Amylolytic and Beta-glucanase Activities of Yam Rot Fungi
CHAPTER ONE
Aim of study
This work is aimed at studying the activities of these two enzymes amylase and beta-glucanase from fungi isolated from rotten yam.
Objectives
- To collect sample from a yam rot and isolate the fungi associated with the rot.
- Test and monitor the fungal isolates for their ability to produce amylase and beta-glucanase.
- Production and characterization of the two enzymes.
CHAPTER TWO
LITERATURE REVIEW
YAM
Yams (Dioscorea spp.) are among the most important staple foods in the world, especially in some parts of the tropics and subtropics. The role played by yam in the food economy in most West African countries cannot be over-emphasized. It is one of the most important dietary sources of energy produced within the tropics (Okigbo and Ogbonnaya, 2006).
Yam is an edible starchy tuberous root of various plants (genus Dioscorea of the family Dioscoreaceae) used as a staple food in tropical areas, also can serve as a source of organic Starch and as a plant producing yams. They are monocotyledonous plant with over 600 varieties of yams and 95% of these crops are grown in Africa. Yam has a skin which is difficult to peel but which softens after heating. The skin varies from dark brown to light pink, black scaly skin which resembles the bark of a tree and off-white, purple or red flesh, depending on the variety (Dumont and Vernier, 2000).
For consumption the parenchyma tissue is cooked and in many instances converted into paste or dough-like products. Yam tuber parenchyma is characterized by the occurrence of randomly distributed vascular bundles.
Classification of yam
Kingdom: Plantae
Sub kingdom: Tracheobionta – Vascular plants
Super division: Spermatophyta – Seed plants
Division: Magnoliophyta – Flowering plants
Class: Liliopsida – Monocotyledons
Subclass: Liliidae
Order: Liliales
Family: Dioscoreaceae
Genus: Dioscorea
Species: cayenensis, alata, rotundataetc.
(Orkwor and Asadu, 1998).
Shape of Yam Tuber
The number and shape of yam tubers vary largely between species (Huber, 1998) D.rotundata (white yam) tubers are generally large and cylindrical in shape with white flesh D. alata (water yam) tubers have variable shape, the majority being cylindrical. Tubers of D. cayenensis (yellow yam) are in many respects similar to that of D. rotundata (Ayensu, 1972). Tuber flesh is white and watery in texture.
CHAPTER THREE
MATERIALS AND METHODS
Sample collection
Rotten yam sample used in this study was kindly provided by Prof F.J.C Odibo of the Department of Applied Microbiology and Brewing.
Fungal isolation
Sabouraud Dextrose Agar was used and prepared according to the manufacturer’s specification. Bacterial inhibition was achieved using chloramphenicol at a concentration of 0.05mg/ml of the sterile medium before pouring into sterile plates (Petri dishes). Small portion of the diseased part of yam was carefully cut with a sterile knife which was properly disinfected and transferred aseptically to a mortar which was then mashed and 5ml of sterile water added. Using a sterile syringe, 2ml was taken and transferred aseptically onto solidified SDA. The plates were incubated at room temperature 37°c for 72 to 96 hours.
CHAPTER FOUR
DISCUSSION
Studies on the fungi implicated in the spoilage of yam showed that it contained population of fungi. The presence of fungi isolated from the yam showed a great concern to post-harvest loss posed by the presence of those organisms. The prevalence of fungi that brings about spoilage is due to a wide range of factors which are encountered at each stage of handling from pre-harvest to consumption and is related to the physiological and physical conditions of the produce as well as the extrinsic parameters to which they are subjected (Akintobi et al., 2011). Damage inflicted on produce at the time of harvest is a major cause of infection since most of the spoilage microorganisms invade the produce through such damaged tissues. The incidence of infection is worsened by poor sanitary practice such as cross contamination and contact infection during the transportation (Singh et al., 2002).
CONCLUSION
The fungi causing rot isolated from yam rot produced amylase and glucanse enzymes which helped them degrade the starch and sugars present in the yam for their nutrition were identified as Aspergillus species by morphological and microscopical characteristics using lactophenol cotton blue stain. Other test like screening on starch agar and carboxymethyl cellulose agar for amylase and β-glucanase respectively. They were also assayed spectrophotometrically at OD540nm using a standard concentration of glucose to get the absorbance. Aspergillus spC showed a better result for the production of β-glucanase while all the isolates were good producers of amylase. From this research, one could conclude that fungal isolates stand a better chance of producing these enzymes because they require cheap raw materials for its production and the microorganism could be genetically engineered to improve the production rate of these enzymes by them.
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