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FUNGI ASSOCIATED D WITH THE SPOILAGE OF COCOYAM (Colocasia esculenta)

ABSTRACT

Fungi associated with the spoilage of cocoyam (Colocasia esculenta) during storage at ambient temperature (28+20c) was investigated in this study. This was done by cutting the damaged portion of the cocoyam tubers and blend with diluents (water) to have even distribution of the microorganism and ensure ease of plating out. This done with the sample and inoculation was done from the 4th test tube on SDA medium and incubated for three to seven days at the temperature 0f 270c. The isolate with the highest population was Fusarium species, which was found to be 38%, followed by Rhizopusspecies 25%, Penicillium species 21%, Botryodiplodia species 7.9% While the isolate with the least population was Aspergillus species which was found to be 6.3%. The total colony count of each isolate are; Fusarium species 72 colony, Rhizopus species 47 colony, Pencillium 15 colony,  Botryodiplodia species 15 colony, and Aspergillus species is 12 colony. The occurrence of mechanical damage should be reduced by leaving the tubers untrimmed during storage at ambient temperature (28+20c) to control these prevalent moulds which lead to the spoilage of cocoyam.

TABLE OF CONTENTS

CHAPTER ONE

1.0     INTRODUCTION

CHAPTER TWO

2.0    LITERATURE REVIEW

2.1     METHODS OF STORAGE TO PREVENT/ CONTROL FUNGI ASSOCIATED WITH THE SPOILAGE OF COCOYAM DURING STORAGE

2.2    NUTRITIONAL VALUE OF COCOYAM

2.3    COCOYAM FOR RURAL AGRO-INDUSTRIALIZATION

2.4    PRESERVATION OF COCOYAM

2.5    USES OF COCOYAM

CHAPTER THREE 

MATERIALS AND METHODS

3.1      SOURCE OF SAMPLE

3.2    STORAGE CONDITION

3.3    MICROBIAL EVALUATION OF SPOILT COCOYAM TUBERS DURING STORAGE AT AMBIENT TEMPERATURE

3.3.1      PREPARATION OF CULTURE MEDIUM

3.3.2     ISOLATION AND IDENTIFICATION OF ASSOCIATED FUNGI

CHAPTER FOUR

4.0      RESULTS

CHAPTER FIVE

5.0     DISCUSSION

5.1     CONCLUSION

5.2     RECOMMENDATION

REFERENCES

LIST OF TABLES

TABLE1: Culture and morphological characteristics of isolated fungal

TABLE 2: Total colonies of fungal isolates counted on the culture plate

TABLE 3: Percentage occurrence of isolates

CHAPTER ONE

INTRODUCTION

Cocoyam (Colocasia esculenta) is widely cultivate and used for food in Nigeria, Ghana and other countries including China.  China and Ghana leading in world production (Onwueme and Charles, 1994). Although its production has increased from 643000 to 1.7 million tones during the past decade, its contribution to root-crop production increased from only 39-6.8% (Agboola, 1979). In Nigeria, Colocasia species are the most important food and the third most important root/tuber crop after yams and cassava (Onwueme, 1978). Besides critical contribution to the national food security and cash  income  producing nations, cocoyam  are also being considered as source of starch for use in biodegradable film materials and for other industrial and pharmaceuticals purposes because of interesting properties of the amylopectin fraction of starch, which is the principal form of cocoyam starch (Cecil, 1992).

Cocoyams have very short post harvest storage life of a few days to weeks (Gollifer and Boot, 1973, Ugwunwanyi and Obeta, 1997). Differing and often conflicting reports have been made on the post harvest losses of cocoyam. But it bears nothing that post harvest storage life is often short and biodegradative losses are extensive and up to 100% losses are common due to the fungi which associates with the spoilage of cocoyam during storage condition,  (Onwueme and Charles, 1994). However, substantial post harvest losses caused  by the fungi associated with the spoilage  of cocoyam tubers during storage is attributed to a number of physical, physiological damage  arising  from harvesting, storage or transportation have  often been implicated as some of the predisposing factors  to cocoyam spoilage or deterioration (Ogundana et al;1970, Snowdon, 1991). Invasion by pathogens either through natural openings or wounds is considered the most critical factor in cocoyam spoilage (Degras, 1993).

A wide range of micro-organisms (Particularly moulds) have been associated with cocoyam decay, relatively few are implicated as primarily pathogens (Aderiye and Ogundana, 1984). The degree of pathogenicity varies and is highly dependent upon storage conditions. It has been stated that fungi take the lead in the spoilage of cocoyam during storage. (Nwufo and Atu, 1987). Under these storage conditions, the fungi which are liable to  attack cocoyam include; Fusarium  solani, Botryodiplodia, theobromae, Rhizopus, stolonifer, Aspergillus  niger, Sclerotium roltsii, Trichoderma hamatum andPythium species. (Nwufo, 1980,Uwgunwanyi and Obeta, 1996). Another factor also attributed to the spoilage of cocoyam is high respiratory activity. Storage temperature to an optimum of 70C and 85% relative humidity increases the storage time. The crops are usually left in the ground and harvested when need, and there  is a limit to how long the crop can be left in the soil since the corms and cormels sprout and produce new growth, which result  in the cocoyam losing its good values.

Therefore, it has been suggested that November and March /April are the ideal time for harvesting cocoyam. However, due to the difficulties in storage, cocoyam are usually utilized or consumed fresh shortly after harvest because of these fungi which lead to their spoilage during storage, (Passam, 1982, and Onwueme, 1987). The objective of this study is to investigate the fungi associated with the spoilage of post harvest cocoyam during storage at ambient temperature (28 ± 20C).

Cocoyam leaves are consumed as green or dry vegetables and the stem is either cooked or eaten on its own or together with other dietary staples or pound into flour. The leaves are consumed because they are rich in protein and vitamins while the roots is rich in carbohydrates and minerals, (Duru and Uma, 2002).

Large quantities of carbohydrate-rich solid waste are produced in the course of processing cormels into starch and this constitute a waste disposal problem, (Duru, 2000). The changing economic, social, political and cultural values of the world have challenged all countries to efficiently use their resources.

In Cameroon, two types of cultivated cocoyam varieties can be differentiated based on the colour of the flesh. The white –flesh cultivar or white cocoyam is the main cultivated variety because of its early maturation (6-(months) and high yield. In addition, the white cocoyam is most preferred in diet because of its excellent taste. The pink-flesh variety or red cocoyam is rarely grown because of its long maturation process (12-16months) Despite its importune, white cocoyam is highly susceptible to cocoyam    root  with attendant yield losses > 90%.  In contrast, fields observations by farmers revealed that the red cocoyam has a certain degree of field tolerance against the cocoyam root rot   disease (Tambong, 2000).

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