Convection combined microwave drying affect quality of volatile oil compositions and quantity of curcuminoids of turmeric raw material

ABSTRACT

Abstract The aim of the work was to estimate the quality of some compositions in turmeric volatile oil and quantity of individual and total curcuminoids in turmeric powder dried under different conditions. Effect of convection time (0-30 min) and microwave time (20-60 min) on quality of volatile oil compositions and quantity of curcuminoids were investigated using computer software. Quality of volatile oil obtained from the hydrodistillation of dried turmeric was analyzed by gas chromatography-mass spectrometry. The quantity of individual curcuminoids (bisdemethoxycurcumin, demethoxycurcumin, and curcumin) and total curcuminoids were analyzed by high performance liquid chromatography. Ten volatile compounds in turmeric volatile oil were used to estimate the variation of their quality. Results showed that ar-turmerone, turmerone, and curlone were the three major compounds found in turmeric volatile oil. The quality of the ten volatile compounds varied depending on convection time and microwave time. The three principal curcuminoids were found in turmeric dried at long convection time and medium microwave time. However, curcumin was also found in high amount in turmeric dried at short convection time and long microwave time. Total curcuminoids in dried turmeric were equal to or greater than 5% (w/w) as stated in the Thai Herbal Pharmacopoeia. It was found that almost all of the drying procedure achieved the standard of the Thai Herbal Pharmacopoeia except at short convection time and short microwave time. In summary, convection combined with microwave drying affected the quality of volatile oil compositions and quantity of curcuminoids of turmeric raw material.