title: Ultrasound-assisted extraction of phenolic compounds from Cratoxylum formosum ssp. formosum leaves using central composite design and evaluation of its protective ability against H2O2-induced cell death.
abstract: OBJECTIVE
  To optimize the processing parameters for phenolic compounds extracted from Cratoxylum formosum ssp. formosum leaves using an ultrasound-assisted extraction and to evaluate its protective ability against H2O2-induced cell death.
  
  
  METHODS
  The influence of three independent variables including ethanol concentration (%), extraction temperature (°C) and extraction time (min) on the extraction yield of phenolic compounds were optimized using a central composite design-based response surface methodology. The obtained extract was assessed for its antioxidant activity by DPPH(•) and ABTS(•)(+) methods. Cellular protective ability against H2O2-induced cell death was evaluated on HEK293 cells using the MTT assay.
  
  
  RESULTS
  The optimal conditions to achieve maximal yields of phenolic compounds were ethanol concentration of 50.33% (v/v), temperature of 65 °C, and extractiontion time of 15 min. The yield of phenolic compounds was (40.00±1.00) mg gallic acid equivalent/g dry powder which matched well with the values predicted from the proposed model. These conditions resulted in a higher efficiency concerning the extraction of phenolics compared to a conventional heat reflux extraction by providing shorter extraction time and reduced energy consumption. 5-O-caffeoylquinic acid identified by high performance liquid chromatography-diode array detector-electron spin ionization-mass spectrometry was the major compound in the obtained extract [(41.66±0.07) mg/g plant extract]. The obtained extract showed a strong ability to scavenge both DPPH(•) and ABTS(•)(+) free radicals and exhibited additionally good ability to protect HEK293 cells death against oxidative stress.
  
  
  CONCLUSIONS
  These results indicate the suitability of ultrasound-assisted extraction for the extraction of phenolic compounds from Cratoxylum formosum ssp. formosum leaves. This phenolic-enriched extract can be used as valuable antioxidant source for health benefits.
authors.affiliation: Institute of Pharmaceutical Sciences, Department of Pharmacognosy, University of Graz, Universitaetsplatz 4/1, A-8010 Graz, Austria; Faculty of Pharmaceutical Sciences, Department of Pharmaceutical Chemistry and Technology, Ubon Ratchathani University, Ubon Ratchathani 34190, Thailand.
authors.forename: Bancha
authors.initials: B
authors.lastname: Yingngam
authors.affiliation: Institute of Pharmaceutical Sciences, Department of Pharmacognosy, University of Graz, Universitaetsplatz 4/1, A-8010 Graz, Austria.
authors.forename: Marlene
authors.initials: M
authors.lastname: Monschein
authors.affiliation: Institute of Pharmaceutical Sciences, Department of Pharmacognosy, University of Graz, Universitaetsplatz 4/1, A-8010 Graz, Austria. Electronic address: adelheid.brantner@uni-graz.at.
authors.forename: Adelheid
authors.initials: A
authors.lastname: Brantner
keywords: Antioxidants; Cratoxylum formosum ssp. formosum; Optimization; Oxidative stress; Phenolics; Response surface methodology; Ultrasound-assisted extraction