Effect of carbonation and ultrasonication assisted hybrid drying techniques on physical properties, sorption isotherms and glass transition temperature of banana ( Musa ) peel powder

Banana peels ( Cavendish and Nay poovan) in ripe and raw form were dried using tray drying (T), microwave (M), microwave-convection (MC) and freeze drying (F) with ultrasonication (U) and combined treatment of carbonation and ultrasonication (CU) as pretreatments. SEM analysis showed microscopic channels in samples after U treatment, which were more ravine after CU. Based on bulk density, tapped density, porosity, angle of repose, colour parameters, viscosity, CU + F was found best drying combination followed by CU + MC. For selected samples, relative water sorption changes induced by U and CU were positive as the sorption surface area increased after given pre-treatments. Peleg model fitted best to experimental data for sorption studies. The water plasticizing effect of U and CU treatments on glass transition temperature (Tg) was predicted using Gordon-Taylor model. State diagram predicted critical moisture content (X c ), 0.106 kg H 2 O/kg dry matter and critical water activity (a wc ), 0.525 at 16 °C.