Advances in adulteration and authenticity testing of turmeric (Curcuma longa L.)
Former Head, Division of Crop Improvement & Biotechnology,
ICAR-Indian Institute of Spices Research, Kozhikode-673 012, Kerala.
Received 04 November 2019; Revised 13 December 2019; Accepted 30 December 2019
Synthetic colorants such as metanil yellow, lead chromate, Acid orange 7, Sudan Red; rhizomes
of related Curcuma sp. besides spent turmeric, starch, chalk and yellow soapstone are the main
adulterants in traded turmeric while synthetic curcumin is an adulterant of natural curcumin. Both
branded products as well as the produce from the unorganized sector are found adulterated. The
adulterants, added either to increase the bulk, improve the colour and appearance or enhance the
prot margin, oen result in corroding the biological ecacy of the commodity and eroding the
public impression besides posing health risks to the consumers. Various physical, chemical and PCR
based methods are available to detect the adulterants in traded turmeric. While chemical methods
are suited to detect the synthetic adulterants and spent turmeric, DNA based methods are the best
options for detecting the biological adulterants (except spent turmeric) in the commodity. Along
with adopting a supply chain system and quality linked pricing in turmeric trade, commercial
adulteration diagnostic kits, if they can be developed and deployed, will be a very convenient way
to ensure the quality of the traded produce.
Keywords: adulterants, detection, food safety, methods, supply chain, turmeric
Spices are high value, export-oriented
commodities and are extensively used for
flavouring food and beverages as well as
in medicine, cosmetics and perfumery.
Traded forms of spices include dried or
fresh whole commodity, powdered forms,
pastes, dehydrated material, oils, oleoresin
and extractives. Good quality spices are very
relevant for the perceived biological eciency
of these commodities, their avour or aroma.
The health-conscious public all over the world
is increasingly looking for quality spices, be it
for health, culinary or cosmetic uses. However,
spices are often adulterated with inferior,
similar-looking entities leading to erosion of
the perceived biological value and public faith
in these products.
Turmeric [Curcuma longa L. (Zingiberaceae)],
already well known as a spice, a colouring agent
for food, and cosmetic, is becoming increasingly
important as a medicinal herb for its anti-
1Current Address : SEKT D6, Varada, Kurup’s Lane, PO Sasthamangalam, Thiruvananthapuram-10, Kerala.
Journal of Spices and Aromatic Crops
Vol. 28 (2) : 96-105 (2019) Indian Society for Spices
doi : 10.25081/josac.2019.v28.i2.6072
97Adulteration detection in turmeric
inflammatory, anti-cancerous, anti-oxidant,
antimicrobial, and anti-viral properties; as an
antiseptic; and in the treatment of diabetes and
Alzheimer’s disease (Sasikumar 2005; Bejar
2018). Turmeric has a history of 5000 years as a
herb in folk medicine as well as in Indian and
Chinese systems of medicine. India is the largest
producer, consumer, and exporter of turmeric,
which is traded mainly in the form of whole-
dried rhizomes, as powder and as valued-added
forms. In the powder form, which is mainly
used in commerce and by the food, cosmetic
and pharmaceutical industries, turmeric consists
of particles approximately 0.2–0.25 mm in size
(60–80 mesh). The powdered form has the
highest share in exports, constituting about 42%
of the world trade in turmeric. Many branded
turmeric powders, besides the produce from
the unorganized sector, are available in India
and these products constitute the bulk of the
domestic consumption of turmeric.
Recent reports on the medicinal value of
turmeric in treating a variety of ailments have
further increased the demand for turmeric all
over the world. Major importers of turmeric
powder are USA, UAE, Saudi Arabia, UK,
Australia, and Canada. Consumer preference for
natural /organic products has also spurred the
demand for turmeric. Unfortunately, as common
to other powdered spices, turmeric powder
too is being adulterated, with ller materials,
synthetic dyes, inert or biological entities, that
go visually undetected while synthetic materials
are the sole adulterants of the whole commodity
(Singhal et al. 1997; Dhanya & Sasikumar 2010)
and the natural curcumin with the synthetic
product. These adulterants/extraneous maers
besides adding bulk and increasing appearance,
result in diluting the main product and thereby
making it less eective, which, in turn, erodes
consumer confidence besides posing health
hazards (synthetic colorants).
The Bureau of Indian Standards suggests
a minimum of 3% curcumin for powdered
turmeric, whereas the mandatory Prevention of
Food Adulteration (PFA) Act of 1954 does not
specify any minimum curcumin limit (Dixit et al.
2009). Despite the regulations in place in India,
the quality of turmeric products in the Indian
market is highly variable owing to a variety of
reasons such as genotype, location and cultural
practices (Sasikumar 2001). Adulteration is
another reason for the variation in curcumin
content of traded turmeric powder (Ali et al.
World organizations like the International
Organization for Standardization (ISO),
American Spice Trade Association (ASTA),
The Food Safety and Standards Authority, India
(FSSAI), impose strict regulations on the quality
of spices and herbs imported and exported.
The globalization of food trade requires the
development of integrated approaches, such as
traceability of origin, quality and authenticity
to ensure food safety and quality (Barbuto et al.
2010). In the post-WTO era, importing countries,
as well as the consumers, pay more and more
aention to food quality, demanding clearer
product traceability as well as the use of detailed
and accurate product labels.
Adoption of a supply chain system in turmeric
trade and quality linked pricing coupled
with developing and deploying easy and fast
adulteration detection kits are sure shots to
ensure the quality of the traded turmeric.
Adulterants in turmeric
Adulteration may be defined as mixing or
substituting the original material with other
spurious, inferior, defective, spoiled, useless
parts of the same or dierent plant, harmful
substances or synthetic chemicals which do not
conform with ocial standards. Adulteration can
be in two ways- direct/intentional adulteration
and indirect/unintentional adulteration. Direct/
intentional adulteration includes practices of
substitution partially or fully with inferior
materials owing to their morphological
resemblance or chemicals or inert materials
in order to aain nancial gain. Unintentional
adulteration results mainly from the absence of
a proper evaluation method (Preethi et al. 2014;
Bharathi et al. 2018) and clerical errors (Zhao
et al. 2006).Though adulterants in turmeric are
reported since the 1970s, adulterant detection
in commercial turmeric products is of recent
origin (Salmén et al. 1987; Sasikumar et al. 2004).
The common adulterants in traded turmeric are
given in Table 1.
Techniques for adulterant detection
Many techniques have been developed to detect
adulteration in turmeric owing to the increased
consumer awareness on food safety and quality
The physical methods involved microscopic
observation and other parameters such as
solubility, bulk density, texture etc.
Details on the microscopic features of turmeric
rhizome and other Curcuma species such as C.
aromatica, C. xanthorrhiza, and C. zedoaria have
been reported (Upton et al. 2011; Tandon et al.
2008; Eschrich 1999). However, the microscopic
methods, in general, suer from subjectivity,
phenological variation, expressivity, lack of
distinguishing markers, low throughput etc.
Analytical techniques mainly use the chemical
composition or organic components present
in the plant for their identification and
authentication. Depending on this basic
principle, the techniques can be grouped into
Thin-layer chromatography (TLC) is the
simplest, most versatile and economical way of
obtaining the chemical ngerprints of multiple
herbal samples. Sen et al. (1974) described a
method to detect the adulteration of Curcuma
longa with C. zedoaria and C. aromatica that
involves a three-step colour sequence for the
detection of camphor and camphene, the active
principles of these adulterants, which are absent
in turmeric. Raghuveer et al. (1979) reported a
thin layer-gas chromatographic method to detect
C. aromatica admixture with common turmeric
(C. longa). More recently, the HPTLC Association
published a method to distinguish C. longa and
C. xanthorrhiza (Anonymous 2017). The same
method was earlier used to detect the adulteration
of turmeric with C. aromatica (Booker et al. 2014).
Dixit et al. (2008) reported turmeric adulteration
with synthetic dyes and detected the presence
of organic dyes, such as metanil yellow (1.5–4.6
mg g-1), Sudan I (4.8–12.1 mg g-1), and Sudan
IV (0.9–2 mg g-1) in loose turmeric and chilli
samples from city markets across India. The
curcumin content in turmeric and mixed curry
powder samples ranged from 6.5 to 36.4 mg
g-1 and from 0.3 to 1.9 mg g-1, respectively. In
a more detailed study by the same group, 712
Table 1. Common adulterants in traded turmeric/curcumin
Commodity Synthetic/chemical and non chemical
Turmeric whole/powder Metanil yellow
Sudan Red G
Yellow soap stone
Wild Curcuma sp. (C. zedoaria or C.
malabarica, C. aromatica)
Starch from cheaper source
Spent turmeric powder
Curcumin Synthetic curcumin -
commercial samples in India were tested using
a two-dimensional high-performance thin-layer
chromatography (HPTLC) method. None of the
branded samples (N =100) showed the presence
of articial color, but 105 (17.2%) of the non-
branded samples (N =612) of turmeric powders
were dyed with metanil yellow (Dixit et al. 2009).
Jaiswal et al. (2016) analysed 15 turmeric samples
for synthetic adulterants by TLC and found that
10 out of 15 turmeric samples collected from
Allahabad (now Prayag) were adulterated with
metanil yellow, Sudan III and articial colour.
A detailed study on the quality of 39 commercial
turmeric samples for food, dietary supplement
and cosmetic uses sold in supermarkets and
retail stores in the United Kingdom (27),
India (8), the Netherlands (2), Iceland (1), and
Greenland (1) labeled to contain C. longa (34),
C. amada (1), C. aromatica (2), C. xanthorrhiza
(1), and C. kwangsiensis (1) by HPTLC showed
that three products did not contain turmeric,
one turmeric product was adulterated with C.
aromatica, and one product from India contained
merely curcumin, with lile to no demethoxy-
and bisdemethoxy curcumin (Booker et al. 2014).
Gas chromatography can also be used to detect
the presence of other Curcuma sp. in turmeric as
many commercial turmeric dietary supplements
contain essential oil in addition to the
curcuminoids. There are substantial dierences
in the composition of the sesquiterpene fractions
and lower amounts or absence of turmerones in
some of the adulterating species (Raghuveer et
al. 1979; Sasikumar 2005).
A number of HPLC methods have been used for
the detection and estimation of curcuminoids
as a tool for the evaluation of the quality of
commercial ingredients and products. The
methods include a variety of detection systems
(UV, diode array, mass spectrometric, and
uorescence) and chromatographic techniques
(HPLC, GC, CE) (Hong et al. 2017; Mudge
et al. 2016; Rohman 2012; Lee & Choung
2011). For typical turmeric extracts, HPLC
chromatograms showing a characteristic
fingerprint of the three curcuminoids in a
consistent ratio (~77% curcumin (Curcumin
I) ~17% demethoxycurcumin and ~3%
bisdemethoxy curcumin) has been, for many
years, the approach to determine the product
identity and quality (Li et al. 2011; Rohman
2012; Lee & Choung 2011; Wichitnithad et al.
2009; Jayaprakasha et al. 2002). Bisdemethoxy
curcumin is reportedly absent in C. aromatica
and C. xanthorrhiza, allowing for a distinction
from C. longa based on this compound (Booker et
al. 2014; Anonymous 2017). Curcuma zedoaria has
demethoxy curcumin as the main curcuminoid,
contrary to C. longa where curcumin I is the
most abundant curcuminoid (Avula et al. 2012;
Thomas et al. 2011; Paramapojn et al. 2009).
However, adulteration detection based solely on
the curcuminoid prole may not be appropriate
due to varietal, location and seasonal variations
besides the solvent used in the curcuminoid
proling (Li et al. 2011).
Spectroscopic analysis and chemo metrics
Spectroscopy, the study of the interaction
between electromagnetic radiation and maer,
includes techniques like UV, visible, mid or near
infrared (MIR, NIR), Raman, uorescence, and
nuclear magnetic resonance (NMR) that allow
non-destructive testing and the use of small
samples to achieve identication (Meuren 2010;
Bharathi et al. 2018). Tiwari et al. (2013) using
Laser-Induced Breakdown Spectroscopy (LIBS)
analysed four commercial samples of whole
dried rhizomes of turmeric collected randomly
from four dierent areas of the spice market
of Allahabad (Prayag), India, for possible
adulteration. The analysis demonstrated that
one of the four samples had spectral signatures
corresponding to lead (Pb) and chromium (Cr),
suggesting they might contain lead chromate
as an adulterant providing color to make them
more aractive to consumers.
1H NMR spectroscopy-metabolomics has
been used to identify Curcuma species and
authenticate turmeric samples. Using this
method it was possible to dierentiate C. longa
from C. aromatica and C. xanthorrhiza based
on Principal Component Analysis (PCA). A
Adulteration detection in turmeric
contribution plot also allowed determination
of the main curcuminoid dierences among the
Curcuma species (the absence of bisdemethoxy
curcumin in C. aromatica and C. xanthorrhiza
being one of the main distinguishing traits) and
among C. longa extracts made with dierent
solvents (Booker et al. 2014).
Fourier Transform-Raman (FT-Raman) and
Fourier (FT-IR) spectroscopy are very useful in
detecting metanil yellow in turmeric powder.
Dhakal et al. (2016) demonstrated the application
of FT-Raman and FT-IR spectroscopy in
detecting metanil yellow in turmeric. These
authors utilized Fourier Transform-Raman
(FT-Raman) and Fourier Transform-Infra
Red (FT-IR) spectroscopy as separate but
complementary methods for detecting metanil
yellow adulteration of turmeric powder.
Simulated samples of turmeric powder and
metanil yellow were prepared at concentrations
of 30%, 25%, 20%, 15%, 10%, 5%, 1%, and
0.01% (w/w). FT-Raman and FT-IR spectra
were acquired for these mixtures as well as
for pure samples of turmeric powder and
metanil yellow. Spectral analysis showed that
the FT-IR method could detect the metanil
yellow at 5% concentration, while the FT-
Raman method appeared to be more sensitive
and could detect the metanil yellow at 1%
concentration. Relationships between metanil
yellow spectral peak intensities and metanil
yellow concentration were established using
representative peaks at FT-Raman 1406 cm−1 and
FT-IR 1140 cm−1 with correlation coecients of
0.93 and 0.95, respectively. The potential of a
1064 nm Raman chemical imaging system for
the identication of azo color contamination in
turmeric and curry powders were further studied
by this group (Dhakal et al. 2018). Metanil yellow
and Sudan-I, both azo compounds, were mixed
separately with store-bought turmeric and curry
powder at the concentration ranging from 1%
to 10% (w/w). Each mixture sample was packed
in a shallow nickel-plated sample container (25
mm × 25 mm × 1 mm). One Raman chemical
image of each sample was acquired across the
25 mm × 25 mm surface area using a 0.25 mm
step size. A threshold value was applied to the
spectral images of metanil yellow mixtures (at
1147 cm-1) and Sudan-I mixtures (at 1593 cm-1)
to obtain binary detection images by converting
adulterant pixels into white pixels and spice
powder pixels into the black (background)
pixels. The detected number of pixels of each
contaminant is linearly correlated with the
sample’s concentration (R2 = 0.99). This study
demonstrates the 1064 nm Raman chemical
imaging system as a potential tool for food
safety and quality evaluation.
The use of HPLC-MS provides even lower
sensitivity with a limit of detection of as lile
as 100 pg mL-1 metanil yellow in turmeric
powder (Feng et al. 2011). Fourier Transform
Near-Infrared (FT-NIR) spectroscopy coupled
with chemometrics was also used to detect corn
starch illegally added to turmeric powder, using
simulated samples (Kar et al. 2019a). In this work,
the pure turmeric powders were blended with
corn starch to generate dierent concentrations
(1-30%) (w/w) of starch-adulterated turmeric
samples. The reectance spectra of a total of 224
samples were taken by FT-NIR spectroscopy.
The exploratory data analysis was done by
Principal Component Analysis (PCA). The
starch related peaks were selected by Variable
Importance in Projection (VIP) method and were
explored by examination of original reectance
spectra, 1st derivative spectra, PCA loadings and
β coecients plot of the Partial Least Square
Regression (PLSR) model. The coecient of
determination (R2) and root-mean-square error
of partial least square regression (PLSR) models
were found to be 0.91-0.99 and 0.23-1.3%,
respectively, depending on the pre-processing
techniques of spectral data. The Figure Of Merit
(FOM) of the model was found with the help
of the Net Analyte Signal (NAS) theory. These
authors recently estimated the potential of Near-
Infra Red (NIR) spectroscopy coupled with
chemometrics as a rapid and non-destructive
tool for the detection as well as quantication
of Sudan dye I adulterated turmeric powder
using simulated samples. The concentrations
of the adulterants were 0.05%, 0.1%, 0.2%, 0.5%,
1%, 1.5%, 2%, 5%, 10%, 15%, 20%, 25% and 30%
(w/w), respectively. Exploratory data analysis
was done for the visualization of the adulterant
classes by Principal Component Analysis
(PCA). In the classication approach, Principal
Components (PCs) extracted by PCA were fed
as the inputs of the Support Vector Machine
(SVM) classier. The average accuracy of the
adulterants classes noted was greater than 90%
(Kar et al. 2019b).
Using Atomic Absorption Spectroscopy (AAS),
Quratey & Kwarkey (2018) reported the
highest level of chromium in turmeric samples
amongst ten spices collected from the Ghana
market. Turmeric recorded the highest mean Cr
concentration (0.42 ± 0.03 mg kg-1). Nallappan
et al. (2013) used terahertz spectroscopy, a
non-intrusive method, to eectively identify
adulteration of turmeric with chalk powder in
PCR based molecular methods
Polymerase Chain Reaction (PCR) has a high
potential in biological adulterant detection
and authentication of commodities due to its
simplicity, sensitivity, specicity as well as rapid
analysis time and low cost (Sasikumar et al. 2016;
Swetha et al. 2016; Dhanya & Sasikumar 2011;
Mafra et al. 2008; Vidal et al. 2007).
PCR based adulteration detection in turmeric
has been started by our group as early as
2004. Sasikumar et al. (2004), analysed three
popular market samples of branded turmeric
powder from the Indian market using Random
Amplied Polymorphic DNA [RAPD] analysis
and revealed the presence of C. zedoaria in the
samples though the curcumin levels of the
samples met the quality standards. Dhanya
et al. (2011) developed RAPD based Sequence
Characterized Amplified Region (SCAR)
markers to detect plant-based adulterants
in traded turmeric. Six samples of branded
turmeric powder procured from a local market
at Calicut (Kozhikode), Kerala, India were
analyzed using the two SCAR markers and both
markers detected the presence of adulteration
with C. zedoaria or C. malabarica in four out of six
market samples and in simulated mixtures, i.e.,
samples of turmeric powder and the adulterants
made at dierent concentrations. Parvathy et
al. (2015) successfully used the DNA barcoding
locus ITS to detect the plant-based adulterants
in commercial samples of branded turmeric
powder. Though band level discrimination of
the adulterants and the genuine sample was
not possible, single nucleotide polymorphisms
(SNPs) related to the adulterants and genuine
product was observed (Table 2). One out of the
10 samples analysed was found adulterated
with C. zedoaria.
After the first report of adulteration of
natural curcumin with synthetic curcumin in
2011, research on using radiocarbon dating
techniques to analyze curcumin products on
the market to determine the percentage that
contained synthetic versus natural curcumin,
or a combination of both gained momentum
(Rafi 2016; Watson 2011; Krishnakumar &
Sanandakumar 2011). The 14C testing of ve
commercial samples of curcumin showed that
four of the materials contained curcumin that
was 32-45% synthetic, while the h sample
was 100% natural (Press release –Sabinsa,
2015). Using the same testing approach other
commercial samples too were analysed for
synthetic curcumin (Anonymous 2017).
Sen et al. (2017) developed physical and
chemical methods to detect yellow lead salt
chalk, metanil yellow, aniliue dye and starch in
Future perspectives and conclusion
Turmeric powder and turmeric extracts are
valued both for their medicinal properties and
as a culinary spice. Turmeric-based dietary
supplements (which also include standardized
extracts with high concentrations of curcumin)
have seen a steady increase in popularity
globally. In the United States, the largest market
for turmeric supplements, sales have almost
Adulteration detection in turmeric
Table 2. SNPs that discriminate between C. longa and C. zedoaria
Species Position of SNP and nucleotide substituted
293 388 410 439
C. longa G G G G
C. zedoaria A A T C
Source: Parvathy et al. (2015)
tripled from 2013 to 2016, totaling over US $69
million in 2016. Unfortunately this high value,
low volume commodity, has been subjected to
deliberate, economically-motivated adulteration
leading to reduced perceived biological value
and posing health risks besides eroding public
faith. Adulteration is also a major economic
fraud involving public health. Reliable, easy,
sensitive and high throughput traceability and
authentication methods coupled with quality
standards thus assume signicance. Adoption
of a supply chain practice in turmeric trade and
quality linked pricing in addition to commercial
adulteration diagnostic kits, if they can be
developed and deployed, will be a sure shot to
ensure the quality of the traded produce.
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