Kinetic behaviour of ascorbic acid - fructose browning reaction in alkaline medium

Ascorbic acid and fructose react in an aqueous alkaline solution at temperature below 50°C in a Maillard-type reaction to from brown coloured end products. The kinetics of browning of alkaline solution of fructose in presence of ascorbic acid has been studied by measuring the absorbance of browning development in the reaction. The development of brown colour due to heating of either reducing sugar alone or ascorbic acid alone in the presence of alkali is found to be very slow even at high temperature (~70°C). However, in the presence of ascorbic acid the development of brown colour due to heating of alkaline fructose is sufficiently fast even at low temperature ~50°C. The rate of development of colour (browning reaction) has been found to be first order dependence with respect to [alkali] and [fructose] and fractional order dependence with respect to [ascorbic acid] at low concentrations of ascorbic acid. A mechanism consistent with the observed kinetic data has also been proposed.