Analytical strategies to determine the labelling accuracy and economically-motivated adulteration of “natural” dietary supplements in the marketplace: Turmeric case study

[Display omitted] •A case study was performed to test turmeric dietary supplements’ “natural claim”.•Synthetic curcumin was attributed to synthetic ingredients found in samples.•Cheaper turmeric products are more likely to contain less curcuminoids.•Orthogonal turmeric quality control approach is preferred by using Carbon-14 and HPLC. Turmeric has faced authenticity issues as instances of economic-adulterations to reduce the cost. We used carbon-14 and HPLC analyses as complementary methods to verify “all-natural” label claims of commercial dietary supplements containing turmeric ingredients. A high percentage of curcumin-to-curcuminoids value was used as an indicator to imply the presence of synthetic curcumin. However, using the HPLC method alone did not provide direct evidence of curcuminoids’ natural origin, whereas using only the carbon-14 method cannot test for potency label claims and determine which constituent(s) contain 14C radiocarbon. By analyzing results from both methods, a significant correlation between the percentage of curcumin-to-curcuminoids and % biobased carbon (Pearson’s r = −0.875, p