STUDIES ON MICROORGANISMS ASSOCIATED WITH DETERIORATED DIOSCOREA ROTUNDATA L. (WHITE YAM)

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