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 andpopularity as the consumption of herbs and spices continues to grow. Valuablecondiments as well as long and complex supply chains offer the motivation andthe opportunity for fraudsters to carry out economically motivated adulteration(EMA) and pose economic and public health risks in doing so. Spectroscopy inconjunction with chemometrics, allow for nontargeted qualitative methods to bedeveloped to detect the ever-evolving criminality of adulteration in herbs andspices. In this study, sage, paprika, garlic and black pepper were prioritisedby industry experts in relation to their risk of adulteration as determined byherb and spice industry.


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


The spectroscopic instruments used in this study were nearinfrared (NIR) and Fourier transform infrared (FTIR). The sage method,developed using FTIR, resulted in binary and multiclass supervised models witha 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 underthe curve (AUC) of 1 indicated excellent method performance when a validationset was analysed. Additionally, it was found that sage could be classifiedaccording to its species.


The detection of spent material in paprika was investigatedwith both NIR and FTIR instrumentation. Although separation was observedbetween spent material and paprika, these methods detected adulterationconsistently from 50-90% using NIR spectral data and 40-90% using FTIR spectraldata but was less accurate at low level adulteration. Correct classificationrates 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 foundto have no effect on the outcome of the results when detecting spent paprikaadulteration.


Binary supervised classification models were createdfollowing the collection of spectral data from garlic and its adulterants onNIR and FTIR. Validation of the methods resulted in 100% correct classificationfor 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 anunsupervised model.


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


These screening methods for EMA are vital to ensuring theauthenticity of herbs and spices for the protection of the industry and theconsumer. As these are non-targeted methods, they can also cover a wide rangeof 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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