Sesquiterpene lactones and inulin from chicory roots : extraction, identification, enzymatic release and sensory analysis

Chicory ( Cichorium intybus L.) is one of the many species of the family Compositae. Chicory has been cultivated for the production of leaves or chicons, which have been used as a vegetable since approximately 300 BC, and for its roots, which can be used as a coffee substitute after roasting.Chicory leaves are appreciated for their slightly bitter taste. Two bitter compounds were known at the start of this project: lactucin (Lc) and lactucopicrin (Lp), both sesquiterpene lactones with a guaiane skeleton. These compounds are also present in the roots, which remain as a waste product after harvesting of the chicons. Chicory roots contain besides bitter substances also inulin, a linear β-(2-1) linked fructose polymer terminated by a sucrose unit residue and the main carbohydrate of the chicory plant.In Chapter 2 all known constituents of chicory roots are discussed as well as the effect of roasting on these compounds. A survey is given of work carried out on the isolation and identification of bitter principles in Compositae, especially chicory. The aim of this project was to isolate the bitter constitutents and inulin in one step from waste chicory roots. A one step process is only possible when enzymatic liquefaction is applied. Both bitter compounds and inulin will then pass into the liquid phase. The obtained bitter, sweet liquid can be used as a raw material for soft drinks. Quinine eventually could be replaced by the bitter principles from chicory roots.An isocratic HPLC method was developed for the analysis of the sesquiterpene lactones. Three components were identified in the chicory root extract: Lc, Lp and 8-deoxylactucin (8dLc). Various extraction solvents were tried for the isolation of the sesquiterpene lactones from chicory roots. Polar solvents gave many unknown polar compounds, which eluted at the beginning of the HPLC chromatogram. More apolar solvents gave the sesquiterpene lactones and hardly any of the polar components.Storage of the roots and further processing, such as drying and milling, affects the amount of sesquiterpene lactones in the roots and thus the composition of the chicory extract (Chapter 4).The release of bitter compounds and inulin has been studied during enzymatic liquefaction of chicory roots with commercial pectinases and cellulases (Chapter 5 and 7). An increase was seen in the amount of Lc and 8dLc found in the liquid phase during enzymatic liquefaction. After improvement of the HPLC method (gradient elution instead of isocratic method) it was found that the increase of Lc and 8dLc was due to the increase of their dihydro derivatives, which eluted at the same place as Lc respectively 8dLc with the isocratic method.Endogenous chicory root enzymes have also been studied in this context, because they have proven to be capable to release bitter components as well (Chapter 6). However, the optimum pH and temperature for the performance of endogenous chicory root enzymes are different from those of the commercial enzyme preparations tested, and may therefore not play a role in the release of sesquiterpene lactones during enzymatic liquefaction.Cichorioside B (glycoside of ll(S),13-dihydro-lactucin), crepidiaside B (glycoside of ll(S),13-dihydro-8-deoxylactucin), cichorioside C (glycoside of a germacranolide), and ll(S),13-dihydrolactucopicrin were identified in chicory roots. Compound N could not be identified, but there are indications that this compound is a diglycoside of dHLc. The presence of the glycoside of Lc is plausible, but to date this compound was not extracted from the chicory roots.The threshold value of six pure sesquiterpene lactones (Lc, Lp, 8dLc, dHLc, dHLp, dH8dLc) was determined (Chapter 8) and related to the theories on bitterness as discussed in Chapter 3.The effect of processing and storage on the bitter taste of bitter orange lemonade was investigated. A comparison was made between quinine as bitter substance and chicory root extract as the bitter ingredient.The storage in daylight of the bitter orange containing quinine caused a tremendous decrease of the bitterness of the beverage. No decrease in bitterness was seen in the beverage with chicory root extract. Pasteurization did not affect the bitter taste of bitter orange with chicory root extract.The bitterness of the various chicory root extracts made for sensory analysis differed in bitter intensity in spite of standardisation of the Lc content.Bitter intensities of chicory root extract before and after incubation with pectolytic and cellulolytic enzymes were determined. Thus the bitterness of the precursors was compared with that of the aglycons. However, no judgement could be given on whether the enzyme treatment of the chicory root extractcould be given on whether the enzyme treatment of the chicory root extract gave rise to a more bitter taste. About half of the panellists judged the extract with the glycosides more bitter than the extract with the aglycons, the other half could not taste any difference between these samples.