Fructan:fructan 1-fructosyltransferase and inulin hydrolase activities relating to inulin and soluble sugars in Jerusalem artichoke (Helianthus tuberosus Linn.) tubers during storage

Abstract

Influences of harvest time and storage conditions on activities of fructan:fructan1-fructosyltransferase (1-FFT) and inulin hydrolase (InH) in relation to inulin and soluble sugars of Jerusalem artichoke (Helianthus tuberosus L.) tubers were investigated. Maturity affected 1-FFT-activity, inulin contents, and inulin profiles of the tubers harvested between 30 and 70 days after flowering (DAF). Decreases in 1-FFT activity, high molecular weight inulin, and inulin content were observed in late-harvested tubers. The tubers harvested at 50 DAF had the highest inulin content (734.9 ± 20.5 g kg^-1 DW) with a high degree of polymerization (28% of DP >30). During storage of the tubers, increases in InH activity (reached its peak at 15 days of storage) and gradual decreases in 1-FFT activity took placed. These changes were associated with inulin depolymerization, causing decreases in inulin content and increases in soluble sugars. As well, decreasing storage temperatures would retain high inulin content and keep low soluble sugars; and freezing at -18 °C would best retard 1-FFT, InH, and inulin changes.

Keywords: 1-FFT activity; Fructan; InH activity; Inulin content; Soluble sugars.

Fig. 1

HPAEC-PAD chromatograms of inulin in Jerusalem artichoke tubers

Fig. 2

Inulin profile (a), glucose, fructose, and sucrose (b) in Jerusalem artichoke tubers at different harvest time

Fig. 3

Activities of 1-FFT (a) and InH (b) in Jerusalem artichoke tubers stored at different temperatures for 30 days

Fig. 4

Inulin content (a), glucose (b), and free fructose (c) in Jerusalem artichoke tubers harvested at 50 DAF and stored at different temperatures for 30 days

Fig. 5

Sucrose (a), kestose (b), and Nystose (c) in Jerusalem artichoke tubers stored at different temperatures for 30 days