Abstract
Large-scale inulin production from chicory roots (Cichorium intybus L.) is hampered by the induction of 1-FEH activity (fructan 1-exohydrolase) and concomitant fructose production in autumn, coincident with a period with low night temperatures that cause leaf damage. To understand whether leaf damage per se is sufficient for 1-FEH induction and fructan breakdown, we defoliated mature chicory plants at a preharvest stage (September 10) and investigated the changes in carbohydrate levels and 1-FEH activities. Also, the activities of 1-SST (sucrose:sucrose 1-fructosyl transferase, EC 2.4.1.99), 1-FFT (fructan:fructan 1-fructosyl transferase, EC 2.4.1.100), and acid invertase (EC 3.2.1.26) were determined. Defoliation did not result in a prompt fructan breakdown and increase in 1-FEH activity, but after 10 days fructan breakdown and 1-FEH activities became higher in the defoliated plants. Defoliation resulted in a sharp decrease in 1-SST activity over the first 24 h. Afterwards, root 1-SST activities of defoliated plants remained at a lower level than in control plants. 1-FFT and invertase activities were not affected by defoliation. It can be concluded that defoliation of plants at the preharvest stage by itself did not induce the same rapid changes as observed in naturally induced October roots by low temperature (harvest stage). Taken together with our finding that 1-FEH is not induced in chicory roots when plants are transferred to the greenhouse early autumn (minimal temperature 14°C), we conclude that low temperatures might be essential for 1-FEH induction.
Highlights
Fructans are the main reserve carbohydrate in the highly evolved and economically important plant families Poaceae, Liliaceae, and Asteraceae[1]
We demonstrated that defoliation of chicory seedlings resulted in fructan breakdown by the induction of a specific 1-FEH (1-FEH II) in the roots[20]
Fructan depolymerisation by induction of 1-FEH activity at the preharvest stage is a major problem for carbohydrate industries dealing with inulin extraction from chicory roots
Summary
Fructans are the main reserve carbohydrate in the highly evolved and economically important plant families Poaceae, Liliaceae, and Asteraceae[1]. Their specific role remains obscure, but evolutionary and other data suggest a correlation with drought resistance or frost tolerance[2,3,4]. Large-scale inulin production from chicory is hampered by the induction of 1FEH activity and concomitant Fru production in autumn[11,16], necessitating an early harvest and quick processing. The resulting high fructose concentrations together with high 1FFT activity invariably lead to the production of reducing low DP fructans which lack a terminal glucose (Fn series)[17] and participate in the Maillard reaction with amino acids during processing
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