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Page 115 Yacon Yacon (Polymnia sonchifolia) is a distant relative of the sunflower, but this Andean crop is grown not for seed but for its edible tubers. 1 These enlarged storage organs have a clean, crunchy crispness, set off by a refreshing sweetness. They have been described as being like a fresh-picked apple with mild, sweet flavor reminiscent of watermelon. Yacon (pronounced ya-kon) 2 should prove agreeable to a wide range of palates, and it also has a future as an industrial crop. Most other roots and tubers store carbohydrate in the form of starch—a polymer of glucose; yacon, on the other hand, stores carbohydrate in the form of inulin—a polymer composed mainly of fructose. 3 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 hydrolyze 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 percent 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 family garden plot. Much is grown in northern Argentina, for instance, and in Latacunga, Ecuador, yacon is sold in large quantities, especially on the traditional Day of the Dead. 4 On the other hand, in other areas, it is seldom abundant in markets; in some places it is almost unknown. 1 Strictly speaking, these are not tubers, but an integrated mass of root and stem. 2 In Ecuador it is frequently called “jicama.” Internationally, that name is used for another plant (see page 39). 3 Yacon shares this form of carbohydrate storage with most members of the Compositae, or sunflower family. Rarely, however, does inulin appear so abundantly or in so pure a form. 4 Information from R. Castillo.
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Page 116 The plant grows fast and easily, and survives even in poor soil. It is not restricted to upland areas, and has shown excellent growth at sea level. Outside the Andes, yacon is almost unknown. However, in New Zealand a few nurserymen now offer it for home gardeners and commercial planting, and the tubers are being packaged like carrots for sale in stores. It has been successfully introduced into southern Europe, but is not widely known. It has only recently been introduced to the United States, and amateur gardeners have found that it thrives in many parts of the country—in California, Oregon, New Mexico, Florida, Alabama, and northern Virginia, for instance. There seems a good likelihood that it could be viable in most parts of the temperate and subtropical zones. PROSPECTS The Andes. Yacon is little exploited even in its native habitat. There is probably an untapped demand in many urban areas, both among immigrant highlanders and urbanites themselves. Thus, given promotion and consumer education, this crop has a future throughout the Andes. The region is the logical center for the selection and development of cultivars, and it seems likely that researchers will discover varieties with unexpected qualities. (Those now available have not been improved and are considered landraces at best.) Yacon could prove to be a profitable source of high-fructose sweeteners as well as a fresh snack vegetable. It might also be a useful, perennial fodder crop. Other Developing Areas. Yacon seems to have promise worldwide. It is already popular in some South American regions outside the Andes, as well as in parts of Southeast Asia. Although fresh yacon is not nutritious, it is an easy-to-grow sweet treat that could become popular in many areas of the tropics and subtropics. Industrialized Regions. Yacon is easy to grow, widely adaptable, and seems to be unrestricted by differences in daylength. It is refreshing, low in calories, and can yield an industrial sweetener. Any plant with these features seems destined to become commercially valuable. Like jicama and jerusalem artichoke before it, yacon might find its way into upscale markets in the United States, Europe, Japan, and other industrialized areas as a food for dieters.
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Page 117 ~ enlarge ~ Yacon is a root crop that can be eaten raw. It has been called “apple of the earth” because of its sweet taste and crunchy texture. (N. Vietmeyer) In addition, yacon could be a source of inulin for use in sucrose-free foods for diabetics. As noted, the high-fructose sugars produced from inulin might also eventually compete with other, less-efficient sources. USES Yacon is usually eaten raw. The sweet, crunchy tuber is often chopped and added to salads, imparting flavor and texture. The tubers are also consumed boiled 5 and baked. In cooking, they stay sweet and 5 If boiled “in the jacket,” the skin separates from the flesh and can be peeled off like a boiled egg.
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Page 118 THE RISING DEMAND FOR FRUCTOSE In the past, crystalline sugar was the main commercial sweetener, and fructose (which is hard to get in crystalline form) was of little interest. But now, syrups dominate the industrial use of sugar, and this has brought fructose to the forefront. With today's greater interest in high-fructose sweeteners, yacon might be economically more suitable than ever before. Indeed, “super-high-fructose” syrups from inulin could have value on their own account in addition to diluents to raise the fructose level in normal syrups. In recent years, fructose has gained much attention as a sweetening agent. It has twice the sweetening power of normal sugar (sucrose). So far, it has been made by using enzymes that transform the glucose in corn syrup. Most of the resulting “high-fructose corn syrups” contain less than 60 percent fructose. With yacon, however, no transformation of one sugar to another would be needed, and the resulting syrup would likely contain more than 90 percent fructose. The solids in a yacon tuber may be 60–70 percent inulin, which is readily hydrolyzed (by acid, or by the enzyme inulase) to fructose. In spite of previous interest in using inulin to produce fructose, there has been little effort to do it in practice. Yacon might be the key to making the process economically attractive. A few other crops, mostly of the family Compositae, contain inulin. The best known are jerusalem artichokes (Helianthus tuberosus) and chicory ( Cichorium spp.). Yacon tubers, however, are like big fat fingers with smooth skin, unlike the knobby irregularity of jerusalem artichokes, and are thus more easily processed. Yacon yields are also higher than those of jerusalem artichokes, and the fresh tubers contain almost 19 percent inulin. * The strong flavor of chicory roots limits their usefulness as a sweetener source (they are used as a coffee substitute). Compared to the competition, yacon has the advantages of providing both a specialty food and animal fodder, giving high yields, and probably being easy to harvest and process. * Calvino, 1940. slightly crisp. They usually weigh 180–500 g, but some are said to weigh as much as 2 kg 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.
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Page 119 As previously mentioned, the main stem of the plant is used as a cooked vegetable. Yacon might have potential as a forage crop. The foliage is luxuriant, and the leaves have a protein content of 11–17 percent (on a dry-weight basis). When cut, the foliage sprouts again from the underground stems. The tubers may also be good cattle feed, for inulin is rapidly metabolized by ruminants. Additionally, the plant may be useful in agroforestry, because it grows well beneath a canopy of trees. NUTRITION The food value of the tubers is low and consists chiefly of carbohydrates. Fresh tubers have been analyzed as containing 69–83 percent moisture, 0.4–2.2 percent protein, and 20 percent sugars. The sugars consist mainly of inulin. Dried tubers vary from 4–7 percent ash, 6–7 percent protein, 0.4–1.3 percent fat, 4–6 percent fiber, and approximately 65 percent 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 3,000–5,000. 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 percent protein, 2–7 percent fat, and 38–41 percent nitrogen-free extract. AGRONOMY Yacon is propagated with offsets (small “plantlets” taken from the base of the above-ground part of the main stem) with a few cylindrical roots attached. Single-node stem cuttings root readily. Moreover, the storage tubers can be easily divided. In addition, selected clones and disease-free materials can be derived from tissue culture propagation. 6 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 tops wither and die back, at which time the tubers are harvested. 6 Unlike many Andean root crops, a tested sample of yacon was found free of several common tu ber viruses, including the potato leaf-roll virus, and potato viruses X, Y, S, M, and A. Information from J. Martineau.
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Page 120 HARVESTING AND HANDLING The plant must be dug carefully to prevent breaking the brittle tubers. These tubers are separated from the central stem, which is often fed to livestock. Yields of 38 tons of tubers per hectare have been reported. 7 Once soil is removed, the roots can be stored in a dark, dry place for months. (Thus, unlike sugar-beet growers, yacon producers could spread out the time they harvest and process the crop.) LIMITATIONS Yacon provides little in the way of human nutrition. It is consumed for flavor and variety rather than for sustenance. Outside its native region, yacon is little known either in agriculture or as food. Whitefly and looper caterpillars have been reported to be pests. RESEARCH NEEDS As a first step, an international effort is needed to scout out the available types, evaluate them, and store them in gene banks. 8 Yacon could be an attractive crop for producing alternative sweeteners, and research to determine this should be undertaken at a university or industrial research laboratory. There is a need to develop strains that produce tubers of uniform flavor. At present, one plant may be as sweet as candy, whereas its neighbor is scarcely sweet at all. Also needed is research to determine how flavor is related to growing conditions. Research on improving the storage of the tubers is vital. (One question, for example, is whether yacon can be stored without breakdown or alteration of its inulin.) The plant's potential as fodder has been little explored in the last 40 years. As in other Polymnia species, the leaves may contain sesquiterpene lactones that make them of little use as foodstuffs. 9 The prevalence of diseases—especially viruses—needs to be detrmined. Virus-free material could potentially expand yield and is essential for the movement of germplasm. In particular, quick inexpensive procedures (such as the ELISA test used in potatoes) need to 7 Kay, 1973. 8 There is a collection of about 25 Peruvian clones at the University of Ayacucho. 9 Information from T. Johns.
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Page 121 YACON IN ITALY ~ enlarge ~ Before World War II a far-sighted Italian agronomist, Mario Calvino, came across yacon while working in the Dominican Republic. He took some tubers to northern Italy, hoping the plant would make a palatable high-protein forage, as well as a possible source of sugar for producing alcohol for fuel. From Calvino's fields, yacon was introduced to other parts of southern Europe; however, war brought this work to an abrupt halt. After the war, Calvino and his plant were forgotten, but the fact that yacon grew vigorously in this temperate lowland region, so far from its Andean homeland, demonstrates to us, 50 years later, that, like the potato before it, this is an Inca crop with worldwide potential. The photograph, reproduced from one of Calvino's papers, illustrates the magnificent growth of yacon at Sanremo, Italy, on December 20, 1939. be available for monitoring the presence of viruses. As of now, however, yacon seems to be virus free. Capabilities to produce elite clones inexpensively need to be greatly expanded. Apparently, tubers are especially amenable to meristem tissue culture, as they are composed of stem material with numerous buds.
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Page 122 SPECIES INFORMATION Botanical Name Polymnia sonchifolia Poeppig & Endlicher Family Compositae (sunflower family) Synonym Polymnia edulis Weddell, Smallanthus sonchifolia 10 Common Names Quechua: yacón, llakuma Aymara: aricoma, aricona Spanish: yacón, jacón, llacón, llamón, arboloco, puhe, jícama (not the common jicama of commerce, see page 39), jíquima, jíkima, jiquimílla English: yacon, yacon strawberry, jíquima French: poir de terre Cochet German: Erdbirne Italian: polimnia Origin. Yacon grows wild in Colombia, Ecuador, and probably Peru, and 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 celerylike leaves. The aerial stems can reach 2 m in height, and are hairy with purple markings. Small, daisylike 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. 11 On the outside, they are tan to purplish brown, but inside they are white, yellow, purple, orange, or yellow, sometimes with magenta dots. A tuber usually weighs 200–500 g, but can reach 2 kg. 10 The genus Smallanthus has been suggested for yacon and many of its relatives (H. Robinson. 1978. Studies in the Heliantheae (Asteraceae). XII. Re-establishment of the genus Smallanthus. Phytologia 39(1):47-53.) 11 Yacon actually produces two types of edible underground portions—rhizomataceous 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.
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Page 123 Environmental Requirements Daylength. The plant is daylength neutral for stem- and root-tuber formation, at least for some clones. Rainfall. The annual foliage and perennial underground stems make yacon adaptable to seasonal cycles of drought or cold. Altitude. Generally between 900–2,750 m in the Andes, but it has been grown at sea level in New Zealand and the United States and reported at elevations up to 3,500 m in Ecuador. Low Temperature. Although foliage is damaged or killed by frost, apparently the underground tissues are not affected unless frozen. High Temperature. Tolerant of a wide range of temperatures. Soil Type. Although it grows in a wide range of soil conditions, yacon does best in well-cultivated, rich, well-drained soil. ~ enlarge ~
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