Nondestructive Prediction of Tilapia Fillet Freshness During Storage at Different Temperatures by Integrating an Electronic Nose and Tongue with Radial Basis Function Neural Networks

This study developed principal component analysis and radial basis function neural networks (PCA-RBFNNs) for predicting freshness in tilapia fillets stored at different temperatures by integrating an electronic nose and electronic tongue. Total volatile basic nitrogen (TVB-N), total aerobic counts (TAC), and K value increased at 0, 4, 7, and 10 °C, while sensory scores decreased significantly. The electronic nose and tongue acquired the volatiles and dissolved chemical compounds in the stored samples. Gas chromatography-mass spectrometry (GC-MS) verified the changes in gas species and contents in fillets stored for different periods of time at different temperatures. PCA-RBFNNs based on data fusion were developed and presented good performance for prediction of TVB-N, TAC, K value, and sensory score in tilapia fillets. The established PCA-RBFNNs based on feature variables of the electronic nose and tongue is a promising method to predict changes in the freshness of fillets stored from 0 to 10 °C in the cold chain.     

Detection of Viable <Emphasis Type="Italic">Vibrio cholerae</Emphasis> Cells in Seafood Using a Real-Time Visual Loop-Mediated Isothermal Amplification Combined with Propidium Monoazide

Vibrio cholerae is an important foodborne pathogen causing severe intestinal infectious diseases that have high incidence and mortality. Almost all of rapid testing methods including immunological and molecular assays for V. cholerae are incapable of distinguishing live cells from dead ones, which may overestimate the number of bacteria and result in many false positive results. To address the problems, live cell-specific dye such as propidium monoazide (PMA) is employed. The loop-mediated isothermal amplification (LAMP) assay is a nucleic acid amplification method that is fast, specific, and sensitive. In this study, we developed a real-time visual LAMP assay using PMA dye to detect thyA gene, thereby identifying viable V. cholerae cells. The results showed that only V. cholarae strains could be detected, and there was no cross-reaction with non-V. cholarae strains. Besides, the sensitivity of the PMA-LAMP assay was 1.1 × 10² CFU/mL and the entire reaction could be accomplished within 1 h. The sensitivity was on par with that of the PMA-qPCR assay. The detection limit in different artificially inoculated samples was 5 CFU/25 g materials for the tested pathogens. In the practical test, the PMA-LAMP assay performed well in comparison with PMA-qPCR and the culture method. Hence, PMA-LAMP assay can provide a highly effective and rapid approach for detecting viable V. cholerae.     

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.