UNIVERSITI PUTRA MALAYSIA CHARACTERISTICS AND …

UNIVERSITI PUTRA MALAYSIA

CHARACTERISTICS AND POTENTIAL USE OF GUAVA (PSIDIUM GUAJAVA L) FOR PROCESSING OF

CONCENTRATE

SALMAH BINTI YUSOF

FSMB 1989 2


CONCENTRATE

SALMAH BINTI YUSOF

DOCTOR OF PHILOSOPHY UNIVERSITI PERTANIAN MALAYSIA

1989


CONCENTRATE

By

SALMAB BINTI YUSOF

Thesis Submitted in Fulfi�ent of the Requirements for the Degree of Doctor of Philosophy

in the Faculty of Food Science and Biotechnology Universiti Pertanian Malaysia

June 1989

Dedic ated to be loved husband :

s ons :

Zakaria Abd . Rah man

Azlan Sazali Izham

Razwan Ahmad Faisal

and daughte r :

L iyana Yasmin

ACKNOWLEDGEMENTS

The author wishes to exp res s her gratitude and thanks to

Dr. Abdullah Abu Bakar and Dr. Suhaila Mohamed for their

s upervis ion , c ons truc tive c ritic isms and guidance in c arrying

out this study.

Gratitude and thanks are als o due to As s o c iate Pro fes s o r

Oh Beng 'Tatt , fo rmerly a lec turer at the Department o f Animal

Sc ience , Faculty o f Veterinary Medic ine and Animal Sc ienc e ,

UPM for allowing the fir s t part o f the s tudy to be c onduc ted

at his guava farm; to Puan Aminah Ju s oh o f th e s ame faculty

for helping with the u s e o f Elec tron Mis c r oscope; to A s s o c iate

Profes s o r Dr. Ruth Kiew and Ms. Sulika Madhavan , Department of

Biology , Faculty o f Sc ience and Environmental Studies , UPM,

for extending their help during the identific ation o f s tone

c ells and to Puan Zaharah Talib , Statis tic s Department,

for helping with th e Statis tical Analy s is Sys tem

graphic s .

MARDI

( SAS )

The author is als o ind ebted to the s upport and

c ooperation given by c olleages and s taff o f the Fac ulty of

Food S c ienc e and Biotechnology in many way s es pec ially to Puan

Naimah Ahmad for typing the manu s c r ip t and to UPM for

extend ing the fund needed to c ar ry out the research.

iii

Last but not least, the author would like to express her

gratitude to her hus band and children for their encouragement ,

love and understanding during the cours e of this s tudy .

iv

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS iii

LIST OF TABLES

LIST OF FIGURES

LIST OF PLATES

x

xii

xv

xvi

xvii

LIST OF ABBREVIATIONS

ABSTRACT

ABSTRAK

CHAPTER

1

2

xx

INTRODUCTION 1

LITERATURE REVIEW 12

Growth and Development of Guava . . . . . . . . . . . 1 2

Proximate Composition

Nutritional Value

13

15

Important Biochemic al Composition . . . . . . . . • . 1 6

Acid Content . . . • . . . • . • . • • . . . • • • . . . . . . . • 16

Pigment 1 6

Flavour Components . . . . . . . . . . . . . . . . . . . . . 1 7

Tannins

Pectic Substances

v

1 8

20

3

4

Page

Problems As s oc iated With Guava Product . • . . . 21

Stone Ce l l s 21

Non-enzymatic Browning 23

Pulp Separation . . • . . • . • . • . . . . . . . . . . . . . 24

PHYSICO-CHEMICAL CHANGES DURING DEVELOPMENT AND MATURATION OF GUAVA ( PSIDI UM GUAJAVA L ) • . • . . . . • . • • • . . . . . . • . • . .

Int roduction

Materia l s and Methods

Materia l s

Sampl ing

Phy s ical Analy s i s

Chemical Analy s is

Re sults and Discus s ion

Phy s ical Changes During Growth

Chemical Change s During Growth

29

29

30

30

31

31

32

32

32

40

SUIrlDlary • • • • . i • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 54

EFFECT OF FRUIT MATURITY ON THE STRUCTURE OF STONE CELL S . . • . . • • . . . . . . . . . . . 55

Introduc tion 55

Ma terial s and Me thods . . . . . . . . . . . . . . . . . . . . . . 56

Materials 56

Det e rminat ion of Stone Cel l s 61

vi

5

Result s and D is cus s ion

S umma ry

EFFECT OF MATURITY ON THE QUALITY AND ACCEPTABILITY OF GUAVA P UREE

Int roduc tion

Mate rials and Methods

Mate rials

Phy s ic a l and Chemic a l Ana ly s is

Sampling P rocedure

Preparation of Puree

Measurement of Colour

Measurement of Vis c o s ity

Sensory Evaluation

Re sults and Discus s ion

Hardnes s and Mois ture Content

Total Soluble Solids and Suga r

Page

62

6 6

68

6 8

69

69

69

70

70

70

71

71

72

72

Content . • . • . . • . . . • • . • . • • . . . . . . .... .. . 75

Tit ratable Ac idity 78

Tannin 81

As corbic Ac id 84

Sensory Evaluation o f Puree 84

Co lour 86

vii

6

7

Page

Vis co s ity. Soluble Pectin and Cellulo s e . • . . . . . . • . • . • • • . . . • . . . . • . . . . . 89

Sununary

INFLUENCE OF pH. BRIX AND PROCES S I NG TEMPERATURE ON THE PHYS I CAL. CHEMI CAL AND SENSORY CHARACTERI STICS OF GUAVA CONCENTRATE .............................. .

Introduction

Materials and Methods

Materials

Methods

93

94

94

95

95

96

Exp erimental Des ign . • . . . • • . . . . . . • . • . . . . 96

Evaluation

Results and Dis cu s s ion

Statis tical Analysis

Respon s e Contou r s

Sununary

EFFECTS OF TEMPERATURE. STABILI ZERS AND ANTIBROWNING AGENTS ON THE S TORAGE S TABI LITY OF GUAVA CONCENTRATE • . . . . . • . . . . •

Introduction

Materials and Method s

Materials

Methods

viii

99

101

101

105

119

121

121

122

122

122

8

Page

Results and Discus s ion 125

Qual ity Changes During Storage of Guava Puree • • . . . . . . • . • . • . . • . • • . . . . . . . . 125

E ffect of Ant ib rowning Agents . . . . . . . . . 1 42

E ffe ct of Stabilizers on Stored Guava Puree 146

l\JIIID.a ry . • • • • • . • • . • . . • • • . • . . • • • • . • . • • • . • . • 149

CONCLUSION AND RECOMMENDATIONS 150

BIBLIOGRAPHY 153

APPENDICES 1 6 4

PUBLICATIONS 189

BIOr,RAPHICAL SKETCH 228

ix

Table

1

2

3

4

5

6

7

8

9

10

11

12

LIST OF TABLES

Area Under Guava Cultivation According to States and Number of Farmers Involved in Guava Cultivation in Peninsular

Page

Malaysia in 1 987 • • • . • • . . • • • • . • . • . . . . • . • . . . 3

Area Under Guava Cultivation According to District and Number of Farmers Involved in 1 987 . . . . . . • • • • . . . • . . . . . • . . . . . .

Area (hectares) Under Guava Cultivation According to State and Type of Guava Planted in 1987 • . • . • . . . . . . . . . • • . . • . . . . . . . •

Total Production of Guava (metric tons ) According to State and Type of Fruit in 1 987 • . . • • • . . . • • . • . . . . • . . . . • . . . • . . . . • . • .

Composition of Guava per 100g of Edible Portion . . . . . • . . . . . . . . • • . . . . . . . . . . . .

Means of Sensory Panel Score for Flavour and Aroma . . . . . . . . • . . • • . . • . . . . . . . • .

Effect of pH, Temperature, Brix Combination on Seven Dependent Variables . . . . . • . • . . . . . .

Levels of Independent Variables and Their Codes • . • • • • . . . . • . . • . . • . • . . . . . . . . . . . .

Central Composite Rotatable Design for Three Factors • . . • • • . • . • • . . • . . . . . • • • . . .

Analysis of Variance for Seven Dependent Variables ...................... .

Regression Coefficients for Five Dependent Variables .... . .... . . ........... .

Means of Sensory Panel Scores for Colour, Flavour and Aroma . • . . . . . . . . • . . . . . . . . . . . . . .

x

4

8

1 0

1 4

86

9 7

9 8

9 9

102

1 0 4

1 4 1

Table

13

14

15

16

17

Mean Values and Standard Deviation (±) for Various Physical and Chemical Changes During Development and Maturation ................................. .

Mean Values and Standard Deviation (±) for Various Physical and Chemical Characteristics of Guava at Different Stages • . . . . . . . . . • . . • . • . • • • . . • • . . . . . . . • . . . . . .

Mean Values and Standard Deviation (+) for Colour 'L' Value of Concentrate After Treatment with Antibrowning Agents .......... .

Mean Values and Standard Deviation (±) for Height of Separation of Pulp ............ .

Mean Values and Standard Deviation (+) for Various Physico-chemical Characteristics of Guava Concentrate During Storage . . . . . . . . • .

xi

Page

172

179

186

187

188

Figure

1

2

3

4

5

6

7

8

9

10

LIST OF FIGURES

Weight of Guava Fruits During Development and Maturation . . . . . . . • . . . • . . . . • . • • • . . . . . . . . . •

Diameter of Guava Fruits During Development and Maturation • . . • • . • . . . • • . . . • • . . • . . . . . . . . . •

Log Transformation for Weight and Diameter

Average Density of Guava Fruits During Development and Maturation • . . . • . . . . . • . . . . . . . .

Texture of Guava Fruits During Development and Ma tura tion . . • • . . • . • • • • . . • • • . • • . . . . . . • . . •

Moisture Content of Guava Fruits During Development and Maturation . • . . . . . . . . . . . . . . . .

Chlorophyll Content of Guava Fruits During Development and Maturation . . . . . • . . . . . . . . . . . . .

Titratable Acidity of Guava Fruits During Development and Maturation . . . . • . . . . . . . . . • . . . .

pH of Guava Fruits During Development and Maturation .............................. .

Sugar Content of Guava Fruits During Development and Matu.:ation • . . . . . . . . . . . . • . . . .

Page

33

35

36

38

39

41

42

44

45

47

11 Total Phenol Content of Guava Fruits

12

During Development and Maturation . . . . . . . . . . . . 49

Pectin Content of Guava Fruits During Development and Maturation .................. . 51

13 Ascorbic Acid Content of Guava Fruits

14

During Development and Maturation . . . . .. . . . . . . 53

Texture of Guava Fruits at Different Stages of Maturity .......................... . 73

xii

Figure

15

16

17

18

19

20

21

22

Moi sture Content of Guava Fruit s at Different S tage s o f Maturity . . • • . . . . . . . . . . . . . . . .

Protope c t in Content o f Guava Fruits at Different S tage s o f Maturity . . • . . . . . . . . . . . • . .

Total Soluble Solids Content o f Guava Fruits at Different S tage s o f Maturity . . . . . . . . . . . . . .

Sugar Content o f Guava Fruit s at Different Stage s of Maturity . . . . . • . . . • . . . . . . • . . . . . . . . . .

Titratable Ac idity o f Guava Fruits at Different S tage� 9f Maturity . • • . . • . . . . . . . . • . •

pH of Guava Fruit s at Diffe�ent St ages of Maturity . . . . . . . . . • . . . 0 • • • • • • • • • • • • • • • • • • • • •

Tannin Content of Guava Fr�ifs at �ifferent S tage s of Maturity . . . . • . . . . . . . . . . . . . . . . . . . . . .

Ascorbic Ac id Cont ent o f Guava Fruits at Different S tage s o f Maturity . . . . . . . . . . . . . . . .

23 Colour of Puree from Fruit s at Dif ferent

24

25

26

27

28

29

S tage s of Maturity

Viscos ity of Puree from Fruits at Different Stage s of Maturity . . . . . . . . . . . . . . . . . . . . . . . . . .

Cellulo s e Content o f Guava Fru i t s at Different S tages o f Ma turity . • . . . . . . . . . . . . . .

Soluble Pect in Content of Guava Fruits at Different S tages o f Ma turity • . . . • . . . . . . . . . . .

Contours for Colour Re s pon s e at Cons tant pH (A) and Brix (B ) ; Con s t ant Temperature (C ) and Brix (D) ............................ .

Contours for Colour Re s pons e at Cons tant Brix and Constant pH . . . . . . . . . . • . . . . . . . . . . . . .

Contours for Overall Acceptabil ity Re sponse at Cons tant pH . • . . . . . . . . . . . . . . . . • . .

xiii

Page

74

76

77

79

80

82

83

85

87

90

91

92

107

109

112

Figure

3 0

3 1

32

33

3 4

3 5

3 6

3 7

3S

3 9

4 0

4 1

4 2

4 3

4 4

Contours for Overal l Accep tab il ity Response at Con s tant B r ix . • . • • . . . . . . . . . . . � .

Contours for Optimum Flavour Response

Colour ' a ' Value o f Guava Concentrate Sto red at 28°C and 3 8°C . • . . • . • . . . . . . . . . . . . .

Colour ' L ' Value o f Guava Conc ent rate Stored at 2S o C and 3S o C • • . • . . • • . . • . . . . . . . .

Asc orbic Ac id Content o f Guava Concent rate Sto red at 28°C and 3 8°C . . • • • . . • • . . . . . . . . . .

Total Ca rbohydrate Content or Guava Concent rate Stored at 28°C and 38°C

Amino Nit rogen Content of Guava Concent rate Sto red at 28°C and 38°C . . . . . . . . . . . . . . . . . . .

pH of Guava Conc entrate Sto red a t 2SoC and 38°C . . . . . • . . . . . . . . . . . . . . . . • . . . . . . . . . . . .

Total Solub le Solids Content of Guava Concent rate at 2SoC and 3SoC . • . . . . . . . . . . .

Titratable Ac idity o f Guava Conc ent rate Sto red at 2SoC and 3S o C . . . . • • . . . . . . . . . . . .

Viscos ity of Guava Concent rate Sto red at 28°C and 3 8°C . • . . . . . . . . . . . . . . • . . . . . . . . . . . . .

Effec t o f Ant ibrowning Agent s on Colour o f Guava Concentrate . . . . . . . • . . . • . . . . . . . . . . .

React ion o f Cy s t ein Hydrochloride with Polypheno l s . . . . . . . . . . . . . . . . . . . . . . . . . . .

Effect o f Stabil izers on Guava Pulp S tab i l ity at 28°C . . . . . . . . . . . . . . . . . . . . . . . . .

Effec t o f Stab i l izers on Guava Pulp Stability at 38 °C . . . . . . . . . . . . . . . . . . . . . . . . .

xiv

Page

115

118

126

1 2 7

128

131

132

1 3 4

1 3 5

1 3 6

1 4 0

14 3

1 4 4

1 4 7

148

LIST OF PLATES

Plate Page

7

1 Stage 1: Dark Green Guava Fruit . . . . . . . . . . . . . 57

2 Stage 2: Green Guava Fruit . . . . . . . . . . .. . . . . . . 57

3 Stage 3: Light Green Guava Fruit . . . . . . . . . . . . 58

4 Stage 4: Yellowish Green Guava Fruit . . ........ 58

5 Stage 5: Light Yellow Guava Fruit . .. . . . ..... . 59

6 Stage 6: Bright Yellow Guava Fruit . . . . . . . . . . . 59

& 8 Types of" Stone Cells Found in Guava (Both x 40) . . . . . . . . . . . . . . . . . . . . ... . . . . . 64

9 Initial Thickening of Certain Parenchyma Cells (x 300) . . . . • • • • • . . . . . . . . . . . . . 64

10 Prominent Thickening of Parenchyma Cells (x 400) . . . . . . . . . . . . . . . • • . . . . . . . . . . ... . . 64

11 Structure of Cell Wall (x 3000) ............... 65

12 Stone Cells in Actual Arrangement in the Tissue of Guava (x 72) ................... 65

13 & 14 Appearance of Fully Developed Stone Cells (x 300, 200 r�spectively) .............. 65

15 Pulp Separation During Storage of Guava Concentrate . . . . . . . . • . . . . . . . . . . . . . . . . . . . 138

xv

LIST OF ABBREVIATIONS

kg kilogram g gram mg milligram m meter mm millimetre ml millilitre mt metric tonne cm centimeter sq square min minute hr hour ppm parts per million ha hectare N normality

J.L micron r.p . m. revolution per minute

xvi

Abstract of the The sis P re s ented to the Senate of Unive rsiti Pe rtanian Malay s ia in Fulfilment of the

Requi rement s for the Degree o f Doctor of Philosophy


CONCENTRATE

By

SALKAH BT. YUSOF

June , 1989

Supe rvisor Abdul lah Abu Bakar Ph . D .

Co- supervisor: Suhaila bt . Mohamed Ph . D .

Faculty Food Sc ience and B iotechnology

Studie s were conducted to determine the cha racte ri stics o f

guava ( P s id ium guajava L) cv. Vietname s e of its potential use

for proce s s ing it into guava concentrate . A matur ity study

showed that the guava took 16 weeks to reach maturity .

The be s t indice s of maturity we re s ize , mo isture , suga rs and

tannin content s . The moi s ture content at the mature stage was

94% . The fructo se , glucos e and sucro s e contents were 2 . 02% ,

1 . 08% and 1 . 54% , respect ively . The tannin content in the

matured guava was low ( 37. 0 mg/10 gm s ample ) but the vitamin C

c ontent was high ( 76 mg / 100 g s amp le ) .

xvii

The s t ruc ture o f s tone c e l l s in guava fruit s we re examined

mic ros c opically . The s tone c e l l s became more prominent with

inc rease in fruit matur ity , hence the prepared puree we re

pulve rised in o rde r to improve i t s texture . S tudie s on the

qua lity of puree produc ed from fruits at diffe rent s tage s of

maturat ion showed that a puree of de s ireable quali ty wa s

obtained from fruit s at the ye l low green s tage ( s tage 4 ) .

Art ific ial r ipening was nec e s s a ry to soften the fruits to make

them ideal for p ro c e s s ing into conc entrate o r puree . F ruit s at

the yel low green s tage had an inc rease in solub le pectin

content to 67% . Thi s inc re a s e d the v i s c o s i ty of puree . The

vitamin C c ont ent also inc rea sed from 79 . 7 mg - 131 . 1 mg / lOO g

s ample . The puree showe d l e s s tendency to turn brown due to

the low tannin c ontent s (21 mg / 10 g s amples) .

The optimum condit ions o f pH , p roc e s s ing tempe rature and

total soluble s o l ids c ontent ( b rix ) to p roduc e an acceptable

guava concent rate was de t e rmined u s ing a Re sponse Surface

Methodo logy . Maximum ove rall ac ceptability was obtained from

guava c oncent rate having an opt imum pH - 3 . 3 - 3 . 9 ; proc e s s ing

tempe rature - 79 . loC and brix - 35 ° B - 55 ° B was cho s en .

Storage s tudies on guava c oncent rate showed that browning

and pulp sepa rat ion we re the main prob lems , followed by lo s s e s

in a s c o rbic ac id c ontent and titratable ac idity . The re we re no

s ignificant change s in amino nit rogen content. total suga rs.

xviii

brix and pH. Temperature showed no influence on the rate of

loss of viscosity. The use of 0.1% and 0.3% sodium

carboxymethyl cellulose (NaCKC) was effective in stabilizing

the pulp for 9 weeks.

xix

Abs t rak Te s is Yang Dikemukakan Kepada Senat Unive r s it i Pertanian Malay s ia S ebagai Memenuhi Syarat

Keperluan Untuk Ijazah Doktor Fal s a fah

CIRI-CIRI DAN POTENSI PENGGUNAAH BUAH JAHBU (PSIDIUM GUAJAVA L) JENIS VIETNAM UHTUK PEHPROSESAN

PATI JAMBU

Oleh

SALHAH BT. YUSOF

Jun , 1989

Penye l ia Abdul l ah b in Abu Bakar Ph. D .

Penye lia Bersama : Suhaila bt . Mohamed Ph . D .

Fakulti Sains Makanan dan Biotekno logi

Kajian te lah dijalankan untuk mengkaji c iri-c iri buah

j ambu ( P s idium guajava L) kul t ivar Vie tnam tentang potens inya

untuk pemprose s an pati jambu . Kajian kematangan menunjukkan

buah jambu mengambi l ma s a 16 minggu untuk mencapai kematangan .

Petunjuk kemat angan yang te rbaik ialah saiz , kandungan

kelembapan , gula dan tannin. Kandungan kelembapan buah di tahap

kemat angan ialah 94% . Kandungan frukto s a , gluko sa dan sukro sa

ialah ma s ing-ma s ing 2 . 02% , 1 . 08% dan 1 . 5 4% . Kandungan tannin

didapa ti rendah (3 7 . 0 mg / l O g s ampel) tet api kandungan vitamin

C ada lah tinggi ( 7 6 mg / lO O g sampe l) .

xx

S truktur s e l batu didalam buah j ambu telah dite l i t i dengan

menggunakan mikro skop . Sel-sel batu didapati menj adi bertambah

besar semakin buah mas ak , o leh itu pulpa yang disediakan perlu

dihaluskan untuk mempe rbaiki tekstur pur i . Kaj ian ke atas

kualiti puri yang diha s ilkan dari buah pada tahap kematangan

yang be rlainan menunjukkan bahawa puri yang mempunyai kua liti

yang d ipe rlukan dapat dihas i lkan dari buah pada peringkat

kekuningan ( pe r ingkat 4 ) . P ro s e s peme raman diperlukan untuk

me lembutkan buah s upaya mudah dipro s e s kepada pati atau puri

jambu . Buah di peringkat ma s ak kuning hijau mempunyai

kandungan pektin larut air yang bertambah kepada 67% . Ini

menjadikan puri lebih pekat . Kandungan vi tamin C bertambah

dari 79 . 7 mg - 1 3 1 . 1 mg / 100 g samp e l . Puri yang didapati juga

tidak mudah bertukar warna menjadi pe rang dis ebabkan kandungan

tannin yang rendah ( 2 1 mg /IO g sampe l ) .

Keadaan opt imum bagi pH , s uhu pemp ro s e s an dan kandungan

pepejal larut ( brix ) bagi mcngha s ilkan pati jambu yang s e suai

te lah ditentukan dengan menggunakan kae dah ' Re sponse Surface . '

Satu komb ina s i yang s e suai bagi pene r imaan k e s e lu ruhan yang

maks imum, pH - 3 . 3 - 3 . 9 ; suhu pemprose san = 79 . 1°C dan brix

35°B - 55°B te lah dipilih .

Keputusan kajian s impanan keatas pati jambu menunjukkan

b ahawa peme rangan dan p e rp i s ahan pulpa menjadi masalah utama,

diikut i dengan kehilangan kandungan a s id askorb ik dan

xxi

keasidan. Tiada perubahan yang ke tara didapati bagi kandungan

amino nitrogen, gula, brix dan pH. Suhu tiada mempengaruhi

kadar penurunan kepe katan puri. Penggunaan 0.1% dan 0.3%

naterium karboksime tilselulos (NaCKC) didapati berke san

menghalang pemisahan pulpa sehingga 9 minggu.

xxii

CHAPTER 1

INTRODUCTION

Guava ( P s idium guajava ) h a s been cul t ivated in Ma lay s ia

for a long t ime (Al len , 1 9 6 7 ) but has neve r rece ived a s much

attent ion a s today . The plant which originated f rom t rop ical

Ame rica ( Ruehle , 1948 ) ha s sp r�ad t o all t ropical and s ubtro

p ical count rie s and has become e specially important in Cuba

(Coit , 1945 ) , Hawa ii ( Haye s , 1 9 5 7 ) and India ( Sams on , 198 0 ) .

The genus P s idium cons i s t s o f about 1 5 0 spe c i e s o f which

only P s idium guajava is o f economic importanc e . Nume rous

varie t ie s are in existence ranging from the wild or unse lected

forms having sma l l thick rinde d , th in fle shed fruits to highly

imp roved produc t ive precoc ious c l one s with large exc e l lent

fruit s . Previous ly , in Ma lay s i a , it wa s reported that the re

we re 18 varie ties grown (Mohd . Noo r et a l . , 198 0 ) . Howeve r ,

due to the ir relative ly low fruit qua l ity coup led with

difficult maintenance none of the recommended varie t ies (Gu 3 ,

Gu 4 , Gu 5 , Gu 6 and Gu 7 ) had been grown on la rge s c ale .

Guava f ruit i s a very r ich s ourc e of vitamin C . The plant

i s ve ry hardy and is able to grow in a wide range o f soil

c ondition . In countrie s l ike Cuba and Hawa ii guavas have

become a mi l l ion dollar indus t ry . Loc a l ly , it wa s only during

late sevent ie s and early 1 9 8 0 that the re wa s renewed intere s t

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UNIVERSITI PUTRA MALAYSIA CHARACTERISTICS AND …

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