DEVELOPMENT OF ELECTROCHEMICAL METHOD FOR THE DETERMINATION OF AZO DYES BASED

COLORANTS IN FOOD AND BEVERAGE PRODUCTS

ROVINA KOBUN

THESIS SUBMITTED IN FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF

PHILOSOPHY

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UNNEFSfTI MALAYSIA SABAH

BIOTECHNOLOGY RESEARCH INSTITUTE UNIVERSITI MALAYSIA SABAH

2018

DECLARATION

I hereby declare that the material in this thesis is of my own effort, except for

quotations, excerpts, equations, references and summaries, which have been duly

acknowledged and cited clearly its sources.

22 March 2018

Rovina Kobun

DZ1511001T

11

UNIVERSITI MALAYSIA SABAH

BORANG PENGESAHAN STATUS TESIS

JUDUL DEVELOPMENT OF ELECTROCHEMICAL METHOD FOR THE DETERMINATION OF AZO DYES BASED COLORANTS IN FOOD AND BEVERAGE PRODUCTS

IJAZAH DOKTOR FALSAFAH (BIOTEKNOLOGI)

Saya ROVINA KOBUN, Sesi pengajian 2015-2018mengaku membenarkan tesis Doktoral ini disimpan di Perpustakaan Universiti Malaysia Sabah dengan syarat-syarat kegunaan seperti berikut: -

1. Tesis ini adalah hak milik Universiti Malaysia Sabah. 2. Perpustakaan Universiti Malaysia Sabah dibenarkan membuat salinan

untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan

pertukaran antara institusi pengajian tinggi. 4. Sila tandakan (/)

0 F-1

F

SULIT (Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA 1972)

TERHAD (Mengadungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)

TIDAK TERHAD

NURULAIN BINTILSueu .. PU ýqýWW KÄNAN"ien, LAYSIA SABAII

(Tandatangan pustakawan) DZ1511001T

Tarikh: 22 Mac 2018

(Prof. Dr harifudin Md Shaarani) Penyelia Bersama

CERTIFICATION

NAME ROVINA KOBUN

MATRIC NO DZ1511001T

TITLE DEVELOPMENT OF ELECTROCHEMICAL METHOD FOR

THE DETERMINATION OF AZO DYES BASED

COLORANTS IN FOOD AND BEVERAGE PRODUCTS

DEGREE DOCTOR OF PHILOSOPHY (BIOTECHNOLOGY)

VIVA DATE 01 MARCH 2018

CERTIFIED BY;

1. SUPERVISOR

Assoc. Prof. Dr. Md. Shafiquzzaman Sidiqquee Signature

J-

fý / v

2. CO-SUPERVISOR

Prof. Dr. Sharifudin Md Shaarani Signature

III

ACKNOWLEDGEMENT

First and foremost, I would like to express my gratitude to the almighty God for giving

me the strength, patience and good health to go through all obstacles in order to

complete this PhD journey in banner "Development of Electrochemical Method for

the Determination of Azo Dyes Based Colorants in Food and Beverage Products".

Then, I would like to express my deepest gratitude and appreciation to my helpful

supervisor, Assoc. Prof. Dr. Md. Shafiquzzaman Siddiquee and my co-supervisor, Prof. Dr. Sharifudin Shaarani, for all their advices, guidance, encouragement and

constant support in this research work that lead to the completion of thesis on time.

The supervision and support that they gave truly help the progression and

smoothness of this research. The co-operation is much indeed appreciated.

Deepest thanks and appreciation to my family for supporting in all aspect and truly motivate me to finish this research. My grateful thanks also go to Mdm.

Samsidar Anwar and UMS Biosensor team, for giving me the necessary guidance and

assistance throughout my research. For providing a stimulating research working environment, special thanks to lab assistants at Biotechnology Research Institute, Universiti Malaysia Sabah, Mdm. Vidarita Maikin, Mr. Mony Mian, Mdm. Azian Awang Besar and Mr. Muhd. Adam Hairie Dailis Abdullah for providing guidance and assistance in utilizing the apparatus and machinery accurately, as well as for locating the required reagents in ensuring that the project can be completed on time.

Last but not least, I would like to express my heartfelt thanks to all of my friends and everyone that has been contributed by supporting my work and help

myself until this research fully completed. May God repay your kindness and help in the future.

Rovina Kobun 07 March 2018

iv

ABSTRACT

Development of a rapid and sensitive electrochemical method is important for monitoring synthetic colorants in food and beverage products which caused toxicity and pathogenicity to human health when excessively consumed. Herein, an electrochemical sensor was developed based on the modifications of glassy carbon electrode (GCE) with chitosan (CHIT), graphene oxide (GO), multi-walled carbon nanotubes (MWCNTs) and gold nanoparticles (AuNPs) for the determination of azo colorants (Amaranth (AM), Allura Red (AR), Sunset Yellow (SY) and Tartrazine (TZ)) in food and beverage products. The hybrid nanomaterials of CHIT/MWCNTs/GO/AuNPs were effectively enhanced electron-transfer and promoted the current response of azo colorants. Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behavior with the modified GCE in the present of methylene blue as a redox indicator. The morphological characteristics of nanomaterials were observed high porosity, under scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscope (TEM). Potential peak currents were found in the order of bare GCE>CHIT/GO>CHIT/GO/MWCNTs> CHIT/GO/MWCNTs/AuNPs. The modified-GCE showed optimum response when operated at 25 ±1 °C at pH 7 of PBS as working solution (0.1 M) for all tested colorants. Meanwhile, the scan rate was found of 0.35 V s-1 for AM, 0.2 V s-1 for AR, 0.25 V s-1 for SY and 0.3 V s-1 for TZ, within 5,10,30 and 50 sec, respectively. Under optimal conditions, the developed sensor was tested with different concentrations of standard AM, AR, SY and TZ in the ranged of 10 to 90 mg mL71. The limits of detection and quantification ranges were found to be 0.032 to 0.5 mg mL-1 and 0.096 to 0.92 mg mL-1, respectively. Sensitivity value of AM, AR, SY and TZ were calculated to be 0.01,0.02,0.06 and 0.05 pA/mg mL-1 mm3, respectively. The developed sensor was successfully applied to determine AM, AR, SY and TZ in candy, jelly and soft drinks samples, and good recovery values range from 93.19 to 104.03 %. This simple and sensitive sensor offers low cost and rapid detection of specific colorants without skilled operators and sophisticated instruments.

V

ABSTRAK

PEMBANGUNAN KAEDAH ELEKTROKIML4 UNTUKMENGESAN PEWARNA

AZO DALAM PRODUK MA KA NA N DAN MINUMAN

Pembangunan kaedah e%ktrokimia yang pantas dan sensitif adalah penting untuk memantau pewama sintetik da/am produk makanan yang menyebabkan ketoksikan dan patogenik kepada kesihatan manusia apabila digunakan secara berlebihan. Di sini, sensor e%ktrokim/a dibangunkan berdasarkan pengubahsuaian e%ktrod karbon berkaca keras (GCE) dengan campuran chitosan (CHIT), graphene oxide (GO), nanotube karbon mu/ti-walled (MWCNTs) dan nanopartike/ emas (AuNPs) untuk mengesan pewarna azo (Amaranth (AM), Allure Red (AR), Sunset Yellow (SY) dan Tartraz/ne (TZ)) dalam produk makanan dan m/numan. Penggabungan bahan nano CHIT/MWCNTs/GO/AuNPs berkesan untuk meningkatkan pemindahan elektron dan mencetus tindak ba/as terhadap pewama s/ntet/k yang disasarkan. Voltammetry kftaran dan voltammetri pulse-berbeza digunakan untuk mengkaji tingkah /aku elektrok/m/a dengan GCE yang to/ah diubah suai dengan kehadiran metilena b/ru sebagaf petunjuk redoks Cir/-c/ri mon`o%gi nanomater/al diperhatikan menggunakan mikroskop elektron (SEM), spektroskop/ sinar-X pembiasan tenaga (EDX) dan mikroskop elektron penghantaran (TEM). Arus elektrik meningkat na/k daripada GCE>CNIT/GO>CHIT/GO/MWCNTs>CHIT/GO/MWCNTs/AuNPs GCE yang diubahsuai menunjukkan tindak balas optimum apab/la dikendalikan pada 25 f1 °C pada pH 7 PBS (0.1 M) untuk semua sintetik wama yang d/uj/. Sementara itu, kadar fmbasan mas/ng-mas/ng mendapati untuk warna AM /a/ah 0.35 Vs; AR /a/ah 0.2 V s; SY/a/ah 0.25 Vs' dan 7Z 0.3 Vsl untuk 77, da/am 5,10,30 dan 50 Saat. Da/am keadaan yang optimum, teknik mengesan yang dibangunkan diuji dengan kepekatan AM, AR, SY dan TZ yang berbeza di antara 10 hingga 90 mg mL-'. Had pengesanan dan limit kuantifikas/ d/dapatr sebanyak 0.032 hingga 0.5 mg mL--' dan 0.096 hingga 0.92 mg mL-'. N//a/ sensitif terhadap kepekaan AM, AR, SY dan 7Z telah dfkfra, masing-masing 0.01,0.02,0.06 dan 0.05 Wmg mL-' mn73. Teknik mengesan yang dibangunkan berjaya digunakan untuk menentukan AM, AR, SYdan TZ da/am sampel gu/a-gu/a, je// dan m/numan r/ngan, dan menunjukkan tahap pemul/han yang sangat balk bem/la/ darf 93.19 h/ngga 104.03 %. Teknik pengesanan yang sens/tif dan se%t/vfti fnf menawarkan kos yang rendah, prosedur yang mudah, pantas, mengesan da/am kepekaan tfnggf sehingga rendah, dan terteniv tanpamenggunakan pengenda/i yang mahir dan fnstrumen yang cangg/h.

vi

TABLE OF CONTENTS

TITLE

DECLARATION

CERTIFICATION

ACKNOWLEDGMENT

ABSTRACT

ABSTRAK

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF SYMBOLS

LIST OF ABBREVIATIONS

LIST OF APPENDICES

CHAPTER 1: INTRODUCTION

1.1 Research background

1.2 Problem statement 1.3 Research objectives 1.4 Scope of work 1.5 Research flow chart 1.6 Significance of study

Page

11

III

IV

V

vi

vii

XII

XIII

xvl

xvii

xviii

1

4

5

5

8

9

vii

CHAPTER 2: LITERATURE REVIEW

2.1 Food colorants 10

2.1.1 Natural colorants 11

2.1.2 Synthetic colorants 11

a. Amaranth 12

b. Allura Red 13

c. Sunset Yellow 13

d. Tartrazine 14

2.2 Toxicological effects of AM, AR, SY and TZ colorants 15

2.3 Analytical techniques for the determination of synthetic azo 16

colorants 2.3.1 High performance liquid chromatography (HPLC) 17

2.4 Advances detection techniques of electrochemical sensor 20

2.5 Modification of glassy carbon electrode (GCE) 26

2.5.1 Chitosan 26

2.5.2 Gold nanoparticles 26

2.5.3 Graphene 28

2.5.4 Multi-walled carbon nanotubes 29

2.6 Principles of electrochemistry 30

2.6.1 Fundamental and theoretical part of electrochemical 31

techniques

a. Cyclic voltammetry 32 b. Differential pulse voltammetry 34

2.6.2 Electrolytic cells 35

CHAPTER 3: METHODOLOGY 3.1 Chemicals and reagents 36

3.2 Apparatus and equipments 36

3.3 Modification of glassy carbon electrode 39 3.3.1 Pretreatment of glassy carbon electrode 39 3.3.2 Synthesis of gold nanoparticles 39 3.3.3 Synthesis of graphene oxide 39

viii

3.3.4 Fabrication and immobilization of 40

CHIT/GO/MWCNTs/AuNPs

3.4 Electrochemical measurements 40

3.5 Optimization of CHIT/GO/MWCNTs/AuNPs/GCE 41

3.5.1 Methylene blue (MB) 41

3.5.2 Effect of volume CHIT/GO/MWCNTs/AuNPs/GCE 41

3.5.3 Effect of pH 41 3.5.4 Effect of interaction time 41 3.5.5 Effect of scan rate 42

3.6 Characterization of CHIT/GO/MWCNTs/AuNPs 42

3.6.1 SEM and EDX 42

3.6.2 TEM 43

3.6.3 Ultraviolet-visible spectrometer (UV-Vis) 43

3.7 Electrochemical analysis of the modified GCE 43 3.8 Electrochemical determination of specific synthetic colorants 43 3.9 Analytical performance 44

3.9.1 Repeatability 44 3.9.2 Reproducibility 44 3.9.3 Storage stability 45 3.9.4 Interference study 45

3.10 Analytical application 45 3.10.1 Extraction of real samples 45 3.10.2 Analysis of real samples 46

3.11 Validation by RP-HPLC 46 3.11.1 Chromatography condition 46 3.11.2 Analysis of real samples 46

3.12 Statistical analysis 47

CHAPTER 4: RESULTS AND DISCUSSION 4.1 Morphological characterization of CHIT/GO/MWCNTs/AuNPs 49

4.1.1 SEM analysis 49 4.1.2 EDX analysis 51 4.1.3 TEM analysis 53

ix

4.1.4 UV Vis spectroscopy analysis 55

4.2 Optimization of CHIT/GO/MWCNTs/AuNPs 56

4.2.1 Effect of methylene blue (MB) 56

4.2.2 Effect of pH 58

4.2.3 Effect of interaction time 60

4.2.4 Effect of volume CHIT/GO/MWCNTs/AuNPs 62

4.2.5 Effect of scan rate 63

4.2.6 Electrochemical mechanism of four synthetic colorants 66

a. Irreversible 66 b. Reversible 67

4.3 Electrochemical characterization of CHIT/GO/MWCNTs/AuNPs/GCE 68 4.4 Electrochemical behavior of CHIT/O/MWCNTs/AuNPs/GCE 71

4.4.1 Repeatability analysis 71

4.4.2 Reproducibility analysis 72 4.4.3 Storage stability analysis 73 4.4.4 Interference/selectivity analysis 74

4.5 Calibration curves and detection limit 77 4.5.1 Comparison to previous research 83

4.6 Recovery study and analytical application 85 4.7 Validation by reverse phase-high performance liquid 88

chromatography (RP-HPLC)

4.7.1 Standard curve 88 4.7.2 RP-HPLC analysis of real samples 92

CHAPTER 5: CONCLUSION AND RECOMMENDATIONS FOR 94 FUTURE RESEARCH

REFERENCES 96

APPENDICES 121

X

LIST OF TABLES

Page

Table 2.1 Properties of Amaranth, Allura Red, Sunset Yellow and 14

Tartrazine used in the study. Table 2.2 The toxicological effects of Amaranth, Allura Red, Sunset 16

Yellow and Tartrazine. Table 3.1 Chemicals and reagents used in this study 37

Table 3.2 RP-HPLC conditions for chromatography analysis 48 Table 4.1 The composition elements of hybrid nanomaterials 52

(CHIT/ GO/ MW CNT/Au N Ps) . Table 4.2 The optimum condition of developed electrochemical sensor 65

are mentioned. Table 4.3 Electrochemical behaviors of the modified electrodes are 74

summarized towards Amaranth, Allura Red, Sunset Yellow

and Tartrazine. Table 4.4 Post-hoc Tukey HSD test of Amaranth, Allura Red, Sunset 76

Yellow and Tartrazine. Table 4.5 The summary of electrochemical determination of Amaranth, 78

Allura Red, Sunset Yellow and Tartrazine. Table 4.6 Comparison studies between different modification of 84

working electrode for the determination Amaranth, Allura Red, Sunset Yellow and Tartrazine.

Table 4.7 Analysis of AM, AR, SY and TZ in commercial products by 86

using the developed electrochemical sensor. Table 4.8 Recovery study of real samples by RP-HPLC. 92 Table 4.9 Comparison of real samples analysis between developed 93

electrochemical sensor and RP-HPLC.

XI

LIST OF FIGURES

Page

Scheme 1.1 The sensing processes (CHIT/GO/MWCNTs/AuNPs/GCE) 7

for the determination of AM, AR, SY and TZ.

Figure 1.1 The research flow chart for the determination of azo dyes. 8

Figure 2.1 The classification of food colorants. 11

Figure 2.2 Structure of Amaranth (a), Allura Red (b), Sunset Yellow 15

(c) and Tartrazine (d).

Figure 2.3 Single walled carbon nanotubes (A) and multi-walled 30

carbon nanotubes (B).

Figure 2.4 Potential-time excitation signal in cyclic voltammetric 33

experiment. Figure 2.5 Typical cyclic voltammogram for a reversible 0+ ne- 33

R redox process. Figure 2.6 Excitation signal for differential pulse voltammetry. 34

Figure 2.7 Illustration of a typical three electrode electrolytic cell. 35

Figure 3.1 Setup of electrochemical cell with working, reference and 38

counter electrodes. Figure 4.1 SEM images of the (a) CHIT, (b) CHIT/MWCNTs, (c) 50

CHIT/GO, and (d) CHIT/GO/MWCNTs/AuNPs with

nanoscale of 10 µm. Figure 4.2 EDX spectrum of the CHIT/GO/MWCNTs/AuNPs. 52

Figure 4.3 TEM images of the AuNPs (a), MWCNTs (b), 74

MWCNTs/AuNPs (c) and CHIT/GO/MWCNTs/AuNPs (d)

with nanoscale of 50 nm. Figure 4.4 UV spectra of different layers of nanomaterials. 55

Figure 4.5 Relationship between oxidation peak currents measured 57

with and without MB towards Amaranth (AM), Allura Red

(AR), Sunset Yellow (SY) and Tartrazine (TZ). Figure 4.6 Relationship between peak currents pH values in the 60

presence of 100 mg mL71 of AM, AR, SY and TZ.

XII

Figure 4.7 Relationship between peak currents and interaction time in 61

the presence of 100 mg mL-1 of AM, AR, SY and TZ.

Figure 4.8 Relationship between peak currents based on different 62

volume of CHIT/GO/MWCNTs/AuNPs in the presence of 100 mg mL-1 of AM, AR, SY and TZ.

Figure 4.9 Relationship between peak currents and different scan 64

rate, in the presence of 100 mg mL-1 of Amaranth (a),

Altura Red (b), Sunset Yellow (c) and Tartrazine (d).

Scheme 4.1 Mechanism for the electrochemical processes of Amaranth 66 (AM), Allura Red (AR) and Tartrazine (TZ).

Scheme 4.2 Mechanism for the electrochemical process of Sunset 67

Yellow (SY). Figure 4.10 Comparison studies of bare GCE, CHIT/GO/GCE, 70

CHIT/GO/MWCNTs/GCE and CHIT/GO/MWCNTs/AuNPs/GCE in the presence of 100 mg

mL71 of Amaranth (AM), Allura Red (AR), Sunset Yellow (SY) and Tartrazine (TZ).

Figure 4.11 The repeatability studies of the modified electrode in the 71

presence of 100 mg mL-1 of Amaranth, Allura Red, Sunset Yellow and Tartrazine.

Figure 4.12 The reproducibility studies of the modified electrode in the 72

presence of 100 mg mLL1 of Amaranth, Allura Red, Sunset Yellow and Tartrazine.

Figure 4.13 The storage stability studies of the modified electrode in 73 the presence of 100 mg mL-1 of Amaranth, Allura Red, Sunset Yellow and Tartrazine.

Figure 4.14 The interference/selectivity studies of the modified 75 electrode; Amaranth (a), Allura Red (b), Sunset Yellow (c)

and Tartrazine (d). Figure 4.15 (a) DPV measurement of the different concentrations of 79

AM with the modified electrode (pH 7.0, PBS, 1 mM MB). (b) Calibration curve between the oxidation peak currents

XIII

obtained by DPV and the logarithm of AM concentrations (Ia vs IogM).

Figure 4.16 (a) DPV measurement of the different concentrations of AR 80

with the modified electrode (pH 7.0, PBS, 1 mM MB). (b)

Calibration curve between the oxidation peak currents

obtained by DPV and the logarithm of AR concentrations (Ia vs IogM).

Figure 4.17 (a) DPV measurement of the different concentrations of SY 81

with the modified electrode (pH 7.0, PBS, 1 mM MB). (b)

Calibration curve between the oxidation peak currents

obtained by DPV and the logarithm of SY concentrations (Ia vs logM).

Figure 4.18 (a) DPV measurement of the different concentrations of TZ 82

with the modified electrode (pH 7.0, PBS, 1 mM MB). (b)

Calibration curve between the oxidation peak currents

obtained by DPV and the logarithm of TZ concentrations (IX vs IogM).

Figure 4.19 RP-HPLC standard curve of Amaranth (a), Altura Red (b), 90

Sunset Yellow (c), and Tartrazine (d).

XIV

LIST OF SYMBOLS

% Percentage

t Plus minus °c Degree Celsius

Ng Microgram

pg/mL Microgram per milliliter

NL Microliter

Nm Micrometer

cm Centimeter

g Gram

h Hour

M Molar

mg Milligram

mg/mL Milligram per milliliter

min Minute

mL Milliliter

mm Milimolar

mm Millimeter

nm Nanometer

xv

LIST OF ABBREVATIONS

AM

AR

AuNPs

CHIT

cv

dH2O

DPV

EDX

GCE

GO

LOD

LOQ

MB

MWCNTs

NPs

PBS

RP-HPLC

SEM

SY

SPE

TZ

TEM

Amaranth

Allura red Gold nanoparticles Chitosan

Cyclic voltammetry Distilled water Differential pulse voltammetry Energy dispersive x-ray Glassy carbon electrode Graphene oxide Limit of detection

Limit of quantification Methylene blue

Multi-walled carbon nanotubes Nanopartides

Phosphate buffer saline Reverse phase-high performance liquid chromatography Scanning electron microscope Sunset yellow Solid phase extraction catridge Tartrazine

Transmission electron microscope

xvi

LIST OF APPENDICES

Appendix A Fourier-transform infrared spectroscopy (FUR) analysis of CHIT/MWCNTs/GO/AuNPs

Optimization of CHIT/GO/MWCNTs/AuNPs/GCE by presence

of methylene blue (MB)

Page

121

Appendix B Optimization of CHIT/GO/MWCNTs/AuNPs/GCE by different 124

pH value of electrolyte solution. Appendix C Optimization of CHIT/GO/MWCNTs/AuNPs/GCE by 126

investigate the effect of different time interaction.

Appendix D Optimization of CHIT/GO/MWCNTs/AuNPs/GCE by 128

investigate the effect of difference volume nanomaterials. Appendix E Optimization of CHIT/GO/MWCNTs/AuNPs/GCE by 130

investigate the effect of different scan rate. Appendix F RP-HPLC chromatogram retention time of AM, AR, SY and 132

TZ. Appendix G RP-HPLC chromatogram of AM, AR, SY and TZ. 134 Appendix H List of publications 148

xvii

CHAPTER 1

INTRODUCTION

1.1 Research background

Color provides the first impression of a food taste, texture and freshness to

consumers that will influence their choices on food. Generally, food colorants are

categorized into two types which are natural and synthetic colors. Natural colors are known as natural-identical that extracted from plant, fungi and insect. However,

natural colors have some drawback such as easy to degrade, more sensitive to light,

temperature, pH and costly. Prior to that, synthetic dyes have been discovered as the most reliable and economical compound because of their several advantages

such as high stability to light, oxygen, pH, color uniformity, less microbiological

contamination and low production cost (Wu et a/., 2013a; Llamas et al.., 2009).

Synthetic colors are mainly involved as azo colors, triphenylmethane colors, xanthene

colors, indigotine colors, and quinolone colors.

Azo colors with the azo group (-N=N-) as the chromophore in the molecular

structure is the largest group of colors accounting more than half of global dyes

production while approximately 65 % of colors used as food additives came from azo dyes (Yamjala et al., 2016; U et al., 2015; Rebane et al., 2010). Synthetic colorants have been used to substitute natural food color due to more stable during food

processing. Regrettably, it is more concern synthetic food colorants due to

pathogenicity, particularly when they are excessively consumed (Wang eta/., 2010b; Yadav et at.., 2013). In this research project focused azo colorants which are Amaranth (AM), Allura Red (AR), Sunset Yellow (SY) and Tartrazine (TZ). Those

synthetic colorants are belonging to azo dyes and widely used in food products such as carbonated beverage, candies, prawn slice, cakes and many more (Gomez et al., 2012). Unfortunately, high concentration of these colorants in food products can lead to severe problems to human health due to the presence of azo group (-N=N-) (de

Campos Ventura-Camargo, and Marin-Morales, 2013; Muhd Julkapli et al.., 2014).

The usages of the azo colorants in food products are strictly controlled by World

Health Organization (WHO) laws and regulations. The EU and Joint FAO/WHO Expert

Committee on Food Additives (JECFA) in 1982 and EU Scientific Committee for Food

(SCF) in 1984 have standardized an acceptable daily intake (ADI) for each azo

colorant in food and beverage products (Aguilar et a/. 2014). Previously, several

analytical methods have been applied for the determination of azo colorants, including spectrophotometry (Oakley et al., 2012), high performance liquid

chromatography (HPLC) (Ma et a/., 2006), column chromatography (Alves et a/., 2008), and capillary electrophoresis (Jager et a/., 2005).

Nanocomposite membrane of chitosan (CHIT) is an interesting natural biopolymer that containing of reactive amino and hydroxyl functional groups which

commonly used for immobilization process of electrochemical sensor combined with

nanomaterial because of the high absorption, excellent film-forming ability, high

permeability, high heat-stability, mechanical strength, non-toxicity, biocompatibility,

low cost and availability. Moreover, chemically modifications of the amino group of CHIT have provided hydrophilic environment for the biomolecules and soluble in diverse acids that able to interact with polyanions to form complexes and gels (Shukla

et a/., 2013; Lin et a/., 2007). However, hybrid materials based on CHIT has been

developed such as conducting polymers, carbon nanotubes, redox mediators, metal nanoparticles and oxide reagents due to excellent properties of individual

components and outstanding synergistic effects simultaneously for electrochemical

sensing platforms (U eta/., 2010; Lin eta/., 2009).

Graphene has been widely used as carbon nanomaterials-based sensor because of the superior mechanical strength, thermal stability, low density and high heat conductance, good electrical conductivity and high aspect ratio properties (Punetha et al., 2017; Novoselov et a/., 2012). Graphene is a highly promising material for biosensors due to its excellent physical and chemical properties which facilitate electron transfer. It is a single sheet of carbon atoms arranged in a honey-

comb lattice which effectively enhanced their electronic and electrochemical properties (Wisitsoraat et al., 2017; Hla, 2012). Various applications referring to in

2

electrochemical sensing are phytohormone (Gan et al., 2011), biomolecular (Huang

et a/., 2012), pharmaceuticals (Wei et a/., 2012), toxic food additives (Wu et a/., 2012), and environment pollutants (Gan et at.., 2012a). In chemical and biosensor

applications, graphene has shown superior performances compared with other

carbon-based materials including its nearest counterpart, carbon nanotubes (CNTs),

because of its double surface area compared to CNTs, higher chemical reactivity due

to larger number of edge plane per unit mass and higher electron mobility and

conductivity (Wisitsoraat et al., 2017; Ratinac et al., 2011; Pumera, 2010).

Furthermore, carbon nanotubes have extraordinary tensile strength, excellent

electrical conductivity, and high chemical stability that can create good electron transfer rates (Ajayan, 1999). There are two types of carbon nanotubes available

which are multi-walled carbon nanotubes (MWCNTs) and single-walled carbon

nanotubes (SWCNTs). MWCNTs and gold nanoparticles (AuNPs) are extremely

attractive materials in electrochemical sensor (Messaoud et a/., 2017; Saha et al., 2012). Metal nanoparticles having broad range of dimensions are endowed with size- dependent optical, magnetic, electronic and chemical properties appropriate for

catalysts, optoelectronic devices, as well as for chemical and biosensor applications (Ionitä et al., 2017; Stassen et al., 2017). In this study, the candidate was used AuNPs for modification of glassy carbon electrode in electrochemical system. AuNPs

are exploited as a potential material for sensing due to high surface area, strong adsorption ability, good biocompatibility, chemical stability and nontoxicity. AuNPs

are more suitable for the determination of food coloring via the development of electrochemical and colorimetric sensors. One of the considerable advantages of using AuNPs based assay, the molecular recognition event can be translated into

visible color changes (Wu et al., 2011; U et al., 2010).

3

1.2 Problem statement Nowadays, various additives including synthetic food colorants are widely applied in

food industry to make food attractive to consumers. However, some synthetic food

colorants can be toxic to aquatic organisms and carcinogenic effects on humans,

particularly when they are extremely consumed (Ceyhan eta/., 2013). Food colorant

can induce food intolerance (non-immune mediated) and allergic reactions (immune

mediated, ranging from urticaria and/or angioedema and asthma to anaphylaxis).

Previous studies reported that AM, AR, SY and TZ can cause the appearance of

allergies and asthma and childhood hyperactivity (Silva et al., 2007; Nevado et al.,

1997).

McCann et al. (2007) have reported that two mixtures of synthetic azo colors

had caused hyperactivity to increase in children age 3 to 9 years old. As for previous

study conducted by Hashem et a/. (2010) on the toxicological impact of three types

food coloring caused depressing effect on cellular immune response on albino rats.

AR has caused DNA damage in pregnant mice's colon after three hours of

administration at concentration 0 to 2000 mg kg-' body weight (Sasaki et al., 2002;

Tsuda et a/., 2001). Besides, SY and AR can cause binding of human serum albumin

that lead to complex formation which may interfere their function in human body

(Masone and Chanforan, 2015). AM is reduced rapidly by gastrointestinal microflora

to naphthionic acid and 1-amino-2-hydroxy-3,6-naphthalene disuiphonic acid that

may cause caecal enlargement and renal pelvic nephrocalcinosis in rats, because of

the effects on mineral absorption and increased faecal water loss (König, 2015: EFSA,

2010).

Facing with increasing legal restrictions, food dye determination became an

analytical challenge. Until now, several researches have been conducted for the

determination of azo colorants in food and beverage products by using various

analytical methods such as high performance liquid chromatography (HPLC) (U et

al., 2015; Shen eta/., 2014), thin layer chromatography (TLC) (Andrade eta/., 2014),

spectrophotometric (Sha and Zhu, 2015; Uamas et al., 2009), capillary

electrophoresis (Patsovskii et al., 2004) as well as liquid chromatography/tandem

mass spectrometry (LC-MS/MS) (Martin et al., 2016; Tsai et al., 2015). However,

4

these above methods have some drawback such as time consuming, required high

skilled manpower and high-tech instruments. Thus, a rapid and reliable method is

needed for the determination of synthetic colorants in food and beverage products.

1.3 Research objectives The aim of this research was to develop a simple and effective way for the

determination of azo colors in commercial food and beverage products. Chitosan

nanocomposite membrane, graphene oxide, multi-walled carbon nanotubes, and

gold nanoparticles were incorporated onto the GCE and enhanced the sensitivity for

the determination of azo colorants.

The following specific objectives were formulated to achieve the overall objectives of

this study:

a) To modify glassy carbon electrode (GCE) with chitosan nanocomposite

membrane, graphene oxide, multi-walled carbon nanotubes, and gold

nanoparticles. b) To characterize the modified GCE by using SEM, EDX, TEM and UV-Vis.

c) To evaluate the analytical performance of the developed sensor.

d) To validate the performance of the developed sensor with RP-HPLC method for the determination of azo dyes.

1.4 Scope of work Advances in chemistry, physics, biochemistry and molecular biology have led to the

developed electrochemical sensor that can able to detect wider range of biochemical

elements due to their simplicity, low cost, sensitivity, selectivity, and possibility for

miniaturization (Farre et al.., 2009). An electrochemical sensor is developed based on

nanomaterials and nanocomposite membrane, a small amount of sample requires for

rapid detection of synthetic colorants. Electrochemical system found efficient method in the analysis of compound, especially identifying and quantifying the specific food

colorant. This technique has been received high attention in the world due to high

ý .

ý5 S

a.

L

5

efficiency and sensitivity, quick response, simple procedure and relatively low costs (Ansari et all 2017; Zhu et all 2014). The performance of the electrochemical

system is critically dependent on the properties of the presence of nanomaterials and

nanocomposite membrane which increased active site and conductivity for the

determination of specific compound (Ahmed et all 2016).

The main aim of this study was to develop an electrochemical sensor based on

CHIT nanocomposite membrane, graphene oxide, multi-walled carbon nanotubes

and gold nanoparticles modified glassy carbon electrode (CHIT/GO/MWCNTs/AuNPs/GCE) in the presence of methylene blue as a redox indicator for the determination of azo colorants (AM, AR, SY and TZ) (Scheme 1.1).

To the best of our knowledge, highly sensitive electrochemical method was firstly

developed and applied for the determination of azo colorants in commercial food and beverage products using the developed glassy carbon electrode (CHIT/GO/MWCNTs/AuNPs). The prepared nanomaterials were characterized by

SEM, TEM and DPV. The experimental parameters were optimized as pH, interaction

time and scan rate, and investigated the interaction mechanism between azo

colorants and the modified GCE. The combination of nanomaterials is more precise,

accurate, sensitive, rapid, cheap and simple with effective protocol for the determination at the presence level of AM, AR, SY and TZ. The modified electrode has emerged as powerful platforms in electrochemical sensor for identifying and quantifying the presences of azo colorants. Subsequently, the developed method was successfully applied and compared with RP-HPLC technique for the determination of AM, AR, SY and TZ in candy, jelly and soft drinks with satisfactory levels.

6

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