Chemistry of Tropical Root Crops

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Chemistry of
Tropical Root Crops:
Significance for Nutrition and Agriculture
in the Pacific
The Australian Centre for International Agricultural Research (ACIAR) was eqah
lished in June 1982 by an Act of the Australian Parliament. lis mandate is to help
identify agricultural problems in developing countrics and to commission collabora
tive research bctween Australian and developing country researchers in fields where
Australia has a special research competence.
\Vhere trade names are used thi,., does not constitute endorsement of nor discrimi
nation against any product b) the Centre.
I
ACtAR MONOGRAPH SERIES
This peer-reviewed series contains the results of original research supported
hy ACIAR, or material deemed relevant to ACIAR\ re.search ohjcctives. The
series is distributed internationally, with an emphasis on the Third World.
Australian Centre for International Agricultural Resl'arch
Ci.P.O. Box 1571, Canherra, A.e.T. 2601
Bradbur), J. H., and Hollo\\"ay, W. D. 19RR. Chemistry or Tropical Root Crop"
significance for nutrition and agriculture in the Pacific. ACIAR 1\1onograph No. 0,
201 p.
ISBN 0 949511 61 7
Typeset and laid out by Union Offset Co. Pty Ltd, Canherra
Printed by Ramsay Ware Printing, Melhourne
Chemistry of
Tropical Root Crops:
Significance for Nutrition and Agriculture
in the Pacific
J. Howard Bradbury and Warren D. Holloway
Chemistry Department
Australian National University, Canberra
Australian Centre for International Agricultural Research
Canberra 1988
Co-Workl'p; at Chl'mistr~ Ikpartml'lIf, ,\w,tralian 'lialional l'lliH'rsit~
Ro" L Ikatt", l-:a\c Ilrad'ha\\. Ilrcmloll Hammer, \\CI\ne .Icalou, . .I,,,cph 1 au, John I Cl',
Tuc N!!lI"l'll, Tum l'iJilllpi,allc ~lIld \)1 L!llnid :-'ill~dl (\i,i!illL' Icllo\\ Oil ,abhalica! ka\c
fnllll ICRIS,\T. H"lkrabad).
( 'ollahomtors
S(J/OII/(l1I /.'/111/(/1 J)r CJrahalllc \'. H . .Iac~'()1l (L't'\J)P, /-\()-SI'C Plan! 1'I,)!,:ction Llli!,
Su\a, hji) \,h,) ,\ith the pn1jl'ct lcadcl (JH.H.) dc,clop,'d the (lri!!ill~ll AC/-\R pro!!ram ill
1%-'; \Ir Petcr R. [inion, IYS3-S5 and \11 Stc\e Caigcr, 1%('-1)7, (\iini,tl\ llj ,\grielllture
and Land,. 1',0. Bo\ (j 13, I-\oniara),
Fiji \lr Param :-,i\C1n, 19S3-87 (Korolli\ia Rc,carch St~llilln, 1'.0. 131),77. Nau\ori).
r/i'l[ern Sail/oa Dr .I III L Wil,on. 1%.1-87 (I Rl:TA. Uni\l'rsilv ul' 'South Pacilic School
uf ,\gricullure. Apia).
Timga ,VIr I'ita TallfalOlua and :Vir Finau S, Pule, 191\-l-87 (Departmcnt 01 Agl'iculturc,
P.O, Box l-l, Nuku'alola).
Kirihari :vl, Bruce Ratieta, 198-l-85 (deceased), \11' John Finlay, 1986-87 (Atoll Research
and Development Unit, 1'.0. Box 206, Bikenibeu, Tar'aI,a).
Papua New Guinea Dr I,. Margarct Quin, 1984-85; Or Brian M. ThisllelOIl, 191\4-87
(Department of Primary Industry, Kuk Agricultural Research Station, P.O. Box 339, Ml
Hagen); I\Jr :Vlalcolm P. Lcvett, 1984·-87 (Department of Primary Industry, Aiyura, P.O.
Bux 384, Kainantu, F.H. 1'.); Mr Graham A. King, 1985-87 (Dcpartment of Primary
Industry, Bubia Agricultural Research Centre, P.O. Box 1639, Lac).
f'cdcrated Srates of ,\,1icrollcsia (Pohll{Jei) :\lr Adclino !.orens, 1985; Mr Williarn S.
v\,illiam, 1985-87 (Office of the Director of Comervation and Resource Surveillance,
Pohnpei State (JO\crnmcnl).
Vallll(/{U l\lr Fraser Bule, 1986-87 (Department of Agriculture, 1'.0. Box lOO, Santo).
AlIstralia M r Rms B. Cunningham, 1985-87, who has advised on statist ical dcsig!! of
experimcnts (Department of Statistics, Australian National Universily, Canberra).
The Authors
J. Howard Bradbury, PhD (Birm), DSc
(Melb), DSc (ANU) is a Reader in
Chemistry at the Australian National
University. He has published over 160
papers on food and nutrition in develop
ing countries, and on the chemistry of
macromolecules and biological material.
In recognition of this work he was
awarded the Rennie Memorial Medal
and the H. G. Smith Memorial Medal of
the Royal Australian Chemical Institute
and the David Syme Research Prize of
the University of Melbourne.
Warren D. Holloway obtained his PhD
from Massey University in New
Zealand. For some years he was the bio
chemist in charge of the gastroentero
logy laboratory at Auckland Hospital.
During 1985-86 he was a postdoctoral
fellow at ANU working on the ACIARI
ANU program and, with Dr Bradbury,
supervised the analytical work. He is
now with Syrinx Research Institute,
Bundaberg, Queensland.
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Contents
Foreword G. J. Persley 11
Preface 13
Chapter 1 Introduction
1.1 Agriculture 17
1.1.1 Sweet potato, I. batatas 18
1.1.2 Taro, C. esculenla 20
1.1.3 Taro, X. sagittifolium 22
1.1.4 Giant taro, A. macrorrhiza 22
1.1.5 Giant swamp taro, C. chamissonis 24
1.1.6 Elephant foot yam, A. campanulatus 2S
1.1.7 Yam, Dioscorea spp. 27
1.1.8 Cassava, M. esculenta 28
1.2 Nutrition 30
1.2.1 Comparison of tropical plant foods 30
1.2.2 Nutrition in the South Pacific 33
1.3 Chemical Composition in Relation to Nutrition and Agriculture of
Root Crops 36
Chapter 2 Experimental Methods
2.1 Sample Collection 39
2.2 Sample Preparation 39
2.3 Sampling Procedures 40
2.4 Moisture Analysis 40
2.5 Nitrogen Analysis 40
2.6 Protein Content and Non-Protein Nitrogen 40
2.7 Lipid Analysis 41
2.8 Analysis of Starch 41
2.9 Dietary Fibre 41
2.10 Total Sugar 42
2.11 Content of Individual Sugars 42
2.12 Energy Calculated from Protein, Fat, Starch and Sugar Contents 42
2.13 Energy Calculated from Moisture Content 43
2.14 Ash Analysis 43
2.15 Atomic Absorption Analysis of Calcium and Iron 43
2.16 Mineral Analyses by Inductively Coupled Argon Plasma Emission 43
2.17 Vitamin A and Vitamin O 44
2
2.18 Thiamin 44
2.19 Riboflavin 44
7
2.20 Nicotinic Acid 45
2.21 Vitamin C (Ascorbic Acid + Dehydroascorbic Acid) 45
2.22 Amino Acid Analysis 45
2.23 Organic Acids, Calcium Oxalate and Free Calcium 46
2.24 Trypsin Inhibitor Assay 47
2.24.1 Diffusion inhibitor assay 48
2.25 Chymotrypsin Inhibitor Assay 48
2.26 Cyanide Analysis in Cassava 49
Chapter 3 Chemical Composition of Root Crops
3.1 Sweet Potato 51
3.2 Taro 56
3.2.1 Taro, C. esell/enta var. eseu/en/a 56
3.2.2 Taro, X. sagittifo/illlll 62
3.3 Giant Taro, A. maerorrhiza 62
3.4 Giant Swamp Taro, C. ehall1issonis 66
3.5 Elcphant Foot Yam, A. eall1panll/aflls 68
3.6 Yam, Dioseorm spp. 68
3.6.1 Yam, D. a/ata 68
3.6.2 Yam, D. eseu/el1ta 72
3.6.3 Yam, D. l1ummu/aria 73
3.6.4 Yam, D. bu/hijcra 73
3.6.5 Yam, D. pel1laphylla 73
3.6.6 Yam, D. rolllndata 73
3.6.7 Yam, D. trZ/ida 76
3.7 Cassava, 1\1. eseu/enta 76
3.11 Comparisons of Chemical Compositions of Tubers and Corms of All
Root Crops 81
3.9 The Variability of Composition of Nutrients and Antinutritional Factors
Across Tubers and Corms 87
Chapter 4 Effects of Cooking and Storage
4.1 Changes Produced by Cooking 89
4.2 Methods of Cooking Root Crops 90
4.2.1 Boiling, steaming and baking s\veet potato, taro, yam and
cassava 90
4.2.2 Boiling and baking methods used for vitamin analyses 91
4.3 Effects of Cooking on Nutrients in Sweet Polato, Taro, Yam and
Cassava 91
4.4 Effects of Cooking on Vitamin Content of Sweet Potato, Taro, and Giant
Taro 93
4.5 Cooking l\lethods and Human Nutrition 95
4.6 Storage of Root Crops 96
4.6.1 Storage of sweet potato 96
4.6.2 Storage of taro C%casia and Xanthosoma 97
4.6.3 Storage of giant taro, A. macrorrhiza, and giant swamp taro, C.
chamissonis 97
4.6.4 Storage of yams 97
4.6.5 Storage of cassava 98
11
Chapter 5 AntinutritionaI .'actors in Root Crops
5,1 Cyanide in Cassava 101
5,1.1 Selection/breeding of cyanide-free cassava 103
5.1.2 Post harvest processing (including cooking) of cassava to reduce
cyanide 104
5.1.3 South Pacific situation 104
5.2 Tryp,in and Chymotrypsin Inhibitors 105
5.2.1 Physiological role in the plant 105
5.2.2 Types of inhibitor and their mode of action 106
5.2.3 l\lolecular structure of inhibitors in root crops 106
5.2.4 Inhibitor content and distribution in tubers and corms 107
5.2.5 Stability of trypsin inhibitor to heat and on cooking 107
5.2.6 Implications for nutrition of trypsin and chymotryp~in
inhibitors 109
5.3 Calcium Oxalate and Soluble Oxalate 110
5.3.1 Medical effects of intake of oxalate and calcium oxalate 110
5.3.2 Calcium oxalate, soluble oxalate and free calcium content of root
crops 114
5.4 Acridity of Edible Aroids 115
5.4.1 The nature of acridity 116
5.5 Possible Physiological Role of Proteinase Inhibitors, Calcium Oxalate and
Acridity 119
Chapter 6 Effects of Environmental Constraints on Yield and Composition
6.1 Environmental Constraints on Yield and Composition of Sweet Potato:
Literature Review 122
6.1.1 Soil moisture content 122
6.1.2 Length of growing season (time to harvest) and method of
harvest 122
6.l.3 Fertilizer application (N, P, K) 123
6.2 Present Environmental Studies on Yield and Composition of Sweet
Potato 123
6.2.1 Length of growing season (time to harvest) 123
6.2.2 Irrigation trial 124
6.2.3 Fertilizer and gypsum trial 125
6.2.4 Effect of environment on energy and protein 126
6.3 Effect of Environment and Fertilizer on Nutrient Content of Yam, D.
esculenta 126
6.4 Taro, C. esculenla, Three Successive Harvests of Same Cultivars 127
6.5 Effect of Age of Giant Swamp Taro and Environment on Nutrient
Composition 127
6.6 Effect of Age of Giant Taro Corms on Nutrient Composition 128
Chapter 7 Conclusions
7.1 Chemical Composition 129
7.1.1 Variability of composition 129
7.1.2 Highlights of composition of various root crops 130
9