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Quality assessment of turmeric dietary supplements and food samples

Regulation of dietary supplements regarding their quality is still not well developed worldwide [1]. Many such products, mostly those available online, are not subjected to quality control and are either fraudulently underdosed, demonstrating no efficacy, or adulterated with synthetic active substances or alien herbal species, possibly leading to overdosage and toxicity. Furthermore, inadequate dissolution of active substances can lead to decreased bioavailability. The aims of this work were, therefore, to assess the content of curcuminoids and piperine, active substances of turmeric and black pepper (often used in conjunction with turmeric as piperine enhances the absorption of curcuminoids [2]), in widely used marketed turmeric dietary supplements and food samples, as well as to examine the dissolution of tableted and capsulated products according to the United States Pharmacopoeia (USP). A total of 20 dietary supplement and 13 food samples were investigated. High-performance liquid chromatography with spectrophotometric detection was the technique of choice. Firstly, optimization of extraction of active substances from a representative food sample (as the more complex sample type) was performed using Box Behnken response surface methodology. After model optimization, maximum yield for all substances was achieved using 76.9% (V/V) ethanol as extraction solvent, 75 °C as extraction temperature and 30 min as sonication time. Food samples contained 1.7 to 4.7% curcuminoids (of turmeric rhizome mass) save for two purchased online, which showed higher content (9.1 and 10.5%, possibly implying adulteration). The content of piperine ranged from 3.9 to 5.8% of black pepper fruit mass. Only 9 of 20 and 1 of 8 dietary supplement samples conformed to the USP regulations of 90 to 110% of declared curcuminoid and piperine content, respectively. Dissolution studies using USP Apparatus 2 revealed only 3 of 15 formulated products conformed to minimum of 75% active substance release, which could be due to lower expected curcuminoid amounts present in products on the American market. In conclusion, more than half of the investigated samples failed to conform to active substance content and/or dissolution criteria of revelant regulations, which points to an increased need of quality control of herbal preparations and dietary supplements.

turmeric ; quality control ; piperine ; dissolution

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