Isolation And Identification Of Rhizopus From Decaying Bread

Project and Seminar Material for Science Laboratory Technology SLT

Isolation And Identification Of Rhizopus From Decaying Bread


The Isolation and Identification of Rhizopus from a Decaying Bread were conducted. The black mould used in the practical was collected from bread. It is allowed to stay in moist environment or at room temperature for 2 to 3 days. The mould is then inoculated in the nutrient egar (N.A.) incubated and was isolated and view under the microscope for cultural characteristics.

In the experiment a mass of soft, closely woven white, silky threads was observed. In the microscope examination, non-deptate masses of round black spores, rhizoid. This characterized by Rhizopus SP.

In conclusion, since foodstuff from which the mould is isolated is bread, Rhizopus SP which is more prominent in bread than in any other foodstuff.

Chapter One


Rhizopus nigricans belongs to a group of fungi known as the “black moulds”. It is also known commonly as the “read mould” because if grows freely on moist, state bread. It appears as a delicate black mass. It is a common mould, which is widespread in occurrence. Rhizopus forms a mass of soft, closely woven white silky threads. This mass, which is known as a mycelium is the vegetative part of the Fungs. Each silky thread like structure is a hypha. The ‘mycelium grows not only on the surface of the bread but into it as well. The bread is known as the substrate.
The mycelium consists of three sorts of hyphae. These three sorts of hyphae as stolons which grow horizontally on the substrate (bread), rhizoid or root like hyphae which arise at points where the stolons come into contact with the substrate and sport-angiophores. The rhizoids are much branched hyphae which penetrate into the substrate. They are able to digest and absorb organic food. The sporangiophores are erect unbranched hyphae arising from the stolons at the same points where rhizoids are formal.

They grow vertically upwards and give rise to the reproductive structures called sporangia. (Sargini et al, 1979).
The common bread mould (Rhizopus) finds new bakery items by means of air-born spores. Once the baked good is invaded, it won’t be long before black sporangia full of spores are formed. Rhizopus stolonifera (black mould) causes the black bread mould that forms cottony masses on the surface of moist bread exposed to the air. Rhizopus is aerobic and grow easily on bread since the slight acidity of bread is conductive to their development it can also grow on solid substance such as cloth, vegetables, leather, paper, food, and many other materials when they are neglected in cupboard, boxes or other damp places, especially during the wet seasons.

Effect of contaminated bread in the society can lead to an epidemic of gastro-intestine disorder, where by that particular environment that consumed the contaminated bread becomes affected. As a result of this, a lot of consideration should be given to breads that are served into the community to be sold, and this is done by the standardized system called “Hazard Analysis Critical Control Point” (HCCP).

This method is now generally considered as a choice for ensuring safety of foods. (Jay, 1996, De Beer and Beunier 1999). Hazard analysis critical control point involves in identifying places in the production process where hazards could occur i.e. the ccp “Critical Control Point)” and put monitoring procedures in place to prevent these hazard occurring. Even with this system in place. A sample still needs to be tested for the presence of microorganisms.

1.1 Aim and Objectives of the Study

This project work is based on the Isolation and Identification of the fungal organism responsible for the spoilage of Bread. It is also to determine the rate of growth of the Organisms and to know its ability to grow on inhibitory media. To examine the species of fungi that infests breads at room temperature.

1.2 Hypothesis

  • Ho – Fungi (filamentous) and yeast has no affect on bread.
  • Hi – Filamentous fungi and Rhizopus are responsible for spoilage of bread when infested.

1.3 Statement of Problem

Problem encountered by the society as a result of the consumption of contaminated bread ingested with fungal organisms at circulation in the market places are related health wise. Health wise in the sense that when contaminated breads are eaten, it leads to gastrointestinal disorder which is as a result of ingestion of toxins deposited by some fungal organism on the bread. This can lead to an epidemic, when a batch of contaminated bread is in circulation and is being purchased and consumed by various individual.

1.4 Significance of Study

The justification of this research study is to ensure that well prepared baked bread devoid of fungal growth is being circulated or sold. It is also carried out on the basis of selling well-baked breads, uncontaminated so as to avoid any sort of food poising associated with the ingestion of bread.

1.5 Limitation of the Study

This research work will be limited to the isolation and identification of fungal organism present i.e. (Rhizopus nigrican), incubated under room temperature. This is also limited or restricted on the examination of the end product, which is the baked bread and not its raw material which is the flours. Practical works won’t be carried out on the pathogenicity of species identified, on. This could be another area of study for interested microbiologists.

Chapter Six

Conclusion and Recommendation

6.1 Conclusion

It has been observed that most of the food materials like garri, yam and bread are being spoiled by rhizopus. It has also been noted that rhizopus are generally aerobic plants whose growth has facilitated by little moisture and that the best growth was from the one cultivated for four (4) days.

When the organisms were inoculated in nutrient agar and incubated for four (4) days, it was found that the organisms has over grown and had already been sporulated, showing that 4 days is too much for incubation. When the plate were incubated for two (2) days, the growth occurred but not well pronounced but on incubating the plate for three (3) days at 37oC, the organisms grow very well and all the parts are seen. This shows that the best or maximum period for incubation of mould is three days.

Again when isolating muoulds, one has to look for the best media for the growth. These media have to be carefully prepared to avoid contamination.

In the experiment, nutrient agar was carefully prepared and poured in a sterilized petri-dishes. The organisms were inoculated using a sterilized wire-loop. Even the slide on which the colony was placed before mounting on a microscope was carefully sterilized.

Juging from the result, rhizopus sp was isolated indicating that the culture was pure. Therefore the aim (to determine the rate of growth of the organism) was achieved.

6.2 Recommendation

Since it is known that after three (3) days of baking bread, there will be infestation which leads to growth of rhizopus on the product (bread), we thereby recommended that NAFDAC should inspect all the bakery industries to ensure that the manufacturing and expiration date of the bread is written on the label before distributing, so that the basis of selling well-baked breads/uncontaminated breads will be employed in order to avoid any sort of food poising associated with ingestion of bread.

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