Effect of sequential treatments of fermentation and ultrasonication followed by extrusion on bioactive content of apple pomace and textural, functional properties of its extrudates

Apple pomace (AP) is a potential source of phenolic compounds, and most of the phenolics are presented in the bound form. Liberation of these bound phenolics is required to improve their health functionality. In this context, AP was naturally fermented followed by the ultrasonication and microwave drying. Fermentation time (FT), pomace to water ratio (PWR), ultrasonication intensity (UI) and microwave power (MWP) had significant (P<0.05) effect on total phenolic content (TPC) and antioxidant activity (AA) of AP. At the optimum pretreatment conditions of 24h FT, 5% (w/v) PWR, 37Wcm(-2) UI and 90W MWP, TPC and AA of AP were 40.3% and 92.9%, respectively, higher than that of the control AP. Extrudates from pretreated AP also had improved textural (hardness, brittleness, crispness) and functional (water absorption index, water solubility index) properties. Pretreatment reduced crystalline fraction amount and enhanced solubility of AP.