Black Turmeric (Curcuma caesia Roxb.): A Review of its Ethnomedicinal Standing, Phytochemistry , Pharmacology & its Therapeutic Uses

Abstract

Curcuma caesia Roxb. (Zingiberaceae), known throughout the Indian subcontinent as black turmeric or kali haldi, is a perennial rhizomatous herb separated from every other commonly encountered member of its genus by the deep bluish-black interior of its rhizome, a colouration now attributed to an anthocyanin content of roughly 1.3 to 7.1 per cent. The species is a mainstay of tribal and folk medicine across north-eastern and central India, where the rhizome is applied to leucoderma, leprosy, rheumatic complaints, bronchial disorders, gastrointestinal and menstrual problems, neurological conditions, cancer and diabetes. This review consolidates the published botanical, phytochemical and pharmacological literature on the species, with particular attention to its antifungal and antioxidant properties. Analyses of the volatile fraction across geographical accessions have identified camphor, 1,8-cineole, ar-turmerone, ar-curcumene, curzerenone, ocimene, linalool, zingiberol and tropolone as principal constituents, with furanodienone and curzerenone proposed as quality markers for the rhizome. Bioassay-guided fractionation has yielded eighteen secondary metabolites, predominantly germacrane, guaiane and elemane sesquiterpenoids, several of which were first reported from this species. Antifungal activity has been demonstrated against Candida albicans, C. glabrata, Aspergillus fumigatus, A. niger, Saccharomyces cerevisiae and a range of phytopathogenic fungi, while antioxidant capacity has been established across DPPH, ABTS, FRAP, nitric oxide, hydroxyl and superoxide radical systems and correlates with total phenolic and flavonoid content. Further reported activities include anticancer, anti-inflammatory, antidiabetic, anti-ulcer, neuropharmacological, thrombolytic, antimutagenic and anthelmintic effects. Notwithstanding this breadth of evidence, the species remains under-studied relative to Curcuma longa, and its endangered status in several Indian states lends urgency to both conservation and continued pharmacological investigation.