EVALUATION OF MICROBIAL SUCCESSION AND PHYSIOCHEMICAL CHANGES IN FERMENTATION OF CASSAVA FOR GARRI

ABSTRACT

The evaluation of microbial succession of Cassava for Garri processing was carried out using grated or homogenized cassava for microbial analysis. The media used were Nutrient agar for total viable count, Violet red bile agar for enumeration of Enterobacteracea, Potatoe dextrose agar for enumeration of yeast and moulds and De, man Rogosa and sharpe agar for enumeration of Lactic acid bacteria. A serial dilution was done and Pour plate method was employed, Gram staining and bio-chemical tests were used for identification of the bacteria.The total aerobic plate count for the fermenting cassava ranged from 5.4 x109 C.F.U/ML to 2.5 x 103 C.F.U/ML, for yeast and mould count 5.2 x 109 C.F.U/ML to 6.5 x 103 C.F.U/ML and Lactic acid bacteria ranged from 9.8 x 109 C.F.U/ML to 4.4 x 103 C.F.U/ML and Enterobacteracea ranged from 5.2 x 109 to 6.5 x 103 C.F.U/ML respectively. The bacteria isolated from the fermenting cassava were Lactobacillus species, Aspergellus niger, Bacillus subtilis, Corynebacterium manihot, Leuconostoc mesenteroides, Geotrichum species, Saccharomyces cerevisea. An evaluation of microbial succession done revealed that Bacillus subtilis and Lactobacillus plantarum showed the highest acid producing ability, Bacillus subtilis and Klebsiella species contributed to the fermenting of the cassava The study concluded that a large number of microorganisms are involved in fermentation of cassava.

TABLE OF CONTENT

Certification                                                                                                                            i

Dedication                                                                                                                              ii

Acknowledgement                                                                                                                  iii

Table of content                                                                                                                      iv-vi

Abstract                                                                                                                                   vii

CHAPTER ONE

1.0 INTRODUCTION                                                                                                            1

1.1 Justification of the Study                                                                                                  3

1.2 General Objectives                                                                                                           3

1.3 Aims and Objectives of the Study                                                                                    3

CHAPTER TWO

2.0 LITERATURE REVIEW

Overview on Cassava (Manihot Esculenta Crantz)                                                               4

2.2 Pest and Diseases                                                                                                              4

2.3 Economic Importance                                                                                                       5

2.4 Composition                                                                                                                     5

2.5 Toxic Compounds in Cassava                                                                                          6

2.6 Toxic Effects and Diseases Associated with Cyanide Exposure                                     9

2.7 Diseases Related To Cassava Toxicity                                                                             11

2.8 Processing into Different Products                                                                                   12

2.8.1 Garri:                                                                                                                              12

2.8.2 Fufu:                                                                                                                              13

2.8.3  Chickwangue:                                                                                                               14

2.9 Cassava Processing Techniques for Garri                                                                        14

2.9.1 Peeling                                                                                                                           15

2.9.2 Grating and Chopping                                                                                                   15

2.9.3 Drying (Sun- And Oven-Drying)                                                                                  15

2.9.4 Fermentation                                                                                                                  16

2.9.4.1 Physical and Biochemical Changes During Cassava Fermentation.                                     18

2.9.4.2 Biochemical Changes                                                                                                             19

CHAPTER THREE

3.0 MATERIALS AND METHODS                                                                                    

3.1 Study Area                                                                                                                        22

3.2 Sterilization of Materials                                                                                                  22

3.3 Fermenting Procedure                                                                                                      22

3.4 Microbiological Population Studies                                                                                 24

3.4.1 Media Used                                                                                                                    23

3.5 Isolation of Bacteria and Yeast                                                                                        23

3.6 Isolation Using Pour Plate Method                                                                                  24

3.6.1 Sub-Culturing:                                                                                                               24

3.6.2 Identification of Bacterial Isolates                                                                                24

3.6.3 Identification of Fungal Isolates                                                                                    24

3.7 Gram Staining                                                                                                                   24

3.8 Biochemical Tests                                                                                                            25

3.8.1 Catalase Test:                                                                                                                26

3.8.2    Indole Test                                                                                                                  26

3.8.3    Citrate Test                                                                                                                 26

3.8.4 Oxidase Test                                                                                                                  27

 3.8.5 Carbohydrate Fermentation Test:                                                                                 27

3.8.5 Motility Test:                                                                                                                 27

3.9 Determination of Physiocochemical Parameters                                                              27

3.9.1 _PH                                                                                                                                   28

3.9.2 Titrable Acidity                                                                                                             28

3.9.3 Cyanide Content                                                                                                            28

3.9.5 Fermentation Modulation                                                                                              29

3.9.6 Effect of Temperature                                                                                                   29

CHAPTER FOUR

4.0 RESULTS                                                                                                                         30

4.1 Microbial Counts                                                                                                              30

4.2 Microbial Succession during Fermentation of Cassava for Garri Production                   30

4.3 Identification of Organisms                                                                                              31

4.9.2 Effect of _PH, Titrable Acidity (%) and Cyanide Content on Cassava Fermentation   39

4.9.3 Fermentation Modulation                                                                                              39

Discussion                                                                                                                               40

CHAPTER FIVE

5.1 Conclusion                                                                                                                        44

References                                                                                                                              45

CHAPTER ONE

1.0 INTRODUCTION

Cassava, Manihot esculenta Crantz, is an important root crop in Africa, Asia, South America and India Padmaja, (1995). Cassava is a staple food for at least 500 million people in the tropics Bradbury, (2006) that provides carbohydrates, or energy. It counts as a higher producer of carbohydrates per hectare than the main cereal crops and can be grown at a considerably lower cost Taiwo, (2006). The percentage of dry mater (starch content) in the harvested root is an important criterion of quality both for human consumption and for processing uses. 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 & Mings, (2006).

Additionally, the roots contain considerable quantities of antinutrient factor cyanide. Cyanides occur in cassava in the form of two cyanogenic glucosides, linamarin and a small amount of methyllinamarin – lotaustralin – located inside the plant cells together with a specific hydrolytic enzyme, linamarase, located in the cell wall Bradbury, (2006). However, under normal conditions, they are separated from the substrate. Any process that ruptures the cell walls will bring the enzymes into contact with the glycosides and will thus release free cyanide and reduce the glycosides‟ content of the final product. Based on the amount of cyanides in the cassava roots, cassava has been classified into “bitter” – and “sweet” – cassava. Thus the sweet varieties can be eaten boiled while the bitter varieties have to be processed before it can be consumed Tewe, (1992).

The various fermentation processes have been broadly categorized into submerged fermentation process, which involves the soaking of the roots under water as in fufu production (retting), and the solid fermentation process, which does not involve soaking as in the garri production (garifying)  Oyewole, (2001). Traditionally, cassava roots are processed in a number of ways that vary from region to region. The processing methods involve several steps including peeling, soaking, grinding, steeping in water or in the air to allow fermentation to occur, drying, milling, roasting, steaming, pounding, and mixing in cold or hot water Taiwo, (2006). A very popular processing method in Nigeria is grating of the peeled cassava tubers and dewatering for 1-3 days during this period, fermentation occurs and then the fermented product is sieved and roasted in a hot open pan (garified). The different techniques of processing cassava roots have one common goal: the reduction of cyanogenic compounds in order to obtain a safe food. All the traditional processes for processing cassava permit the enzyme linamarase to interact with cyanogenic compound to release HCN (hydrocyanic acid). The HCN then dissolves in water or escapes into the air. However, it is often impossible to remove all the cyanogenic compounds through processing.

Cassava toxicity in humans is a well-documented problem. Cassava tubers vary widely in their content of cyanogenic glycosides, although the normal range of cyanogenic glycoside content is from 15 to 400 mg HCN/kg fresh weight. Cyanide doses up to 50 to 100mg/kg fresh peeled tuber are reported to be moderately poisonous to adults whereas over 100mg HCN/kg fresh peeled tuber is dangerously poisonous Alloys and Ming, (2006). Several diseases are associated with the consumption of inadequately processed cassava roots, such as hypergoitre, tropical ataxic neuropathy, epidemic spastic paraparensis Tewe, (1992) and konzo, Bradbury, (2006). Sublethal doses of cyanogenic compounds are usually detoxicated in the body by conversion to thiocyanate, a sulphur-containing compound with goitrogenic properties if in excess, which is excreted in the urine Tewe, (1992). A chronic overload of thiocyanate in conjuction with low iodine intake, however, results in goiter and, in extreme cases, in cretinism in children (Oke, 1994).

Garri is a creamy white granular cassava based grit, produced from fermented cassava by dewatering the grated cassava for 1-3days, it is a staple food in many communities in Africa Akinrele et al. (1985) and could be eaten as snacks with coconut, groundnut or sugar, or it could be prepared into semi-solid meal with hot water called eba and eaten with varieties of soup. Garri is by far, the most popular form in which cassava is consumed in Nigeria and other African countries Ihekoronye and Ngoddy. (1985).

1.1 Justification of the Study

Cassava is a traditionally fermented food and  contributes substantially to the daily diets. These indigenous food is locally prepared in small scale, in village homes; and its quality depends on the skill of the household occupants, as inherited over years. The study will focus on microbial evaluation of microbial succession and physiochemical changes in fementation of cassava for garri.

1.2 General Objectives

To evaluate the microbial succession and physiochemical changes in fermentation of cassava for garri

1.3 Aims and Objectives of the Study

To isolate microorganisms from cassava during fermentation for garri processing

To identify and characterize microorganisms from cassava during fermentation for garri processing

To determine physical parameters of the fermenting material (Cassava)

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