Investigation of Chlorpyrifos and Its Transformation Products in Fruits and Spices by Combining Electrochemistry and Liquid Chromatography Coupled to Tandem Mass Spectrometry

The identification of transformation products (TPs) of pesticides in food is a crucial task difficult to tackle, due to the lack of standards. In this work, we present a novel methodology to synthesize five main TP standards of the insecticide chlorpyrifos (CPF) and to investigate their occurrence in selected fruits and spices. TPs were electrochemically (EC) synthesized using a boron-doped diamond electrode (BDD) and identified by EC coupled online to mass spectrometry, LC-MS/MS, and high-resolution mass spectrometry. CPF and its TPs were analyzed in the food samples by LC-MS/MS on multiple reaction monitoring (MRM) after dispersive solid-phase extraction. A good recovery of 83–103% for CPF and 65–85% for TPs was obtained. Matrix effects, which cause signal suppression, ranged between 81 to 95% for all targeted analytes. The limit of detection and quantification for CPF were 1.6–1.9 and 4.9–5.7 μg/kg, respectively. Among investigated samples, CPF was determined in fresh lemon (104 μg/kg), fenugreek seed (40 μg/kg), and black pepper (31 μg/kg). CPF content in all samples was lower than the EU maximum residue level (MRL). The most frequently detected TPs were diethylthiophosphate and diethylphosphate. Other TPs, CPF oxon and trichloropyridinol, were also detected. Hence, EC is a versatile tool to synthesize TP standards which enables the determination of contaminants and residues in foodstuffs even if no commercial standards are available.     

Loquat Bruise Detection Using Optical Coherence Tomography Based on Microstructural Parameters

Slight postharvest bruises of loquats remarkably affect the quality and shelf life of the fruits, but they are difficult to identify using visual inspection. Sub-surface structural changes in cells caused by mechanical injury or impact can be detected using spectroscopy-based methods from different angles. Optical coherence tomography (OCT), a non-destructive technology, can acquire cross-sectional images to analyze sub-surface structures of loquats, thus offering the potential to identify fruit bruises. This study proposes an automated OCT image processing method for extracting large cells from loquat images, which involves a series of steps including image denoising, boundary detection, filtering, binarization, segmentation, and region selection. Parenchyma cells in loquat tissue were visualized and characterized, and the five-cell morphological parameters, including total cell surface area, average cell surface area, average cell Feret diameter, equivalent diameter, and cell amount were measured. The bruised and non-bruised loquat groups showed significant differences in the total cell surface area and cell amount, suggesting that these two parameters might be used as indictors for bruise identification. No significant differences in other parameters were observed between the two groups. The microcosm approach proposed in this study sheds some light on ways to improve fruit quality evaluation. Overall, combined with appropriate image processing, OCT is an efficient and non-destructive tool for loquat bruise detection. The proposed strategy might also be expanded to other agricultural applications.     

Use of Sorbent-Based Vacuum Extraction for Determination of Volatile Phenols in Beer

A novel method based on vacuum-assisted sorbent extraction (VASE) used with gas chromatography-mass spectrometry (GC-MS) for isolation of volatile phenols was described. The method is based on extraction of analytes into sorbent traps (sorbent pen) filled with Tenax in a vacuum system—vials with traps from which air was evaluated. The method was applied for extraction of volatile phenols from aqueous matrix and smoked beer was used as a food example. Methyl-, dimethyl-, and trimethylphenols, along with 4-ethylphenol, 4-methylguaiacol, 4-ethylguaiacol, 4-propylguaiacol, and eugenol, were used in method development. Optimal extraction parameters were elaborated. For the analysis of volatile phenols in beer matrix, the method was characterized with satisfactory linearity (r²?≥?0.99) in a range of 0.005–0.5 mg/L. Limits of detection (LODs) for analyzed compounds ranged from 0.0006 to 0.018 mg/L and repeatability for majority of compounds was <?5% for a single trap extraction. The detected volatile phenols in beer samples ranged from 0.003 to 0.672 mg/L.     

Development of Rapid and Label-Free Fluorescence Sensing of Tetracyclines in Milk Based on Poly(Adenine) DNA-Templated Au Nanoclusters

In this work, a rapid and label-free fluorescent sensing method has been established for tetracycline (TC) detection by using poly(adenine) (poly A) DNA-templated Au nanoclusters (AuNCs) as fluorescence indicator. The obtained AuNCs exhibited excellent fluorescence intensity and good stability. In the presence of tetracycline, the fluorescence intensity of AuNCs was obviously reduced due to the interactions between the tetracycline and the poly A DNA-templated AuNCs. Under the optimum conditions, the strategy permitted sensitive detection of tetracycline in a linear range from 0.1 to 60 μM and with a limit of detection of 20 nM. In addition, the sensor was successfully applied to determinate the tetracycline content in milk samples. More importantly, it could be easily performed within 10 min at room temperature. Thus, it could provide a rapid, convenient, label-free, and high-sensitive fluorescent platform for tetracycline detection.     

Rapid In Situ SERS Analysis of Pesticide Residues on Plant Surfaces Based on Micelle Extraction of Targets and Stabilization of Ag Nanoparticle Aggregates

A structure of polyurethane micelle/Ag nanoparticle (Ag NP) cluster was fabricated as surface-enhanced Raman scattering (SERS) substrate for in situ extracting organic compounds on the surface of different matrixes, in which polyurethane micelles acted as the host material to capture target molecules and stabilize nanoparticle cluster. This method provided stable aqueous suspensions of Ag NP cluster due to the amphiphilic properties of polyurethane. We demonstrated SERS-based in situ detection of pesticides on vegetables and fruit skin, by simply dropping polyurethane micelle/Ag NPs substrate on the sample surface where the target molecules could be detected without a previous elution and extracting. The obtained results showed that this polyurethane micelle/Ag NP cluster substrate had excellent SERS performance for pesticide molecules with ideal stability and reproducibility. With further optimization, the limit of detection of 0.03 μg/mL acetamiprid, 0.08 μg/mL phosmet, and 0.002 μg/mL thiabendazole was obtained, respectively.     

Evaluation of Phthalic Acid Esters in Fish Samples Using Gas Chromatography Tandem Mass Spectrometry with Simplified QuEChERS Technique

Phthalic acid esters (PAEs) have become an important food safety concern due to their lipophilic properties and propensity to accumulate in adipose tissue in edible fish. In this study, a simple, sensitive, and accurate analytical method was successfully established for simultaneous determination of 19 PAEs in fish samples using gas chromatography coupled with tandem mass spectrometry (GC–MS/MS). A simplified Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) procedure was applied for sample preparation, and the Plackett-Burman factorial design was utilized for optimizing extraction parameters. The calibration curves were linear in the range 0.01–0.5 mg/kg for all of the analyzed PAEs, and the limits of quantification (LOQs) were 0.05–20 μg/kg which are much lower than those in previous reports. The average spiked recoveries ranged from 71.2 to 116.3%, with relative standard deviations (RSDs) of 3.9 to 16.2% (n?=?6). Finally, the method was applied to analyze 60 real fish samples taken from Shanghai Municipality, China, and the diisobutyl phthalate (DIBP), dibutyl phthalate (DBP), and bis(2-ethoxyethyl)phthalate (DEHP) were found in almost all fish samples tested in this study. The present study demonstrated that the established method was suitable for market surveillance of 19 PAE residues in fish samples.     

Simultaneous Determination of TBH<Subscript>2</Subscript>Q and BHA Antioxidants in Food Samples Using Eosin Y Film Modified Electrode

A glassy carbon electrode (GCE) was modified with eosin Y that was electrodeposited on GCE via continuous cycling between ??1.6 and 1.5 V (vs Ag/AgCl). This electrode was characterized by scanning electron microscopy and electrochemical impedance spectra. The resulting electrode exhibited excellent electrocatalytic activity toward the oxidation of butylated hydroxyanisole (BHA) and tert-butyl hydroquinone (TBH₂Q); in addition, the oxidation products of BHA and TBH₂Q were found to be the same, which was studied by CV and in situ FT-IR spectroelectrochemistry. Under the optimized condition, the oxidation peak currents were linear to BHA/TBH₂Q in the range from 0.10 to 7.00 μg mL^?1 with the detection limits of 0.01 μg mL^?1 (S/N?=?3) for BHA and 0.015 μg mL^?1 (S/N?=?3) for TBH₂Q, respectively. Moreover, the reproducibility and repeatability of the electrode were determined. The proposed method was successfully applied in the simultaneous determination of BHA and TBH₂Q in several edible oil samples, and satisfactory results when compared with those obtained using high-performance liquid chromatography.     

Reproducible Molecularly Imprinted QCM Sensor for Accurate,Stable, and Sensitive Detection of Enrofloxacin Residue in Animal-Derived Foods

This study describes the development of a novel reproducible molecularly imprinted quartz crystal microbalance (QCM) sensor for the accurate and sensitive analysis of the residue of enrofloxacin (ENRO) in animal-derived foods. This proposed sensor was easily fabricated by directly immobilizing molecularly imprinted polymer (MIP) of ENRO on the surface of a QCM Au chip, which combined the advantages of selective recognition from the MIP with the high sensitivity and portability of a QCM sensor. The parameters in the fabrication and measurement process were optimized and discussed in detail. It was verified that the MIP-modified QCM Au chip performed favorably for the detection of ENRO residue in common animal-derived food products and demonstrated acceptable accuracy (recovery: pure milk 77.2–84.2%, egg 77.3–85.6%, chicken muscle 73.5–89.1%, pork 74.7–85.8%), precision (relative standard deviation (RSD, n = 3), pure milk 2.9–8.0%, egg 2.9–6.4%, chicken muscle 3.4–6.8%, pork 2.2–4.7%), and sensitivity (limit of detection, pure milk 0.31 μg L^?1, egg 0.44 μg kg^?1, chicken muscle 0.54 μg kg^?1, pork 0.57 μg kg^?1). The MIP-modified QCM Au chip for sensing ENRO was portable, could be stored for an extended period of time, and reused for more than 30 analysis cycles with a response attenuation of 7.8%. These results have demonstrated that the proposed MIP QCM sensor presents an accurate, sensitive, rapid, and low-cost methodology for ENRO residue detection in animal foods. This research is very promising for the development of novel effective devices applied to the detection of various contaminants in the field of food safety.     

Volatile Constituents of Jambolan (<Emphasis Type="Italic">Syzygium cumini</Emphasis> L.) Fruits at Three Maturation Stages and Optimization of HS-SPME GC-MS Method Using a Central Composite Design

The volatile compounds of jambolan (Syzygium cumini L.) fruit were determined at three different maturity stages (unripe, half-ripe, and ripe) by headspace solid-phase microextraction (HS-SPME)–gas chromatography-mass spectrometry (GC-MS) technique using five different fibers (Fused silica PDMS/DVB, DVB/CAR/PDMS, PEG, Stable flex PDMS/DVB, and PDMS). The optimal extraction conditions were evaluated using different variables such as adsorption temperature (minimum 25 °C, maximum 55 °C), salt quantity (minimum 0, maximum 30.0%), and extraction time (min 10, max 30 min). The major classes of compounds identified were ester, terpene, alcohol, aldehyde, and carboxylic acid. Ninety volatile compounds with characteristics aroma attributes were identified, and the primary compounds linked with development of characteristics aroma of ripe jambolan fruit pulp were trans-β-ocimene, β-ocimene, caryophyllene, humulene, D-α-pinene, L-β-pinene, β-pinene, D-limonene, α-terpineol, neo-allo-ocimene, 2-hexenal (E), δ-cadinene, 3-hexen-1-ol, (Z) β-linalool, terpinolene, eremophilene, valencene, 1-hexanol, longipinene, γ-terpinene, γ-muurolene, endo-borneol, o-cymene, nonanal, terpinen-4-ol, β-terpineol, α-muurolene, fenchol, α-fenchene, β-thujene, benzaldehyde, (E)-2-hexenal, β-cadinene, and decanal.