Effect of seasonal changes on content and profile of soluble carbohydrates in tubers of different varieties of Jerusalem artichoke (Helianthus tuberosus L.)

A high content (60-65% of dry mass DM) of water soluble carbohydrates was found in early harvested varieties (Bella and Bianka) and middle early varieties (Topstar and Gigant) harvested 22-25 weeks after plantation. In late varieties (Waldspindel, Violet de Rennes, Rote Zonenkugel) a similar amount was obtained (55-60% of DM) when harvested 29-33 weeks after planting. There was a distinctive impact on maturing process as well as frost period alterations which resulted in conversion of high polymer inulin to low polymer inulin as well as to sucrose. In early/middle early varieties a correlation between sucrose and inulin level (r = - 0.952**) with a linear regression of y = - 1.35x + 62.32 was observed, whereas the dpn of inulin decreased from 12-14 to 6-8. In late cultivars this correlation was not as exact (r = - 0.502**); dpn of inulin decreased from 12-16 to 7-10. This knowledge about carbohydrate profiles for different varieties of Jerusalem artichoke offers the possibility of selecting suitable cultivars and deciding the appropriate harvest time for an optimum processing of tubers for their application as prebiotic and novel food component.

Single crystals of inulin

Lamellar crystals of inulin were grown by crystallizing sharp fractions of low molecular weight inulin from dilute aqueous ethanol solutions. The crystals were analyzed using three-dimensional electron diffraction and X-ray powder diagrams. Two crystalline polymorphs were observed, depending on the hydration conditions: a hydrated form which indexed on an orthorhombic unit cell, with space group P2(1)2(1)2(1) and with cell dimensions of a = 1.670 nm, b = 0.980 nm and c (chain axis) = 1.47 nm, together with a pseudo-hexagonal semi-hydrated form with unit cell parameters a = 1.670 nm, b = 0.965 nm and c (chain axis) = 1.44 nm. These parameters, together with the density data, indicate that inulin crystallizes along a pseudo-hexagonal six-fold symmetry with an advance per monomer of 0.24 nm. The difference between the hydrated and the semi-hydrated unit cells does not seem to correspond to any change in the conformation of inulin, but rather to a variation in water content.

On the presence of inulin and oligofructose as natural ingredients in the western diet

The classic definitions of inulin and oligofructose are constructively criticized. It is observed that inulin cannot unequivocally be described as a polydisperse 1-kestose-based (GFn) beta (2-->1) linear fructan chain, but that inulin always contains small amounts of Fm and branched molecules. This review article describes the presence of inulin and oligofructose in common foodstuffs. Historical data on human consumption add an extra dimension. Modern analytical techniques (HPLC, LGC, HPAEC-PAD) are used to check the variety of data mentioned in the literature throughout the past century. Methods to determine inulin and oligofructose in natural foodstuffs (cereals, fruit, and vegetables) are optimized and used to determine the loss of inulin during storage and during preparation of the food. These findings allow quantification of the amount of inulin and oligofructose in the average daily western diet. The daily per capita intake is estimated to range from 1 to 10 g, depending on geographic, demographic, and other related parameters (age, sex, season, etc.). Inulin and oligofructose are not measured by classic methods of dietary fiber analysis and consequently are often not mentioned in food tables. Their significant contribution (1 to 10 g/d/per capita) to the dietary fiber fraction (recommended at 25 g/d/per capita) is not taken into account in any nutritional recommendations. In view of this, inulin and oligofructose deserve more attention, both in food composition tables and in diet or nutrition studies.