Dp 212

Source: Adapted from Van Loo, J., Coussement, P., De Leenheer, L., Hoebregs, H., Smits, G., On the presence of inulin and oligofructose as natural ingredients in the Western diet, Critic. Rev. Food Sci. Nutr, 35, 525-552, 1995.

hectare. A strict crop rotation is necessary (once every 5 years). Commercial inulin production is essentially from chicory (Cichorium intybus). Jerusalem artichoke shows a rather high inulin content (17-20.5%). The tubers are small and irregular, hence a high amount of soil is attached to them. Jerusalem artichoke inulin has only 20% of chains with a degree of polymerization longer than 10. Many dahlia cultivars are available, but they have all been selected for their flowers, rather than for inulin production. The tuberous roots can be propagated only if they are attached to stem tissue. When propagated from seed, sowing has to be delayed until late spring, given dahlia's extreme sensitivity to frost. Mechanical harvesting of the tubers is feasible only in sandy soil. Although the degree of polymerization of dahlia inulin is higher than that for chicory, the yield is only half that of chicory. For all these reasons, dahlia does not appear to be an interesting crop for inulin production, and practically only chicory (Cichorium intybus) is used today as an industrial crop; its fructan is known as chicory inulin.2425

3.2.4 Biological Functions of Inulin in Plants

Despite major advances in understanding the metabolism of fructans, the exact physiological functions of inulin is still a subject of debate. Most documented is its role as a long-term reserve carbohydrate stored in underground overwintering organs. Two other functions are often quoted: cryoprotection and osmotic regulation, allowing not only just survival but also growth under conditions of water shortage, whether induced by drought or by low temperatures. During drought, increased amounts of glucose, fructose, sucrose, and inulin are found in the roots and in the leaves.26 In winter (e.g., 3 weeks at 4°C), chicory inulin becomes hydrolyzed, resulting in lower-DP fractions and increased amounts of free fructose, which are osmotically more active than native inulin. The role of fructans as true cryoprotectant is still under discussion because the increase in free fructose and sucrose upon depolymerization of fructans would only account for a decrease in the freezing point of 0.2-0.5°C.27 On the other hand, inulin was shown to interact directly with membrane lipids upon freeze-drying, preserving the membranes in a liquid-crystalline phase at room temperature, and preventing a phase transition and solute leakage during rehydration.28

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