Acid-assisted extraction and hydrolysis of inulin from chicory roots to obtain fructose-enriched extracts
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ORIGINAL ARTICLE
Acid-assisted extraction and hydrolysis of inulin from chicory roots to obtain fructose-enriched extracts Katrin Stökle 1
&
Dennis Jung 1 & Andrea Kruse 1
Received: 22 July 2020 / Revised: 19 October 2020 / Accepted: 22 October 2020 # The Author(s) 2020
Abstract Chicory (Cichorium intybus var. foliosum) roots are an agricultural residue and a low cost feedstock for the production of the platform chemical 5-Hxdroxymethylfurfural (HMF). In a first step, inulin and fructose have to be extracted from the roots. The resulting aqueous extract represents the starting material for the HMF production. In the reaction to HMF, inulin has to be hydrolyzed first to fructose. For this reason, two methods to increase the fructose content in these extracts before the reaction were investigated. This was conducted within the framework of integrating acid hydrolysis into a biorefinery process for HMF production. The first method (one-step process) was acid-assisted extraction to directly hydrolyze inulin in the course of the extraction process. Chicory roots were extracted at 60 and 80 °C at pH 2 and 4 using buffer solutions. The second approach (twostep process) was aqueous extraction at neutral pH followed by nitric acid hydrolysis of the extract at 60 and 80 °C under reduced pH. It was found that in the first approach, the pH of 2 led to a fivefold increase in the fructose content of the extract, resulting from inulin hydrolysis and corresponding to 56% of theoretical fructose yield. For the second approach, it was possible to achieve complete hydrolysis at pH below 2.5 and at 80 °C. Separating extraction and hydrolysis was found to be more suitable in terms of including this process step into a biorefinery concept for HMF production. It was possible to reduce the initial inulin content by 95%. Keywords Acid hydrolysis . Chicory . Extraction . Inulin . Biorefining . Fructose
1 Introduction The production of biobased materials from agricultural residues is an indispensable component of the transformation of a fossil-based to a biobased economy. Zero-waste approaches can lead to a reduction in worldwide CO2 emissions and material cycles can be closed. For this purpose, residual materials are processed in biorefineries, which are part of a wellfunctioning bioeconomy. Chicory roots (Cichorium intybus var. foliosum) are an agricultural residue. After field cultivation, these are harvested and then stored up to several months at low temperatures [1]. After storage, etiolated buds (chicons) are produced in dark
* Katrin Stökle [email protected] 1
Institute of Agricultural Engineering, Conversion Technologies of Biobased Resources, University of Hohenheim, Garbenstraße 9, 70599 Stuttgart, Germany
forcing chambers for 21 days at 15–20 °C [2]. The chicons are sold as salad; the roots are, from this point, an agricultural waste with only low-value application like biogas production. But also the unforced roots that represent the fraction of rejected roots after harvest, which do not match the standard
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