TEMPERATURE DEPENDENCY OF QUALITY CHANGE DURING FAR-INFRARED DRYING OF KOMATSUNA LEAVES

In this study, we determined changes in energy consumption and quality parameters including surface color, L-ascorbic acid, β-carotene, lutein, and chlorophyll contents during far-infrared drying and hot air drying of komatsuna leaves. The temperature dependency of the drying rate and the quality changes observed when employing the two types of drying methods were also examined. In both methods, drying was carried out at three surface temperatures between 44.4 to 54.5°C. The changes in moisture content data for each drying method and set of conditions showed good agreement with the results calculated from an exponential model. An Arrhenius-type equation was used to fit the drying rate constant k to the surface temperature. It was found that the energy consumption for far-infrared drying was 17% lower than that for hot air drying. Moreover, the far-infrared drying did not negatively affect the surface color or the content of L-ascorbic acid, β-carotene and lutein. These results suggest that far-infrared drying was more suitable and effective for drying komatsuna leaves than hot air drying. Additionally, under ideal drying conditions of far-infrared application, the cumulative temperature of the sample surface served as a useful index of the decrease in L-ascorbic acid content. The surface color of the komatsuna leaves showed better retention of its original color with the decrease of cumulative temperature of the sample surface.