Effects of ultrasound treatment and concentration of ethanol on selectivity of phenolic extraction from apple pomace

Summary The extraction of polyphenols from apple pomace was studied using ultrasound, ethanol/water mixtures and moderate temperatures, 20–37 °C. The extraction kinetics and extraction yields of catechin and total phenolic content ( TPC ) were evaluated at different times of ultrasound treatment ( t u ) and concentrations of ethanol ( C e ). The highest extraction efficiency of TPC was observed at t u  = 30 min, C e  = 50% and total extraction time of t e  = 60 min. The high selectivity of catechin extraction was demonstrated by analysing the relative content of catechin ( R   =  C c / TPC ) in dependence of applied extraction protocol. The initial portions of extracts at small levels of TPC (≤50 mg per 100 DM ) were richer in catechin content ( R  ≈   15%–31%), whereas the last portions of extracts with high level of TPS were more exhausted in catechin ( R  ≈   2%).