Studies of degradation of pectin derived compounds from onion skins in subcritical water

Abstract

The degradation kinetics of Galacturonic Acid (GalA) in subcritical water (SubW) was studied in a batch reactor. GalA degradation was faster than other monosaccharides and could be described by the first order kinetic model. The initial concentration of GalA did not affect the degradation kinetics, but the heating rate and the reaction temperature played an important role in the degradation of GalA. The energy of activation was calculated according to the Arrhenius equation and resulted to be 97 ± 3 kJ/mol. Degradation products formation, mainly formic acid and furfural, was faster with temperature until a maximum concentration was reached (0.2 g C in formic acid/g C in initial GalA at 155°C and 45 min, severity factor 3.2), followed by a fast degradation whereas a plateau concentration was reached in the case of furfural (around 0.16 g C /g C in initial GalA at 185 °C after 45 min).