Effects of Extraction Methods on Inulin, Fructooligosaccharides and Microbial Inulinase Production from Stevia rebaudiana

In this study, Stevia fractions (root, leaf, stem and their mixture) were used for inulin extraction using aqueous extraction, enzyme-assisted extraction and enzyme-assisted decanter extraction. The extracts were used as carbon sources in submerged (SmF) fermentation, whereas the remaining solid residues were used as substrates in solid-state (SSF) fermentation for inulinase and FOS production by Aspergillus niger. The highest inulin concentration was obtained from the root extract produced by aqueous extraction at a 1:5 (w/v) ratio (197.55 g/L). The highest fructooligosaccharides (FOS) concentration (12.64 g/L) was achieved by root enzyme-assisted extraction. In SmF, the highest total FOS concentration (13.99 g/L) was obtained from leaf enzyme-assisted extracts (LEE), whereas in SSF, the maximum total FOS concentration (20.80 g/L) was achieved using leaf enzyme-assisted decanter extracts. Inulinase from the aqueous root extracts was 609.72 U/mL during SmF and the leaf enzyme-assisted decanter extracts was 450.86 U/mL during SSF. Inulin extraction from fractions of Stevia, high inulinase production in Smf, and enhanced FOS production from residual biomass in SSF enable the generation of multiple value-added products and support circular economy and biorefinery principles.