YACON

SCIENTIFIC NAME: Polymnia sonchifolia
FAMILY: Asteraceae

A root crop, also called "apple of the earth" because of its sweet taste. Yacon, Polymnia sonchifolia, of the Compositae family, is a distant relative of the sunflower, but this Andean crop is grown not for seed but for its edible tubers.

Origin
Yacon grows wild in Colombia, Ecuador, and probably Peru. It is commonly naturalized at medium altitudes in South America. It has been found in pre-Incan tombs in Peru, indicating a wide dispersal in early times.

Description
Yacon is a handsome, compact, herbaceous plant with dark-green celery-like leaves. The aerial stems can reach 2m in height, and are hairy with purple markings. Small daisy-like yellow or orange flowers are packed close together at the top of the plants and on additional stems arising from the lower leaf axils.

Yacon tubers are irregularly spindle-shaped to round (somewhat resembling those of the garden dahlia) and can vary considerably in shape, size and sweetness. Fused to the swollen stem (4-5 or even 20 in a bunch), they splay out like fat spokes from a hub. On the outside, they are tan to purplish brown, but inside they are white, yellow, purple, orange or yellow with magenta dots. A tuber usually weighs 300-500 g, but can reach up to 2 kg.

Yacon actually produces two types of edible underground portions - rhizomatous stems (used by the plant for vegetative reproduction) and tuberous roots (used by the plant for food storage) . The swollen roots are preferred for eating as they are sweeter, juicier and not fibrous. The stems, although succulent when young, coarsen (lignify) as they mature.

Propagation
A) Yacon is easily propagated with offsets - small plantlets taken from the base of the above-ground part of the main stem with a few cylindrical roots attached.

B) By cuttings. Use single node stem cuttings; they root readily.

C) By division of the storage tubers.

D) Selected clones and disease-free material can be derived from tissue culture. Unlike many Andean root crops, a tested sample of Yacon was found free of several common tuber viruses, including the potato leaf-roll virus, and potato viruses X, Y, S, M and A.

Yacon is planted throughout the year providing there is adequate soil moisture and warmth. Early growth is rapid, and it requires little attention apart from weeding.

The plant reaches maturity in 6-7 months. Having flowered, the top withers and dies back, at which time the tubers are harvested.

Harvesting
The plant must be dug carefully to prevent breaking of the brittle tubers. These tubers are separated from the central stem, which is often fed to livestock. Yields of 38 tonnes of tubers per hectare have been reported.

Once soil is removed, the roots can be stored in a dark dry place for months. Unlike sugar-beet growers, yacon producers could spread out the time they harvest and process the crop.

Uses and Nutrition
The large tubers or storage organs have a clean crispness, set off by a refreshing sweetness. They have been described as being like a fresh-picked apple with a mild, sweet flavour reminiscent of watermelon.

Yacon should prove agreeable to a wide range of palates. It also has a future as an industrial crop. Most other root and tubers store carbohydrate in the form of starch, a polymer of glucose; yacon, on the other hand, stores carbohydrates in the form of inulin - a polymer composed mainly of fructose. Yacon therefore may possibly be a fructose-sugar counterpart of sugar beets.

Yacon tubers also may have potential as a diet food. The human body has no enzyme to hydrolize inulin, so it passes through the digestive tract unmetabolized, which means that yacon provides few calories. This could be an attractive marketing feature to dieters and diabetics.

In addition, the main stem of the young plant is used as a cooked vegetable.

The species also shows promise as a fodder crop because the leaves contain 11-17% protein on a dry-weight basis.

From Colombia and Venezuela to northwestern Argentina, yacon is found at elevations below about 3,300 m. Children in particular consider its roots a special treat. In some areas, almost everyone has a few plants in the garden. Much is grown in northern Argentina and in Latacunga, Ecuador where yacon is sold on the markets in large quantities, especially on the traditional "Day of the Dead". On the other hand, in other areas it is seldom seen on the markets and in some places it is almost unknown.

The food value of the tubers is low and consists chiefly of carbohydrates. Fresh tubers have been analyzed as containing 69-83% moisture, 0.4- 2.2% protein and 20% sugars. The sugars consist mainly of inulin.

Dried tubers vary from 4-7% ash, 6-7% protein, 04-1.3% fat, 4-6% fibre and approximately 65% sugars. The tubers are said to be high in potassium.

The inulin molecule in yacon is uncharacterized, but in related species (other Compositae), it has a molecular weight of 3000-5000. It is a polymer of fructose but the terminal unit is a glucose sugar. Thus, inulin contains a small amount of glucose.

The dried herbage contains 11-17% protein, 2-7% fat and 38-41% nitrogen-free extract.

Yacon is usually eaten raw. The sweet crunchy tuber is often chopped and added to salads, imparting flavour and texture. The tubers are also consumed boiled and baked. If boiled 'in the jacket', the skin separates from the flesh and can be peeled off like a boiled egg. In cooking they stay sweet and slightly crisp; They usually weigh 180-500g, but some are said to weigh as much as 2kg each. In the Andes, they are often grated and squeezed through a cloth to yield a sweet refreshing drink. Sometimes this is concentrated to form dark-brown blocks of sugar called chancaca.

The skin can have a resinous taste, so the tubers are usually peeled before eating. Undamaged tubers keep well, and in Spanish colonial times, yacon was used as a food for sailors.

ADDITIONAL INFORMATION

Botanical name -Polymnia sonchifolia poeppig & endlicher
Synonyms -Plymnia edulis, Weddell, and Smallanthus sonchifolia.
Common names -Quechua; yacon, ilakuma
Spanish.; yacon, ilamon
English; yacon, jiquima
French; poir de terre cochet
German; erdbirne
Italian; polimnia

Daylength: The plant is daylight neutral for stem and root tuber information, at least for some clones.

Cardwell/Johnstone Newsletter. Vol.7, 6/93

DATE: January 1994

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