Fungi Associated With the Spoilage of Cocoyam (Colocasia Esculenta)
Chapter One
PREAMBLE OF THE STUDY
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).
CHAPTER TWO
LITERATURE REVIEW
Cocoyam is one of the oldest cultivated crops in the world. It belongs to the sub-class of monocotyledonous plants and contains several species (Fayemi, 1999). Compared with the yams and cassava, cocoyam is a minor root crop cultivated in many parts of the forest Zone on Southern Nigeria.
Like cassava, cocoyam also has some poisonous verities, but the methods of getting rid of the poisons element in cocoyam are less well known (Agboola, 1979)
Cocoyam is cooked as yam but has an inferior tastes resulting in it being considered as a stand-by crop worth eating only during the seasonal famine period. Thus its cultivation has received only limited attention. (Agboola, 1987)
The main species of the crop produced in Nigeria Are Colocasia esculenta, Xanthosoma sagittifolium, and Colocasia antiguorum. The first of these was established early, and the second was introduced from the west Indies. There are many local varieties of each species in different parts of the country; the root crop research unit of the Federal Department of Agricultural research, based at Umudike, Imo State, has identified Fourteen varieties of Xanthosoma sagittifolium and Eleven of Colocasia esculenta (Agoola,1979)
Physical damaged arising from harvesting caused the spoilage of cocoyam by fungi. Damage can occur as a result of the harvesting tool injuring the corm or as a consequence of rough handling (e.g. corm-t—corm impact by throwing harvested corm into a pile). Physical damage such as punctures, cuts or abrasion leads to high rates of moisture loss and provides avenues for microbial infection. These conditions lead to high incidence of shrinkage and post harvest losses of cocoyam during storage down the handling chain. Physical damage during the process of transportation caused the attack of fungi with cocoyam during storage. The quantity of crop and expected market value are important to be considered in selecting an appropriate transport system. Mechanized transport has the Potential to induce physical damage during haulage on “bumpy” roads, food shock and vibration absorbers and careful driving will assist in reducing the incidence of damage. The curing of cocoyam tubers slows down the rates of physiological and pathological deterioration which leads to losses in quality and quantity. Several wounds are made on cocoyam tubers when the cormels are removed and cut off from the parent corm. Curing is achieved at elevated temperature in high humidity environment, but chemical application like fungicide is used for the treatment of cocoyam to suppress sprouting and to cause an inhibitory effect on wound healing and peridem formation in order to prevent subsequent infection and spoilage caused by the attack of fungi during storage at ambient temperature (Passam, 1982).
Improper cleaning during the process of post harvest handling system can lead to the association of fungi with cocoyam under storage condition, which caused their spoilage. The method of packaging also caused the association of fungi which lead to the spoilage of cocoyam during storage. During mechanical transportation, wooden or plastic creates are preferred because they are firm and reduced the incidence of mechanical damage to corms. Plastic crates are cleaned and thereby contributing to better hygiene and reduced microbial infection of corms (tubers), (Snowdon, 1991).
CHAPTER THREE
MATERIALS AND METHOD
The material used in this research work include cocoyam, distilled water, incubator autoclave, SDA, measuring cylinder, chloramphenicol, Petri dishes, beaker, pipette, test tube, test tube rack, weighing balance, filter paper.
SOURCE OF SAMPLE
The raw cocoyam (Colocasia esculenta) tubers were purchased from Ariaria market in Aba, Abia state Nigeria.
STORAGE CONDITION
The sample was damage using a Knife and stored in a cool dry place inside an empty room at ambient temperature of (28 + 20c) by leaving it in a black polythene bag in order for it to spoil.
SAMPLE PREPARATION
A sterile small knife were used to cut through the spoil portion of each cocoyam tubers as described by (Ugwuanyi and Obeta,1996) and Okafor 1966) and put into a sterile foil paper and wrapped properly. 25g of the sample was weighed out with the aid of a weighing balance. The sample after weighing, was put into a sterile laboratory motar and pounded to become powdery and then transferred into sterile beaker and covered with foil paper. 225ml of diluents (water) were measured using measuring cylinder and added to the pounded cocoyam sample in the beaker and stirred with a glass rod to dissolved properly and blend together to form a solution.
CHAPTER FOUR
RESULTS
TABLE 1: Cultural and morphological characteristics of isolated fungal
CHAPTER FIVE
DISCUSSION
The fungi which associated with the spoilage of cocoyam during storage under ambient temperature condition were found to be moulds. This is in agreement with the result reported in the previous study by (Ugwunwanyi and Obeta, 1996, Nwufo, 1980). In this present study, five genera of moulds were isolated from spoilt damage portion of cocoyam tubers. The five genera isolated are listed in order of frequency of occurrence which are; Fusarium Species, Rhizopus Species, Penicillium Species, Botryodiplodia Species, and Aspergillus Species. The cultural and Morphological characteristics used for the descriptions of the fungi isolated in this present study was described by (Barnett and Hunter, 1992, Samson et al, 1984) as shown in (Table 1).
The isolated moulds with the highest population which caused the spoilage of coco- yam during storage were Fusurium species which has the frequency of 38%, Rhizopus species has 25%, Penicillium Species has 21%, Botrydiplodia Species 7.9%, which Aspergillus Species were found to have the lowest occurrence of 6.3% as observed in (Table 3).
This result indicates that the most prevalent moulds associated with the spoilage of cocoyam during storage at ambient temperature are Fusarium and Rhizopus species followed by Penicillium Species.
CONCLUSION
In conclusion, the fungi associated with the spoilage of cocoyam during storage under ambient temperature were found to be the following moulds, Furarium species, Rhizopus species, Penicillium species, Botryodiplodia species and Aspergillus species.
It therefore means that cocoyam with wounds or cut are liable to deterioration by fungi when stored at room temperature.
Cocoyam is an important tuber crops, which has so many usefulness to mankind. By putting into consideration, its wide range of uses, domestically and industrially. Its great medicinal use for the treatment of several chronic disease like chronic liver problems, Peptic ulcer and pancreatic diseases have been implicated. To avoid the attack of cocoyam under storage condition by these moulds, the occurrence of mechanical damage should be minimized or reduced by leaving the corms untrimmed during storage. Also, different methods of storage conditions such as traditional, ventilated and refrigerated storage should be used as this will be beneficial to reduced the fungi which lead to their storage rots (Spoilage)
RECOMMENDATIONS
Hence, adequate measure should be taken to avoid inflicting injury to cocoyam before storage.
Also, those with wounds should be separated from those without wounds to avoid contamination.
REFERENCES
- Agboola, S.A. (1987). Cocoyam Storage and its potential for food sufficiency and Future economic Recovery of Nigeria. Macmillan Press Ltd, Ibadan, page 80.
- Agbola, S.A. (1979). An Agricultural Atlas of Nigeria. Nigeria, Great, Oxford university Press Page 53-71
- Aderiye, B.I and Ogundana, S.K. (1984). Survival of Botroyodiplodia Theobromae in yam Tissues. Nova Hedwigia Pp 171-176
- Barnett, H.L and Hunter, B.B. (1972). Illustrated Genera of Imperfect Fungi, 3rd edition
- Bradury, J.H. and Holloway W.D. (1988). Chemistry of tropical Root crops Significance for Nutrition and Agriculture in the pacific Aliar Monograph No 6, 201
- Cecil, J.E. (1992). Small medium and large scale starch processing. FAO agricultural Service Bulletin, page 98
