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Experiments were conducted to study the color change kinetics of green bell pepper during vacuum-assisted microwave (VAM) drying at three levels of microwave power (100, 200, and 300 W) and vacuum (200, 400, and 600 mmHg). The color change, measured by a tristimulus colorimeter, in VAM dried sample was found better with least browning at lower microwave power and higher vacuum level combinations. L^*, ΔE^* and H^* were fitted well to zero-order kinetic model, while a^*, b^*, C^* and BI^* followed a first-order kinetic model. All these color parameters were fitted to a quadratic equation as a function of microwave and vacuum level ratio. Both ΔE^* and BI^* increased with the increase in microwave power and decrease in vacuum level, whereas other color parameters decreased under the same condition of the process variables. The rate constant was assumed to have Arrhenius-type dependence on power density. The activation energy was calculated for color change kinetic parameters by using an exponential expression based on Arrhenius equation. The activation energy values were calculated and found within the range of 3.20-13.58 Wg^‒1, except for b^* (E_a = 26.708 Wg^‒1) and C^* value (E_a = 20.4105 Wg^‒1). The b^* and C^* values obtained were relatively higher and thus were more sensitive measures of color change, which must be taken care of during postharvest drying of green bell pepper for getting a quality product.
 

Keywords: Activation energy, Arrhenius equation, Color parameters, Zero-order kinetic model.

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