Analysis of curcumin in Curcuma longa, C. wenyujin, C. kwangsiensis by HPLC Standardization and digitization of fingerprint gas chromatograms of essential oil of Curcuma longa Chemical constituents from rhizomes of Curcuma longa Comparison of curcumol contents in essential oil from four species of rhizoma Curcumae L. Cloning and sequence analysis of phenylalanine ammonia-lyase gene from Curcuma longa