ANTIOXIDATIVE VALUES AND CUSTOMER
PREFERENCE OF SWEETPOTATO (Ipomoea batatas)
FLOUR AS COMPARED TO
WHEAT (Triticum aestivuni) FLOUR
BY
MOHAMAD RAZLAN ABD RAHMAN
A dissertation submitted in partial fulfilment of
the requirements for the degree of Master of Medical
Sciences (Biochemistry)
Kulliyyah of Medicine
International Islamic University Malaysia
FEBRUARY 2009
ABSTRACT
Sweet potato is one of the most widely consumed root crops in the tropics especially
in Malaysia. This study aims at comparing the antioxidative values of wheat and sweet
potato flours and to evaluate customers’ preference towards bakery products made
from the flours. The study was divided into 3 phases which were phase 1 (Sampling
and flour production), phase 2 (Extraction, determination of components and activity
of antioxidants in sweet potato and wheat flours), and phase 3 (Food processing and
evaluation). Phase 1 concluded that the recovery rate from fresh sweet potatoes
(Ipomoea batatas) roots to flour was about 20-30%. In phase 2, antioxidant activities
of MeoH extracts of the flours were evaluated by two in vitro systems, the DPPH
radical scavenging and β-Carotene bleaching assays. The extracts had different levels
of antioxidant activity in the systems tested where it ranged from 0.09 to more than 10
mg/ml. The antioxidant activities (effective concentration, EC50 mg/ml) of the three
varieties of sweet potatoes are in the order of VitAto steam (0.69 mg/ml) > Jalomas
steam (0.81 mg/ml) > Telong steam (0.94 mg/ml) and with a p-value of 0.11 when
compared to raw-treated sweet potatoes. Also, the phenolic contents ranged from 1.55
to 8.34 mg/g among the sweet potato extracts. Total phenolic concentration, expressed
as mg gallic acid equivalents (GAE)/g of methanolic extracts did not show correlation
with the antioxidant activity (R2 = DPPH/Phenolics was 0.051). Nevertheless phase 3
showed participants’ preference for buns 1 and 2; and muffins 1 and 2 where (1 = 75%
sweet potato flour) and (2 = 100% wheat flour). Results showed a p-value of 0.028 for
muffins and 0.006 for buns, concluding that there was a significant difference between
preference for buns 1 and 2; and between muffins 1 and 2. In short, our local sweet
potato flours have potential as alternatives to wheat flour because of comparable
antioxidative values and they can be a source of staple food besides rice in our
country.
ii
‫‪ ‬‬
‫ﺨﺺ اﻟﺒﺤﺚ‬
‫ﻣﻠ ّ‬
‫ﺗﻌﺘﺒﺮ اﻟﺒﻄﺎﻃﺎ اﻟﺤﻠﻮﻩ )‪ (Ipomoea batatas‬واﺣﺪﻩ ﻣﻦ اآﺜﺮ اﻟﻤﺤﺎﺻﻴﻞ اﻟﺰراﻋﻴﻪ اﻟﻨﺎﻣﻴﻪ ﻓﻲ‬
‫اﻟﻤﻨﺎﻃﻖ اﻻﺳﺘﻮاﺋﻴﻪ وﺧﺼﻮﺻﺎ ﻣﺎﻟﻴﺰﻳﺎ‪ .‬هﺪﻓﺖ هﺬﻩ اﻟﺪراﺳﻪ اﻟﻰ ﺗﻘﻴﻴﻢ ﻓﻌﺎﻟﻴﺔ اﻟﺒﻄﺎﻃﺎ اﻟﺤﻠﻮﻩ‬
‫آﻤﻀﺎدات ﻟﻼآﺴﺪﻩ ﺑﺎﻻﻇﺎﻓﻪ اﻟﻰ ﺗﻘﻴﻤﻬﺎ آﻤﺼﺪر ﻣﻦ ﻣﺼﺎدر اﻟﻐﺬاء ﻣﻦ ﻗﺒﻞ اﻟﻤﺴﺘﻬﻠﻜﻴﻦ‪ .‬ﻗﺴﻤﺖ‬
‫هﺬﻩ اﻟﺪراﺳﻪ اﻟﻰ ﺛﻼﺛﺔ ﻣﺮاﺣﻞ اﻻوﻟﻰ ﺟﻤﻊ اﻟﻌﻴﻨﺎت وﺗﺤﻀﻴﺮ اﻟﺨﺒﺰ ﺣﻴﺚ ﺗﻢ اﺳﺘﺨﻼص ‪-20‬‬
‫‪ 30%‬آﺨﻼﺻﻪ ﻧﻬﺎﺋﻴﻪ ﻣﻦ اﻟﺒﻄﺎﻃﺎ اﻟﻄﺎزﺟﻪ‪ .‬اﻟﻤﺮﺣﻠﻪ اﻟﺜﺎﻧﻴﻪ وﻓﻴﻬﺎ ﺗﻢ ﺗﻘﻴﻴﻢ ﺧﻼﺻﺔ اﻟﻤﻴﺜﺎﻧﻮل‬
‫آﻤﻀﺎدات ﻟﻼآﺴﺪﻩ ﺑﺎﺳﺘﺨﺪام‪ DPPH radical scavenging‬و ‪β-Carotene bleaching‬‬
‫‪ assays‬ﺣﻴﺚ اﻇﻬﺮت اﻟﻨﺘﺎﺋﺞ ﻓﻌﺎﻟﻴﺘﻬﺎ اﺣﺼﺎﺋﻴﺎ )‪ (p-value of 0.11‬ﺑﻤﻌﺪل ‪ 0.09‬اﻟﻰ‬
‫‪10‬ﻣﻠﻐﻢ‪/‬ﻣﻞ وآﺎﻧﺖ ﺗﺴﺎوي ‪0.69‬ﻣﻠﻐﻢ ﻟﻨﻮع ‪ VitAto steam‬و‪ 0.81‬ﻟﻨﻮع ‪Jalomas steam‬‬
‫و‪ 0.94‬ﻟﻨﻮع ‪ Telong steam‬آﻤﺎ آﺎﻧﺖ ﻣﻜﻮﻧﺎت اﻟﻔﻴﻨﻮل ﻓﻴﻬﺎ ‪ 1.55‬اﻟﻰ ‪ 8.32‬ﻣﻠﻐﻢ‪/‬غ اﻣﺎ‬
‫ﺗﺮآﻴﺰ اﻟﻔﻴﻨﻮل اﻟﻜﻠﻲ )‪ (Total phenolic concentration‬ﻟﻢ ﻳﻈﻬﺮ اي ﻣﻌﺎﻣﻞ ارﺗﺒﺎط ﻣﻊ‬
‫ﻓﻌﺎﻟﻴﺘﻬﺎ آﻤﻀﺎدات ﻟﻼآﺴﺪﻩ‪ .‬اﻟﻤﺮﺣﻠﻪ اﻟﺜﺎﻟﺜﻪ ﻓﺎﻇﻬﺮت اﻟﻨﺒﺘﻪ ﻗﻴﻤﻪ ﻏﺬاﺋﻴﻪ ﻋﺎﻟﻴﻪ ﺑﺎﻟﻤﻘﺎرﻧﻪ ﻣﻊ‪buns‬‬
‫‪ 1‬و‪ 2‬وﻣﻊ‪ 1 muffins‬و ‪) 2‬ﺣﻴﺚ ان اﻟﺮﻗﻢ ‪ 1‬ﻳﺸﻴﺮ اﻟﻰ اﻟﺨﺒﺰ اﻟﻤﺤﺘﻮي ﻋﻠﻰ ‪ %75‬ﺑﻄﺎﻃﺎ‬
‫واﻟﺮﻗﻢ ‪ 2‬اﻟﻰ اﻟﺨﺒﺰ اﻟﺨﺎﻟﻲ ﻣﻦ اﻟﺒﻄﺎﻃﺎ( وآﺎﻧﺖ اﻟﻨﺘﺎﺋﺞ اﻻﺣﺼﺎﺋﻴﻪ ﺗﺸﻴﺮ اﻟﻰ وﺟﻮد اﺧﺘﻼف‬
‫ﻣﻌﻨﻮي ﺑﻴﻦ‪ buns‬و ‪ . muffins‬ﺑﺎﻻﻋﺘﻤﺎد ﻋﻠﻰ اﻟﻨﺘﺎﺋﺞ اﻟﺴﺎﺑﻘﻪ ﺗﻌﺘﺒﺮ اﻟﺒﻄﺎﻃﺎ اﻟﺤﻠﻮﻩ ذات ﻓﻌﺎﻟﻴﻪ‬
‫ﻋﺎﻟﻴﻪ آﻤﻀﺎدات ﻟﻼآﺴﺪﻩ وذات ﻗﻴﻤﻪ ﻏﺬاﺋﻴﻪ ﻋﺎﻟﻴﻪ ﻳﻤﻜﻦ اﺳﺘﺨﺪاﻣﻬﺎ آﻤﺼﺪر ﻟﻠﻐﺬاء اﻟﻰ ﺟﺎﻧﺐ‬
‫اﻻرز‪.‬‬
‫‪iii‬‬
‫‪ ‬‬
APPROVAL PAGE
I certify that I have supervised and read this study and that in my opinion it conforms
to acceptable standards of scholarly presentation and is fully adequate, in scope and
quality, as a dissertation for the degree of Master of Medical Sciences (Biochemistry).
…………………………
Mazidah Ahmad Mansur
Supervisor
I certify that I have read this study and that in my opinion it conforms to acceptable
standards of scholarly presentation and is fully adequate, in scope and quality as a
dissertation for the degree of Master of Medical Sciences (Biochemistry).
…………………………
Nor Zamzila Abdullah
Examiner
This dissertation was submitted to the Department of Basic Medical Sciences
and is accepted as partial fulfilment of the requirements for the degree of Master of
Medical Sciences (Biochemistry).
…………………………
Pakeer Oothuman Syed Ahamed
Head, Department of
Basic Medical Sciences
This dissertation was submitted to the Kulliyyah of Medicine and is acceptable as
partial fulfilment of the requirements for the degree of Master of Medical Sciences
(Biochemistry).
…………………………
Mohammed Fauzi Abdul Rani
Dean, Kulliyyah of Medicine
iv
DECLARATION
I hereby declare that this dissertation is the results of my own investigations, except
where otherwise stated. I also declare that it has not been previously or concurrently
submitted as a whole for any other degrees at IIUM or other institutions.
Mohamad Razlan Abd Rahman
Signature………………………
Date……………………..
v
A
INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA
DECLARATION OF COPYRIGHT AND AFFIRMATION
OF FAIR USE OF UNPUBLISHED RESEARCH
Copyright @ 2009 by Mohamad Razlan Abd Rahman. All rights reserved.
ANTIOXIDATIVE VALUES AND CUSTOMER PREFERENCE OF
SWEETPOTATO (Ipomoea batatas) FLOUR AS COMPARED TO
WHEAT (Triticum aestivuni) FLOUR
No part of this unpublished research may be reproduced, stored in a retrieval
system, or transmitted, in any form or by any means, electronic, mechanical,
photocopying, recording or otherwise without prior written permission of the
copyright holder except as provided below:
1.
Any material contained in or derived from this unpublished research
may only be used by others in their writing with due
acknowledgement.
2.
IIUM or its library will have the right to make and transmit copies
(print or electronic) for institutional and academic purposes.
3.
The IIUM library will have the right to make, store in a retrieval
system and supply copies of this unpublished research if requested
by other universities and research libraries.
Affirmed by Mohamad Razlan Abd Rahman.
…………………………………
Signature
vi
……………………
Date
Foremost is for ALLAH for Him to accept this and succeeding works as my Ibadah,
and for the betterment of quality of life for man and animals.
vii
ACKNOWLEDGMENTS
First and foremost, tremendous gratitude is for ALLAH alone Who gave me
opportunity to go through this Masters programme until the end. Then my gratitude
also goes to my caring and concerned supervisor, Prof. Dr. Mazidah Ahmad Mansur,
who was always ready to help me for my success in the Masters programme. My
parents Zulaikha Hj. Ismail and Abd Rahman Hj. Md. Khalid who always prayed for
my success in this life and the thereafter. Bro Erman, Najib, Dr. Qamar Uddin,
Adisham, sis Sri, and all of the Kulliyyah of Pharmacy’s MLTs and lecturers; Sis
Rozila, Nadia, and all of the Kulliyyah of Allied Health Science’s MLTs and
lecturers; Bro Muzammil from Kulliyyah of Science, my postgraduate colleagues, Bro
Mustafa from Sudan, all of the lecturers from Kulliyyah of Medicine, and Kulliyyah
of Science, and those who are not listed here whom have helped me throughout my
learning process during the Masters programme. Lastly for my new inspiration that
came into my life during the duration of the programme which is my beloved
companion, sis Azmahani Hj. Zainudin, my wife.
viii
TABLES OF CONTENTS
Abstract ...................................................................................................................... ii
Abstract in Arabic ...................................................................................................... iii
Approval Page ............................................................................................................ iv
Declaration Page ........................................................................................................ v
Copyright Page........................................................................................................... vi
Dedication .................................................................................................................. vii
Acknowledgments...................................................................................................... viii
List of Tables ............................................................................................................. xii
List of Figures ............................................................................................................ xiii
List of Abbreviations ................................................................................................. xvi
CHAPTER ONE: INTRODUCTION .................................................................. 1
1.1 Background ............................................................................................... 1
1.1.1 Import substitution / export potential ............................................. 1
1.1.2 Production of sweet potatoes ......................................................... 2
1.1.2.1 Global .................................................................................. 2
1.1.2.2 In Malaysia .......................................................................... 3
1.1.3 The importance of sweet potato today ........................................... 3
1.1.3.1 As an alternative staple food ............................................... 3
1.1.3.2 Low glycemic index (GI) control ........................................ 3
1.1.3.3 As an antioxidant ................................................................. 4
1.1.4 Production of sweet potato flour .................................................... 5
1.2 Significance of study ................................................................................ 6
1.3 Research questions ................................................................................... 6
1.4 Research hypotheses ................................................................................. 6
1.5 Objectives ................................................................................................. 7
1.5.1 Main objectives .............................................................................. 7
1.5.2 Specific objectives ......................................................................... 7
CHAPTER TWO: LITERATURE REVIEW ..................................................... 8
2.1 Free radicals .............................................................................................. 8
2.1.1 Sources and reactions of reactive oxigen species (ROS) and
reactive nitrogen species (RNS) .................................................... 9
2.1.2 Effects of free radicals on cells ...................................................... 10
2.1.2.1 Aging Biology ...................................................................... 10
2.1.2.2 Oxidative nuclear and mitochondrial DNA damage ........... 10
2.1.3 Some diseases related to free radicals ............................................ 11
2.1.3.1 Atherosclerosis ............................................................................ 11
2.1.3.2 Cancer ................................................................................. 12
2.1.3.3 Inflammation........................................................................ 13
2.1.3.4 Autoimmune diseases........................................................... 13
ix
2.1.3.5 Diabetes ............................................................................... 14
2.1.3.6 Rhuematoid arthritis ............................................................ 15
2.1.4 Importance of free radicals ............................................................ 15
2.2 Oxidative stress .................................................................................................. 16
2.2.1 Oxidative stress and redox environment of a cell ................................... 16
2.2.2 Metal-induced oxidative stress....................................................... 17
2.3 Oxidative damage to biomolecules........................................................... 17
2.3.1 Lipid peroxidation .......................................................................... 17
2.3.2 Protein oxidation ............................................................................ 18
2.4 Phytochemicals and antioxidants.............................................................. 20
2.4.1 Antioxidant phytochemicals and human health ............................. 21
2.4.2 Enzymatic antioxidants .................................................................. 23
2.4.2.1 Superoxide dismutase (SOD) ............................................... 23
2.4.2.2 Glutathione peroxidase ....................................................... 23
2.4.2.3 Glutathione reductase (GR) ................................................ 24
2.4.2.4 Catalase (CAT) .................................................................... 24
2.4.3 Non-enzymatic antioxidants .......................................................... 25
2.4.3.1 Vitamin C ............................................................................. 25
2.4.3.2 Vitamin E ............................................................................. 26
2.4.3.3 Selenium .............................................................................. 27
2.4.3.4 Flavonoids ........................................................................... 28
2.4.3.5 Plant antioxidant phytochemicals ....................................... 31
2.4.3.5.1 Carotenoids (β-Carotene) ......................................... 31
2.4.3.5.2 Polyphenolic compounds .......................................... 33
2.4.4 Evaluation of antioxidant activity .................................................. 34
2.5 Antioxidant defense .................................................................................. 34
2.5.1 Antioxidant mechanisms of action ................................................. 35
2.6 Sweet potatoes (Ipomoea batatas) and antioxidants ................................ 36
2.6.1 Sweet potatoes (Ipomoea batatas) storage roots as a source of
antioxidant activity ......................................................................... 36
2.7 Wheat (Triticum aestivuni) and antioxidants............................................ 37
2.7.1 Antioxidant content in wheat (Triticum aestivuni) flour ............... 37
2.8 Health benefits of phytochemicals in whole foods—food synergy .......... 38
2.9 Effect of food processing on antioxidants ................................................ 39
CHAPTER THREE: METHODOLOGY.............................................................. 42
3.1 Phase 1 - Sampling and flour production ................................................. 43
3.1.1 Research samples ........................................................................... 43
3.1.2 Materials and Methods for Sweet potato Flour Production ........... 44
3.2 Phase 2 - Extraction, determination of components and activity of
antioxidants in sweet potato and wheat flours .......................................... 47
3.2.1 Sweet potato and wheat flour extraction ........................................ 47
3.2.2 Materials and methods for sweet potato and wheat flour
extraction ....................................................................................... 47
3.2.3 Determination of activity of antioxidants in sweet potato and
wheat flours ................................................................................... 49
3.2.4 Materials and methods for the determination of activity of
antioxidants in sweet potato and wheat flours ............................... 49
x
3.2.5 Determination of components of antioxidants in sweet potato and
wheat flours ................................................................................... 52
3.2.6 Materials and methods for the determination of components of
antioxidants in sweet potato and wheat flours ............................... 52
3.2.7 Statistical analysis .......................................................................... 54
3.3 Phase 3 - Food processing and evaluation ................................................ 55
3.3.1 Food product evaluation................................................................. 56
3.3.2 Statistical analysis .......................................................................... 56
CHAPTER FOUR: RESULTS ............................................................................... 57
4.1 Percentage of flour recovery from sweet potato storage roots ................. 57
4.2 Antioxidant capacity ................................................................................. 57
4.3 Comparison of antioxidant activity between wheat (Triticum aestivuni)
flour varieties ............................................................................................ 58
4.4 Comparison of antioxidant activity between treatments for sweet potato
(Ipomoea batatas) flour variaties ............................................................. 59
4.5 Total phenolic compounds........................................................................ 66
4.6 Total flavonoids ........................................................................................ 67
4.7 Correlation between total phenolic compounds and scavenging capacity70
4.8 Food product evaluation ........................................................................... 71
CHAPTER FIVE: DISCUSSION ......................................................................... 74
5.1 Research limitations ................................................................................. 82
CHAPTER SIX:
CONCLUSION ...................................................................... 83
BIBLIOGRAPHY: .................................................................................................. 84
APPENDIX I:
APPENDIX II:
APPENDIX III:
APPENDIX IV:
APPENDIX V:
.................................................................................................. 99
.................................................................................................. 100
.................................................................................................. 101
.................................................................................................. 102
.................................................................................................. 103
xi
LIST OF TABLES
Table No.
Page No.
1.1
Glycemic index of certain food
4
4.1
Antioxidant activity between wheat samples
58
4.2
EC50 values (mg/ml) of sweet potato and wheat flour
extracts in the antioxidant activity evaluation assays
64
4.3
Antioxidant activity between wheat and sweet potatotreated samples
65
4.4
Contents of total phenols (mg GAE/g) and flavonoids (mg
QE/g) in sweet potato and wheat flour extracts
68
4.5
Phenolic contents in sweet potato and wheat extracts
69
4.6
Flavonoid contents in sweet potato and wheat extracts
69
4.7
Preference for bakery products made from sweet potato and
wheat flours
73
Appendix
VI
Some nutritional contents of sweet potato and wheat flours
87
Appendix
V
Product score sheet
88
xii
LIST OF FIGURES
Figure No.
Page No.
2.1
Reaction of guanine with hydroxyl radical
10
2.2
Three stages model of carcinogenesis and the level of
carcinogenic effect vs. level of free radicals at various
stages of carcinogenic process
12
2.3
Classification of Phytochemicals
22
2.4
The accepted structural configuration of ascorbic acid
(vitamin C), an α-ketolactone with the formula C6H8O6,
with a molecular weight of 176.13, and containing an acidionizing group in water with pKA 4.19
25
2.5
Chemical structure of tocopherols and tocotrienol
(α-tocopherol without a phytyl chain)
26
2.6
Generic structure of flavonoids
28
2.7
Structure of a flavonoid subclass, quercetin
28
2.8
Hypothesis of the links between the working mechanisms
of flavonoids and their effects on disease. NO, nitric oxide
29
2.9
Reactive oxygen species that can be scavenged or whose
formation can be inhibited by flavonoids
30
2.10
Structure of all-trans-β-carotene
31
2.11
Important Physical and Chemical Properties of
Carotenoids
32
xiii
Page No.
Figure No.
2.12
Example of a standard phenolic compound
33
2.13
Cellular generation of reactive oxygen species and
antioxidant defence system in an organ (lung).
35
2.14
Interactions between components in whole grains and the
microflora that have important implications in health and
disease
38
2.15
Possible scheme for Carotenoid degradation
40
3.1
Flow chart of research methodology
42
3.2
Researcher at MARDI Telong station in Kelantan
43
3.3
Steamed and dried VitAto sweet potato (Ipomoea batatas)
45
3.4
Pictogram of end products of flour production that were
used in the research
46
3.5
Freeze drying process of sweet potato extracts
48
3.6
Pictogram of product distribution to participants
55
4.1
Scavenging effect of 80% methanolic extracts of wheat
flours on DPPH radicals 58
4.2a
Scavenging effect of 80% methanolic extracts of raw and
steamed sweet potato (Telong) on DPPH radicals.
59
4.2b
Antioxidant activity of sweet potato (Telong) with
different treatments using a β-carotene-linoleate model
system
59
xiv
Page No.
Figure No.
4.3a
Scavenging effect of 80% methanolic extracts of raw and
steamed sweet potato (Jalomas) on DPPH radicals.
61
4.3b
Antioxidant activity of sweet potato (Jalomas) with
different treatments using a β-carotene-linoleate model
61
system
4.4a
Scavenging effect of 80% methanolic extracts of raw and
steamed sweet potato (VitAto) on DPPH radicals.
63
4.4b
Antioxidant activity of sweet potato (VitAto) with
different treatments using a β-carotene-linoleate model
system 63
4.5
Standard curve for phenolics using Gallic acid 66
4.6
Standard curve for flavonoids using Quercetin 67
4.7
Correlation between DPPH scavenging capacity % and
total phenolics mg GAE/g in methanol extracts of sweet
potato and wheat samples 70
4.8a
Customers’ preference for Muffin
71
4.8b
Customers’ preference for Buns
71
Appendix
I
Sweet potato flour (75%) : wheat flour (25%), based buns
84
Appendix
II
Wheat flour (100%) based buns 85
Appendix
III
Government studies sweet potato as a substitute for rice
(in Malay)
86
xv
LIST OF ABBREVIATIONS
AlCl3.6H2O
CVD
DNA
DPPH
et al.
etc
e.g.
g
Ho
H2 O2
H2 O
i.e.
kg
MARDI
mbar
MeoH
mg
min
ml
mm
mV
NADH
NADP+
nm
n.d.
OH.
O2
O2 .
pKA
ppm
ROI
ROO.
R2
µg
µm
Aluminium chloride hexahydrate
Cardiovascular Disease
Dinucleotide Acid
1,1-diphenyl-2-picrylhydrazyl radicals
(et alia): and others
(et cetera): and so forth
For example
gram
Null Hypothesis
Hydrogen peroxide
Water
Included example
kilogram
Malaysian Agricultural Research Development and Innovation
millibar
Methanol
milligram
minute
milliliter
millimeter
millivolt
Nicotinamide adenine dinucleotide (reduced form)
Nicotinamide adenine dinucleotide phosphate
nanometer
no date
Hydroxyl radical
Oxygen molecule
Superoxide anion
negative logarithm of acid dissociation constant
part per million
Reactive oxygen intermediates
Peroxide radical
Symbol for correlation in graph
microgram
micrometer
xvi
CHAPTER ONE
INTRODUCTION
1.1
BACKGROUND
Containing about 50 genera and 1000 species, the Convolvulaceae family is a
cosmopolitan in distribution but most diverse in the tropics. Most members are
herbaceous vines annual or perennial, colonizing naturally open artificially distured
habitats, and often spreading vegetatively by rooting at nodes. Several genera include
garden ornamentals. Only Ipomoea has been domesticated for food crops. Ipomoea is
a cosmopolitan genus of about 400 species whereby Ipomoea batatas (sweet potato)
has far wider importance (Jonathan D. Sauer, 1993).
The sweet potato that we know today comes from the Kingdom of Plantae,
Division of Magnoliophyta, Class of Magnoliopsida, Order of Solanales, Family of
Convolvulaceae, Genus of Ipomoea, and Species of Batatas. Therefore the binomial
name is Ipomoea batatas.
The root and tuber crops are grown widely throughout the world in hot and
humid regions. The root and tuber crops contain 70-80% water, 16-24% starch and
trace quantities (<4%) of proteins and lipids (Hoover, 2001). The sizes and shapes
varies and are 2-42 round cm (Seog, et al., 1987), oval or polygonal (Tian, et al.,
1991).
1.1.1
Import substitution / export potential
A tropical climate such as that of Malaysia is not favourable or unsuitable to planting
crops such as wheat, corn and Irish potato. Malaysia spends on imports of wheat
1
products worth RM800 million a year (Anon., 2002), while the total import of Irish
potato is more than RM167 million. Malaysia will be able to reduce foreign exchange if
at least parts of these imports are met by local production of sweet potato for flour.
Most of the snacks in the market today are made from wheat flour, corn and Irish
potato which are imported ingredients. Extruded snacks can be produced from sweet
potato flour mixed with cassava flour or rice flour at different proportions.
Food products made from sweet potato flour substituting the use of wheat flour
have a niche market among sufferers of coeliac disease (an allergy to wheat gluten). This
market which exists in Europe and North America is currently largely untapped,
especially for products traditionally made from wheat, i.e. bakery goods. These include
western-style cakes, bread, buns, muffins and biscuits.
Thus, a lot of people can benefit from the consumption of sweet potato especially
in Malaysia. These will benefit people involved in the industry such as patients,
farmers, and food makers (bakery products).
1.1.2 Production of sweet potatoes
1.1.2.1 Global
The sweet potato crop, which has its origin in the tropical Americas, has spread to
most of the world’s tropical, sub-tropical, and warmer temperate regions. According
to the FAO, sweet potatoes are grown in 111 countries, of which 101 are classified as
‘developing nations. Among the world’s root crops the sweet potato ranks second only
to the potato in economic importance (Woolfe, 1992).
Field studies in Asia, Africa, and Latin America show a diversity of sweet
potato production practices and final uses in different kinds of food systems. For
example on the island of Java, sweet potato is intensively cultivated as a cash crop by
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farmers who are linked to a well-organized marketing chain supplying the major cities
for fresh consumption or food processing into snacks. In the neighbouring island of
Sumatra, sweet potato is grown as an off-season staple food between rice crops
(Watson, 1988; 1989).
1.1.2.2 In Malaysia
Sweet potato (Ipomoea batatas) is a minor root crop in Malaysia, and one of the popular
cash crops grown by small holder farmers for the fresh market. However the demand for
sweet potato for table consumption is somewhat small, and can be one of the reasons
why the cultivated area for this crop has remained around 2,000 hectare a year in
Peninsular Malaysia (Anon., 1990-2000).
1.1.3 The importance of sweet potato today
1.1.3.1 As an alternative staple food
Sweet potato tolerance against extreme weather conditions such as typhoon, drought,
and against pests, and diseases as well as their importance as a source of starch and
vitamins, has led Japan establishing a strong sweet potato breeding program
(Kukimura, et al., 1990). The germplasm collections include Japanese local cultivars;
breeding lines from China, Fiji, Indonesia, New Zealand, Papua New Guinea, the
Philippines, Solomon Islands, and the U.S.; and wild sweet potatoes from Latin
America (Rodriguez-Amaya, 1997).
1.1.3.2 Low Glycemic Index (GI) control
The glycemic Index (GI) is the rate of food converting to glucose in the blood
circulation. The GI of sweet potato is (54), which is low when compared to white bread
3
(96) or white rice (70). This means sweet potato is a better alternative for glucose
control consumed by diabetic patients (MARDI, 2007).
Table 1.1
Glycemic index of certain food
Types of food
Glycemic Index
____________________________
Glucose
100
White bread
96
Cornflakes
84
Rice Krispies
82
French fries
75
Honey
73
Carrot
71
White rice
70
Soft drinks
70
Roasted peanuts
68
Ice-cream
61
Hamburger
61
Sweet potato
54
___________________________
(MARDI, 2007)
1.1.3.3 As an antioxidant
Important sources of antioxidants in the Hawaiian diet include sweet potato, taro, bok
choy, konbu, nori, and wakame for β-carotene; breadfruit, sweet potato, turnip,
guava, lychee, mango, and pineapple for vitamin C; and macadamia nuts, sweet
potato, and mango for vitamin E (Laurin, et al., 2004).
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1.1.4
Production of sweet potato flour
A viable agri-business was introduced, covering field production of sweet potato varieties,
Telong and Jalomas, and then processing it into flour, and subsequently into premix flours
for traditional cakes, extruded products (snacks and breakfast food) and a range of bakery
products.
Most local varieties of sweet potato which are high-yielding are very low in root dry
matter or starch content, and therefore unsuitable for sweet potato flour products. It was
found that varieties like Telong and Jalomas, have moderately high root yields of 20-25 t/ha
(metric ton per hectare) and have significant higher root dry matter contents, and
therefore higher flour recovery rate. Jalomas with its orangey coloured flesh has also a
moderately high carotenoid content. Carotenoids are favoured for their antioxidant properties
which have health benefits. These two varieties, the first in Malaysia, are adapted to be
cultivated on a range of soils, particularly sandy soils such as bris and sand-tailings.
Flour made from Telong and Jalomas varieties can be further processed into a
number of value-added food products. Prior to the introduction of Telong and Jalomas
varieties, there were no sweet potato processing varieties dedicated for flour
production. Most of the existing popular varieties have very low dry matter or starch
content, which means very low conversion rate to flour unlike that of Telong and Jalomas
varieites.
Most extruded products for snacks and breakfast food, as well as bakery products
are dependent on imported raw materials such as wheat, corn or potato. Sweet potato
flour from Telong and Jalomas offers an alternative local raw material for processing
such products.
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1.2
SIGNIFICANCE OF STUDY
It is expected that the nutritional contents of the varieties of sweet potatoes established
by MARDI (Lian, et al., 2007) and in other studies conducted by other groups (Huang,
et al., 2006; Salma & Zaidah, 2006) could be verified and supported. These
discoveries will promote growth of sweet potato especially those with higher
nutritional contents, for commercial purposes as well as means to prevent certain
diseases related to free radical effects. These certainly will contribute to new venture
by food industries to provide more choices to customers and create more
employments. Furthermore, this can increase the income of local farmers. This will
reduce foreign exchange due to import of wheat flour and contribute to positive
economic impact to the country.
1.3
RESEARCH QUESTIONS
1)
Is sweet potato flour better compared to wheat flour in term of the
antioxidative values?
2) Do consumers prefer sweet potato flour bakery products over wheat flour
bakery products?
1.4
RESEARCH HYPOTHESES
1)
The antioxidative values in sweet potato flours are significantly higher
than in wheat flours.
2)
Customers prefer sweet potato flour bakery products than wheat flour
product.
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1.5
OBJECTIVES
1.5.1 Main Objectives
1) To determine the antioxidative values of sweet potato and wheat flours.
2)
To determine customers’ preferences in choosing a bakery product made
of sweet potato or wheat flour.
1.5.2 Specific Objectives
1)
To compare the antioxidative values between raw and steam treated sweet
potato flours.
2)
To compare the antioxidative values among the various types of sweet
potato and wheat flours.
3)
To compare customers preferences between sweet potato and wheat
bakery products.
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CHAPTER TWO
LITERATURE REVIEW
Frequent consumption of fruits and vegetables is associated with a lowered risk of
cancer, heart disease, hypertension and stroke. This has been attributed to the presence
of various forms of phytochemicals and antioxidants present in the foods, e.g.
carotenoids and polyphenol compounds including flavonoids and anthocyanins (Lako,
et al., 2007).
2.1
FREE RADICALS
Free radicals can be defined as molecules or molecular fragments containing one or
more unpaired electrons. The presence of unpaired electrons usually confers a
considerable degree of reactivity upon a free radical. Those radicals derived from
oxygen represent the most important class of such species generated in living systems
(Valko, et al., 2004).
Harmful free radical and reactive oxygen species (ROS) have been found to
play an important role in the major chronic health problems (German & Dillard, 1998;
Keher, 1993).
Radicals and ROS such as the superoxide anion (O2•−), hydroxyl radical (OH•)
and peroxy radical (ROO•) have been implicated as mediators of degenerative
inflammatory, and autoimmune diseases (Nice, 1997; Heliovaara, et al., 1994), as well
as diabetes, vascular disease (Tsao & Deng, 2004), and cancer (Ames, et al., 1993;
Ferguson, 1994).
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