UNIVERSITI PUTRA MALAYSIA

TENG LI YUEN

FK 2011 124

TEXTURAL AND RHEOLOGICAL CHARACTERISATIONS OF SAGO STARCH AND SAGO STARCH SUGAR GELS

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TEXTURAL AND RHEOLOGICAL CHARACTERISATIONS OF SAGO

STARCH AND SAGO STARCH SUGAR GELS

By

TENG LI YUEN

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia,

in Fulfilment of the Requirements for the Degree of Master of Science

September 2011

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Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment

of the requirement for the degree of Master of Science

TEXTURAL AND RHEOLOGICAL CHARACTERISATIONS OF SAGO

STARCH AND SAGO STARCH SUGAR GELS

By

TENG LI YUEN

September 2011

Chair : Assoc. Prof. Ir. Chin Nyuk Ling, PhD

Faculty : Faculty of Engineering

The behaviour of native sago starch was investigated through characterisation,

rheological and textural measurements in finding its use as a gelling agent in frozen-

baked products. The effects of sago starch (6-8%), sugar (25-35%), and shearing

speed of mixer (20-50 rpm) on rheological and textural characteristics of gel were

investigated by means of response surface methodology. Increase in sago starch and

sugar levels both increased (P < 0.01) gel stiffness. Higher shearing speeds reduced

(P < 0.05) gel stiffness due to a decrease in starch swelling and an increase in starch

breakdown during cooking.

The values of the experimental variables which minimised and maximised the

textural parameters of hardness, gumminess, resilience, cohesiveness, and

springiness were estimated by means of ridge analysis to determine the processing

conditions at which these extremes can be reached. The maximum gel cohesiveness

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brought by the processing variables was set as the criterion to obtain optimum

formulation and processing of sago-starch based gels.

Utilising the optimised formulation and processing condition for gel setting, the

pasting behaviour, rheological and textural characteristics of sago starch-sugar gels

were compared with those of corn, wheat, tapioca, and potato starches. The

morphological and thermal properties of these starches were investigated via

scanning electron microscopy and differential scanning calorimetry respectively.

High-amylose cereal starches (wheat and corn) produced harder gels (hardness =

225.1–248.0 g), while low-amylose root starch (tapioca) produced softer gels

(hardness = 4.9 g). Sago and potato starches produced gels with high cohesiveness

(0.90–0.94), indicating good setting of gels.

The effect of freezing and thawing on rheological and textural characteristics of gels

were investigated. The freezing and thawing processes greatly increased the

viscoelasticity and hardness of sago starch-sugar gels. These negative effects were

significantly reduced by reheating the freeze-thawed gels at high temperature (80 °C).

The freeze-thaw stability of various starch gels were investigated by gravimetric

measurements of the water of syneresis after three freeze-thaw cycles. Sago starch

produced gels with relatively low syneresis (3.23%) compared with corn (15.5%)

and wheat (4.26%) starches. The high cohesiveness and low syneresis of sago starch-

sugar gels, and their ability to recover from structural changes caused by freezing

and thawing, implied potential use of sago starch as a gelling agent in frozen-baked

products.

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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai

memenuhi keperluan untuk ijazah Master Sains

TEKSTUR DAN SIFAT REOLOGI KANJI SAGU DAN GEL SAGU GULA

Oleh

TENG LI YUEN

September 2011

Pengerusi : Prof. Madya Ir. Chin Nyuk Ling, PhD

Fakulti : Fakulti Kejuruteraan

Sifat kanji sagu telah dikaji-selidik melalui pengukuran reologi dan tekstur untuk

memperluaskan penggunaannya sebagai ejen gel dalam produk bakeri sejukbeku.

Pengaruh kanji sagu (6-8%), gula (25-35%) dan kelajuan putaran pengaduk (20-50

rpm) pada sifat-sifat reologi and tekstur gel telah diselidik dengan menggunakan

kaedah permukaan tindakbalas (response surface methodology). Peningkatan

kepekatan kanji sagu and gula didapati meningkatkan (P < 0.01) keteguhan gel.

Kelajuan putaran pengaduk mengurangkan (P < 0.05) keteguhan gel sebab kadar

pembengkakan granul kanji telah berkurang manakala kadar pemecahan granul telah

meningkat dalam proses memasak.

Nilai-nilai pembolehubah eksperimen yang meminimalkan serta memaksimumkan

parameter tekstur kekerasan, kebergetahan, ketahanan, kepaduan dan kekenyalan gel

telah dianggar melalui analisis bubungan (ridge analysis) untuk menentukan keadaan

pemprosesan di mana ekstrim-ekstrim parameter tersebut boleh diperoleh. Kepaduan

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gel maksimum telah ditetapkan sebagai kriteria untuk mendapatkan formulasi dan

keadaan pemprosesan bagi menghasilkan gel kanji sagu yang optimum.

Dengan menggunakan rumusan dan keadaan pemprosesan bagi penghasilan gel yang

optimum, sifat pempasturan serta ciri-ciri reologi dan tekstur gel sagu telah

diperbanding dengan gel kanji jagung, gandum, ubi kayu dan ubi kentang. Sifat

morfologi and sifat termal kanji ini juga telah dikaji dengan menggunakan

mikroskop penskanan elektron dan kalorimetri penskanan pembezaan. Kanji bijirin

(gandum dan jagung) yang tinggi dengan amilosa menghasilkan gel yang lebih keras

(kekerasan = 225.1–248.0 g), manakala kanji ubi kayu menghasilkan gel yang lebih

lembut (kekerasan = 4.9 g). Kanji sagu dan kanji ubi kentang menghasilkan gel yang

berkepaduan tinggi (0.90-0.94). Ini merupakan satu ciri gel yang sempurna.

Pengaruh pembekuan dan penyahbekuan pada sifat reologi dan tekstur gel telah

dikaji-selidik. Proses pembekuan dan penyahbekuan telah meningkatkan viskoelastis

dan kekerasan gel sagu dengan ketara. Kesan negatif ini dapat dikurangkan dengan

memanaskan gel pada suhu yang tinggi (80 °C). Kestabilan sejukbeku-nyahbeku gel

kanji telah dikaji melalui penyukatan air sineresis selepas tiga kitaran sejukbeku-

nyahbeku. Gel kanji sagu menunjukkan tahap sineresis yang rendah (3.23%)

berbanding dengan gel kanji jagung (15.5%) dan kanji gandum (4.26%). Nilai

kepaduan gel yang tinggi dan tahap sineresis yang rendah, serta keupayaan gel sagu

untuk memulih daripada perubahan struktur akibat proses sejukbeku-nyahbeku

ternyata potensi kanji sagu untuk digunakan sebagai ejen gel dalam produk bakeri

sejukbeku.

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ACKNOWLEDGEMENTS

My deepest gratitude to Dr. Chin Nyuk Ling, whose combination of intellect,

creativity, and patience were invaluable to the final fruition of my work. I wish to

thank Dr. Yus Aniza Yusof for her valuable comments and advice throughout my

time in research. I would like to acknowledge the editors and reviewers of Food

Hydrocolloids and Carbohydrate Polymers who critically analysed and took great

interest in my work. I am also grateful to my late professor, Dr. Kassim A. Abbas,

for his inspiring lectures. May peace be with him forever.

For the completion of my experimental work, I would like to thank the following

people for their helping hands and invaluable assistance: Andy for the modification

and set-up of the jacketed mixer; Dr. Siti Mazlina and Soh Jo Yong for providing the

sago starch; Dr. Abel Gaspar-Rosas, Chua Sheng Keong, Jasmine Ooi, and Josh Lai

from Research Instruments Sdn. Bhd., for their guidance and expertise in rheometry;

Tracy Ng from Lee Hung Scientific Sdn. Bhd. for her guidance and help with the

Texture Analyser; Kobra for her guidance in differential scanning calorimetry; Dr.

Tey Beng Ti, Chew Few Ne, Adli Nazri, and Ismail of Department of Chemical and

Environmental Engineering, for their help with centrifugations and scanning electron

microscopy; and all the departmental laboratory staffs, for their help and support.

My love and thanks to my colleagues for their thoughtful comments, suggestions,

and support, and to my family and friends for their continued patience,

understanding, and love. From the bottom of my heart, thank you, for everything.

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I certify that a Thesis Examination Committee has met on 6 September 2011 to

conduct the final examination of Teng Li Yuen on his thesis entitled “Textural and

Rheological Characterisations of Sago Starch and Sago Starch Sugar Gels” in

accordance with the Universities and University Colleges Act 1971 and the

Constitution of the Universiti Putra Malaysia [P.U.(A) 106] 15 March 1998. The

Committee recommends that the student be awarded the Master of Science.

Members of the Thesis Examination Committee were as follows:

Farah Saleena binti Taip, PhD

Senior Lecturer

Faculty of Engineering

Universiti Putra Malaysia

(Chairman)

Rosnah binti Shamsudin, PhD

Senior Lecturer

Faculty of Engineering

Universiti Putra Malaysia

(Internal Examiner)

Siti Mazlina binti Mustapa Kamal, PhD

Associate Professor

Faculty of Engineering

Universiti Putra Malaysia

(Internal Examiner)

Norziah Mohd Hani, PhD

Professor

School of Industrial Technology

Universiti Sains Malaysia

(External Examiner)

________________________

SEOW HENG FONG, PhD

Professor and Deputy Dean

School of Graduate Studies

Universiti Putra Malaysia

Date: 20 December 2011

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This thesis was submitted to the Senate of Universiti Putra Malaysia and has been

accepted as fulfilment of the requirement for the degree of Master of Science. The

members of the Supervisory Committee were as follows:

Chin Nyuk Ling, PhD, Ir

Associate Professor

Faculty of Engineering

Universiti Putra Malaysia

(Chairperson)

Yus Aniza Yusof, PhD

Associate Professor

Faculty of Engineering

Universiti Putra Malaysia

(Member)

_________________________________

BUJANG BIN KIM HUAT, PhD

Professor and Dean

School of Graduate Studies

Universiti Putra Malaysia

Date:

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DECLARATION

I declare that the thesis is my original work except for quotations and citations which

have been duly acknowledged. I also declare that it has not been previously, and is

not concurrently, submitted for any other degree at Universiti Putra Malaysia or at

any other institution.

_______________________

TENG LI YUEN

Date: 6 September 2011

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TABLE OF CONTENTS

Page

ABSTRACT ii

ABSTRAK iv

ACKNOWLEDGEMENTS vi

APPROVAL vii

DECLARATION ix

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF ABBREVIATIONS xvi

CHAPTER

1 INTRODUCTION 1

1.1 Research Background 1

1.2 An Introduction to Sago Starch 3

1.3 Objectives of This Research 4

2 LITERATURE REVIEW 6

2.1 Introduction 6

2.2 Composition and Structure of Starch 7

2.2.1 Molecular Composition: Amylose and Amylopectin 8

2.2.2 Microscopic Structure 10

2.2.3 Macroscopic Organisation 11

2.3 Functional Properties of Starch 12

2.3.1 Gelatinisation 13

2.3.2 Pasting 13

2.3.3 Retrogradation 14

2.4 Methods and Measuring Techniques 15

2.4.1 Measuring Gelatinisation and Retrogradation Properties 15

2.4.2 Measuring Pasting Properties 17

2.4.3 Measuring Gel Viscoelasticity 19

2.4.4 Measuring Gel Texture 20

2.4.5 Measuring Freeze-thaw Stability of Gel 22

2.5 Factors Affecting Behaviours of Starch Gel 23

2.5.1 Compositional Factors 23

2.5.2 Processing Factors 26

2.6 Physico-Chemical and Rheological Studies on Sago Starch 27

2.7 Applications of Sago Starch 29

2.8 Summary 31

3 MATERIALS AND METHODS 32

3.1 Introduction 32

3.2 Materials 32

3.2.1 Starch 32

3.2.2 Sugar and Water 33

3.2.3 Jacketed Mixer 34

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3.3 Rheological and Textural Characterisation of Gels 35

3.3.1 Gel Preparations 35

3.3.2 Oscillatory Rheometry Measurements 37

3.3.3 Texture Profile Analysis 40

3.3.4 Starch Pasting Measurements 43

3.3.5 Syneresis Measurements 45

3.3.6 Microstructure of Gel 46

3.4 Native Starch Analysis 48

3.4.1 Morphological Analysis 48

3.4.2 Thermal Analysis 48

3.5 Experimental Design and Statistical Analysis 51

3.5.1 Response Surface Methodology 52

3.5.2 Ridge Analysis and Optimisation of Sago Starch-Sugar Gel 54

3.5.3 Comparison of Starches 55

4 RESULTS AND DISCUSSION 58

4.1 Introduction 58

4.2 Characterisation of Sago Starch-Sugar Gel 59

4.2.1 Gel Preparations and Experimental Design 59

4.2.2 Rheological Behaviour of Gels 60

4.2.3 Textural Characteristics of Gels 66

4.3 Optimisation of Sago Starch-Sugar Gel 75

4.4 Analysing Starch Structure 76

4.4.1 Morphological Properties 77

4.4.2 Gelatinisation and Retrogradation Properties 79

4.5 Effect of Starch Source 82

4.5.1 Gel Preparations 82

4.5.2 Pasting Properties 83

4.5.3 Viscoelastic Properties 86

4.5.4 Textural Properties 87

4.5.5 Pearson Correlation 88

4.6 Effect of Freezing, Thawing and Reheating on Stability of Gels 90

4.6.1 Gel Preparations 90

4.6.2 Viscoelastic Properties 90

4.6.3 Textural Properties 93

4.6.4 Syneresis 96

4.6.5 Microstructure of Gels 98

5 SUMMARY, CONCLUSION AND

RECOMMENDATIONS FOR FUTURE RESEARCH 100

5.1 Summary and Conclusion 100

5.2 Recommendations for Future Work 102

REFERENCES/BIBLIOGRAPHY 104

APPENDICES 110

BIODATA OF STUDENT 127

LIST OF PUBLICATIONS 128