EDIBLE AROIDS - Food and Agriculture Organization of the United

28 Pages·2013·0.9 MB·English

EDIBLE AROIDS
Post-harvest Operations
- Post-harvest Compendium
EDIBLE AROIDS: Post-Harvest Operation

Organisation: Massey University, Private Bag 11-222, Palmerston North, New Zealand
Massey University
Author: Linus U. Opara
Edited by AGST/FAO: Danilo Mejía, PhD, FAO (Technical)
Last reviewed: 28/08/2003

Contents
Preface.................................................................................................................................... 2
1. Introduction ........................................................................................................................ 2
1.1 Economic and Social Impact of Edible Aroids ............................................................ 2
1.2 World Production and Trade ........................................................................................ 3
1.3 Primary products .......................................................................................................... 3
1.4 Secondary and derived product .................................................................................... 4
1.5 Requirements for export and quality assurance ........................................................... 4
1.6 Consumer Preferences ................................................................................................. 5
1.7 Nutritional Facts........................................................................................................... 5
2. Post-Production Operations ............................................................................................... 8
2.1 Pre-harvest Operations ............................................................................................ 8
2.2 Harvesting ................................................................................................................ 8
2.3 Transport .................................................................................................................. 8
2.4 Corm Curing ............................................................................................................ 9
2.5 Cleaning ................................................................................................................. 10
2.6 Packaging............................................................................................................... 10
2.7 Storage ................................................................................................................... 10
2.8 Processing .............................................................................................................. 13
2.9 Aroids for Rural Agro-Industrialisation ................................................................ 17
3. Overall Losses .................................................................................................................. 20
4. Control of Pests, Diseases and Disorders ........................................................................ 21
5. Economic and Social Considerations............................................................................... 22
5.1 Overview of costs and losses ................................................................................. 22
5.2 Major problems...................................................................................................... 22
5.3 Gender aspects ....................................................................................................... 22
6 References ......................................................................................................................... 23
7 Annex – ............................................................................................................................. 26
List of tables ..................................................................................................................... 26
List of figures ................................................................................................................... 27
Preface
One of the characteristics of the post-production sector in developing countries is that it is
generally subsistence-oriented in regions that are increasingly faced with high population
growth rates, food insecurity, malnutrition and poverty. In addition, the incidence of post-
harvest losses remains high at all stages from harvesting to consumption. Innovations in post-
harvest management and agro-processing are therefore necessary in order to derive maximum
benefits from crop production outputs by reducing losses and maintaining product quality and
nutritional value. These outcomes will also catalyse the development of rural-based agro-
processing industries which provide employment to the rural population in value-adding and
processing activities, thereby reducing poverty. Although they have less economic value
compared with other major root crops, the edible aroids are important food materials in the
diet of many regions in developing countries. Women in particular, play the most significant
roles in their cultivation and post-production operations. Improvements in the post-harvest
handling and processing of these crops will take account of women‟s specific interests and
make work easier, improve productivity and raise income through the delivery and marketing
of good quality produce.
1. Introduction
Edible aroids (family Araceae) comprise of many underground food crops grown in several
tropical and sub-tropical countries. Taro or cocoyam (Colocasia esculenta) and tan(n)ia or
new cocoyam (Xanthosoma sagittifolium) are the most important species. Together they are
also called cocoyams in many parts of the world, especially in Africa. For the purpose of this
Compendium, the terms „edible aroids‟ or „cocoyams‟ will be used when both Colocasia and
Xanthosoma are referred to collectively. Where a distinction is warranted to emphasise
differences in post-harvest characteristics, the term „taro‟ will be used for Colocasia , and
„tannia‟ for Xanthosoma. Other edible aroids, notably Alocasia Cyrtosperma and
Amorphophallus, are cultivated globally to a very limited extent, and they are important food
crops in some parts of India, Southeast Asia, and the Pacific Islands. However, considering
their high economic importance in relation to other types of edible aroids, the information
covered in this article will be based on taro (Colocasia esculenta) and tannia (Xanthosoma
sagittifolium).
1.1 Economic and Social Impact of Edible Aroids
Edible aroids contribute an important part to the carbohydrate content of the diet in many
regions in developing countries. They produce edible starchy storage corms or cormels.
Although they are less important than other tropical root crops such as yam, cassava and
sweet potato, they are still a major staple in some parts of the tropics and sub-tropics. In the
South Pacific Island countries in particular, edible aroids represent a very high proportion of
the root crops. In the South Pacific and parts of Africa taro is a staple food crop, and in the
Caribbean and West Africa in particular, tannia is the main edible aroid. Despite the
economic importance of edible aroids as a food material in these regions, there is limited
scientific information on their post-harvest characteristics, which perhaps contributes to the
very limited application of improved post-harvest technologies to maintain quality and
improve marketing potential.
EDIBLE AROIDS: Post-harvest Operations Page 2
1.2 World Production and Trade
Data on world production and trade of edible aroids is difficult to estimate because of their
very limited significance in terms of total production of root and tuber crops. Estimated world
production in 1988 was around 5.5 million Mt, and constituting about 3.3% of all root crops
(FAO, 1988). Total world production area of taro alone was estimated to be about 993 x 103
ha in 1983, with 80% in Africa. During this period, global production of taro was 5.607
million Mt, with about 61.33% in Africa and 38.67% in Asia. Estimates made about a decade
ago indicated that total world production of the major edible aroids (taro and tannia) was
about 5.23 million Mt in an area of 983 million ha, with average yield of 5314 kg.ha-1 (FAO,
1991). Production declined by 5.3% from 5.64 million Mt in the 1979-81 period to 5.34 Mt in
1989. Current statistics indicates that increased slowly during the past 5 years from 5.6
million to 8.8 million Mt (Table 1). Although exports increased by over 23% in volume, the
value of exports remained fairly uniform over this period. Farmers and exporters interested in
future business must ascertain the factors contributing to this trend and the potential impacts
on business.
Table 1: World production and trade in edible aroids (cocoyams)
2000 1999 1998 1997 1996 1995
Production (Mt) 8,834,79 8,823,62 8,697,13 6,621,51 5,977,82 5,586,37
6 5 3 9 8 2
Exports, Quantity (Mt) - 108,845 108,067 90,881 101,670 88,099
Exports, Value - 70,840 88,245 73,710 80,971 70,420
(1000US$)
Source: FAOSTAT, 2000
1.3 Primary products
Aroids are grown mainly for food. The mature corms and young shoots of edible aroids are
mostly used as boiled vegetables, but the corms are also roasted, baked, or fried. Roasted or
boiled corms can be eaten alone or with stew. In parts of West Africa, the boiled corms are
mashed and used as weaning diet. Mature edible aroids are also processed into flour, which is
used to prepare „fufu‟ that is commonly eaten in Nigeria with stew. In southeastern part of
Nigeria in particular, tannia is used in small quantity as soup thickener after boiling and
pounding to obtain a consistent paste. Taro chips is another important secondary product. In
the South Pacific, young taro leaves are used with coconut cream to prepare a dish called
„luau‟, which is then used to eat the boiled or roasted taro, breadfruit and banana.
EDIBLE AROIDS: Post-harvest Operations Page 3
Fig. 1. Taro plants in the South Pacific.
1.4 Secondary and derived product
Despite their considerable potential as animal feed, renewable energy source and industrial
raw material, the development of agro-industries based on aroids as major inputs remains a
theoretical concept despite several positive indicators from research and development. Some
aspects of these secondary and derived products will be discussed later in detail in Sections
2.9 and 5.1.
1.5 Requirements for export and quality assurance
Edible aroids are grown mainly on subsistence farms for household consumption or sale in
local and regional markets In some growing regions, however, improvements in postharvest
handling and availability of airfreight have facilitated export marketing to developed
countries, mainly servicing the needs of migrants from the producing areas. There are no
international quality standards for export but exporting companies or individuals must meet
the phyto-sanitary requirements of the importing country, in addition to the agreed product
specifications. This requires good sanitation, clean produce free of debris and soil, good
packaging and evidence of quality assurance system to meet the importer‟s requirements.
Corms are susceptible to physical injury during harvesting and postharvest handling and
affected corms are downgraded. Extra care should be taken to avoid damage to the corms
since this may lead to rapid deterioration during subsequent handling and storage. Taros
harvested for fresh marketing are normally washed and the roots and fibres discarded. They
are then graded and packed in crates for transportation. Crates are preferred because they are
firm and reduce the incidence of mechanical damage to corms. Corms destined for storage
are cleaned but not washed, and may also be cured to enhance repair of any physical injury
present. Under ambient conditions of high temperature and high relative humidity common in
most tropical regions, wet tissue provides conducive environment for microbial growth and
spread to healthy produce.
EDIBLE AROIDS: Post-harvest Operations Page 4
1.6 Consumer Preferences
There are regional differences in consumer preference and utilisation of cocoyams. In areas
such as the South Pacific where they constitute a staple diet, taro (Colocasia esculenta (L.)
Schott and Alocasia spp) are most widely grown and used, whereas in many parts of Africa,
these of less importance. In southeastern Nigeria in particular, these are seldom eaten alone,
but commonly pounded in a mixture with gari or yam. In fact this consumer preference
pattern threatens the future contribution of many cocoyam varieties to the agricultural (food
& raw materials) system in these regions. Local and international efforts are necessary to
preserve the existing genetic biodiversity of these important crops.
1.7 Nutritional Facts
Notwithstanding their high starch content, edible aroids have a higher content of protein and
amino acids than many other tropical root crops (Kay, 1987). Protein quality is essentially the
same for all aroids determined with lysine as first limiting amino acid (chemical score 57-70)
(Bradbury, 1988). The nutritional values of the major edible aroids are presented in Table 2.
A summary of comprehensive chemical analysis of large samples of aroids from different
countries is also presented (Table 3). The highlights of the nutritional and chemical
composition are presented (Table 4). The purpose of these data is to assist food process
engineers and many other scientists in developing improved food processing operations as
well as new food products, particularly those aimed at enhancing the nutritional status of
people living in regions that produce cocoyams. Considering the huge variation in
compositional data of raw material in general, these data must be used only as a guide in
making nutritional calculations.
Table 2: Nutritional content of the major edible aroids per 100g edible portion.
Constituent Taro Tan(n)ia
(Colocasia esculenta) (Xanthosoma saggittifolium)
Major nutrients Corms Corms Leaf Corms Leaves Shoots
stalks
Calories 102 94 24 133 34 33
Protein (g) 1.8 202 0.5 2.0† 2.5 3.1
Fat (g) 0.1 0.4 0.2 0.3 1.6 0.6
Carbohydrate (g) 23 21 6 31 5 5
Fibre (g) 1.0 0.8 0.9 1.0 2.1 3.2
Calcium (mg) 51 34 49 20 95 49
Phosphorous (mg) 88 62 25 47 388 80
Iron (mg) 1.2 1.2 0.9 1.0 2.0 0.3

Vitamins
ß-carotene equiv. trace trace 180 trace 3300
(µg)
-
Thiamine (mg) 0.10 0.12 0.02 0.10 - -
Riboflavin (mg) 0.03 0.04 0.04 0.03 - -
Niacin (mg) 0.8 1.0 0.4 0.5 - -
Ascorbic acid (mg) 8 8 13 10 37 82
Source: (FAO, 1972; Platt, 1962; Tindall, 1983)
EDIBLE AROIDS: Post-harvest Operations Page 5
Table 3: Data on nutritional and chemical composition of different varieties of edible
aroids from different countries
Taro Tannia Giant taro Giant Elephant
swamp taro foot yam
Number of samples and 71 samples 37 samples 37 samples 27 samples 7 samples
countries from 3 from 2 from 2 from 2 from one
countries countries countries countries cultivar
Moisture % 69.1 67.1 70.3 75.4 77.8
Energy kJ.100 g-1 480 521 449 348 336
Protein % 1.12 1.55 2.15 0.51 2.24
Starch % 24.5 27.6 21.5 16.8 16.6
Sugar % 1.01 0.42 0.96 1.03 0.14
Dietary fibre % 1.46 0.99 1.85 2.78 1.45
Fat % 0.10 0.11 0.10 0.16 0.06
Ash % 0.87 1.04 0.92 0.67 1.36
Minerals (mg.100 g-1)
Ca 32 8.5 38 182 97
P 70 53 44 16 67
Mg 115 27 52 21 47
Na 1.8 6.6 30 72 4.1
K 448 530 267 67 622
S 8.5 7.9 12 3.3 12
Fe 0.43 0.40 0.83 0.61 0.51
Cu 0.18 0.19 0.07 0.11 0.18
Zn 3.8 0.52 1.57 2.3 1.05
Mn 0.35 0.17 0.62 0.69 0.31
Al 0.38 0.53 0.36 1.36 0.41
B 0.09 0.09 0.10 0.09 0.17
Vitamins (mg.100 g-1)
Vitamin A (ret. + -car./6) 0.007 0.005 0 0.005 0.07
Thiamin 0.032 0.024 0.021 0.025 0.06
Riboflavin 0.025 0.032 0.018 0.019 0.05
Nicotinic acid 0.76 0.80 0.48 0.46 1.2
Pot. Nic. Acid = Trp/60 0.19 0.33 0.46 0.07 -
Total vitamin C (AA + DAA) 15 14 17 16 3.8
Limiting amino acids + score
First Lys 66 Lys 57 Lys 64 Lys 70 -
Seconds Thr 94 Leu 81 His 91 Leu 97 -
Ileu 93
Organic acid anions and
calcium oxalate (mg.100 g-1)
Total oxalate (Ox) 65 42 42 288 18
Soluble oxalate 35 44 17 45 -
Calcium oxalate 43 23 37 399 -
Free calcium 10 0 15 10 -
Malate 107 211 320 106 105
Citrate 102 314 278 86 142
Succinate 168 506 370 295 0
Trypsin inhibitor (TIU.g-1) 14 0.3 269 2.5 0.56
Chymotrypsin inhibitor (CIU.g-1) 0 0 57 0 -
Source: (Bradbury, 1988)
EDIBLE AROIDS: Post-harvest Operations Page 6
Table 4: Explanatory summary on nutritional and chemical characteristics of main
edible aroids.
Edible aroid Nutritional and chemical composition

Taro (Colocasia esculenta) Middle range energy, protein and vitamins, high K. Zn,
low Na, medium trypsin inhibitor; some cultivars acrid.

Tannia (Xanthosoma spp) Like taro, but high in nicotinic acid, lowest in free Ca
(zero) and low trypsin inhibitor; some cultivars acrid.

Giant taro (Alocasia spp.) Middle range energy, highest protein, lowest -carotene
(zero), thiamine and riboflavin, high Fe and Mn, low K
and Cu, very large amount of trypsin/chymotrypsin
inhibitor; acrid.

Giant swamp taro Low energy and protein, high dietary fibre, low vitamins,
(Cyrtosperma chamissonis) high Na, Zn and Mn, very low K, large amount of total
oxalate and calcium oxalate; some acridity.

Elephant foot yam Low energy, highest protein, high total Ca, calcium
(Amorphophallus oxalate, total oxalate, K, Mg, P, Zn, and Mn; some
campanulatus) acridity.
Source: (Bradbury, 1988).

Fig. 2. Edible Aroids at thr local market,
Nuku'aloga, the Kingdom of Tonga, Infront are
tannia and at the back with the stem intact are tano.

EDIBLE AROIDS: Post-harvest Operations Page 7
2. Post-Production Operations
2.1 Pre-harvest Operations
The condition of the leaves is a good maturity index for assessing the readiness of corms for
harvest. The length of the growing season and yield varies among the cocoyam varieties.
Taro matures in 240-300 days from planting but the eddo type matures in 180-210 days. Taro
yields may range from 4-6 t.ha-1 and up to 15 t.ha-1. Tannia matures in 240-420 days after
planting and produces small edible cormels 15-22 cm in length attached to large corms.
These cormels should be harvested before they produce new shoots. Tannia yields about 6-12
t.ha-1 of corms, but yields of 12-20 t.ha-1 can be achieved. Data on length of growing season
and crop yield are useful in planning harvesting and post-harvest requirements for labour,
packaging, transportation, storage, quality control and marketing.
2.2 Harvesting
Edible aroids are mature for harvesting when the leaves begin to turn yellow and start to
wither. Harvesting is carried out by lifting the corms by hand. Simple tools such as hoe and
knife are used to remove the soil around the corm. Shovels are also used. Although
experimental mechanical lifters have been studied, there are no commercial equipment
dedicated to harvesting aroids. Mature taro produces a large edible main corm and a few
lateral cormels, about 4-10 in number. The main tuber is often harvested with the smaller
corms left to develop later. For tannia, on the other hand, mature cormels may be harvested
continuously for 500 days or more, leaving the main corm in the ground to develop new
cormels.
The main objective of harvesting is to remove the mature crop without physical damage.
Most subsistent small-scale farmers harvest their crop for immediate consumption and/or sale
while the rest are left underground as a storage strategy until required. Corms are susceptible
to damage during harvesting. Damage can occur as a result of the harvesting tool injuring the
corm, or as a consequence of rough handling (e.g. corm-to-corm impact by throwing
harvested corms into a pile). Physical damage such as punctures, cuts or abrasion lead to high
rates of moisture loss and provide avenues for microbial infection. These conditions lead to
high incidence of shrinkage and postharvest losses down the handling chain. In many regions,
corm harvesting is generally carried out by women who also have to trek considerable
distance back to the family house or market. Developing simple and appropriate tools to
remove the drudgery of manual harvesting, particularly when the soil is dry and „hard‟ would
be beneficial engineering inputs under these conditions.
2.3 Transport
Harvested corms are stored on-farm or transported immediately to the home, nearby market
or handling facility. In many rural subsistence farming systems, the corms are put in a woven
basket and carried on the head as in parts of West Africa or on the shoulder where a basket is
tied to each end of a stick as in the South Pacific. Bicycles and motorised transport are
increasingly being used for transportation, especially where a large quantity of crop is
harvested. The quantity of crop and expected market value are important considerations is
selecting an appropriate transport system. Mechanised transport has the potential to induce
physical damage during haulage on “bumpy” roads. Good shock and vibration absorbers and
careful driving will assist in reducing the incidence of damage.
EDIBLE AROIDS: Post-harvest Operations Page 8
Fig. 3. Baskets for transporting root crops and other food crops in the South Pacific.
2.4 Corm Curing
Although not desirable for good quality produce, wounding of corms occurs during
harvesting and trimming, and it is therefore important that harvested crop is cured before
long-term storage so as to promote a rapid wound repair process. Curing slows down the rates
of physiological and pathological deterioration which lead to losses in quality and quantity.
Several wounds are made on tannia corm when the cormels (usually 4-10 in number) are
removed, and one wound is ultimately made on taro cormels when they are cut off from the
parent corm. Additional wound is also made during trimming to remove the residual planting
material from the base of the corms and the petiole of leaf base. These regions have poor
healing properties and require curing to prevent subsequent infection and spoilage.
Under traditional post-harvest systems, curing is accomplished by placing corms in the sun
until the wounded surface dries out. Corms can also be cured in naturally ventilated barns or
other storage structures. Curing is less effective if damage on corms is extensive. Fungicide
treatment may be necessary if base trimming is practised. Curing can also be achieved at
elevated temperatures in high humidity environment, but chemical application to suppress
sprouting has been suggested to cause an inhibitory effect on wound healing and periderm
formation (Passam, 1982). Curing corms at 35°C and 95% rh for 5 days reduced the rate of
sprouting and weight loss in tannia (Passam, 1982; Been et al., 1975), and temperatures
below 20°C have been reported to cause very slow wound healing of dasheen cormels. It was
recommended that brief storage of corms under tropical ambient conditions (24 or 30°C with
85% rh) promoted curing in taro and tannia corms (Agbo-Egbe and Rickard, 1991). Other
studies reported that the best conditions for wound healing were 34-36°C with 95-100% rh
(Rickard, 1981). Under these conditions, wound healing occurred more readily at the top of
corms than at the base and sometimes did not occur at the base.
EDIBLE AROIDS: Post-harvest Operations Page 9