Tropical Sources of Starches

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1. Introduction

The tropical belt which covers around 40% of the total land area encompassing five continents and many countries harbour a number of starch bearing crops which include cereals, tree, fruit and vegetable crops and most important the root crops [1-8]. However commercial use of these for starch extraction has been limited to a few of these crops. Most important of them are sago starch from sago palm, potato, cassava and sweet potato starches from the corresponding tubers. Minor quantities of starch are extracted from other crops such as Palmyra fruits, and the tuber crops like colocasia, amorphophallus, yams, arrowroot, Canna and Curcuma sp. but they have no commercial importance. Among these different starches, only cassava and sweet potato starches have been studied in detail and this chapter tries to bring out the available information on the tropical starches and also possible avenues of utilisation based on their physicochemical and functional characteristics. The starches and their properties are dealt with under different sections.

1. Tree Crops

   Among the starch bearing tree crops, the most important ones are sago palm, mango, Plantain, jackfruit , breadfruit and Pandanus. The starch is found either in the stem, fruit or seed.

   1. Sago palm

      (Metroxylon sagu)
      is a nonbranching palm cultivated in SE Asia. It grows to 9-12 metres high and flowers after 10-15 years and then dies. At the time of flowering, the palms are felled, the stems are sliced the pith is rasped, sieved and the starch granules are allowed to settle. The starch is collected, dried and used to make sago pearls by granulation. Originally all the sago pearls were obtained exclusively from sago starch, but now the sago pearls are obtained from cassava starch, which is more abundantly available.

   2. Mango

      (Mangifera indica)
      is widely grown in the tropics for its delicious fruits. The trees grow upto 40m metres in height. The seeds which form around 20-40% of the fruit contains upto 30% starch. The starch can be extracted by crushing the seeds, filtering and allowing to settle. No work has been carried out on this starch.

   3. Jackfruit

      (Artocarpus indica)
      is a large tropical fruit tree with a dense crown and reaching upto 50 metres in height. The large fruits contain a fleshy portion covering oval shaped seeds. The seeds form around 5% of the fruit and contains nearly 30% starch. Often the seeds are roasted and eaten. Very little study has been carried out on the starch properties.

   4. Breadfruit

      (Artocarpus altilis)
      a tall tree 30 metres high and branching. It yields about 600- 700 medium size round fruits per year. They are consumed as vegetable and have a very delicious taste. The fruits contain around 20% starch. Only very little work has been carried out on the starch of breadfruit.

   5. Screw pine

      (Pandanus lerum)
      is a tall slender palm, 12-18 metre in height found in various tropical countries and Andaman and Nicobar islands of the Indian Ocean where it is very common. Its fruit (10-18Kg) is fleshy and contains nearly 20% starch. The local population consume the tubers after cooking and also extract starch, by crushing the fruits, sieving and drying. The starch has not been studied in detail.

2. Cereal starches

   Maize, sorghum and a number of millets are cultivated in the tropics and form important crops in many areas. They serve as a cheap source of food. Most of them contain good quantity of starch, the most important being maize.

   1. Maize

      (Zea Maize)
      Maize is grown in large areas of tropical and subtropical belt and form a staple food. The yield of the crop is and the starch content as high as 70% in the dry cob. The extraction of starch from maize has been well standardised and is carried out extensively. The starch is commercially extracted and used in various food and industries.

   2. Sorghum

      Sorghum bicolor
      is grown widely in tropics and is considered as poor mans cereal .The starch content is quite high, but very little work has been carried out on the starch properties.

   3. Tef

      (Eragostis tef)
      is a major cereal staple in Ethiopia and its flour is used for making various products. The starch content in the grains is similar to other cereals and can be easily extracted using water.

3. Herbs / shrubs

   There are a number of herbs/shrubs which produce starch in their grains, fruits or seeds. But these have not been exploited as starch source. Among them a few important ones are outlined below.

   1. Amaranthus.

      The amaranth plant family include more than 60 species that grow in many tropical regions. Although most of them produce edible leaves a few species are cultivated for their grains. The chief ones are A. hypochondriacus, A. caudatus, and A. edulis. They are perennial herbs widely differing in height and appearance. The grains contain 40-50% starch mainly waxy starch. The small size of the granules and low amylose conetent in the starch make them very valuable as a type of starch with special food applications.

   2. Plantain/banana

      Banana (Musa sp.) is grown extensively in most parts of the tropic for its fleshy fruits and there are a number of species having widly varying tast and texture. It is a straight annual yielding upto t/ha of fruits. The unripe fruits contain nearly 35% starch which has been rarely extracted.

   3. Okenia

      (Okenai hypogeae)
      is a perennial herbaceous crop distributed in central and south America. And the seeds contain nearly 35% starch.

   4. Quinoa

      (Chenopodium quinova)
      the anciednt andes crop is widely gromn in S. America produce grains which serve as important food source. These are perennial herbs producing a grain yield of t/ha which contain approximately % starch. yielding grains

4. Pulses

   The pulses also contain starch to a good extent. (20-30%). However they are never obtained pure due to presence of lipids and proteins accompanying the starch. Extraction of starches from the pulses are rarely reported except for some isolated reports on the study of their starches. A few of these are given below.

5. Tropical root crops

   Tropical root and tuber crops are important food crops serving either as subsidiary or subsistence food in different parts of the tropical belt. They are rich sources of starch [9-12] besides many vitamins, minerals etc. Although there has been some decline in their use as food, their industrial application, especially that of cassava, is making rapid advances. Cassava and to a small extent, sweet potato (Ipomoea batatas Lam.) are used for starch extraction in countries like India, Brazil, Thailand, Indonesia, Philippines and China. Studies at different laboratories have brought to light the wide diversity in the starch characteristics of tuber crops and the possibility of using these native starches instead of chemically modified starches [12,13].

   1. Cassava

      (Manihot esculenta
      Crantz)is a sturdy perennial crop grown in many parts of Asia, Africa and South America. The yield of the crop is normally around 20t/ha and the starch yield forms nearly one fourth of the total yield. The starch has been studied in detail and finds use in a large range of industries.

   2. Sweet potato

      (Ipomoea batatas Lam.)
      is a herbaceous perennial vine and is grown extensively over the tropics and also in some parts of the USA for its tubers. The tubers have different sizes, shapes and colour. The yield varies anywhere from 8-30t/ha and it has been possible to have three crops in a year thus giving a very high annual starch yield. The starch content in the tubers vary from 12-30%.(fresh weight basis)

   3. Taro

      (Colocasia esculenta)
      is a small herbaceous plant with large leaves found in most parts of the tropics, but are very important in the pacific regions. The crop is harvested at 8-10 month stage and produces a number of cormels around a corm. The yield is 5-10t/ha and starch content is 10-18%.

   4. Tannia

      (Xanthosoma sagittifolium)
      is a large herbaceous plant grown widely for its cormels which are much larger than taro cormels. The yield is around 10-25t/ha and starch content in the tubers nearly 20%.

   5. Elephant Foot Yam

      (Amorphophallus paeoniifolius)
      grown extensively for its huge corms. It is a big perennial herb harvested after one year and the corms can weigh over 15 Kg. The yield is over 20t/ha and starch content in the tubers nearly 20%.

   6. Yams

      is a large genus with over 600 species out of which a few are more commonly cultivated. Most of them are trailers. The tubers are harvested at 8-12 months after planting and the tubers especially those of D. alata are very large. Some of the species produce aerial tubers also. The starch yield also varies considerably and D. rotundata tubers have the highest starch content. In addition, there are a number of other minor tuber and root crops which contain starch, but their utilisation is limited.

   7. African yam bean

      (Sphenostylis stenocarpa)
      belongs to Luguminosae a vigorous herbaceous climbing vine reaching 1.5 -2.0 m in height producing pods as well as small spindle shaped tubers about 5-8 cm long similar to sweet potato. The crop is found mainly in Africa yielding upto 4 t/ha. The tubers are rich in starch ( 25% ) but there are no studies on this starch.

   8. Arracacha,

      Peruvian carrot,( Arracacia xanthorrhiza).
      A stout semi-caulescent herb, resembling celery grown in south America and parts of Africa grown mainly at high altitudes. The edible secondary tubers are usually 6-10 in number with a yield of 3-18t/ha. The tubers which contain nearly 20% starch are used as a source of edible starch

   9. Chinese water chest nut

      (Eleocharis dulcis)
      a variable annual stout aquatic plant and producing corms found in Asian region. The yield is 20-40t/ha and starch content around 7%. In China the starch is extracted by rasping and settling.

   10. East Indian arrowroot

       (Tacca leontopetaloides)
       is a perennial herb with1.4.8 tuberous rhizome producing large/small sized tubers, found in triopical areas.. The tubers are similar to potato and harvested after 8-10 months. They are used in Tahiti to make ‘ poi’ a traditional food. The tubers are rich in starch (20-30 %) and starch extracted and used widely.

   11. Giant taro

       ( Alocasia macrorrhiza)
       is a tall succulent herbaceous plant upto 4.5 metres in height producing big corms upto 18 Kg. It is grown in Asia and South America and harvested 10-12 months after planting. The tubers contain 17-25% starch.

   12. Coleus

       (Plectranthes rotundifolius)
       is a small herbaceous annual 15-30 cm high found in Africa and Asia At maturity ( 6 months) they yield round to oval tubers very priced for delicate flavour. The yield 7-15 t/ha and the starch content is nearly 15%.

   13. Kudzu

       (Pueraria lobata)
       known as arrowroot vine is a small perennial twining herb or shrub with elongated tuberous roots often weighing upto 40 Kg Root are starchy 30-60 cm long used as source of edible starch used instead of arrowroot starch or gelatine in many foods. The starch content is over 20% and is extracted in small scale in Japan.

   14. Lotus root

       (Nelumbo nucifera)
       is a perennial aquatic herb, rooting in mud found in S and SE Asia, Africa and Australia The white globulous rhizomes which are harvested at 6-9 months measure 60-120 cm in length. The yield is 5 t/ha and starch content is nearly 18%. In china a fine starch is isolated from the rhizomes.

   15. Oca

       (Oxalis tuberose)
       a small compact annual tuberous herb 20-30 cm high Oca is a ancient food plant of the Andes and found in many parts of Soth America. The rhizomatous tubers are harvested at 8 months maturity and are similar to potato ( 5-8cm in length) The tuber yield is 4-5t/ha while starch content is 12%.

   16. Queensland arrowroot

       (Canna sp)
       A perennial herbaceous monocotyledon found in many parts of Asia, Africa and S. America. The shape of the rhizomes vary from cylindrical to tapering with 5-9 cm in size. The tuber yield is 15-40t/ha and the starch content varies from 24-30%.

   17. Shoti

       (Curcuma zeodoaria)
       known as Indian arrowroot is a robust perennial with a fleshy branching rhizomes cultivated in Asia . The starchy finger rhizomes are greyish in colour, grow to 15 cm in length and have a musky odour. The tuber yield is 8-12 t/ha and starch content is 2-15%. The starch is extracted by rasping the tubers, sieving and settling and serves as a source of easily digested starch.

   18. Swamp taro

       (Cyrtosperma chamionensis)
       is a giant herbaceous perennial 3-4 m in height with huge leaves. It is cultivated in many parts in Asia , Africa and Pacific islands. The yield of corms is 7-10t/ha and the starch content 28-30.

   19. Winged bean

       (Psophocarpus tetragonolobus)
       is a leguminous, climbing perennial found in Asia and Africa. Tubers are obtained 5-8 months after palnting with a yield of . Root tubers are 5-12 cm in length and contain nearly 20% starch.

6. Other minor sources

   In addition there are a few other sources of starch which have not been exploited. They are :

   1. Bamboo

      (Guadua flabellate)
      is a perennial crop grown largely as a source of wood. However the culm of the crop has nearly 20% starch which can be easily extracted and can serve as a source of starch.

   2. Black pepper

      (Piper nigrum)
      termed king of spices grown in Asia and Africa is a branching climbing perenneial shrub. The annual yield of dry pepper is 100-300 kg/ha and the seeds contain over 40% starch but has not found any application.

   3. Buffalo Gourd

      (Cucurbita foetidissima)
      produces roots which can be very large even upto 75Kg. The roots contain 15% starch and can be used a source of starch.