ABSTRACT
The enzymatic potentials of microorganisms isolated from retting cassava were evaluated for the purpose of cellulase and amylase activities. Cassava tubers of 12 months old were collected from 3 different sources: Ahieke, Ndoru, Umudike, Awawom and Umuariga in Abia State. They were hand peeled, cut into cylinders, washed, submerged into water and allowed to ret. After retting a dilution of the retted tubers was inoculated into different media plates: De-Man Rogosa Sharp agar, Sabouraud Dextrose agar, Nutrient agar, Mannitol salt agar and MacConkey agar. Thirty- Five (35) isolates were identified in the retting cassava samples which were bacteria 25(71.43%) and fungi 10 (28.57%). The bacterial isolates identified include Bacillus subtilis, Escherichia coli, Staphylococcus aureus, Lactobacillus spp and Proteus spp while fungi isolated were Aspergillus niger, Rhodotorula spp and Saccharomyces cerevisiae. The total viable counts of the isolates increased as the retting hours increased. Lactobacillus spp and Saccharomyces cerevisiae dominated the later stage of the fermentation. Bacillus subtilis has the highest percentage occurrence 8(22.9%) while Rhodotorula spp has the lowest percentage occurrence 2(5.7%). The production of amylase enzyme was recorded with all the isolates with the exception of Staphylococcus aureus. Production of cellulase and pectinase enzymes was selective among the isolates. Results from this study shows that enzymes like amylase, pectinase and cellulase from microorganisms played an important role in retting of cassava tubers
TABLE OF CONTENTS
Title
Page i
Certification
ii
Dedication
iii
Acknowledgements
iv
Table
of Contents v
Lists
of Tables viii
List
of Figures ix
Abstract
x
CHAPTER ONE
1.0 Introduction 1
1.1 Aim and Objectives 2
1.2 Objectives 2
CHAPTER TWO
2.0 Literature Review 3
2.1 Fermentation 3
2.2 Cassava Fermentation 4
2.2.1 Submerged Fermentation 5
2.3 Physical and Biochemical Changes
during Cassava Fermentation 5
2.3.1 Physical Changes 5
2.3.1.1 Dry Matter 5
2.3.1.2 Softening of the Roots 6
2.3.2 Biochemical Changes 6
2.3.2.1 pH 6
2.3.2.2 Titrable Acidity 7
2.3.2.3 Organic
Acid 7
2.3.2.4 Vitamins and Minerals 7
2.3.2.5 Fiber 7
2.3.2.6 Sugar and Starch Content 8
2.4 Microbiology of Cassava
Fermentation 8
2.5 Cassava Retting 10
2.6 Microbial Community of Cassava
Retting 11
2.7 Enzymes Involved In
Detoxification and Root Softening During Cassava Retting 13
2.7.1 Amylase
13
2.7.2 β-Amylases 14
2.7.3 Hemicellulases 14
2.7.4 Pectinases 16
CHAPTER THREE
3.0 Materials and Methods 17
3.1 Sample Collection
17
3.2
Media Used 17
3.3 Sterilization 17
3.4
Sample Processing and Retting Procedure 17
3.6 Microbial Enumeration and Analysis 18
3.7
Identification and Characterization of Isolates 18
3.7.1 Gram staining 19
3.7.2 Motility Test 19
3.8 Biochemical and Cultural
Characteristics 20
3.8.1 Catalase test 20
3.8.2 Coagulase Test 20
3.8.3
Citrate Test 20
3.8.4 Indole Test 21
3.8.5 Methyl Red Test 21
3.8.6 Oxidase Test 21
3.8.7 Urease Test 22
3.8.8 Voges-proskaeur Test 22
3.8.9 Hydrogen Sulphide Test 23
3.8.10 Sugar
Fermentation Test 23
3.9 Identification of Fungal
Isolates 24
3.11 Determination of Activities of
Microbial Enzymes during Cassava Retting
24
3.11.1 Screening for Enzyme
Production 24
3.11.2 Production of cellulase
enzyme 25
3.11.3 Screening of isolates for the
pectinase activity 25
CHAPTER FOUR
4.0 Results 26
CHAPTER FIVE
5.0
Discussion, Conclusion And Recommendation 36
5.2 Conclusion 38
5.3 Recommendation 38
LIST OF TABLES
Table Title
Page
1.
Identification and characterize of
bacterial Isolate from retting cassava samples 27
2. Identification
and characterization of fungal isolates 29
3. Total viable
count 31
4. Percentages Occurrence of bacteria
Isolates from the Retting Cassava Samples 33
5. Enzymatic
activities of isolates from cassava retting
(mm) 35
CHAPTER ONE
1.0 INTRODUCTION
Cassava (Manihot esculenta crantz) is a potential shrub with an edible
starchy root, which grows in the tropical and sub-tropical areas of the world
(Burell, 2013). It is one of the staple foods consumed in Africa and other
parts of the world. It was estimated that the crop provides about 40% of all
the calories consumed in Africa and ranks second only to cereal grains as the
chief source of energy in Nigerian diet (Roger , 2014). The tuber consists of
64-87% starch depending on the stage of the growth or maturity of the tuber but
very limited quantities of protein, fats, vitamins, and minerals (Alloys and
Ming, 2016). The roots contain considerable quantities of anti-nutrients
factors, cyanogenic glucoside. The cyanogenic potential of cassava is by far
the single factor that adversely constraints the use of cassava as food and
feed for animals. This is as a result of the toxic effect of cyanide on humans
and animals that rely on cassava as food. Cassava has bitter and sweet
varieties. The presence of cyanogenic compounds which predominates in bitter
varieties and processes to reduce them were recently reviewed by (Montagnac et al., 2009).
Different processing techniques are
used to reduce cassava toxicity and selected antinutrients such as, boiling,
drying, steaming, baking, frying, soaking, fermentation, steam distillation,
etc. Fermentation is the common method of cassava processing and through it,
cassava can be processed into different food products such as Fufu, garri,
Lafun, chikwangue, etc. Cassava retting (fermentation) is a technique involving
long soaking of cassava roots in water to affect the breakdown of tissues.
Retting is one of the simplest and lactic acid fermentation process for the
processing of cassava tubers into various African staple foods. It simply
involves steeping of cassava roots in water until they soften. However, this
takes about three to four days under optimal condition. In other conditions
retting may take considerable longer for example, tubers older than 24months or
during the colder seasons of the year. During the consequent fermentation,
roots are softened by the activities of microorganisms producing various
enzyme, the endogenous cyanogenic glycosides (linamarin and lotaustralin) are
subsequently hydrolyzed to glucose and cyanohydrins, which easily break down to
ketone and hydrogen cyanide (HCN) and
characteristic flavour developed through a pH decrease and organic acid
production (Ampe and Brauman, 2014). The
fermentation process (retting) is characterized by the activities of certain
microorganisms which produces enzyme such as pectinases, amylase, etc resulting
in the breakdown of cassava tissues. The presence of unspecified microorganisms
complicates the control of the fermentation process and lead to the production
of objectionable odours (Achi and Akomas, 2016)
1.1 AIM AND OBJECTIVES
The aim of this study is to
determine microorganisms associated with cassava retting and their enzymatic
activities.
1.2 OBJECTIVES
- To isolate microorganisms associated with
cassava retting.
- To identify and characterize
microorganisms associated with cassava retting.
- To determine the enzymatic
potentials of microorganisms associated with cassava retting.
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