Impact of air-drying on polyphenol extractability from apple pomace

Little data are available on the impact of pomace pre-treatment, notably drying, on the nature and yield of polyphenols. Pomace from two apple varieties ('Avrolles' and 'Kermerrien'), pressed with and without oxidation, were air-dried to different degrees. Drying led to the loss of native molecules, notably 5-O-caffeoylquinic acid and flavan-3-ols. Total polyphenol yields, after sequential pressurized liquid extraction (water 10 MPa, 70 °C, then ethanol 48%, 10 MPa, 70 °C), varied between 5 and 15 g/kg dry weight but showed no marked trend with drying. Extracts from dried pomace contained few native polyphenols. Water extracts from 'Kermerrien' contained flavonols, flavanols and phloridzin and those from 'Avrolles' contained phloridzin. Water:ethanol extracts were rich in procyanidins, especially from 'Avrolles', where they represented >80% of analysable polyphenols. Presence of polyphenol molecules with modified structures in the extracts of dried pomaces might lead to different biological properties than those with native molecules.