Jerusalem artichoke has beneficial effects on digestion. It is a good source of dietary fiber, for instance, which helps to bulk food and reduce constipation. However, there can be digestive downsides too.
Human digestive enzymes do not target inulin. Around 89% (and up to 97%) of the inulin and fructooligosaccharides that we consume, on average, remain intact in the small intestine (Andersson et al., 1999; Molis et al., 1996). As it is not digested, there tends to be a lot of inulin in the large intestine or colon after eating a meal rich in inulin. However, none reaches the stools, and only a small fraction occurs in the urine (Molis et al., 1996). This is because inulin is completely fermented by the general microbial fauna in the large intestine, especially by bifidobacteria and lactobacilli (Nilsson and Bjorck, 1988; Nilsson et al., 1988). The digestion of inulin and fructooligosaccharide is accompanied by the production of hydrogen, carbon dioxide, and other gaseous products (Stone-Dorshow and Levitt, 1987). This leads to an undesirable side effect of eating Jerusalem artichoke and other inulin-rich foods: flatulence.
The wind-inducing effects of Jerusalem artichoke have been known for many years. Although the tuber spread rapidly throughout France in the 10 years after its introduction in 1607, it was not universally popular due to overindulgence of the unfamiliar vegetable revealing its digestive downsides. Jean-Luc Hennig, in Le Topinambour et Autres Merveilles, writes of the variety of nicknames the street sellers and people gave the tubers after their introduction, before the visit of the Topi-nambous Indians from Brazil in 1613 suggested an exotic moniker that stuck. The names, often derived from the coarse vocabulary of the countryfolk, referred to a perceived indigestibility and invoked lice (pou-terre), swine (soleil de pourceau), and rotten feet. Philibert Guybert, in le Médecin Charitable (1629), described the topinambour as giving wind ("crudités et vents à ceux qui en usent"), giddiness, and headaches. Meanwhile, in England, Tobias Venner, a physician in Bath, warned in 1622 that the vegetable was "somewhat nauseous or fulsome to the stomach, and therefore very hurtful to the melancholic, and them that have weak stomachs." In Johnson's 1633 revision of Gerard's Herball, John Goodyer's entry for Jerusalem artichoke concluded: "In my judgement, which way soever they be dressed and eaten, they stir up and cause a filthie loathsome stinking wind within the body, thereby causing the belly to be much pained and tormented, and are a meat more fit for swine than man; yet some say they have usually eaten them, and have found no such windy quality in them."
In addition to flatulence, excessive inulin consumption can cause a range of abdominal symptoms, such as osmotic diarrhea, pain, and bloating (Roberfroid et al., 2002a). There are recognized upper limits to the amount of inulin that it is wise to eat in a day. This takes into account figures for human tolerance to inulin, which is dependent on fructan chain length or degree of polymerization, and the amount consumed (Rumessen and Gudmand-H0yer, 1998). Human tolerance to fructans with a degree of polymerization over 5 is greater than for short-chain fructooligosaccharides with a degree of polymerization less than 5. The literature suggests that up to 70 g of inulin per day can be consumed in various foods without causing undesirable side effects (Coussement, 1999; Kleessen et al., 1997; Tungland, 2003). Studies have shown that daily inulin doses of 5 to 20 g produce beneficial effects, and these relatively small amounts are usually well tolerated by the human digestive system (Rumessen et al., 1990).
The amount of inulin that can be eaten without digestive difficulties can depend on an individual's physiology, with some people relatively tolerant to the side effects and others much more susceptible to digestive disturbance. To a certain extent, it also depends on how much inulin has been eaten in the past. Although there is no evidence of physiological adaptation to inulin over the short term, the microflora population in the colon may evolve enzymes that target inulins in the long term. Therefore, the more Jerusalem artichoke that is eaten over a long period of time, the more likely it is that the digestive system can adapt to it. Where Jerusalem artichoke is utilized as a sustenance crop, for instance, people appear to be able to eat significantly more of it without experiencing problems of flatulence or digestive disturbance. This accounts for a tendency to exaggerate the problems of flatulence arising from Jerusalem artichoke consumption, as it is mainly inexperienced consumers who complain of their "loathsome stinking wind." Nevertheless, Jerusalem artichoke will never become a widely accepted staple like potato, because its popularity will always be tempered by its digestive downsides. It is best consumed for its benefits a little at a time.
Harold McGee (1992) has outlined culinary procedures to tone down the undesirable side effects of Jerusalem artichoke. These procedures either remove some of the inulin from the tubers prior to consumption or alter its composition. Raw or quickly cooked tubers have a high inulin content and should only be used as a minor component of a meal. Boiling the tubers in copious amounts of water, which is then discarded, reduces inulin and fructooligosaccharide content — the fructans remain in the pan as a fine white precipitate. The effectiveness of boiling is increased if the tubers are sliced to increase the surface area exposed to the water. Fifteen minutes of boiling draws out around 40 to 50% of the indigestible carbohydrate from sliced tubers. Precooking the tubers (e.g., in water or in water and milk) has been a culinary practice for many years and is mentioned, for instance, in the 1633 edition of Gerard's Herball and in the 1738 edition of La Varenne's le Cuisinier François (McGee, 1992; Schneider, 1986). The most dramatic reductions in inulin content, however, are obtained by slow cooking. Another inulin-rich plant, the camas lily (Camassia spp.), was traditionally pit cooked by Native Americans. This involved burying the camas lily bulbs in a pit and covering them with dry wood and stones and, once the fire had established, earth and grass. The food was cooked for between 12 and 36 h. This method was also possibly used for Jerusalem artichoke tubers. McGee adopted a slow-cooking method in a kitchen for Jerusalem artichoke tubers, over a 12-h period. Cooking by this method eventually turns all the inulin to fructose, leaving a very sweet and soft-textured food (McGee, 1992). The inulin and fructooligosaccharide content is also reduced in chilled and stored tubers, due to chemical breakdown (Edelman and Jefford, 1968; Rutherford and Flood, 1971). Cooked tubers that have been stored under cold conditions for a month or two will therefore have less inulin than fresh tubers, although the effect is small compared to differences obtained through different cooking procedures (McGee, 1992).
Apart from flatulence and minor digestive disturbances, inulin has few adverse effects in the human body. However, there has been one report of a severe allergic reaction (four episodes of anaphylaxis) attributed to an accumulated dosage of inulin from multiple sources, including vegetables and processed food (Gay-Crosier et al., 2000). Inulin and fructooligosaccharides are being added to an ever-increasing range of processed foods, where they are classified as food ingredients rather than additives, and are considered safe to eat. There is therefore a very small chance that their increased use in processed foods might make allergic reactions to them more frequent than is currently recognized.
The aboveground parts of Jerusalem artichoke are not consumed as human food, but both the tops and tubers can be utilized as animal feed, either fresh or in silage and feed formulations. Jerusalem artichoke typically yields around 500 to 700 tha-1 of green material. As a forage crop, it can be grown as a permanent planting since the tops are regenerated each year from tubers left in the ground (Gunnarson et al., 1985). All the aerial parts are included in fodder, although the leaves and stems differ in their nutrient and mineral content (Table 6.2). The leaves contain more protein than the stems, while the stems contain more carbohydrate than the leaves (e.g., Hay and Offer, 1992; Luske, 1934). The leaves are therefore generally considered better in terms of fodder than the stems (Hay and Offer, 1992; Malmberg and Theander, 1986; see also Table 5.3).
The leaves are a good source of protein for animal forage, being particularly rich in the amino acids lysine and methionine compared to other forage (Stauffer et al., 1981). The protein dry matter content of the leaves can be as high as 20% of the total aerial parts, of which 5 to 6% is the essential amino acid lysine (Rawate and Hill, 1985). Crude protein content of between 9.5 and 17.3% was recorded for eight Canadian accessions (Stauffer et al., 1981). The amino acids (percent dry weight basis) for herbage protein have been given as: lysine (5.4%), histidine (1.8%), arginine (5.2%), asparatic acid (9.1%), threonine (4.4%), serine (4.0%), glutamic acid (10.5%), proline (4.1%), glycine (5.1%), alanine (6.3%), methionine (1.4%), isoleucine (4.6%), leucine (8.3%), tyrosine
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