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 Table of Contents  
Year : 2022  |  Volume : 16  |  Issue : 2  |  Page : 134-139

Detection of nonpermitted food color metanil yellow in turmeric: A threat to the public health and Ayurvedic drug industry

1 Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh, India
2 Department of Agad Tantra, Faculty of Ayurveda, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India

Date of Submission23-Mar-2021
Date of Decision29-Sep-2021
Date of Acceptance24-Dec-2021
Date of Web Publication4-Jul-2022

Correspondence Address:
Shobha K Bhat
Department of Agad Tantra, Faculty of Ayurveda, Institute of Medical Sciences, Banaras Hindu University, Varanasi - 221 005, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/joa.joa_77_21

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Introduction: The food products available in the market today are made attractive by adding food colors. Fruits, vegetables, spices, sweets, and even the commonest drugs used as medicine in day-to-day life are adulterated with nonpermitted colors. Haridra or turmeric is the most popularly used Vishaharadravya/antitoxic drug which is taken internally almost every day both in diet and as medicine. Metanil yellow (MY) is a “nonpermitted” food colorant used extensively as an adulterant in different spices, especially turmeric. Though the quantity of intake would be small, when taken continuously, it may lead to several adverse life-threatening effects in humans. Methods: 20 different samples of Haridra (Turmeric) were collected randomly from markets in and around Varanasi. The presence of nonpermitted food color-MY in these turmeric samples was first tested with preliminary color test followed by ultraviolet-visible spectroscopic studies. The color change and change in absorption spectra have been used to identify the contaminated samples. Results and Conclusion: Two out of twenty samples of Haridra were found to be adulterated with MY. Food adulteration in daily diet is a matter of great concern and is a strong cause for Garavisha. Mass awareness has to be raised on the issue. Our results suggest that special care has to be taken by the turmeric-based Ayurveda manufacturers to avoid the use of such contaminated turmeric.

Keywords: Adulteration, health hazards, metanil yellow, turmeric

How to cite this article:
Verma A, Saha S, Bhat SK. Detection of nonpermitted food color metanil yellow in turmeric: A threat to the public health and Ayurvedic drug industry. J Ayurveda 2022;16:134-9

How to cite this URL:
Verma A, Saha S, Bhat SK. Detection of nonpermitted food color metanil yellow in turmeric: A threat to the public health and Ayurvedic drug industry. J Ayurveda [serial online] 2022 [cited 2022 Aug 10];16:134-9. Available from: http://www.journayu.in/text.asp?2022/16/2/134/349772

  Introduction Top

In recent times, it is evident that a lot of importance is given to the color and appearance of any food item or spices at the consumer level. In order to make the food look more attractive, food colors are added to edibles. These colors could be pigments, dyes, or any other compounds which impart color to the substances to which it is added.[1] By adding such colors to the food, it may be made more attractive and appealing or enhanced. Food colorants may be either permitted or nonpermitted.[2] Even when being permitted, they should not be added beyond permissible limits. Anyhow several research works published so far show maximum adulteration of samples with nonpermitted colors or with permitted colors exceeding the prescribed value.[3],[4],[5] Rhodamine B and metanil yellow (MY) are among the commonest nonpermitted colors used in food adulteration.[6]

MY is a yellow azo dye which is made from diazotized metanilic acid and diphenylamine.[7] It is generally used in industries for coloring wool, nylon, silk, paper, ink, aluminum, detergent, etc., Though it is specified for industrial use only, it has been observed that MY is added to various food items and spices, especially turmeric, to enhance its color and make it more attractive.[8] Anyhow studies reveal that MY is a potent chemical which even when enters the body in a minimal dose for a long duration of time, may cause several toxic effects on various systems of the body.[9],[10] It is found to cause degenerative changes in the lining of the stomach, kidneys, and liver.[11] It also adversely affects the ovaries and testes, proving to be dangerous to reproductive organs.[12] As this chemical enters the gastrointestinal tract, the intestinal bacteria convert its chemical constituent into aromatic amines which are reportedly carcinogenic.[13] It is also reported to be mutagenic[14] and causes insufficient oxygen supply to skin and mucous membranes causing toxic methemoglobinemia.[15]

Haridra or turmeric (Curcuma longa) is one such spice which is found in every house and is extensively used as spice, food preservative, and coloring material in India. Ayurveda, the traditional system of medicine in India, recommends its use for various disorders both internally and externally.[16] It is interesting to note that this single drug possesses the diverse effects on various systems of the body and several research works are available to exhibit the same.[17] It is a component of several formulations used in Ayurveda. Moreover, routinely it is being consumed by people by adding it to boiled milk as it is considered to enhance the immunity.[18]

Unfortunately, several studies have revealed that MY is used to adulterate foodstuffs like turmeric and honey which are well known for their medicinal values.[19] As turmeric is used on a daily basis either in food or as medicine, if found adulterated, the MY enters the body daily in small quantities and on long-term consumption, may impose adverse health impacts.[20] This concept of intake of small quantities of less potent poisons accounts for Gara Visha (cumulative toxicity) in Ayurveda which may be a cause for several physical or psychological diseases. The present study was planned with a view to estimate the presence of MY in turmeric samples collected from the local market of different places in Varanasi.

  Materials and Methods Top

Sample collection

Standard “MY” chemical was procured from TCI (Japan) chemical and was used without any further purification. MY is an “azo derivative” having yellow-orange color and a chemical structure as depicted in [Figure 1]. Owing to the sodium salt, this powder is quite soluble in water, alcohol, and slightly soluble in benzene, acetone.
Figure 1: Chemical structure of metanil yellow

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Twenty different turmeric samples needed for the study were collected from different regions in and around Varanasi district, India, in the month of May. The collected drug was authenticated as Haridra (C. longa/turmeric) from the experts of the Department of Dravyaguna, Faculty of Ayurveda, IMS, BHU. Out of the 20 samples, four samples were obtained in turmeric rhizome form, dried in shade, and then powdered to fine powder. Six samples were from the organized sector, available in sealed packets in the market. Ten other samples were in the form of loose powders sold by local vendors from the local drug or spice markets in different places of Varanasi. All the samples procured were preserved in clean air-tight plastic polybags and were kept in clean environment.

Study design

The study was conducted in the Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi. The presence of nonpermitted food color-MY in these turmeric samples was first tested with preliminary color test followed by ultraviolet (UV)-visible spectroscopic studies. The color change and change in absorption spectra have been used to identify the contaminated samples. Only adulteration with MY was assessed by the above 2 methods and quantification of MY was not performed.

Hydrochloric acid test for metanil yellow

For the preliminary test, a pinch of turmeric powder was taken in a test tube. A few drops of concentrated hydrochloric acid (HCl) were added to it followed by distilled water. Appearance of pink color instantly and its persistence confirmed the presence of MY in the sample.

Ultraviolet-visible absorption spectrometer

Electronic spectra were recorded on a CARY 100 BIO UV–Visible spectrophotometer which has a DRA reflectance accessory attached for solid sample measurements. The system is capable of measuring absorbance up to four and has a spectral range of 200–800 nm. The spectra of pure MY and all other turmeric samples were recorded in absolute ethanol (~99.8% pure).

  Results Top

Hydrochloric acid test for metanil yellow

Here we present the results of physical and chemical studies of possible contamination of MY for turmeric samples. The appearance of the 20 samples procured for the study is depicted in [Figure 2]. It is important to note that all samples look very similar, and naked eye testing does not allow us to identify the presence of MY in turmeric. According to the observations based on preliminary color test, two turmeric samples S4 and S11 gave pink coloration, as shown in [Figure 3]. First image of cuvette with pink solution is due to pure MY with HCl. Sample 4 and sample 11 clearly shows the persistent pink color indicating the presence of MY.
Figure 2: Optical images of 20 turmeric samples collected for testing

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Figure 3: Optical image showing the hydrochloric acid color test for metanil yellow

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Ultraviolet-visible absorption studies for metanil yellow

Two high-energy bands are observed at 205 and 270 nm in MY. In addition, the n−π* transition at 413 nm is very important as it causes the color that we see. All the turmeric samples show three bands: two high-energy bands ~ 205 and 215 nm and broadband around 420 nm, as depicted in [Figure 4].
Figure 4: Ultraviolet-visible absorption spectra of all the turmeric samples

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The absorption peak maximum for each sample is depicted in [Table 1]. The highlighted values (S4 and S11) show different behaviors in λ max and also show different UV pattern spectra which are different from the standard one as depicted in [Figure 5]. Based on HCl test and UV-Vis absorption analysis, it is clear that samples 4 and 11 are contaminated with MY.
Table 1: Samples and their corresponding absorption peak maxima

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Figure 5: Ultraviolet-visible absorption spectra of the turmeric samples which showed pink color on hydrochloric acid color test

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  Discussion Top

Adulteration of turmeric by MY is of great concern. There have been several efforts devoted in identifying and quantifying the MY by means of spectroscopic and electrochemical methods. Among electrochemical methods, application of impedimetric method/capacitance measurement is reported for estimation of MY in turmeric.[21] HPLC technique, though involves a considerable amount of efforts, is also used in very recent times to quantitatively analyze the presence of MY in turmeric.[22] Among spectroscopic investigation, application of near-infrared spectroscopic studies in identifying the MY is quite popular in recent times though restricted by the involvement of expensive detector and instrumentation.[23] Though reported scantly, UV-visible absorption spectrophotometry is considered an effortless and perceptive method for the estimation of MY.[24],[25] MY, having an azo functional group, absorbs strongly in the range of 420–440 nm in water, alcohol, alkaline, or salt solutions. However, this absorption peak shifts to 520 nm (thereby appearance of pink color) on acidification due to protonation. In this report, a simple and fast spectroscopic method is developed for qualitative detection of MY in turmeric. The sensitivity offered by this spectroscopic method is unparalleled to that of other existing nonspectroscopic methods in terms of linear range and quantification limits. Most importantly, simplicity of sample preparation (no pretreatment is needed) and measurement, and the use of nonrigid experimental conditions could make this method as an effective tool to analyze accurately and precisely the MY in turmeric samples in addition to using of simple instrumentation and low-cost materials.

Turmeric is used to treat various diversified pathological conditions from time immemorial. The ayurvedic treatises explain several formulations containing Haridra/turmeric. Researches have proven various therapeutic potentials of turmeric including anti-inflammatory,[26] antitumor,[27] antibacterial,[28] antiviral,[29] antioxidant,[30] antiseptic,[31] cardioprotective,[32] hepatoprotective,[33] and digestive activities.[34] Moreover, it also constitutes to an important spice in the Indian culinary and is used extensively in daily diet. Adulteration of turmeric with MY would be dangerous to the health of people at all ages. Studies reveal that the dye has a toxic effect on various systems of the body like the nervous system, digestive, cardiovascular, excretory, and reproductive systems.[35] The effects of long-term consumption of MY on the developing and adult brain were studied using Wistar rats, and it was noticed that in the MY administered rats, the amine levels in the hypothalamus, striatum, and brain stem were significantly affected, and the changes were not generally reversible even after withdrawal of MY in developing rats indicating that chronic consumption of MY can predispose both the developing and the adult central nervous system of the rat to neurotoxicity.[36] According to the National Center for Biotechnology Information, the LD50 of MY in rats on oral administration is 5 g/kg.[37] The maximum permissible limit of 100 mg/kg has been specified for MY in the Prevention of Food Adulteration Act of India.[38]

The chances of adulteration with turmeric rhizome are usually less and more with the powder form. The branded turmeric powders are usually expected to be devoid of such adulteration as compared to the loose powders available in open market. In the present study, all the three samples were included for estimation of MY adulteration. Among the 20 samples, four samples were in rhizome form which were dried and powdered for use in the study, six samples were collected from the organized sector, available in the market and the rest 10 samples were the loose powder sold in the local markets in and around Banaras. Two samples out of 20 studied were found to be adulterated with MY. Both these samples were from the local vendors or at retail shops who might have added the food color to make the commodity look more attractive for monetary benefits. But what is important to notice is that both these samples were obtained from those regions in Varanasi which has open market for various such drugs which are used in the preparation of ayurvedic medicines by the small-scale manufacturers. Moreover, common people also depend on the drugs obtained from such markets for daily consumption as it is believed to be market wherein herbs of good quality are sold. Finding of adulterants like MY in such a commonly used herb from such areas is a matter of serious concern for ayurvedic drug manufacturers. Ayurvedic clinicians routinely advise the use of Haridra or turmeric in several diseases more commonly of allergic origin and most of all as a means to boost the immunity. People use it not only as medicine but also as a natural food colorant in the daily diet. Food adulteration, especially with such widely used drug or spice, is hence a matter of concern these days.

  Conclusion Top

Turmeric or Haridra is used extensively by people in day-to-day life both as a medicine and food is a universally accepted fact. Adulteration in edibles is very common and even the commonly used spices like turmeric are not an exception to the same. Turmeric is used extensively in day-to-day life, both in diet and as a medicine. In such a background, adulteration of Haridra or turmeric, especially with MY, is a matter of serious concern. Proper vigilance by the concerned authorities must be made compulsory so that consumers are assured of good quality products. The consumers must also be educated regarding such issues so that they may take proper care during purchase of such items. Drug manufacturers of Ayurveda, especially at small scale level, which do not follow a stringent policy in the screening of raw materials with regards to such toxic nonpermissible food colors must also be sensitized towards this issue which may be a threat to the safety of ayurvedic drug manufacturing and consumption.


The authors gratefully acknowledge the infrastructure provided by the Department of Agad Tantra, Faculty of Ayurveda, IMS, BHU, and the Department of Chemistry, Institute of Science, BHU.

Financial support and sponsorship


Conflict of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]

  [Table 1]


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