REDUCTION OF HCN LEVEL IN CASSAVA (Manihot esculenta Crantz)

LEAVES BY OPTIMIZED HEATED AIR DRYING

HAZEL ASPA CASIMINA

SUBMITTED TO:THE FACULTY OF THE AGRICULTURAL AND BIO-PROCESS DIVISION

INSTITUTE OF AGRICULTURAL ENGINEERING COLLEGE OF ENGINEERING AND AGRO-INDUSTRIAL TECHNOLOGY

UNIVERSITY OF THE PHILIPPINES LOS BAÑOSIN PARTIAL FULFILLMENT OF THE

REQUIREMENTS FOR THEDEGREE OF

BACHELOR OF SCIENCE IN AGRICULTURAL ENGINEERING(Specialized in Agricultural and Bio-Process Engineering)

APRIL 2010

TABLE OF CONTENTS

CONTENTS PAGE

TITLE PAGE

ACCEPTANCE SHEET i

BIOGRAPHICAL SKETCH ii

ACKNOWLEDGEMENT iii

LIST OF FIGURES iv

LIST OF TABLES v

ABSTRACT vi

INTRODUCTION

Background of the Study 1

Significance of the Study 3

Objectives of the Study 7

Time and Place of the Study 7

Scope and Limitations of the Study 8

REVIEW OF LITERATURE 9

Cassava Production 9

Cassava Uses 10

Nutritional Composition of Cassava 11

Nutritional Value of Cassava Leaves 15

Toxicity of Cassava 15

Cassava Varieties 17

Drying: Its Importance and Theory 18

Factors to be considered in Drying 19

Drying Temperature 19

Air Properties 19

Air Flow Rate 20

Relative Humidity 20

Nutritional Value 20

Present Drying Practices 21

Heated Air Drying 21

Box and Behnken Design 21

Colorimetric Method of Chemical Analysis 22

MATERIALS AND METHODS 24

Materials and Equipment 24

Procedure 25

Procurement and Selection of Cassava Leaves 25

Preparation of the Samples 25

Initial Moisture Content Determination 26

Conditioning of the Laboratory Dryer 27

Determination of Drying Air Velocities 27

Drying Procedure 28

Calculation of Response Parameters 29

Final Moisture Content 29

Drying Rate 30

Moisture Ratio 30

Experimental Design 31

Statistical Analysis 33

HCN Level Content Evaluation of Dried Cassava Leaves 34

RESULTS AND DISCUSSIONS 35

Drying Rate 35

Moisture Ratio 36

Dynamic Equilibrium Moisture Content 37

Analysis of the Effects of the Drying Parameters on the Response Variables 38

Response Surface Regression Optimization 43

Verification of the Optimum Conditions for Drying 45

Thin Layer Modeling for Drying Cassava Leaves 46

SUMMARY AND CONCLUSION 65

RECOMMENDATIONS 66

REFERENCES

APPENDICES

Appendix A. Table of Sample data Sheets

Appendix B. Initial Moisture Content Data

Appendix C. Drying Data

Appendix D. The SAS Program Output

LIST OF FIGURES

FIGURE TITLE PAGE

1 Fresh cassava (Manihot eculentaesculenta Crantz) leaves 3

2a Spectrophotometer used for the colorimetric methodof HCN analysis 23

2b Samples to be placed in the spectrophotometer 23

3 Cassava plantation at the Institute of Plant Breeding 25Los Baños, Laguna

4 CarboliteTM Convection Oven 26

5 Initial and Final appearance of the sample inside the oven 27

6 Cassava leaves in trays after placed inside the dryer 29

7 Average Drying Rate of 15 Drying Treatments 35

8 Average Moisture Ratio of 15 Drying Treatments 36

9 Plot of responses at optimum conditions and desirability 44

10 Moisture Ratio vs. Drying Time of Drying Run 1 using (a) Best Fit Model and (b) Exponential Model 51

11 Moisture Ratio vs. Drying Time of Drying Run 2 using (a) Best FitModel and (b) Exponential Model 52

12 Moisture Ratio vs. Drying Time of Drying Run 3 using (a) Best Fit Model and (b) Exponential Model 53

13 Moisture Ratio vs. Drying Time of Drying Run 4 using (a) Best Fit Model and (b) Exponential Model 54

14 Moisture Ratio vs. Drying Time of Drying Run 5 using (a) Best Fit Model and (b) Exponential Model 55

15 Moisture Ratio vs. Drying Time of Drying Run 6 using (a) Best Fit Model and (b) Exponential Model 56

11 Moisture Ratio vs. Drying Time of Drying Run 7 using (a) Best Fit Model and (b) Exponential Model 57

12 Moisture Ratio vs. Drying Time of Drying Run 8 using (a) Best Fit Model and (b) Exponential Model 58

13 Moisture Ratio vs. Drying Time of Drying Run 9 using (a) Best Fit Model and (b) Exponential Model 59

14 Moisture Ratio vs. Drying Time of Drying Run 10 using (a) Best Fit Model and (b) Exponential Model 60

15 Moisture Ratio vs. Drying Time of Drying Run 11 using (a) Best Fit Model and (b) Exponential Model 61

16 Moisture Ratio vs. Drying Time of Drying Run 12 using (a) Best Fit Model and (b) Exponential Model 62

17 Moisture Ratio vs. Drying Time of Drying Run 13 using (a) Best Fit Model and (b) Exponential Model 63

18 Moisture Ratio vs. Drying Time of Drying Run 14 using (a) Best Fit Model and (b) Exponential Model 64

19 Moisture Ratio vs. Drying Time of Drying Run 15 using (a) Best Fit Model and (b) Exponential Model 65

20 Plot of MR against time for Run 3 that represented the best model equation 66

LIST OF TABLES

TABLE TITLE PAGE

1 Complete chemical composition of cassava crop 11

2 Nutritional content of some vegetables and staple foods 15

3 Air Velocity Determination 28

4 Coded values for the independent and dependent parameters. 31

5 Combination of independent parameters for 15 drying runs 32

6 Summary of the experimental data showing the independent variables used and response variables. 37

7 Significance of the effect of the drying parameters on the response variables by ANOVA 38

8 ANOVA showing the independent parameters as a linear, quadratic or interaction terms on each of the response variables. 40

9 Regression Coefficients of the second order polynomials illustrating the relations between the response and independent parameters. 42

10 Predicted responses at optimum conditions of independent parameters 44

11 Summary of the responses observed and verified using the optimum drying conditions 45

12 Regression Models for 15 Drying Runs 46

13 Initial and final HCN content (ppm) of cassava leaves after drying application. 68

ABSTRACT

CASIMINA, HAZEL A., University of the Philippines Los Baños, MARCH 2010. Reduction of HCN Content Level in Cassava ( Manihot esculenta Crantz) Leaves by Optimized Heated Air Drying.

Adviser: Dr. Engelbert K. Peralta

The study dealt with the reduction of hydrocyanide (HCN) content in cassava leaves at the optimum drying conditions obtained through heated air drying. In drying, the Box and Behnken experimental design with 15 experimental test runs was used with temperature (50°C, 60°C and 70°C), air flow rate (0.09 m3/s, 0.075 m3/s and 0.06 m3/s) and tray loading density (100g/tray, 200g/tray, and 300g/tray) as the independent parameters. The experiment investigated the effects of the independent parameters to the response parameters that included the (1) dynamic equilibrium moisture content, (2) moisture ratio and (3) drying rate.

Analysis of Variance (ANOVA) showed that the drying temperature significantly affected the EMC, the drying rate and the moisture ratio at 95% level of confidence; the loading density significantly affected the EMC and drying rate at 95% level of confidence; whereas the air flow rate only had significant effect on the EMC. In addition, regression fitting that adequately described the experimental drying resulted in a polynomial model in the form of:

MR = 1.2565606 – 0.018566653t + 0.000102176t2 – 2.46x10-7t3

The drying experimental results showed an optimum condition of drying cassava leaves at 70°C for drying temperature, 0.06m3/s for air flow rate and 150g/tray for the loading. At this particular optimum condition, the predicted values for the EMC, moisture ratio and drying rate were 23.46%, 0.28 m3/s and 1.13 %db/min, respectively, with a desirability of 76%. The actual values of the response parameters were compared with the predicted values at optimum conditions with deviations ranging from 0.0013 to 0.278.

Three (3) additional runs were conducted to verify the results of the obtained optimum conditions. The dried product of the three runs which used the optimum conditions were subjected to colorimetric method for HCN analysis. Based on the result, a 91.05 – 91.8% removal of HCN was obtained, which gave a low percentage of HCN remained in the leaves.