We screened for microorganisms able to use flavonoids as a carbon source; and one isolate, nominated Stilbella fimetaria SES201, was found to possess a disaccharide-specific hydrolase. It was a cell-bound ectoenzyme that was released to the medium during conidiogenesis. The enzyme was shown to cleave the flavonoid hesperidin (hesperetin 7-O-alpha-rhamnopyranosyl-beta-glucopyranoside) into rutinose (alpha-rhamnopyranosyl-beta-glucopyranose) and hesperetin. Since only intracellular traces of monoglycosidase activities (beta-glucosidase, alpha-rhamnosidase) were produced, the disaccharidase alpha-rhamnosyl-beta-glucosidase was the main system utilized by the microorganism for hesperidin hydrolysis. The enzyme was a glycoprotein with a molecular weight of 42224 Da and isoelectric point of 5.7. Even when maximum activity was found at 70 degrees C, it was active at temperatures as low as 5 degrees C, consistent with the psychrotolerant character of S. fimetaria. Substrate preference studies indicated that the enzyme exhibits high specificity toward 7-O-linked flavonoid beta-rutinosides. It did not act on flavonoid 3-O-beta-rutinoside and 7-O-beta-neohesperidosides, neither monoglycosylated substrates. In an aqueous medium, the alpha-rhamnosyl-beta-glucosidase was also able to transfer rutinose to other acceptors besides water, indicating its potential as biocatalyst for organic synthesis. The monoenzyme strategy of Acremonium sp. SES201 = DSM 24697, [corrected] as well as the enzyme substrate preference for 7-O-beta-flavonoid rutinosides, is unique characteristics among the microbial flavonoid deglycosylation systems reported.

Most aroma compounds exist in vegetal tissues as disaccharide conjugates, rutinose being an abundant sugar moiety in grapes. The availability of aroma precursors would facilitate analytical analysis of plant-based foods. The diglycosidase α-rhamnosyl-β-glucosidase from Acremonium sp. DSM 24697 efficiently transglycosylated the rutinose moiety from hesperidin to 2-phenylethanol, geraniol, and nerol in an aqueousÀorganic biphasic system. 2-Phenethyl rutinoside was synthesized up to millimolar level with an 80% conversion regarding the donor hesperidin. The hydrolysis of the synthesized aroma precursors was not detected in an aqueous medium. However, in the presence of ethanol as a sugar acceptor, the enzyme was able to transfer the disaccharide residue forming the alkyl-rutinoside. The aroma precursors were significantly hydrolyzed (up to 3À4% in 2 h at 30 °C), which indicated the potential use of the enzyme for biotechnological applications, for example, in aroma modulation of fermented foods.

Throughout the article, the fungus which was mentioned Stilbella fimetaria SES201 was re-identified as Acremonium sp. SES201.Although the molecular analysis based on BLAST of the internal transcript spacer region (ITS) and of 5.8, 18 and 28S rDNA gave 99% match with Stilbella fimetaria, the morphological analysis showed conidiophores that belong to Acremonium genus but not synnematous structures typical of Stilbella. The genera Acremonium and morphologically similar Stilbella have not yet been fully studied on a molecular basis. Under the morphological basis, the fungus was reidentified as Acremonium sp. SES201 = DSM 24697.The online version of the original article can be found under