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Development of analytical methods of multi-pesticide residues for controlling the tea quality, from tea plantation to consumer

Ly, Tuan kiet. Development of analytical methods of multi-pesticide residues for controlling the tea quality, from tea plantation to consumer. PhD, Sciences des Agroressources, Institut National Polytechnique de Toulouse, 2020, 258 p.

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Abstract

Tea is the second most-consumed beverage in the world, surpassed only by water, due to its health benefits. However, because of monoculture cultivation practices, the use of pesticides during tea cultivation is common. Over time, the number of pesticides used has increased, and, to protect consumers' health, many countries and regions have established maximum residue limits of pesticides for a variety of foods and beverages, including tea. For instance, the European Union (EU) has set the maximum residue limits (MRLs) for more than 480 pesticides and their metabolites in tea products. Therefore, the development of analytical methods for multi-pesticide residues in tea is a challenge, because tea is a complex commodity with many compounds that can interfere with results, such as polyphenols, pigments, and caffeine. The aim of this thesis is to develop rugged and robust methods with high sensitivity, accuracy, and precision to meet the EU regulations for simultaneous determination of 400 pesticide residues in tea products using ultra performance liquid and gas chromatographies coupled to tandem mass spectroscopy (UPLCMS/ MS and GC-MS/MS, respectively). The first part of thesis focused on elimination of matrix effects in green tealeaves by combining QuEChERS (quick, easy, cheap, effective, rugged, and safe) extraction and mixed-mode SPE (solid phase extraction) clean-up. A C18 SPE cartridge paired with SPE GCB/PSA proved to be the most effective clean-up method and enabled 225 pesticide residues to be quantified, based on solvent calibration curves (154 residues using UPLCMS/ MS and 71 residues using GC-MS/MS). The analytical methods were validated fully in accordance with the SANTE/11945/2015 (EU). LOQs for most pesticides (386/400 or 96.5%) were below 10 μg/kg, i.e., less than the EU MRL (5-70 mg/kg). In the second part, matrix effects for 400 pesticide residues were investigated and improved for the analysis of different types of teas (white, green, oolong and black ones). Results showed that combining QuEChERS extraction and mixed-mode SPE clean-up, and following the reduction of the injection volume were found to be the most effective procedure to overcome matrix effects. More than 190 pesticides (> 95% of the 200 ones) had the matrix effect within the range of ± 20% for UPLC-MS/MS. Therefore, they can be quantified using solvent calibration curves. On the other hand, matrix-matched calibration curves should be used to overcome matrix effects for GC-MS/MS. Moreover, we recognized that matrix effects in GC-MS/MS were not only signal enhancement but also suppression. Finally, in the third part of this work, the established method was successfully applied to the determination of multi-pesticide residues in 106 tea samples. In total, 26 tea samples (24.5%) were containing at least one pesticide violation, with 43 pesticide residue violations. The most frequently detected pesticides were neonicotinoids, synthetic pyrethroids, and triazole fungicides. In terms of origin in this study, Taiwan had the most pesticide-contaminated samples with 83.3%, following by China (73.7%), Vietnam (64.7%), and India (Darjeeling) (55.0%). The results showed that samples exceeding EU MRLs regulations were still high with 24.5%. Therefore, assessments of multipesticide residues in tea need to be continued.

Item Type:PhD Thesis
Uncontrolled Keywords:
Institution:Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
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Research Director:
Behra, Philippe and Tran Thi, Nhu Trang
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Deposited On:30 Mar 2021 13:28

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