Drying methods affects physicochemical characteristics, essential oil yield and volatile composition of turmeric (Curcuma longa L.)

Abstract Turmeric is widely used in dietary supplements and functional foods owing to its high nutritive value with potential health benefits. The present study was carried out to study the effect of five different drying methods namely shade drying (SD), solar drying (SOD), hot air oven drying (HAD), microwave drying (MD), and freeze drying (FD) on the physicochemical properties, essential oil yield and volatile composition of turmeric. Results showed that while FD method led to the lowest moisture content (6.13%), MD method took the shortest drying time (0.5 h) and FD resulted in better color retention, lowest water activity and higher rehydration ratio as compared to other methods. FTIR analysis and glass transition temperature varied significantly with different drying methods. The maximum and minimum essential oil yield was obtained with FD (1.7% v/w) and HAD (0.35% v/w) methods, respectively. The major constituents were ar-turmerone (28.00-38.81%), α-turmerone (17.56-27.03%), β-turmerone (16.53-19.02%) and α-phellandrene (2.47–5.22%), respectively. Significant changes in the volatile constituents in the essential oil were found to be related to drying methods. The percentages of α-turmerone and β-turmerone in the oil significantly increased when the rhizomes were freeze dried. The results showed that freeze drying was the most effective drying method which retained the above mentioned characters as fresh turmeric and the present study will provide a theoretical basis for industrial processing of turmeric.