ABSTRACT

The  eyanogenic, potential of processed and unprocessed roots of two new cassava cultivars TME 41 9 and TMS 98/0505 was studied using spectrophotometric and enzymatic methods. Partial purl licUlioli and some PrOPCr1ieS ol the 3-g1ucosidasc from these cassava cultivars were also determined. These cultivars are planted and distributed to farmers by N RCR I. Umudike but have not been assessed for cyanogenic potential under their new climatic environment. The cyanogcnic potential of the root pulp in their unprocessed form ranged from 40.0 ± 0.2 to 60.0 ± 0.3 mgCNKg, while processing into garri and oven drying of the chips resulted in cyanogenic potential of 0.29±0.01 mgCNKg' for TME 419 cultivar and 0.2 1±0.05 mgCNKg for TMS 98/0505 cu1tivar for garri and 36.06 for TME 419 and 34.16 br TMS 98/0505 respectively for the chips. The protein content of the partially purified enzyme from these cuitivars gave 0.046mg/mi and 0.069mg/mi while mathematical analysis of the data from the degradation of Linamarin by the partially purified enzyme generated FICN values that were used to construct Line Weaver Burk plot that gave apparent Km and Vmax values of 21.7mM and 5.0 x 10.2 imol FICN/ml for TME 419 and 15.6mM and 4.9 x 10.2 jimol I-ICN/ml for TMS 98/0505 cultivars. The partially purified enzyme showed high degree of hydrolysis towards standard linamarin and cyanogenic gi ucosides of the new cassava cultivars.

TABLE OF CONTENTS

Title Page

Certification ii

Declaration iii

Dedication iv

Acknowledgment v

Table of content vi-x

List of tables xi

List of figures xii

Abbreviations xiii

Abstract xiv

CHAPTER 1

1.1 Introduction 1

1.2 Justification 2

1.3 Aim of the study 3

1.4 Scope of the study 3

CHAPTER 2

2.1 Literature review 4

2.2 Basic studies on the cyanide liberation system 5

2.2.1 Cyanogenic glucosides 5

2.2.2. Biosynthesis of cyanogenic glucosides in cassava 5

2.3 Linamarase 8

2.3.1 Characteristics of linamarase 8

2.4 Toxicity studies of cassava 8

2.4.1 Detoxification mechanisms for HCN in animal 9

2.5 Pharmacology of cyanogenic glucosides 9

2.6 Health implications of cyanide toxicity 10

2.7 Goitre, Konzo, and Cassava Consumption in Nigeria 10

CHAPTER 3: Materials and Methods

3.1 Apparatus and Equipments 12

3.1.1 Reagents 12

3.2 Preparation of reagent 12

3.2.1 0.2M Sodium hydroxide 12

3.2.2 0.5% Chloramine 12

3.2.3 0.1M Orthophosphoric acid 12

3.2.4 0.1M Phosphate Buffer pH 6.0 13

3.2.5 Acetate Buffer PH5.5 13

3.2.6 Colour developer 13

3.2.7 Potassium cyanide standard preparation 13

3.3 Sources of the cassava 14

3.4 Extraction and purification of 3- glucosidase 15

3.5 Determination of partially purified B- glucosidase activity (linamarase) 15

3.6 Protein determination 16

3.7 Preparation for cyanide analysis 17

3.7.1 Cassava pulp 17

3.7.2 Cassava peel 17

3.7.3 Cassava leaves 17

3.7.4 Cyanide determination 17

3.7.5 Assay for total cyanide 17

3.7.6 Assay for free cyanide 18

3.7.7 Cyanogenic potential of cassava extracts 18

3.7.8 Cassava chips preparation 21

3.7.9 Determination of glucosidic cyanide in cassava chips 21

3.8 Statistical analysis 21

CHAPTER 4: Results

4.1 Degradation of linamarine by the partially purified B- glucosidase and

cyanide production values from TMS 98/0505 22

4.2 Degradation of linamarin by the partially purified B- glucosidase and the

cyanide produation values from TME 419 23

4.3 Kinetic properties 26

4.4 Nitrogen content of TME 419 and TMS98/0505 27

4.4.1 protein determination 28

4.5 The kinetic properties of cassava B- glucosidase 29

4.6 Determination of free and total cyanide content (cyanogenic potential) in

fresh cassava peel, pulp and leaves for TME 419 29

4.7 Determination of free and total cyanide content (cyanogenic potential) in

fresh cassava peel, pulp and leaves for TMS 98/0505 30

4.8 Determination of glucosidic and non glucosidic cyanide concentration of

processed TME 419 and TMS 98/0505 cultivars 30

4.9 Concentration and percentage loss of glucosidic cyanide in dry cassava chips

of TME 419 and TMS 98/0505 31

CHAPTER 5: Discussion

5.1 Cyanogenic potential of two new cassava cuftivars 35

5.2 'Properties of the partially purified enzyme 37

Conclusion 39

Recommendation 40

References 41

Appendix 45