Benjamin Averill and Shelly J. Schmidt

Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign

While sucrose is traditionally thought to thermodynamically melt then undergo caramelization, recent research demonstrated that caramelization, a kinetic process dependent on time and temperature, can occur well below sucrose’s literature reported melting temperature, albeit over longer times. Additionally, a distinct difference between the DSC thermal profiles of white refined beet and cane sucrose sources has been reported. Beet sucrose exhibits one large endothermic peak, while cane sucrose exhibits two endothermic peaks, with one small peak preceding one large peak. Also, the melting onset temperature is substantial lower for cane compared to beet sucrose. Based on these findings, the objective of this study is to examine the kinetics of caramelization for crystalline beet and cane sucrose using Ozawa’s method. This differs from previous kinetic studies of sucrose caramelization, which examined caramelization of sucrose solutions or of crystalline sucrose at higher temperatures. Additionally, earlier studies only examined cane sucrose caramelization kinetics, not beet. Ozawa’s method is a non-isothermal kinetic model that uses heating rate and onset temperature, measured using DSC, to determine the activation energy (E_a) and pre-exponential factor (A) of the Arrhenius equation for the reaction. To measure the kinetic constants beet and cane sucrose were heated between 0.1 and 10°C/min from 25°C to the temperature at which complete loss of crystalline structure was achieved. The average E_a for cane sucrose was 180.3±10.9 kJ/mol with an average A of 2.88E23 min^-1. For beet sucrose the E_a was 781.9±54.2 kJ/mol and A was 3.2E99 min^-1. These values indicate that cane sucrose requires less energy to initiate caramelization (lower E_a) and that molecules involved in the reaction collide less often (lower A) than in the case of beet. The difference in activation energies for the caramelization reaction between beet and cane sucrose sources suggests that the reaction is inhibited in beet sucrose, otherwise the kinetic constants would be identical. Chemical differences likely cause this discrepancy between beet and cane sucrose. This kinetic information is useful for developing alternative processing conditions using lower temperatures and longer times for caramel flavor and color production, rather than the traditional high temperature short time process.