title: Multi-response optimisation of ultrasound-assisted extraction for recovery of flavonoids from red grape skins using response surface methodology.
abstract: BACKGROUND
  For the characterisation of grape cultivars, the profile and content of flavonoids are important because these compounds impact grape and wine quality. To determine the correct profile and content of flavonoids, the use of robust, sensitive and reliable methods is necessary.
  
  
  OBJECTIVE
  The object of this research is to develop a new ultrasound-assisted extraction (UAE) method for the recovery of flavonoids from grape skins using response surface methodology.
  
  
  METHODS
  Optimisation of UAE was performed using a complementary study combining a Box-Behnken experimental design with qualitative analysis by high-performance liquid chromatography.
  
  
  RESULTS
  Optimal extraction conditions were obtained using the extraction solvent composed of acetonitrile:water:formic acid (26:73:1, v/v/v) at an extraction temperature of 50 °C, an extraction time of 15 min in a single-extraction step and with a solid-to-solvent ratio of 1:80 g/mL. The calculated relative standard deviations for the optimal extraction method were very low, measuring less than 5%.
  
  
  CONCLUSIONS
  This study demonstrates that numerous factors have strong effects on the extraction efficiency, including the type of organic modifier and its percentage in the extraction solvent, the number of extraction steps, the solid-to-solvent ratio, the extraction time and temperature and, finally, the particular nature of analyte and their position within the grape skin cell.
authors.affiliation: Department of Viticulture and Enology, Faculty of Agriculture, University of Zagreb, Zagreb, Croatia.
authors.forename: Ivana
authors.initials: I
authors.lastname: Tomaz
authors.affiliation: Department of Viticulture and Enology, Faculty of Agriculture, University of Zagreb, Zagreb, Croatia.
authors.forename: Luna
authors.initials: L
authors.lastname: Maslov
authors.affiliation: Department of Viticulture and Enology, Faculty of Agriculture, University of Zagreb, Zagreb, Croatia.
authors.forename: Domagoj
authors.initials: D
authors.lastname: Stupić
authors.affiliation: Department of Viticulture and Enology, Faculty of Agriculture, University of Zagreb, Zagreb, Croatia.
authors.forename: Darko
authors.initials: D
authors.lastname: Preiner
authors.affiliation: Department of Analytical Chemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Zagreb, Croatia.
authors.forename: Danijela
authors.initials: D
authors.lastname: Ašperger
authors.affiliation: Department of Viticulture and Enology, Faculty of Agriculture, University of Zagreb, Zagreb, Croatia.
authors.forename: Jasminka
authors.initials: J
authors.lastname: Karoglan Kontić
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D005591:Chemical Fractionation / Q000379:methods*; D002851:Chromatography, High Pressure Liquid; D005419:Flavonoids / Q000032:analysis / Q000737:chemistry / Q000302:isolation & purification*; D005638:Fruit / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013696:Temperature; D014465:Ultrasonics / Q000379:methods; D027843:Vitis / Q000737:chemistry*
chemical_list: D000097:Acetonitriles; D005419:Flavonoids; D012997:Solvents; C032159:acetonitrile
keywords: Grape skins; flavonoids; multi-response optimisation; ultrasound-assisted extraction