title: Conversion of phenolic constituents in aqueous Hamamelis virginiana leaf extracts during fermentation.
abstract: BACKGROUND
  Hamamelis virginiana, known for its high level of tannins and other phenolics is widely used for treatment of dermatological disorders. Although reports on hydroalcoholic and aqueous extracts from Hamamelis leaf and bark exist, knowledge on fermented leaf preparations and the underlying conversion processes are still scant.
  
  
  OBJECTIVE
  Aqueous Hamamelis leaf extracts were monitored during fermentation and maturation in order to obtain an insight into the bioconversion of tannins and other phenolics.
  
  
  METHODS
  Aliquots taken during the production period were investigated by HPLC-DAD-MS/MS as well as GC-MS after derivatisation into the corresponding trimethylsilyl compounds.
  
  
  RESULTS
  In Hamamelis leaf extracts, the main constituents exhibited changes during the observational period of 6 months. By successive depside bond cleavage, the gallotannins were completely transformed into gallic acid after 1 month. Although not completely, kaempferol and quercetin glycosides were also converted during 6 months to yield their corresponding aglycones. Following C-ring fission, phloroglucinol was formed from the A-ring of both flavonols. The B-ring afforded 3-hydroxybenzoic acid from quercetin and 3,4-dihydroxybenzoic acid as well as 2-(4-hydroxyphenyl)-ethanol from kaempferol. Interestingly, hydroxycinnamic acids remained almost stable in the same time range.
  
  
  CONCLUSIONS
  The present study broadens the knowledge on conversion processes in aqueous fermented extracts containing tannins, flavonol glycosides and hydroxycinnamic acids. In particular, the analogy between the microbial metabolism of phenolics from fermented Hamamelis extracts, fermented sourdough by heterofermentative lactic acid bacteria or conversion of phenolics by the human microbial flora is indicated.
authors.affiliation: WALA Heilmittel GmbH, Department of Research and Development, Dorfstrasse 1, D-73087, Bad Boll/Eckwälden, Germany.
authors.forename: Sarina M
authors.initials: SM
authors.lastname: Duckstein
authors.forename: Peter
authors.initials: P
authors.lastname: Lorenz
authors.forename: Florian C
authors.initials: FC
authors.lastname: Stintzing
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003373:Coumaric Acids / Q000378:metabolism; D005285:Fermentation; D044948:Flavonols / Q000032:analysis / Q000378:metabolism*; D005707:Gallic Acid / Q000032:analysis / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry; D006027:Glycosides / Q000032:analysis / Q000378:metabolism; D029501:Hamamelis / Q000737:chemistry*; D047348:Hydrolyzable Tannins / Q000032:analysis / Q000378:metabolism*; D062385:Hydroxybenzoates / Q000378:metabolism; D044949:Kaempferols / Q000378:metabolism; D010636:Phenols / Q000378:metabolism*; D010936:Plant Extracts / Q000032:analysis / Q000737:chemistry*; D018515:Plant Leaves / Q000737:chemistry* / Q000378:metabolism; D010946:Plants, Medicinal / Q000737:chemistry; D011794:Quercetin / Q000032:analysis / Q000378:metabolism; D053719:Tandem Mass Spectrometry; D013634:Tannins / Q000378:metabolism; D013997:Time Factors
chemical_list: D003373:Coumaric Acids; D044948:Flavonols; D006027:Glycosides; D047348:Hydrolyzable Tannins; D062385:Hydroxybenzoates; D044949:Kaempferols; D010636:Phenols; D010936:Plant Extracts; D013634:Tannins; C032948:3-hydroxybenzoic acid; D005707:Gallic Acid; C006552:kaempferol; D011794:Quercetin