Surveillance of the quality of turmeric powders from city markets of India on the basis of curcumin content and the presence of extraneous colours

Curcumin, the principal curcuminoid of turmeric, is responsible for its yellow colour and serves as a measure of turmeric quality. The Prevention of Food Adulteration (PFA) Act of India allows only Curcuma longa L. for the production of turmeric powder and prohibits addition of any foreign matter/artificial colour, but it does not specify a minimum curcumin content. The present surveillance was undertaken to study the quality of loose versus branded turmeric powders vis-a-vis curcumin content and the presence of unwarranted extraneous colours from city markets in India using a newly developed two-dimensional high-performance thin-layer chromatography (2D-HPTLC) method. The results show that curcumin content in branded samples ranged from 2.2% to 3.7%, while non-branded samples had from 0.3% to 2.6%. Though none of the branded turmeric powders contained artificial colours, 17% of loose powders showed the presence of extraneous colour metanil yellow, in the range 1.0-8.5 mg g-1, which may pose health threats. Low curcumin content in the analysed samples may be due to mixing of other curcuma species or their curcumin-depleted matrices and foreign starches as cheaper alternatives. This is supported by the fact that major Indian turmeric trade types are known to possess curcumin contents ranging from 2.1% to 8.6%, with an average of 4.8%. There is thus an urgent need to prescribe realistic curcumin limits for turmeric powder, otherwise there is no obligation on the part of traders to stick to any minimum levels and consumers will keep on getting this nutrient-depleted household spice.