Microwave and hot-air drying of Thai red curry paste

Abstract

Thai red curry paste was dried with two different drying methods: microwave and hot-air drying. The microwave drying was carried out in a microwave oven with output power of 180, 360 and 540 W, while the hot-air drying was carried out at drying air temperatures of 60, 70 and 80 C. The drying time of microwave drying process to reduce the moisture content of red curry paste from 2.58 to 0.08 g water/g dry matter was much shorter than that of the hot-air drying process. An increase in the microwave power significantly decreased the drying time. In the hot-air drying, increasing the drying air temperature also significantly decreased the drying time. Microwave drying process of red curry paste consisted of three drying periods, i.e. heating up, constant rate and falling rate periods, while hot-air drying process consisted of two drying periods, i.e. heating up and falling rate periods. To describe the effect of microwave power and drying air temperature on drying kinetics of red curry paste, three different mathematical thin-layer equations, i.e. Lewis, Page and Henderson-Pabis models, were used to fit the drying data. The fitness by these models was evaluated using the coefficient of determination (R2), the reduced chi-square (2) and the root mean square error (RMSE). The Page model provided the best fit to both microwave and hot-air drying experimental data.

Keywords

• Thai red curry paste
• microwave drying
• hot-air drying