Isolation Identification And Characterization Of Fungi Associated With The Spoilage Of Corn

Project and Seminar Material for Microbiology

Isolation Identification And Characterization Of Fungi Associated With The Spoilage Of Corn


Fungi spoilage organisms are silently invading acidifying, fermenting, discoloring, and disintegrating microbes that render corn (zea mays) unpalatable and unsafe. Fungi spoilage is caused by two factors, (biotic) living which includes insects, birds, rodents and microorganisms and (non-biotic) non-living which includes temperature, humidity and time. Two samples of spoilt corn, red (treated) and white were taken from the store respectivly for investigation to ascertain the microorganism associated with the spoilage of the corn. Attention was focused on fungi. Different methods were used in the identification and five genera were isolated. Mucor spp occurred with a frequency of approximately 6%, Aspergillus spp 9%, Rhizopus spp 15%, Penicillium spp 33% and Fusarium spp. 36%. Fusarium spp was most frequent in occurrence in both samples.

Table Of Contents

  • Title page i
  • Certification page ii
  • Dedication iii
  • Acknowledgement iv
  • Abstract v
  • Table of content

Chapter One

  • 1.0 Introduction
  • 1.1 Statement of the problem
  • 1.2 Aims/Objective of the Study
  • 1.3 Limitation of the Study
  • 1.4 Significance of the Study

Chapter Two

  • 2.0 Literature Review
  • 2.1 Maize as Sweet Corn
  • 2.2 Types of Sugary Corn and Their Qualities
  • 2.2.1 White Corn
  • 2.2.2 Yellow Corn
  • 2.2.3 Bi-Coloured Corn
  • 2.2.4 Mlti-coloured corn
  • 2.2.5 Black Corn
  • 2.3 Sugery Extender and Super Sweet Type of Corn
  • 2.3.1 Yellow Corn
  • 2.3.2 White Corn
  • 2.3.3 Bio-Coloured Corn
  • 2.4 Uses of Maize
  • 2.4.1 Human Food
  • 2.4.2 Table 1: Nutritional Values of Maize
  • 2.4.3 Ornament
  • 2.4.4 Fodder
  • 2.4.5 Bio-Fuel
  • 2.5 Factors That can Enhance Corn Spoilage
  • 2.6 Some Diseases and Pests of Corn

Chapter Three

  • 3.0 Materials and Methods
  • 3.1 Materials
  • 3.2 Methods
  • 3.2.1 Collection of Sample
  • 3.2.2 Sterilization of the Class Wears
  • 3.2.3 Preparation of Culture media
  • 3.2.4 Preparation of sample
  • 3.2.5 Plating Techniques
  • 3.3 Identification and Characterization of Isolate
  • 3.3.1 Culture Characteristics
  • 3.3.2 Colony Morphology
  • 3.3.3 Spore Staining
  • 3.3.4 Motility Test
  • 3.5 Biochemical Test
  • 3.5.1 Carbohydrate Assimilation Test
  • 3.5.2 Amino-Acid Assimilation Test
  • 3.5.4 Lipase Activity Test
  • 3.3.5 Fungi Identification

Chapter Four

  • 4.0 Results
  • 4.1 Identification
  • 4.2 Enumeration of Isolate
  • 4.2.1 Table IV: frequency of Visible Colonies
  • 4.2.2 Figure I: Histogram of Isolate Frequency
  • 4.2.3 Figure II: Colony Plates of Fungi Isolates

Chapter Five

  • 5.0 Discussion And Conclusion
  • 5.1 Discussion
  • 5.2 Conclusion
  • 5.3 Recommendation
  • References
  • Appendix

List Of Table

  • Cultural and Morphological Characteristics Identification
  • Spore Formation, Motility and Biochemical Identification
  • Frequency of visible colonies
  • Figure I; Histogram of Isolate Frequency
  • Figure II; Culture Plates of Fungi Isolates

Chapter One

1.0 Introduction

What food is more synonymous with summon than freshly picked corn on the cob? Corn grows in “ears, each of which is covered in rows of kernels that are then protected by the silk-like threads called “corn silk” and encased in a husk. Corn is known scientifically as Zea Mays. This moniker reflects its traditional name, Maize, by which it was known to the Native Americans as well as many other cultures throughout the world. Although we often associate corn with the colour yellow, it actually comes in host of different varieties featuring an array of different colors, including red, pink, black, purple and blue. Although corn is now available in markets years round, it is the locally grown varieties that you can purchase during the summer months that not only tastes the best but are usually the least expensive (Pitt and Hocking, et al., 2009).

From the time when primitive man began to cultivate crops and store food, spoilage fungi have demanded their tithe. Fuzzes, powders and slimes of white or black, green, orange, red and brown are signs of silently invading, acidifying, fermenting, discoloring and disintegrating microbes rending commodities unpalatable or unsafe (Pitt and Hocking 2002). Pitt and Hocking 2009, also stated that in a prophetic article warned of the danger from common spoilage fungi. Since 1960, a seemingly endless dream of pathogenic fungi discovered. On these ground alone, the statement “it is only a mould” is no longer acceptable to microbiologist, health inspectors or consumers. The demand for accurate identification and characterization of food spoilage fungi has become urgent.

This research work is focused on corn and its spoilage organisms. It set out to document current knowledge on the interaction of corn and fungi in the context of spoilage. Area covered are how the fungi is isolated using the suitable best media and identification of corn spoilage fungi. Mycologist develops preference and peculiarities of the type of fungi that are routinely grown. Media will affect colony morphology and color whether particular structures are formed or not, and may affect whether the fungus will be even in culture (Hunt et al, 2004).

1.1 Statement Of The Problem

Corn (Zea Mays) is a grain grown by farmers in various parts of the world especially in Africa. Its spoilage most times limits its availability to consumers and causes economic waste to farmers. Corn is mostly spoiled by fungi. The identification and characterization of these spoilage organisms will go a long way to profer solution on matter how little to this problem of corn spoilage.

1.2 Aims / Objective Of The Study

To microbiologically evaluate and identify fungi involved in corn spoilage using maize as case study.

1.3 Limitation Of The Study

The study is limited to yellow corn (Maize) one among the two found in Nigeria. It was difficult to get samples from the field (farm) and store as keepers were not known. Finally, this work was money consuming as regard getting the laboratory materials and the laboratory analysis.

1.4 Significance Of The Study

The study will help in the acquisition of the knowledge of fungi associated or involved in the spoilage of corn, factors that enhance spoilage of corn and the risk involved in the consumption of spoilt corn.

Chapter Five

5.0 Discussion And Conclusion

5.1 Discussion

Fungi isolates were identified by their cultural and morphological characteristics as presented in table 1, these includes Mucor spp, Fusarium spp, Rhizopus spp, Aspergillus spp, Penicillium spp, from sample gotten from the field and store usually different biochemical tests as indicated in table III. The result from this work confirms that multiple species corn occur in a single whole plant maize sample both at harvest and in stores (Baath et al., 1990). It is likely that toxin is present but was not investigated though several studies have cultured Aspergillus Fumigatus from maize and tested the ability of the isolate to produce Mycotoxins (Melodos Santos et al 2002). The inability of Mucor spp to persist in stored maize was observed and suggested that they are not capable of surviving the low oxygen, low pH and environment of the store (Baath, et al., 1990).

The optimal pH for growth of Mucor spp ranges from 5-7 (Marin et al 1999). Low pH in combination with the overall inability of Mucor spp to persist in the store as such as the majority of Mucor spp probably are product from the field samples.

In all analyzed samples, the most prevalent genera was Fusarium, its dominant presence denounce that cereals could have been incorrectly manipulated. Insufficient drying and precarious condition of storage given that Fusarium genera needs a great availability in water to develop itself (Harrigan et al, 1988). It is important to indicate that Furarium spp includes diverse producing toxigenic lineage in maize and derived products (Larone, 1998). All maize samples shows fungic contamination. It was proved that the predominating fungi genera in the analyzed samples were Fusarium spp (36.3%) followed by Penicillium spp (33.4%) and Rhizopus spp (15.2%) according to table IV. The result obtained in this study, even with a modest significant data are in accordance with authors who have published similar works on spoilt maize. Fusarium, Penicillum, and Rhizopus genera were identified as the primary contaminants in this cereal although less frequent genera like Aspergillus (9.09%), and Mucor (6.06%).

5.2 Conclusion

It is important to mention that a mycological quality criteria only present a guidance to a mycological survey though it is extremely important to carry on with determination, interpretation and qualification of fungal contamination levels as well as evaluating the storage conditions of products and trace the Zootechnical profile of the animals that consumes it. Maize sample with good mycological quality in general present a diversified flora with reduced total and medium fungic contents. They present a lower frequency of potentially toxigenic moulds as Penicillium spp, Fusarium spp and Aspergillus group. Nevertheless, it is necessary to prevent proliferation of thus variety of flora.

Aspergillus and Penicillum genera are one of the main organisms responsible for the deterioration of products and stored foodstuff. These groups of mould in favourable conditions and synthesis diverse mycotoxins.

One important recognition is that maize can be infected by fungi irrespective of weather condition. The good news is that the infection can be controlled.

5.3 Recommendation

This research work has established that corn can spoil under any weather condition. However, the rate and degree of spoilage has been proved to be higher under moist or high humidity conditions.

Moreover, all the fungal organisms identified, characterized, and isolated in this study are capable of causing death to man and animals resulting from mycotoxins which they produce. Also, the results of this study show that the conditions to which corn is exposed in the field and store, well as the storage method used to preserve it have effect on the type, rate, and extent of infestation of the corn by fungi.

Based on these and other facts, I hereby recommend as follows:

Appropriate fungicide(s) should be used in farms in the preparation of soils (or cultivation period). These types, if used well, help to impede attack of corn in the field by fungi. There are other recommended fungicides which are usually applied on maize cobs soon after they are produced by maize plants in the field. These help to prevent or subdue fungal attacks on corns. Early planting, and harvest of corn reduces the occurrence and extent of fungal attacks on corn. On the other hand late planting or harvest makes room for fungal attacks from other distance and near forms, especially because these organisms are airborne. With regard to store corn (storage), it is recommended that corn should be dried immediately after harvest, and kept as dry as possible throughout its storage period. The drier they are, the lower the extent of fungal attacks on corn. This is because most microbes (fungi inclusive) do not thrive well in conditions of absolute absence of moisture. Natural storage methods such as keeping corn (the grains or the cob) at a safe distance above cooking/kitchen fire is effective, but not absolutely speaking. This storage methodology is recommend but the disadvantages attached include:-

It is for subsistent (low scale) usage only, and it is suitable only for rural dwellers. It must be noted that most other natural methods of preservation do not succeed in keeping fungal attacks away. However, generally speaking, natural preservation methods have no side-effects, but they are not good for prolonged periods of storage. Modern preservation methods (e.g use of preservative chemicals, radiation techniques, etc) are commonly in use these days all over the world. They are hereby recommended for the following reasons also; they can be used on commercial scales, they are more convenient and accessible, they can be used everywhere both rural and urban areas and they preserve corn for longer periods, etc.

However, where these preservatives are to be used for long periods of time, the grains should be moved and mixed (turned over) from time-to-time, each time with a fresh application of the preservative. It is important that any preservation method that would be used should be applied immediately after the corn is brought in from the field to store.

Finally, because these modern preservatives have harmful side-effects on man and animals. And since no preservation method keeps away perfectly all fungal attacks, I recommend that corn should be harvested early and consumed within a short period of time after harvest. I equally prescribe that corn preserved with chemicals and other additives should be parboiled and washed (or washed with boiling water) severally before cooking and consumption by man and/ or animals. This helps to eradicate or reduce the harmful effects of these preservatives.

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