Investigation of low-temperature partitioning with dispersive solid-phase extraction for quantification of pesticides in apples followed by electrospray-ionization mobility spectrometry: Comparison with conventional procedure.

Ion mobility spectrometry (IMS) has a promising application prospect in food surveillance. However, due to the complexity of food matrix and trace levels of pesticide residues, the effective and rapid detection of pesticides by IMS has been a challenge, especially when using electrospray ionization (ESI) as an ion source. In this study, low-temperature partitioning with dispersive solid-phase extraction (LTP-dSPE) was explored and compared with conventional procedures. Both methods were validated for the quantification of eight pesticides in apples, obtaining a limit of detection (LOD) of 0.02-0.12 mg/kg for LTP-dSPE and 0.02-0.09 mg/kg for conventional solid-phase extraction (SPE), lower than those usually stipulated by government legislation in food matrices. For LTP-dSPE, the matrx effect (ME) ranged from -16.3 to -68.6 %, lower than that for the SPE method, ranging from -70.0 to -92.9 %. The results showed satisfactory efficiency and precision, with recovery values ranging from 67.9 to 115.4 % for LTP-dSPE and from 62.0 to 114.8 % for conventional SPE, with relative standard deviations below 13.0 %. Notably, the proposed LTP-dSPE/ESI-IMS has been shown to be more cost-effective, easier to use, more environment-friendly, more accessible, and, most importantly, less matrix effect than the conventional method, thereby being suitably applicable to a wide range of food safety applications.

Implementing of Fourier Deconvolution Multiplexing to Fast Polarity Switching Miniaturized Ion Mobility Spectrometer.

Ion mobility spectrometry (IMS) is a reliable and sensitive technique for the detection and analysis of compounds at the trace level. Depending on the chemical composition of the sample, compounds may be positively or negatively charged to form different polarity ions and detected in positive or negative polarity of the electric field. In order to detect multiple threats simultaneously with miniaturized devices, using a single detection unit to achieve high resolving power and high sensitivity is important. In this work, a miniaturized drift tube with fast polarity switching capabilities integrated with Fourier deconvolution multiplexing techniques is proposed for the first time as a means to improve the performance of ion mobility spectrometry. The sensitivity and resolving power are improved compared to traditional polarity switching signal averaging data acquisition methods. The displayed device had a high resolving power up to 52 at a drift length of 41 mm and a drift tube voltage of 2 kV. Trinitrotoluene (TNT), methamphetamine (MA), benzene, toluene, methyl tert-butyl ether (MTBE), acetic acid, and methylene chloride were evaluated using the proposed fast polarity switching multiplexing spectrometer and exhibited satisfied performance.

Target-activated multivalent sensing platform for improving the sensitivity and selectivity of Hg2+ detection.

Sensitivity and selectivity are critical parameters to evaluate the performance of sensors. For trace detection, it remains a challenge to design a new sensor that achieves high sensitivity and selectivity simultaneously. Here, we present a target-activated dual Mg2+-dependent DNAzyme (MNAzyme) that served as a simple sensing model to explore the multivalency in improving the analytical sensitivity and selectivity for target detection. Mercury ion (Hg2+), a notorious toxic metal ion, was selected as a model target. In the presence of Hg2+, the thymine-rich regions of the hairpin probe and primer could hybridize to form a stable duplex via the thymine-Hg2+-thymine structure. Then, an intact enzyme sequence was exposed and two separate enzyme fragments were close to each other, generating a dual MNAzyme. Benefiting from the localized high-concentration of the enzyme strand, the dual MNAzyme showed a remarkable improvement in binding stability. The catalytic rate constant of the dual MNAzyme was theoretically 1.60 times higher than that of the monomeric counterpart, and the sensitivity and selectivity had 4.50 and 1.44-fold enhancement, respectively. When the dual MNAzyme was used for sensor applications, the limit of detection was determined to be 0.04 and 0.2 nM via UV-vis spectrophotometer and naked eye, respectively. Meanwhile, the method offered desirable selectivity toward Hg2+ against other metal ions. With the advantages of simple operation, high sensitivity, and desirable selectivity, the developed multivalent sensing platform could be easily expanded in the future for the on-site detection of other low-abundance analytes.

Influences of repeated exposure to low levels of TiO2 nanoparticles on Kruppel-like factors in 3D Caco-2 spheroids and mouse intestines.

Kruppel-like factors (KLFs) are a set of transcription factors (TFs) involved in the regulation of many basic biological processes, and recent studies suggested that nanoparticles (NPs) were capable to change KLFs in different models even at non-cytotoxic concentrations. In this study, we repeatedly exposed 3D Caco-2 spheroids and mice to TiO2 NPs, one of the most frequently used metal oxide NPs, and investigated the changes of KLF-signaling pathways based on RNA-sequencing. Although the internalization of TiO2 NPs did not induce cytotoxicity in vitro, repeated exposure (three times within 7 days) to 15.7 ng/ml TiO2 NPs increased KLF4 but decreased KLF6. Consistently, KLF4/KLF6-regulated gene ontology terms were altered, including those involved in the regulation of gene expression. We further verified that repeated exposure to 15.7 ng/ml TiO2 NPs increased the expression of KLF4 and proto-oncogene, bHLH transcription factor (MYC), but decreased the expression of KLF6 and activating transcription factor 3 (ATF3). But with the increase of NP concentrations, the expression of these genes was decreased. In mice following intragastrical exposure to 4.39 and 43.9 mg/kg TiO2 NPs (once a day for 5 continuous days), we observed increased expression of klf4, klf6, myc, and atf3, along with morphological changes of intestines. We concluded that repeated exposure to low levels of TiO2 NPs altered KLF-signaling pathways in intestinal cells both in vitro and in vivo.

Colorimetric aptasensor for the sensitive detection of ochratoxin A based on a triple cascade amplification strategy.

Ochratoxin A(OTA), a highly toxic mycotoxin commonly found in food, poses a serious threat to health even at low concentrations. Developing a sensitive, accurate, simple, and cost-effective detection method is of great significance for food safety and quality control. Herein, a triple cascade amplification strategy was used to construct the colorimetric assay for the detection of OTA, where the amplification process consists of an entropy-driven DNA circuit (EDC), a catalytic hairpin assembly (CHA), and Mg2+-assisted DNAzyme catalysis (MNAzyme). Through the specific binding of ochratoxin A (OTA) and its aptamer, an initiator strand is released to initiate upstream EDC and then produce a new trigger unit that motivates downstream CHA to generate MNAzyme, which further cleaves the substrate strand to induce the formation of G-quadruplex/hemin DNAzyme as a signal readout. The aptasensor was shown to detect OTA, with a low detection limit of 8.7 fM and good selectivity. The developed method could be used as a highly colorimetric aptasensor for the detection of OTA in spiked rice samples.

Quantitative determination of major alkaloids in areca nut products by high-performance liquid chromatography coupled with ion mobility spectrometry.

Areca nut is a popular and addictive food as well as a traditional herbal medicine in many countries. Areca nut contains alkaloids including arecoline, guvacine, and arecaidine, which are the major bioactive compounds in areca products. Areca alkaloids can be carcinogenic, and thus sensitive and specific analytical methods are urgently desired for the identification and quantification of these compounds. High-performance liquid chromatography-based methods are often preferred, but areca alkaloids do not have chromophores, and detection using a traditional UV detector can be difficult. The complexity of areca sample extracts can also lead to the co-elution of peaks leading to poor quantitative performance. We report here high-performance liquid chromatography coupled with an ion mobility spectrometer for sensitive determination of areca alkaloids in various products including areca nut, areca nut products, and herbal oral liquid. An X-Bridge reversed-phase C18 column was used in the experiment and was combined with high-performance liquid chromatography coupled to an ion mobility spectrometer system. A custom-made adjustable post-column splitter acted as an interface between the high-performance liquid chromatography and the ion mobility spectrometer; it also acted as the electrospray ionization source. The mobile phase was methanol and 0.5% ammonium hydroxide. The results demonstrate that the splitter can afford a wide range of split ratios that match the ion mobility spectrometer ionization source while keeping the separation efficiency of high-performance liquid chromatography. Three major alkaloid compounds were then accurately determined using the resulting method without dativization steps. Many coeluted high-performance liquid chromatography peaks are effectively separated in the ion mobility spectrometer dimension, which in turn improved the quantification accuracy.

Miniaturized Photo-Ionization Fourier Deconvolution Ion Mobility Spectrometer for the Detection of Volatile Organic Compounds.

Because of its simplicity, reliability, and sensitivity, the drift tube ion mobility spectrometer (IMS) has been recognized as the equipment of choice for the on-site monitoring and identification of volatile organic compounds (VOCs). However, the performance of handheld IMS is often limited by the size, weight, and drift voltage, which heavily determine the sensitivity and resolving power that is crucial for the detection and identification of VOCs. In this work, we present a low-cost, miniaturized drift tube ion mobility spectrometer incorporated with a miniaturized UV ionization lamp and a relatively low drift voltage. The sensitivity and resolving power are boosted with the implementation of Fourier deconvolution multiplexing compared to the conventional signal averaging data acquisition method. The drift tube provides a high resolving power of up to 52 at a drift length of 41 mm, 10 mm ID dimensions, and a drift voltage of 1.57 kV. Acetone, benzene, dimethyl methyl phosphonate, methyl salicylate, and acetic acid were evaluated in the developed spectrometer and showed satisfactory performance.

Fourier Deconvolution Ion Mobility Spectrometry.

Multiplexing the ion packet injection with advanced signal processing is an effective method to improve both the ion throughput and signal-to-noise ratio for ion mobility spectrometry. Generally used multiplexing methods include Hadamard transform ion mobility spectrometry (HT-IMS), Fourier transform ion mobility spectrometry (FT-IMS), and correlation ion mobility spectrometry (C-IMS). However, HT-IMS sometimes suffer from false peaks and further processing is needed, FT-IMS generally requires longer spectra acquisition time than the traditional signal averaging method, and C-IMS also demonstrated drawbacks such as spectra baseline distortions when using traditional on-off binary gating switches. To improve the performance of multiplexing ion mobility spectrometry, this study investigates the Fourier deconvolution to increase the resolving power and signal-to-noise ratio at the same time. This approach modulates the ion gate with a linear square wave chirp sequence and synchronizes the data acquisition and ion gate modulation and then reconstructs the ion mobility spectra based on convolution theorems. The equivalent ion injection period is decreased to microseconds scale with the signal-to-noise ratio improved by up to 13 times on average, and the resolving power is improved by up to 50% compared with traditional signal averaging methods without hardware modifications.

Simulating, Predicting, and Minimizing False Peaks for Hadamard Transform Ion Mobility Spectrometry.

Multiplexing techniques, including the Hadamard transform, are widely used in the recovery of weak signals from high-level noise. Hadamard transform ion mobility spectrometry (HT-IMS), however, can suffer serious drawbacks due to false peaks. False peaks in HT-IMS are generally attributed to nonperfect gating behavior. This paper confirmed that the origin of false peaks in HT-IMS is not generally due to ion gating but rather to peak shifts by Coulombic repulsion of the ion packets inside the drift tube. The amplitudes of these false peaks are determined by the number of ions inside the ion packets. This phenomenon is simulated and confirmed by the convolution of the spectrum with a shifted s-sequence to reproduce the artifact peaks with the exact position, amplitude, and profile. Two approaches, including preoffset sequence modulation and post-data processing, were evaluated to mitigate the false peaks in HT-IMS, and both methods can work effectively.

Antifungal mechanism of sodium dehydroacetate against Geotrichum citri-aurantii.

This study investigated the potential anti-fungal mechanisms of sodium dehydroacetate (SD) against Geotrichum citri-aurantii. The results showed that the cell wall integrity of G. citri-aurantii was not affected, whereas the membrane permeability of G. citri-aurantii mycelia was visibly altered by SD. Dramatic morphological changes of the mycelia, such as loss of cytoplasm, plasmolysis, and dissolution of intracellular substances, were observed by scanning electron microscopy and transmission electron microscopy analyses, indicating that the mycelium is severely damaged by the SD treatment. Furthermore, SD apparently induced a decrease in the intracellular ATP content before 30 min of exposure. An increase in the activity of the Na+/K+-ATPase was also observed, indicating that Na+ ions might enter the cell and thus disturb the energy supply. Taken together, this study's findings suggest that the anti-fungal activity of SD against G. citri-aurantii can be attributed to the disruption of cell membrane permeability and energy metabolism.

The effect of carbamic acid, (1,2,3-thiadiazole-4-ylcarbonyl)-hexyl ester on Peronophythora litchii infection, quality and physiology of postharvest litchi fruits.

BACKGROUND: Litchi (Litchi chinensis Sonn.) is a subtropical fruit with attractive characteristic of white to creamy semitranslucent flesh and red color in pericap, but it was easily subjected to the infection of Peronophythora litchii and lost its market values. Experiments were conducted to understand the effect of [Carbamic acid, (1,2,3-thiadiazole-4-ylcarbonyl)-hexyl ester, CTE] on the growth of P. litchi and quality properties in litchi fruits during postharvest storage. RESULTS: In vitro experiments, CTE with minimum inhibitory concentration (MIC, 5 mg/L) and minimum fungicidal concentration (MFC, 10 mg/L) were against the growth of P. litchi for 2 and 4 days, respectively, and SEM results showed that hyphae of P. litchii shrank, distorted and collapsed after CTE treatment. In vivo experiments, CTE treatment inhibited the increase of disease incidence, browning index, weight loss and PPO activity in non-P. litchii-inoculated fruits, meanwhile the treatment markedly inhibited the decrease of color characteristic (a*, b* and L*), anthocyanin content, phenolic contents, Vc content and POD activity, but TSS content was not significantly influenced during storage. In P. litchii-inoculated fruits, all these above mentioned parameters in CTE treated fruits were significantly higher than that in control fruits, but anthocyanin content, Vc, TSS and TA content did not have consistent differences between control and CTE treated fruits at the end of storage. CONCLUSION: CTE treatment reduced the disease incidence and browning index of litchi fruits, maintained the fruits quality and, thus, it could be an effective postharvest handling to extend the shelf life of litchi fruits during storage.

Transcriptional profiling analysis of Penicillium digitatum, the causal agent of citrus green mold, unravels an inhibited ergosterol biosynthesis pathway in response to citral.

BACKGROUND: Green mold caused by Penicillium digitatum is the most damaging postharvest diseases of citrus fruit. Previously, we have observed that citral dose-dependently inhibited the mycelial growth of P. digitatum, with the minimum inhibitory concentration (MIC) of 1.78 mg/mL, but the underlying molecular mechanism is barely understood. RESULTS: In this study, the transcriptional profiling of the control and 1/2MIC-citral treated P. digitatum mycelia after 30 min of exposure were analyzed by RNA-Seq. A total of 6355 genes, including 2322 up-regulated and 4033 down-regulated genes, were found to be responsive to citral. These genes were mapped to 155 KEGG pathways, mainly concerning mRNA surveillance, RNA polymerase, RNA transport, aminoacyl-tRNA biosynthesis, ABC transporter, glycolysis/gluconeogenesis, citrate cycle, oxidative phosphorylation, sulfur metabolism, nitrogen metabolism, inositol phosphate metabolism, fatty acid biosynthesis, unsaturated fatty acids biosynthesis, fatty acid metabolism, and steroid biosynthesis. Particularly, citral exposure affected the expression levels of five ergosterol biosynthetic genes (e.g. ERG7, ERG11, ERG6, ERG3 and ERG5), which corresponds well with the GC-MS results, the reduction in ergosterol content, and accumulation of massive lanosterol. In addition, ERG11, the gene responsible for lanosterol 14α-demethylase, was observed to be the key down-regulated gene in response to citral. CONCLUSION: Our present finding suggests that citral could exhibit its antifungal activity against P. digitatum by the down-regulation of ergosterol biosynthesis.

Citral exerts its antifungal activity against Penicillium digitatum by affecting the mitochondrial morphology and function.

This work investigated the effect of citral on the mitochondrial morphology and function of Penicillium digitatum. Citral at concentrations of 2.0 or 4.0 µL/mL strongly damaged mitochondria of test pathogen by causing the loss of matrix and increase of irregular mitochondria. The deformation extent of the mitochondria of P. digitatum enhanced with increasing concentrations of citral, as evidenced by a decrease in intracellular ATP content and an increase in extracellular ATP content of P. digitatum cells. Oxygen consumption showed that citral resulted in an inhibition in the tricarboxylic acid cycle (TCA) pathway of P. digitatum cells, induced a decrease in activities of citrate synthetase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, succinodehydrogenase and the content of citric acid, while enhancing the activity of malic dehydrogenase in P. digitatum cells. Our present results indicated that citral could damage the mitochondrial membrane permeability and disrupt the TCA pathway of P. digitatum.

Influence of α-terpineol on the growth and morphogenesis of Penicillium digitatum.

BACKGROUND: Plant essential oils could act effectively against postharvest diseases, α-terpineol, a typical terpenoid of plant essential oils, exhibited strong antifungal activity in against Penicillium italicum, but the possible action mechanism remains undetermined. In present study, α-terpineol was evaluated for antibacterial activity against Penicillium digitatum along with the mode of their antibacterial action. RESULTS: The results showed that mycelial growth of P. digitatum was strongly inhibited by α-terpineol, with the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 2.00 and 8.00 µl/ml, respectively. Scanning electron microscopy observation revealed that α-terpineol obviously altered the morphology of P. digitatum hyphae by causing the loss of cytoplasm and distortion of mycelia. A rapid increase in the membrane permeability of P. digitatum was observed after treated with MIC or MFC of α-terpineol, evidenced by the release of cell constituents, the extracellular conductivity, and the extracellular pH. In addition, α-terpineol apparently induced a decrease in total lipid contents of P. digitatum cells, indicating the destruction of cell membrane structures after treatment. CONCLUSIONS: Based on our study, α-terpineol might affect the cell wall synthesis and lead to the disruption of cell wall. The cell wall disruption affected fungal morphogenesis, the integrity of membrane and leakage of intracellular components, these results suggested that α-terpineol treatment inhibited the growth of P. digitatum.

Effect of pyrogallol on the physiology and biochemistry of litchi fruit during storage.

BACKGROUND: Litchi (Litchi chinensis Sonn.) fruit are highly perishable and have a very short shelf life, easily turning brown and decaying. This study investigated the efficiency of pyrogallol, a catechin on the physiology and biochemistry in relation to storage life of litchi fruit. RESULTS: Fruit were treated with pyrogallol at 1 mM and then stored at ambient temperature (25°C) or low temperature (4°C). Compared with control, pyrogallol significantly reduced pericarp browning and delayed the rotting of fruit day 4 at 25°C, and on day 30 at 4°C. The chemical treatment reduced respiration rate and the activities of peroxidase (POD) and polyphenol oxidase (PPO), and delayed the loss of membrane permeability. Pyrogallol increased the activity of phenylalanine ammonia-lyase (PAL), delayed the loss of anthocyanin and phenolics, and maintained high 2,2-diphenyl-1-picrlhydrazyl (DPPH) radical scavenging activity and reducing power. High performance liquid chromatograph (HPLC) analysis clearly indicated that treated fruit contained higher concentration of the four phenolic compounds procyanidin B1, (+)-catechin, (-)-epicatechin and (-)-epicatechin-3-gallate. CONCLUSIONS: The application of pyrogallol partially reducing pericarp browning and changed quality-related physiological activities and, thus, pyrogallol could have beneficial effects on pericarp browning and fruit decay control, and could be helpful for litchi fruit postharvest storage.

Integrated application of nitric oxide and modified atmosphere packaging to improve quality retention of button mushroom (Agaricus bisporus).

Button mushrooms (Agaricus bisporus) were dipped for 10min in different concentrations (0.5, 1, and 2mM) of 2,2'-(hydroxynitrosohydrazino)-bisethanamine (DETANO), a nitric oxide donor, then packed in biorientated polypropylene (BOPP) bags, heat sealed and stored at 4°C for 16days (d). Mushroom weight loss, firmness, colour, percent open caps, total phenolics, ascorbic acid and H2O2 contents, superoxide anion (O2(-)) production rate and activities of polyphenol oxidase (PPO), superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) were measured. The results indicate that treatment with 1mM DETANO maintained a high level of firmness, delayed browning and cap opening, promoted the accumulation of phenolics, ascorbic acid and reduced the increases in both O2(-) production rate and H2O2 content. Furthermore, NO inhibited the activity of PPO, and increased the antioxidant enzymes activities of CAT, SOD and APX throughout storage period. Thus it was observed that application of NO in combination with modified atmosphere packaging (MAP) can extend the storage life of button mushroom up to 12d.