MICROBIOLOGICAL FERMENTATION FOR CYANIDE REDUCTION IN CASSAVA TUBERS

ABSTRACT

The white and yellow varieties of the cassava (manihot esculenta) tubers were subjected to a four days fermentation and studied for cyanide content and microorganisms involved in their fermentation process. The microorganisms isolated during the fermentation process include: Staphylococcus aureus, Escherichia coli, Bacillus spp, Lactobacillus spp, Enterobacter spp, Aspergillus spp, Candida spp, and Saccharomyces spp. The physiochemical and the proximate analysis of the cassava roots were carried out. During the fermentation there was reduction in the cyanide content from (9.24±0.01 to 2.93±0.02)mg/100g in yellow cassava and (9.85±0.03 to3.15±0.04)mg/100g in white cassava, indicating that fermentation reduces the cyanide content of cassava. There was a decrease in the pH from (6.20 to 3.38) in yellow cassava and (6.40 to 3.14) and increase in the titratable acidity from(0.02% to 0.06%) in yellow cassava and (0.03% to 0.07%) in white cassava during fermentation indicating that the fermentation took place in an acid medium as a result of the predominance of Lactobacillus spp. The proximate analysis showed that there was significant increase in the protein from (0.72 to 1.86) in yellow cassava and (0.56 to 1.83) in white cassava. There was also a significant increase in moisture content from (69.42±0.01 to 72.42±0.01) in yellow cassava and (67.65±0.01 to70.24±0.01) in white cassava and the fiber content of the cassava roots while there was a decrease in the ash and carbohydrate content of the cassava from (27.90±0.01 to 21.43±0.01) in yellow cassava and (28.40±0.00 to 23.61±0.01) in white cassava. It is obvious that from the findings that microorganisms are involved in cassava fermentation and the cyanide content of the cassava can be considerably reduced by the process of fermentation thereby making the food safe for consumption.

TABLE OF CONTENTS

Title page                                                                                                                         i

Certification                                                                                                                          ii

Dedication                                                                                                                               iii

Acknowledgement                                                                                                         iv

Table of contents                                                                                                                 v

List of tables                                                                                                                  vi

Abstract                                                                                                                                  vii

CHAPTER ONE

1.1       Introduction                                                                                                                      1

1.2       Objective of study                                                                                                      3

CHAPTER TWO

2.0       Literature Review                                                                                                                  4

2.1       Cassava                                                                                                                                 4

2.2       Description of cassava                                                                                                           4

2.3        Botany and cultivation                                                                                                          5

2.4        Nutritional status of cassava                                                                                      5

2.5        Anti nutritional components of cassava                                                                    5

2.6        Composition of cassava                                                                                            6

2.7        Cassava spoilage                                                                                                       6

2.8        Cassava and cyanide                                                                                                 7

2.9        Cyanide                                                                                                                              8

2.10      Cassava processing                                                                                                    9

2.10.1   Why is cassava processed                                                                                                    9

2.10.2    Effects of cassava processing on cyanide level                                                        10

2.10.2.1 Peeling                                                                                                                      10

2.10.2.2 Grating                                                                                                                             10

2.10.2.3 Soaking                                                                                                                10

2.10.2.4 Boiling and cooking                                                                                                 11

2.10.2.5  Drying                                                                                                                    11

2.11      Cassava products                                                                                                      11

2.11.1    Gari                                                                                                                           12

2.11.2    Lafun                                                                                                                         12

2.11.3    Fufu                                                                                                                           12

2.11.4    Abacha                                                                                                                      13

2.11.5    Tapioca                                                                                                                     13

2.12       Toxic effects from cassava cyanogens                                                                     13

2.13       Reduction of cyanide in cassava                                                                            14

2.14       Fermentation                                                                                                             14

2.14.1    Microorganisms involved in cassava fermentation                                                  16

2.14.2    Role and function of fermentation on cassava food                                                           17

2.14.2.1 Aroma and flavor change                                                                                         17

2.14.2.2 Cassava fermented food preservation                                                                       18

2.14.2.3 Anti nutrient decrease in cassava fermented food                                                    18

2.14.2   Cyanide reduction in cassava fermented food                                                                  19

CHAPTER 3

3.0      Materials and Method                                                                                                20

3.1      Collection of samples                                                                                                   20

3.2      Preparation of sample for fermentation                                                                     20

3.3       Cyanide determination                                                                                                20

3.4       Microbiological analysis of sample                                                                   21

3.4.1    Media used and their preparation                                                                               21

3.4.2    Serial dilution                                                                                                           21

3.4.3    Inoculation                                                                                                      21

3.4.5    Total viable count                                                                                              22

3.4.5    Gram stain                                                                                                                22       

3.4.6     Biochemical test                                                                                               23

3.4.6.    Catalase test                                                                                                             23

3.4.6.2  Coagulase test                                                                                                          23

3.4.6.3  Citrate utilization test                                                                                                23

3.4.6.4   Methyl red test/VP                                                                                                 24

3.4.6.5   Oxidase test                                                                                                      24

3.5         Proximate analysis of cassava                                                                                  24

3.5.1     Moisture content determination                                                                        24

3.5.2     Ash content determination                                                                                       25

3.5.3     Fat content determination                                                                                        26

3.5.4    Carbohydrate determination                                                                                    26

3.5.5    Protein determination                                                                                                 27

3.6       Determination of titratable acidity                                                                            28

3.7       Determination of pH                                                                                                 28

3.8       Preparation of fufu                                                                                                                 29

3.9       pH determination of the fufu sample                                                                                    29

CHAPTER FOUR

4.1       Results                                                                                                                        30

4.1       Microbial counts                                                                                                         30

4.2       Occurrence of microorganisms during fermentation                                                      30

4.3        Physiochemical composition                                                                                     30

4.4       Proximate composition                                                                                               31

CHAPTER FIVE

5.1       Discussion                                                                                                                             41

 5.2      Conclusion                                                                                                                  46

5.3       Recommendation                                                                                                        46

References                                                                                                                 

LIST OF TABLES

Table                     Title                                                                                                     Page

1:   Biochemical and sugar fermentation characteristics of bacterial isolates.                       32

2:   Morphology and Identification of fungal isolates (cfu/ml).                                           33

3:   Total bacterial and coliform count (cfu//ml).                                                             34

4:   Total fungal counts.                                                                                                    35

5:   Percentage occurrence of microbial isolates during cassava retting.                          36

6:   Microbial succession at the different fermentation periods.                                          37

7:   Physiochemical composition.                                                                                   38

8:   pH of fufu samples                                                                                                      39    

9: Proximate analysis.                                                                                                       40

CHAPTER ONE

1.1  Introduction

Cassava (Manihot esculenta) is an extensively cultivated river crop and a staple food for millions of people in the tropical regions of Africa, Latin America and Asia. Globally, in terms of annual production, it is the fifth most important food crop after maize, rice, wheat and potato (FAOSTAT, 2011).

            The tuber consists of 20 to 25% starch but very limited quantities of proteins, fats, vitamins and Minerals. Traditionally Cassava roots are processed in a number of ways that vary region to region leading to many different products like gari, fufu, lafun, farinha, pande, yucca etc. Despite all the usefulness of cassava, its use as food source is limited by its perishability, its low protein content and its potential toxicity. Cassava roots are potentially toxic due to the presence of cyanogenic glycosides, linamarin and a small amount of lotaustralin which are catalytically hydrolyzed to release toxic hydrogen cyanide (HCN) when the plant tissue is crushed. Disintegration of the tissue structure results in contact of linamarin with linamarase which is located in the cell walls and subsequent hydrolysis to glucose and cyanohydrins which is easily broken down to ketone and HCN (Seri et al., 2013).

            Hydrolysis and subsequent removal of liberated HCN takes place during various processing stage. Most processing techniques have been developed in different parts of the world to reduce the HCN content to an acceptable level. The processing methods could lead to reduce the cyanide content in cassava products to improve its palatability and convert it into a storable form (Onwuamanam et al., 2010). Traditional technologies have been developed in Africa to eliminate cyanide in cassava, such that they are safe for man and animal consumption. These technologies have fermentation as basis for operation. The use of pure cultures of microorganisms such as saccharomyces spp and lactobacillus spp or combinations of these had been reported to cause a substantial decrease in cyanogenic glycosidic content. Processing steps can include soaking, fermentation, cooking, steaming, chipping, drying and roasting in varying order. Through controlled fermentation, micro flora could be made in large numbers in the mash, thus increasing the protein content of cassava products

In Nigeria as in most African countries, cassava roots are processed into different products as a means of preservation due to their perish ability. Physiological deterioration occurs in cassava roots, 2-5 days after harvesting followed by microbial deterioration 3-5 days later (Victor and Chidi, 2010).

Fermentation has been viewed as a dynamic process during which several catabolic and anabolic reactions depending on the several factor including substrate, microflora and environmental. Food fermentations involve the use of microorganisms and enzymes for the production of foods with distinct quality that are quite different from the original agricultural raw material. Fermentation enhances the nutrient content of foods through the biosynthesis of vitamins, essential amino acids and protein.

            The consumption of cassava and its derived products which contains large amounts of HCN may be responsible for such visible manifestations as goiter and cretinism, tropical ataxic neuropathy and konzo (Cardoso et al., 2005).

            One potential problem in processed cassava roots is flavor of the product which may be undesirable to many people. However, any process that ruptures the cell walls will brings the enzyme in contact with the glycosides and will thus release cyanide and reduce glycosides content of the final point. Unhydrolysed cyanide remaining in cassava roots after fermentation can constitute a health problem for the consumers (Nartley, 2010).

1.2 Objectives of Study

1.     To isolate and identify microorganisms associated with cassava fermentation.

2.     To determine the effect of fermentation on the cyanide content of the cassava tuber.

3.     To determine the effect of fermentation on the proximate composition of cassava.

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