Influence of harvest time and storage temperature on characteristics of inulin from Jerusalem artichoke (Helianthus tuberosus L.) tubers

Jerusalem artichoke (Helianthus tuberosus L.) tubers were harvested 16, 18 and 20 weeks after planting at Kanchanaburi Research Station, Kasetsart University, Thailand. Tuber maturity contributed to changes in inulin characteristics. A decrease in the more polymerised fractions (degree of polymerisation, DP > 10) with an increase in fructose and sucrose composition was observed for late-harvested (20 weeks) tubers. The inulin DP distribution profile from tubers, stored at 2 and 5 °C, significantly changed with increased storage time and temperature. Sucrose and DP 3-10 fractions increased while DP > 10 decreased, particularly after 4-6 weeks of storage. Changes in inulin composition were reflected by formation of a second fructan series, as revealed by HPAEC-PAD chromatograms. These peaks corresponded to inulo-n-ose fructan where inulo-tri-ose (3′) and inulo-tetra-ose (4′) were predominantly found after 2 weeks of tuber storage at 2 and 5 °C. Inulo-n-ose (5′) up to DP 17′ increased as a percentage with longer storage time. Tubers in frozen storage of tubers at −18 °C maintained their DP distribution profiles.