The detection of economically motivated adulteration in the herb and spice industry

Student thesis: Doctoral ThesisDoctor of Philosophy


The herb and spice industry is increasing in value and popularity as the consumption of herbs and spices continues to grow. Valuable condiments as well as long and complex supply chains offer the motivation and the opportunity for fraudsters to carry out economically motivated adulteration (EMA) and pose economic and public health risks in doing so. Spectroscopy in conjunction with chemometrics, allow for nontargeted qualitative methods to be developed to detect the ever-evolving criminality of adulteration in herbs and spices. In this study, sage, paprika, garlic and black pepper were prioritised by industry experts in relation to their risk of adulteration as determined by herb and spice industry.


The carefully selected adulterants in this study were analysed alongside the four herbs and spices for the development of classification models. The adulterants were morphologically similar to the herbs and spices or could be blended in ground form. Green plant cuttings, spent paprika and white powders were analysed alongside sage, paprika and garlic respectively. Black pepper adulterants included extraneous parts of the plant as well as papaya seeds and chili powder.


The spectroscopic instruments used in this study were near infrared (NIR) and Fourier transform infrared (FTIR). The sage method, developed using FTIR, resulted in binary and multiclass supervised models with a measurement of fit (R 2 ) of 0.978 and 0.952 and a measurement of prediction (Q 2 ) of 0.975 and 0.936 respectively. Following validation, the area under the curve (AUC) of 1 indicated excellent method performance when a validation set was analysed. Additionally, it was found that sage could be classified according to its species.


The detection of spent material in paprika was investigated with both NIR and FTIR instrumentation. Although separation was observed between spent material and paprika, these methods detected adulteration consistently from 50-90% using NIR spectral data and 40-90% using FTIR spectral data but was less accurate at low level adulteration. Correct classification rates for authentic paprika were 100% and 83.3% for NIR and FTIR respectively. An additional step was carried with the addition of Sudan dye and it was found to have no effect on the outcome of the results when detecting spent paprika adulteration.


Binary supervised classification models were created following the collection of spectral data from garlic and its adulterants on NIR and FTIR. Validation of the methods resulted in 100% correct classification for all authentic garlic samples and all adulterated samples in the 20-90% range for both spectroscopic techniques. Also, following further investigation, it was found that extraneous parts of the garlic plant could be separated in an unsupervised model.


Advances in technology mean that handheld and portable spectroscopy is being developed and adapted for the detection of adulteration. In this study, black pepper and the adulterants were all analysed using two portable NIR instruments and a benchtop NIR instrument. A comparison was carried out between the three methods and it was observed that the portable instruments were comparable in terms of performance with the benchtop NIR. All three methods had a correct classification rate of >90% for authentic black pepper and 100% correct classification for 20-90% level adulteration.


These screening methods for EMA are vital to ensuring the authenticity of herbs and spices for the protection of the industry and the consumer. As these are non-targeted methods, they can also cover a wide range of adulterants, including those that are not yet known.

Date of AwardDec 2020
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsHerb and Spice Consortium
SupervisorChristopher Elliott (Supervisor)


  • Food fraud
  • herb
  • spice
  • spectroscopy
  • chemometrics

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