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), Emanuela Parrucci (HTML transfer)

CHAPTER XXV EDIBLE AROIDS: Post-Harvest Operation

Preface

1 Introduction

1.1 Economic and Social Impact of Edible Aroids

1.2 World Production and Trade

1.3 Primary products

1.4 Secondary and derived product

1.5 Requirements for export and quality assurance

1.6 Consumer Preferences

Preface

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.

1.2 World Production and Trade

Table 1: World production and trade in edible aroids (cocoyams)

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.

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.

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.

Source: (FAO, 1972; Platt, 1962; Tindall, 1983)

Table 3: Data on nutritional and chemical composition of different varieties of edible aroids from different countries

Source: (Bradbury, 1988)

Table 4: Explanatory summary on nutritional and chemical characteristics of main edible aroids.

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.

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