KINETICS OF NONENZYMATIC BROWNING IN ONION SLICES DURING ISOTHERMAL HEATING

A static method involving the exposure of onion (Allium cepa L., cv. Southport White Globe) slices at different moisture contents to atmospheres of constant temperature (40-80-degrees-C) and water activity (0.26-0.96) was employed to obtain kinetic data on non-enzymatic browning. The results showed that browning in onion slices could be modelled as a zero-order reaction. The reaction was temperature dependent, following the Arrhenius relation, and the reaction rate varied as a quadratic of water activity. The maximum browning rate occurred in the 0.60-0.70 range of water activity. Activation energy and Q10 values for browning in onion slices ranged over 121-139 kJ/mole and 4-5, respectively. A generalised kinetic model of onion browning as a function of time, water activity and temperature of the product was established.