Effects of far-infrared and hot air drying methods on physical, chemical and antioxidant properties of turmeric (Curcuma longa L.)

Abstract

Turmeric (Curcuma longa L.) is one of the most extensively used spices and coloring agents in Asian cuisine. Rhizome of turmeric is rich in curcumin which is also an important natural pigment and has important biological activity. The aim of this study was to investigate the effect of infrared and hot air drying at 60, 70 and 80^oC on color changes, chemical and antioxidant properties of turmeric. For evaluating of heat sources of drying, the results showed that infrared drying rate is higher than drying with hot air at the same temperature. The infrared and hot air drying significantly affected the color of turmeric in L*, a*, b* and ∆E values (p<0.05). The total color was difference increase with decrease of drying temperature. The highest retention of color in the turmeric treated by infrared (80^oC) may be attributed to the uniform and quick heating of the sample compared to the hot air drying. The infrared and hot air   drying methods resulted in a decrease in curcumin, total phenolic and antioxidant activity was statistically significant (p<0.05). Highlights of this research tumuric was dried by infrared at 80^oC has the highest of curcumin, total phenolic and antioxidant activity.