard methods of analysis. A total of 9 isolates (four bacteria and 5 fungi) were isolated after some physiological, morphological and biochemical test were carried out. The study revealed that the yam sample stored at ambient temperature (27oC) (sample E) showed no sign of spoilage up to day 18 while rodent attack, dark cupboard and rain all facilitates spoilage of white yam. The bacteria isolated were Erwinia sp., Pseudomonas specie, Staphylococcus specie and E. coli. The fungi isolated were Aspergillus niger, Aspergillus flavus, Rhizopus stolonifer, Fusarium oxysporium and Mucor spp. The incidence of occurrence of these organisms revealed that Aspergillus niger had the highest occurrence (31.25%) for fungi and occurred more in sample stored with polyethylene bag while Mucor spp had the least occurrence (12.5%). Erwinia sp and E. coli had the highest occurrence (29.41%) for bacteria and was found in the sample stored with polyethylene and ambient temperature. While Staphylococcus specie had the lowest occurrence (17.65%). The research has isolated and identified the microorganisms associated with the spoilage of white yam. 

TABLE OF CONTENTS

Title page i

Declaration ii

Certification iii

Dedication iv

Acknowledgement v

Table of contents vi

List of Tables ix

Abstract x

CHAPTER 1: INTRODUCTION

1.1 Introduction 1

1.4 Aim and Objectives 3

CHAPTER 2: LITERATURE REVIEW

2.1 Botany of yam and its importance 4

2.2 Harvesting of yam tuber 5

2.3 Agronomy of Yam and Storage process 6

2.4 Methods of traditional storage of yams in Nigeria 7

2.5 Factors affecting the shelf life of yams 8

2.6 Storage pathogens 10

2.6.1 Pathogens of yam rot diseases 10

2.6.2 Control of yam rot diseases 12

2.7 Nutrients in Yam 16

2.8 Emergence of post-harvest pathogen in yam 18

2.8.1 Wet rot 19

2.8.2 Dry rot 19

2.8.3 Soft rot 20

2.9 Organisms involve in Post-harvest spoilage of yam 20

2.9.1 Management of post-harvest pathogens of stored yam 21

CHAPTER 3: MATERIALS AND METHODS

1.1 Source of raw material 23

3.2 Sample Preparation 23

3.3 Processing of materials and media 24

3.3.1 Sterilization of materials 24

3.4 Isolation of fungi associated with yam spoilage 24

3.5 Identification of isolated fungi pathogens 24

3.6 Isolation of bacteria pathogens 25

3.7 Identification of isolated bacteria pathogens 25

3.8 Biochemical test 26

3.8.1 Gram staining 26

3.8.2 Oxidase test 26

3.8.3 Coagulase tests 27

3.8.4 Catalase test 27

3.8.5 Indole test 27

3.8.6 Methyl Red test 27

3.8.7 Motility Test 28

CHAPTER 4: RESULTS

4.1 Shelf life determination of the white yam samples 29

4.2 Morphological Characteristics of the Isolates 34

4.3 Biochemical Identification of Isolates 36

4.4 Incidence of occurrence (bacteria) 38

4.5 Total plate count 40

4.8 Total plate count of the white yam samples (cfu/ml) 43

4.6 Morphological Characteristics of fungi Isolates 42

4.7 Incidence of occurrence (fungi) 44

CHAPTER 5: DISCUSSION, CONCLUSION AND RECOMMENDATIONS

5.1 Discussion 46

5.2 Conclusion and Recommendation 49

REFERENCES 50

LIST OF TABLES

Table 4.1: Spoilage progress based on the various storage conditions for week 1 30

Table 4.2: Spoilage progress based on the various storage conditions for week 2 31

Table 4.3: Spoilage progress based on the various storage conditions for week 3 32

Table 4.4: Spoilage progress based on the various storage conditions for week 4 33

Table 4.5 Morphological Characteristics of the Isolates 35

Table 4.6: Biochemical Identification of Isolates 37

Table 4.7: Incidence of occurrence (bacteria) 39

Table 4.8: Total plate count of the white yam samples (cfu/ml) 41

Table 4.9: Morphological Characteristics of fungi Isolates 43

Table 4.10: Incidence of occurrence (fungi) 45