Gafner et al. 2026 — Scoping review of turmeric adulteration across six continents
This is the most comprehensive systematic assessment of turmeric adulteration in the published literature, synthesizing 48 publications representing 2,235 commercial turmeric samples from 22 countries across six continents. The PRISMA-ScR methodology, broad geographic coverage, and distinction between spice and supplement adulteration patterns make this the anchoring prevalence denominator for the wiki’s spice adulteration synthesis. The overall adulteration rate of 20.0% (448/2,235) establishes that turmeric adulteration is not a localized problem confined to South Asian supply chains; it is a global market-integrity failure documented on every inhabited continent with available data.
Key numbers
Total publications included: 48 (28 from database searches, 20 from citation searches and grey literature).
Total commercial turmeric samples: 2,235.
Overall adulteration rate: 20.0% (448/2,235).
Spice samples: 1,767 total, 361 adulterated (20.4%).
Dietary supplement and herbal medicine samples: 332 total, 73 adulterated (22.0%).
Unassigned samples: 136.
Regional adulteration rates (regions with >100 samples):
| Region | n | Adulterated | Rate |
|---|---|---|---|
| Asia | 1,478 | 328 | 22.2% |
| India alone | 1,002 | 165 | 16.5% |
| Europe | 462 | 67 | 14.5% |
| North America | 168 | 25 | 14.9% |
| South America | 39 | — | 35.9% |
| Africa | 15 | — | 20.0% |
| Oceania | 16 | 0 | 0% |
Countries documented: 22 (excluding EU JRC multi-country submission which did not report per-country results).
India is the single largest dataset (n=1,002, 14 publications). Of 947 Indian samples tested for metanil yellow, 150 (15.8%) were positive. Lead chromate adulteration is particularly frequent in Bihar, Assam, and neighboring states of Bangladesh, Pakistan, and Nepal.
Pakistan: 63/233 (27.0%) adulterated. Sri Lanka: 68/79 adulterated.
Bangladesh enforcement success: lead-contaminated turmeric samples dropped from 47% (2019) to 5% (beginning 2020) to 2.3% (fall 2020) to 0% (beginning 2021), following the Bangladesh Food Safety Authority’s implementation of educational measures, XRF testing, prosecutable-act declarations, and fines.
Adulteration restricted to papers using validated methods: 133/949 (14.0%) turmeric samples adulterated; spice rate drops to 9.7% (57/586) while supplement rate increases to 27.1% (62/229).
Adulteration typology
The review documents a critical distinction in adulteration mechanisms by market channel.
Spice adulteration: toxic colorants (lead chromate, metanil yellow, Sudan dyes, tartrazine), bulking agents (starches from cassava, barley, corn, oat, rice, rye, wheat; powdered fennel, cumin, paprika, chili), substitution with other Curcuma species (C. zedoaria, C. aromatica, C. phaeocaulis). Lead chromate is reported mainly from Southern Asia.
Dietary supplement adulteration: synthetic curcumin labeled as natural turmeric extract (the most common issue in Europe and North America, with 17 of 82 European/North American supplement samples containing synthetic curcumin), bulking agents (maltodextrin), and dilution with inert materials.
The geographic pattern of adulteration types is itself a finding: lead chromate contamination concentrates in South Asian spice supply chains (where it poses acute Pb toxicity risk), while synthetic curcumin concentrates in European and North American supplement supply chains (where the health risk is lower but the fraud is commercially significant).
Methods (brief)
PRISMA-ScR scoping review. Systematic searches of Google Scholar, PubMed, ScienceDirect, Scopus, and Web of Science (searched 2025-11-07) covering publications 2000-2025. Inclusion: studies evaluating authenticity of commercial turmeric products in any form (whole, powdered rhizomes, extracts, dietary supplements, herbal medicines). Exclusion: not related to turmeric adulteration (n=206), no commercial product analyzed (n=57), number of adulterated products not provided (n=8). Three researchers performed literature search; two researchers performed data extraction independently. 375 records identified, 76 duplicates removed, 299 screened, 28 included from databases plus 20 from other methods.
Analytical methods across the 48 publications: HPLC or UHPLC with UV/Vis or MS detection (41.6%), genetic methods (13.9%), LC-MS (13.9%), HPTLC (11.1%), UHPLC-UV/Vis (8.3%), NMR (6.9%), ICP-MS (4.2%), microscopy (4.2%), UV/Vis (4.2%), infrared (2.8%), GC-MS (2.8%), isotope MS (2.8%), wet chemistry (4.2%), AA spectroscopy (1.4%). A majority (68%) of HPLC/UHPLC methods used validated analytical methods; however, 19 of 48 publications did not use a validated method and in some cases method validation was unclear.
Extent of adulteration was determined based on assessment by the authors of the published papers and, in some cases, by the scoping review authors themselves. Synthetic curcumin was concluded when curcumin concentration exceeded 90% of total curcuminoids, based on the 85.4% biobased upper limit from You et al. 2022.
Implications
Certification: the 20.0% global adulteration rate is the strongest available denominator for the proposition that any food product containing turmeric carries adulteration risk requiring ingredient-level testing. The distinction between spice-channel adulteration (lead chromate, toxic dyes) and supplement-channel adulteration (synthetic curcumin, bulking agents) means that the testing protocol must differ by supply chain: ICP-MS or XRF for Pb/Cr in spice-channel turmeric, HPLC-UV/Vis or isotope ratio MS for synthetic curcumin in supplement-channel turmeric.
Courses: the Bangladesh enforcement success story (47% to 0% in two years) is the strongest documented case in the corpus of a regulatory intervention producing measurable contamination reduction in a spice supply chain. The mechanism (XRF field testing, prosecutable-act declaration, fines, education) is a concrete curriculum example for supply-chain intervention design.
Microbiome: not directly applicable.