Drying Behavior and Curcuminoids Changes in Turmeric Slices during Drying under Simulated Solar Radiation as Influenced by Different Transparent Cover Materials

Dried turmeric is used as a spice and traditional medicine. The common drying methods for turmeric (Curcuma longa L.) are sun drying and solar drying. In this study, turmeric slices with a thickness of 2 mm were dried at 40, 50, 60, and 70 degrees C in a laboratory hot-air dryer with a simulated solar radiation applied through transparent polycarbonate cover (UV impermeable) and PMMA cover (UV permeable). Air velocity and relative humidity of drying air were fixed at 1.0 M center dot s(-1) and 25 g H2O kg(-1) dry air, respectively. Light significantly increased the sample temperature under both covers. Page was the best model to predict the drying characteristics of turmeric slices. Drying rate correlated with the effective moisture diffusivity, which increased at higher temperature. The hue angle (h degrees) of turmeric was distinctly lower at 70 degrees C under both covers. The dried products were of intensive orange color. Curcumin, demethoxycurcumin, and total curcuminoids were affected by the cumulated thermal load (CTL). The lowest curcumin content was found at 40 degrees C under PMMA (highest CTL). The optimum drying condition was 70 degrees C under polycarbonate cover due to shorter drying time and better preservation of color and curcuminoids in the dried product.

Automated summary

This study examined the effects of different drying conditions on dried turmeric slices. The results showed that higher temperatures increased drying rate and improved color and curcuminoid preservation. 70 degrees C under polycarbonate cover was identified as the optimal drying condition.