ABSTRACTS
The fermentative production of cassava (Manihot esculenta crantz) flour was done in two different methods, which were the fixed and unfixed fermentation method. The cassava tubers were harvested from the N.R.C.R.I, Umudike, peeled, washed, sliced into big bits of about 5 to 8cm in length and allowed to ferment. The microbial load, succession, pH and cyanide content of the cassava were determined during retting and after production. The results showed the presence of E.coli and Lactobacillus spp, Bacillus spp, Staphylococcus spp, Aspergillus spp, Penicillum spp, yeast, and Geotichum spp after the first day of fermentation. The dominant organisms after fermentation were Lactobacillus spp and Yeast. The Bacteria load was 1.59x105 to 0.61x105 cfu/g, fungi load of 1.10x103 to 0.40x 103 cfu/g for fixed fermented cassava flour. The unfixed had the Bacteria load of 1.64 to 0.61x 105 cfu/g and fungi load of 1.10x103 and 0.45x103 cfu/g. On the other hand, the Hydrogen cyanide content and pH decreases as the fermentation period increases in both flour. It is therefore recommended that cassava tubers should be fermented at a minimum of 48 hours as its cyanide content decreases with increase fermentation period.
TABLE OF CONTENTS
Title page i
Certification ii
Dedication iii
Acknowledgement iv
Table of Contents v
List of Figures vii
List of Tables viii
Abstract x
CHAPTER ONE
INTRODUCTION 1
1.1 Background
of Study 1
1.2 Aims and Objectives 2
CHAPTER TWO
LITERATURE REVIEW 3
2.1 Description
of Cassava 3
2.2 Habitat 3
2.3 History of Cassava 3
2.4 Physiology and Morphology of Cassava
Plant 5
2.4.1 Toxicity 5
2.4.2 Varieties 8
2.5 Cassava Processing and Utilization
8
2.6 Nutritional Composition of Cassava 13
2.7 Fermentation Technology 15
2.7.1 Methods of Fermenting Cassava to Flour 16
2.8 Health and Benefits 18
2.9 Acute and Chronic Effects of Cyanide 19
CHAPTER THREE
MATERIALS AND METHOD 21
3.1 Cassava
Roots Used 21
3.2 Sample and Media Preparation 21
3.2.1
Fixed Fermentation Method 21
3.2.2 Unfixed Fermentation Method 22
3.3 Media Preparation 24
3.4 Microbial Analysis 24
3.4.1 Determination of Microbial Load 24
3.4.2 Determination of Microbial Flora 25
3.4.3 Determination of Hydrogen Cyanide 26
3.4.4 Determination of pH 26
3.4.5 Characterization of Bacteria Isolates 27
3.5 Cultural Examination 27
3.5.1 Gram Reaction 27
3.5.2 Microscopic Features 27
3.6 Characterization of Fungi Isolates 28
3.6.1 Viable Counting of the Fungi Growth 28
3.6.2 Identification of Fungi 28
3.6.3 Colony
Features of Fungi Isolates 28
3.6.4 Microscopic Features 28
3.6.5 Identification of Isolates 29
3.7 Biochemical Tests 29
3.7.1 Oxidase Test 29
3.7.2 Coagulase Test 29
3.7.3 Citrate Test 29
3.7.4 Indole 30
3.7.5 Test for Carbohydrate 30
CHAPTER FOUR
RESULTS 31
HCN
CHAPTER FIVE
DISCUSSION,
CONCLUSION AND RECOMMEMDATON 38
5.1 Discussion
38
5.2 Conclusion 39
5.3 Recommendation 39
References 40
LIST OF FIGURES
Figure
Title Page
2.1: Metabolic pathway of Linamarin
and Lotaustralin 7
2.2:
General sequence of unit for
processing cassava roots into various products 12
3.1: Diagram
for the production of Cassava Flour 23
LIST OF TABLES
Table Title Page
2.1: Microorganism
associated with some local Fermented Foods 17
4.1: Cultural
Identification and Biochemical Characteristics of the Isolates 33
4.2: Determination of Microbial Load 34
4.3: Percentage occurrence of Bacteria 35
4.4: percentage
occurrence of Fungi Isolates 36
4.5: Determination of pH and Hydrogen Cyanide content 37
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF STUDY
Cassava
(Manihot esculenta cranzt) is a food crop of great importance for the
nutrition of over 500 million people in the tropic. Cassava roots are
potentially toxic due to presence of cyanogenic glycoside especially linamarin
(Butler, 1965). Microbial deterioration occurs in cassava roots after harvest
accompanied by physiological deterioration. The fermentation of cassava
prevents the root from rapid spoilage after harvest. Cassava roots are more
perishable than other tuber crops, such as yam and sweet potato (Poulter et al., 1995). The fermentation of
cassava roots called retting allows the reduction of potentially toxic
endogenous cyanogens, which are present in variable concentrations (300-500ppm)
and improves their palatability for further processing.
Microorganism
plays a number of roles in cassava processing either positive or negative. The
pH effects are generally regarded as part of fermentation process namely,
product preservation, flavor development, cyanide elimination etc. while the
negative effect include spoilage of cassava product and contamination by
pathogenic microorganism.
Retting
of cassava involves steeping roots in water for 3 to 4 days, during the
consequent fermentation; roots are softened (Okafor et al., 1984). In Africa, the retted roots are mainly processed
into foo-foo (cassava flour). These products provide almost 50% of the caloric
intake of the population.
To
make cassava suitable for human consumption, it is usually subjected to
different processing method, which varies from location to location. Such
method generally aims at reducing the toxicity, improving palatability and
converting the perishable fresh roots into stable product. The fermentation
process is initiated as a result of chance inoculation by microorganisms from
the environment. The presence of unspecified microorganisms complicates the
control of the fermentation process and lead to the production of objectionable
odours.
Despite
the economic importance of these processed products, most of the published work
of cassava retting as focused on the detoxification of the cyanogenic
glycosides during fermentation (Ampe, et
al., 1995). Utilization of cassava for food has been greatly affected by
the presence of cyanogenic glycosides (Linamarin). Cyanide is very poisonous
because it binds to an enzyme cytochrome oxidase and stops its action in
respiration, which is a key energy conversion process in the body. Therefore to
provide a basis for understanding the microbiology of this fermentation is
needed to improve the quality of this staple food, determine the microbial load
of the flour and to monitor the hydrogen cyanide content of the processed
flour.
1.2 AIMS AND OBJECTIVES.
The specific aims of this
research work include:
1. To
produce cassava flour by fermentation
2. To
determine the microbial succession and load of cassava during fermentation and
after production.
3. To
reduce the toxicity of the hydrogen cyanide content in cassava through
fermentation.
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