UNIVERSITI PUTRA MALAYSIA

KEK SIOK PENG

FK 2012 84

MODELLING, OPTIMISATION, AND ULTRASOUND PRE-OSMOTIC TREATMENT OF GUAVA DRYING

MODELLING, OPTIMISATION, AND

ULTRASOUND PRE-OSMOTIC TREATMENT OF

GUAVA DRYING

KEK SIOK PENG

MASTER OF SCIENCE

UNIVERSITI PUTRA MALAYSIA

2012

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MODELLING, OPTIMISATION, AND ULTRASOUND PRE-OSMOTIC

TREATMENT OF GUAVA DRYING

By

KEK SIOK PENG

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

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

August 2012

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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

MODELLING, OPTIMISATION, AND ULTRASOUND PRE-OSMOTIC

TREATMENT OF GUAVA DRYING

By

KEK SIOK PENG

August 2012

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

Faculty : Faculty of Engineering

The drying behaviour and quality attributes of guava slices were investigated

through modelling, optimisation, and ultrasound pre-osmotic conventional hot-air

drying. Modelling studies of drying kinetics and quality attributes are presented

using theoretical and statistical models by varying temperature from 55 to 75 °C and

slice thickness from 3 to 9 mm. The quality of dried fruit was measured for its water

activity, colour, vitamin C, and texture. The superposition technique with Midilli-

Kucuk model showed efficiency in modelling the drying process with R2 = 0.9991.

The second-order polynomial equations adequately described the quality of dried

guava with regression coefficient, R2 > 0.7. Drying time was a good function of

temperature and thickness (P < 0.001); water activity, colour, and vitamin C showed

strong dependence on temperature (P < 0.1); while texture was mainly influenced by

its thickness (P < 0.005). The optimum drying temperature of 70 °C at slice

thickness of 6 mm was determined using the desirability function method.

Simultaneous modelling using the theoretical and statistical drying models provides

information on water diffusion and evaporation with the drying responses and factors.

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With the optimised slice thickness, 6 mm used in subsequent experiments, the effects

of ultrasound pre-osmotic treatments on guava slices with indirect sonication using

an ultrasonic bath system and direct sonication using an ultrasonic probe system

were investigated. Pre-treatments in three osmotic solution concentrations of 0, 35,

and 70 °Brix using ultrasonic bath at power from 0 – 2.5 kW for immersion time

ranging for 20 – 40 minutes or using the ultrasonic probe at amplitude from 0 – 35%

for immersion time of 6 – 20 minutes were investigated. Water loss, solid gain,

weight reduction and colour change significantly increased (P < 0.0005) with

ultrasound power or ultrasound amplitude, immersion time, and osmotic solution

concentration. Indirect sonication with ultrasonic bath at 1.75 kW and 60 minutes of

immersion time with 70 °Brix osmotic solution contributed to a highest water loss of

34.34%, solid gain of 8.85%, weight reduction of 24.17% and acceptable colour

change when compared to the direct sonication with ultrasonic probe.

The effect of optimum ultrasound pre-osmotic treatment at osmotic solution of 0, 35,

and 70 °Brix prior to the hot-air drying at optimum drying temperature of 70 °C on

the transport properties and quality attributes of dried guava was studied. The

application of ultrasound pre-osmotic treatment prior to hot-air drying was able to

reduce the drying time by 33.3%, increased the effective diffusivity by 34.5%,

reduced the dried fruit colour changes by 37.9%, decreased the vitamin C contents

by 32.5%, and resulted to the hardness of 430.1 g – 469.6 g, which was comparable to

the fresh guava. The use of ultrasound in fruit drying is recommended to improve the

drying process and the dried product quality.

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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai

memenuhi keperluan untuk ijazah Master Sains

PERMODELAN, PENGOPTIMASIAN, DAN PRA-RAWATAN OSMOTIK

BERULTRABUNYI BAGI PENGERINGAN JAMBU BATU

By

KEK SIOK PENG

Ogos 2012

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

Fakulti : Fakulti Kejuruteraan

Sifat tingkah laku pengeringan dan sifat kualiti kepada kepingan jambu batu telah

dikaji dengan kajian-kajian permodelan, pengoptimasian, dan pra-rawatan osmotik

berultrabunyi konvensional pengeringan udara-panas. Kajian permodelan untuk sifat

kinetik pengeringan dan sifat kualitinya adalah berdasarkan model teori dan statistik

bagi suhu daripada 55 hingga 75 °C dan ketebalan kepingan daripada 3 hingga 9 mm.

Aktiviti air, warna, vitamin C, dan tekstur telah diukur sebagai kualiti buah-jambu

batu kering. Teknik superposisi dengan model Midilli-Kucuk menunjukkan

kecekapan dalam permodelan proses pengeringan dengan mencapai R2 = 0.9991.

Persamaan polinomial tertib kedua telah berjaya menggambarkan kualiti jambu batu

kering dengan pekali regresi, R2 > 0.7. Masa pengeringan memberi banyak kesan

kepada suhu dan ketebalan (P < 0.001); aktiviti air, warna dan vitamin C

menunjukkan pergantungan yang kuat kepada suhu (P < 0.1); manakala tekstur

terutamanya adalah dipengaruhi oleh ketebalan (P < 0.005). Nilai optimum bagi

suhu pengeringan dan ketebalan kepingan adalah pada 70 °C dan 6 mm selepas

ditentukan dengan menggunakan kaedah fungsi keinginan. Pemodelan serentak

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menggunakan teori dan statistik amat diperlukan untuk memberikan kefahaman

terhadap proses resapan air dan pengewapan air bersama dengan responden

pengeringan dan faktor-faktornya.

Eksperimen seterusnya dijalankan dengan menggunakan ketebalan hirisan yang

dioptimumkan iaitu 6 mm sebagai ketebalan sampel. Kesan-kesan pra-rawatan

osmotik berultrabunyi terhadap kepingan jambu batu telah dikaji dengan sonikasi

tidak langsung yang menggunakan sistem rendaman ultrasonik dan sonikasi

langsung yang menggunakan sistem kuar ultrasonik. Eksperimen pra-rawatan telah

dikaji dalam ketiga-tiga kepekatan larutan osmotik, iaitu 0, 35, dan 70 °Brix dengan

menggunakan rendaman ultrasonik pada kuasa 0 – 2.5 kW untuk masa rendaman

sebanyak 20 – 40 minit dan pada masa yang sama, eksperimen juga dijalankan

dengan menggunakan kuar ultrasonik pada amplitude 0 – 35% untuk masa rendaman,

6 – 20 minit. Kehilangan air, perolehan gula, pengurangan berat dan perubahan

warna telah ditingkatkan dengan ketara (P < 0.0005) dengan kuasa ultrasonik atau

amplitud ultrasonik, masa rendaman, dan kepekatan larutan osmotik. Sonikasi tidak

langsung dengan sistem rendaman ultrasonik pada 1.75 kW dan 60 minit masa

rendaman untuk kepekatan larutan osmostik pada 70 °Brix telah menyumbangkan

kehilangan air yang tertinggi sebanyak 34.34%, perolehan gula yang tertinggi

sebanyak 8.85%, pengurangan berat yang tertinggi sebanyak 24.17% dan perubahan

warna yang boleh diterima berbanding dengan sonikasi langsung dengan kuar

ultrasonik.

Kesan-kesan pra-rawatan osmotik berultrabunyi pada optimum untuk ketiga-tiga

kepekatan larutan osmotik, iaitu 0, 35, dan 70 °Brix sebelum pengeringan udara-

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panas pada suhu optimum, iaitu 70 °C terhadap sifat pengangkutan dan sifat kualiti

jambu batu kering telah dikaji. Aplikasi pra-rawatan osmotik berultrabunyi dalam

pengeringan udara-panas telah mengurangkan masa pengeringan sebanyak 33.3%,

meningkatkan kemeresapan sebanyak 34.5%, mengurangkan perubahan warna bagi

jambu batu kering sebanyak 37.9%, menurunkan kandungan vitamin C sebanyak

32.5%, dan mencapai kekerasannya iaitu 430.1 g – 469.6 g yang setanding dengan

jambu batu segar. Penggunaan ultrabunyi dalam proses pengeringan buah-buahan

amat digalakkan untuk meningkatkan proses pengeringan dan juga kualiti-kualiti

produk kering.

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ACKNOWLEDGEMENTS

I would like to express my highest gratitude and appreciation to my esteem

supervisor, Assoc. Prof. Ir. Dr. Chin Nyuk Ling, for her precious advice, patience

teachings, guidance, encouragement, motivation, and kindness in assisting me

throughout the research. I wish to thank Assoc. Prof. Dr. Yus Aniza binti Yusof for

her valuable comments and advice throughout my time in research.

My sincere appreciation also dedicated to the technicians of Process and Food

Engineering Department laboratory, Mr. Mohd Zahiruddin, Tuan Haji

Kamarulzaman Dahlin, and Mr. Raman Morat. I would like to thank them for their

guidance, advices, and help assistance during my experiments. Thus, I would like to

specially thank to Mr. Raman Morat for his patience waiting and accompanying me

each time I did my experiments till late night and even in the weekends. Thank you

also to Mr. Chong for supplying the big guava for this study.

Last but not least, I would like thank my course-mate, Quek Meei Chien, and seniors,

Teng Li Yuen, Tan Mei Ching, Chia Su Ling, and Chan Ken Wei for their helps,

accompany, comments, and encouragement. My love and thanks to my parents and

family for giving me their endless love and support throughout my study.

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I certify that a Thesis Examination Committee has met on 27 August 2012 to

conduct the final examination of Kek Siok Peng on her thesis entitled “Modelling,

Optimisation and Ultrasound Pre-osmotic Treatment of Guava Drying” 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 degree of Master of Science.

Members of the Thesis Examination Committee were as follows:

Siti Mazlina Mustapa Kamal, PhD

Associate Professor

Faculty of Engineering

Universiti Putra Malaysia

(Chairman)

Rosnita A. Talib, PhD

Senior Lecturer

Faculty of Engineering

Universiti Putra Malaysia

(Internal Examiner)

Farah Saleena Taip, PhD

Senior Lecturer

Faculty of Engineering

Universiti Putra Malaysia

(Internal Examiner)

Ida Idayu Muhamad, PhD

Associate Professor

Faculty of Chemical Engineering

Universiti Teknologi Malaysia

(External Examiner)

________________________________

SEOW HENG FONG, PhD

Professor and Deputy Dean

School of Graduate Studies

Universiti Putra Malaysia

Date:

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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:

Ir. Chin Nyuk Ling, PhD

Associate Professor

Faculty of Engineering

Universiti Putra Malaysia

(Chairperson)

Yus Aniza binti 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.

__________________________

KEK SIOK PENG

Date: 27 August 2012

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TABLE OF CONTENTS

Page ABSTRACT ii

ABSTRAK iv

ACKNOWLEDGEMENTS vii

APPROVAL viii

DECLARATION x

LIST OF TABLES xiv

LIST OF FIGURES xvi

LIST OF ABBREVIATIONS xviii

NOMENCLATURE xix

CHAPTER

1 INTRODUCTION 1

1.1 Significance of this Study 1

1.2 Objectives 3

1.3 Scope of Work and Thesis Outlines 4

2 LITERATURE REVIEW 6

2.1 Guava 6

2.2 Drying 9

2.3 Modelling 11

2.3.1 Theoretical Modelling 12

2.3.2 Time-Temperature Superposition Technique Modelling 15

2.3.3 Statistical Modelling 18

2.4 Ultrasound 19

2.4.1 Ultrasound Application as Pre-treatment in Fruit Drying 20

2.4.2 Ultrasound System 21

2.4.3 Processing Parameters 22

2.5 Dried Fruit Quality Analysis 26

2.5.1 Colour 28

2.5.2 Water Activity 29

2.5.3 Vitamin C 30

2.5.4 Texture 32

2.6 Summary 35

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3 MATERIALS AND METHODS 36

3.1 Introduction 36

3.2 Materials 36

3.3 Drying Process 37

3.4 Determination of Effective Diffusivity 38

3.5 Model Development 40

3.5.1 Theoretical Modelling of Drying Kinetics 40

3.5.2 Superposition Modelling of Drying Kinetics 41

3.5.3 Statistical Modelling of Quality Properties 43

3.5.4 Response Optimisation of Quality Properties 44

3.5.5 Verification of Model 46

3.6 Ultrasound Pre-osmotic Treatments 46

3.6.1 Indirect Sonication 47

3.6.2 Direct Sonication 48

3.6.3 Determination of Effective Ultrasound Intensity 50

3.6.4 Determination of Water Loss, Solid Gain and Weight

Reduction 51

3.7 Ultrasound Pre-osmotic Treatments assisted to Hot-air Drying 52

3.8 Dried Guava Quality Properties Analysis 53

3.8.1 Water Activity 53

3.8.2 Colour 53

3.8.3 Vitamin C 54

3.8.4 Texture 55

3.9 Experimental Design 56

3.10 Statistical Analysis 57

4 MODELLING AND OPTIMISATION STUDIES OF HOT-AIR

DRIED GUAVA SLICES 59

4.1 Introduction 59

4.2 Drying Characteristics of Dried Guava 60

4.3 Effective Diffusivity 62

4.4 Drying Kinetics with Semi-theoretical Models 64

4.5 Drying Kinetics with Time-Temperature Superposition

Technique 69

4.6 Statistical Model for Product Quality of Dried Guava 71

4.7 Optimisation of Dried Guava Attributes 81

4.8 Verification of Optimised Drying 83

4.9 Summary 85

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5 DIRECT AND INDIRECT ULTRASOUND ASSISTED PRE-

OSMOTIC TREATMENT IN DRYING OF GUAVA SLICES 86

5.1 Introduction 86

5.2 Effect of Ultrasound Pre-osmotic Treatment on Guava Slices 86

5.2.1 Temperature Rise Profiles and Effective Ultrasound

Intensity 87

5.2.2 Water Loss 89

5.2.3 Solid Gain 92

5.2.4 Weight Reduction 93

5.2.5 Colour Change 95

5.2.6 The Optimum Condition for Ultrasound Pre-osmotic

Treatment 96

5.3 Effects of Ultrasound Assisted Pre-osmotic Treatment on Hot-air

Dried Guava 98

5.3.1 Drying Time, Effective Diffusivity and Drying Rate

Constant 99

5.3.2 Quality Properties of Dried Guava 102

5.4 Summary 107

6 SUMMARY, CONCLUSION AND RECOMMENDATIONS FOR

FUTURE RESEARCH 108

6.1 Introduction 108

6.2 Summary and Conclusion 108

6.3 Recommendations for Future Work 110

REFERENCES 111

APPENDICES 120

BIODATA OF STUDENT 143

LIST OF PUBLICATIONS 144

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