Summary• An analysis of fructan structures, to increase the understanding of biosynthetic pathways and enzymology of fructan synthesis in root and leaf tissues of Lolium perenne is reported.• Fructan extracted from stubble of L. perenne plants was analyzed by high performance anion exchange chromatography and pulsed amperometric detection (HPAEC-PAD) using a new desalting technique. Structures of fructan isomers, separated up to DP16 (DP, degree of polymerization), were established by chromatographic elution times or by GC-MS.• Fructans of DP8 belonged essentially to three series: inulin series, inulin neoseries and the levan neoseries, which is/are different in glucose (terminal or internal) and linked fructose residues. High DP fructans (DP > 8) comprised 75% molecules with an internal glucose residue. They had some branch points although 1 and 6 kestotetraose could not be detected and the β (2 -6) linked fructose residues were 70 times more abundant than the β (2 -1) linked fructose residues. Roots, sheaths, leaf blades and elongating leaves accumulated similar fructans although amounts of both low and high, and types of low, DP fructans, differed.• It is proposed that fructans in L. perenne are synthesized via four enzymes: 1-SST (1-sucrose-sucrosefructosyl transferase), 1-FFT (1-fructan-fructanfructosyl transferase), 6G-FT (6-glucose-fructosyl transferase) and 6-FFT (6-fructanfructanfructosyl transferase) or 6-SFT (6-sucrose-fructanfructosyl transferase).

Powders of tubers from Jerusalem artichoke (Helianthus tuberosus, L.), cultivar Gigant, of different harvesting times (autumn and spring) were applied in bakery products, particularly in wheat/rye bread. The quality of this bread was compared to bread with cereal flours substituted with commercial products as Raftilin ST and Raftilose P95. Compared to standard and substituted bread, Jerusalem artichoke bread shows a high quality in organoleptic evaluation (grade I with 36.5 and 37.5 scores). In utilised Jerusalem artichoke powders (JAPs) the amount of fructan (inulin) hydrolysis to fructose during the baking process depends on its initial degree of polymerisation (dp). With JAP of autumn harvest (fructan: dpn = 9.9, dpw = 21.8) less fructose (24.6%) is formed than with those of spring harvest (fructan: dpn = 4.9, dpw = 7.1) (40.7%). Compared to this bread, substitution with commercial products Raftilin ST (inulin: dpn = 8.4, dpw = 17.4) and Raftilose P95 (fructo-oligosaccharides: dpn = 2.7, dpw = 3.0) yields 11.9% and 45.8% of fructose upon total hydrolysis, respectively. The loss of fructan content by the bakery process is 38% in bread with JAP of autumn and 43% in bread with JAP of spring harvest; Raftilin ST- and Raftilose P95-bread come up with loss of fructan content of 35% and 47%, respectively.

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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.

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