Effect-directed analysis in food by thin-layer chromatography assays

Advances in mycotoxin detection techniques and the crucial role of reference material in ensuring food safety. A review

Mycotoxins, toxic secondary metabolites produced by fungi, pose a significant threat to food safety and human health. The occurrence of mycotoxins in food commodities necessitates accurate and reliable detection methods. Advanced detection techniques, such as chromatographic techniques and immunochemical assays, have improved sensitivity and specificity. However, the lack of standardized reference material, particularly in less privileged countries, hinders method validation and proficiency testing, ultimately affecting mycotoxin testing and regulation. Moreover, these techniques are complex as they require specialized equipment, and well-trained personnel, thus limiting their practical applications. This comprehensive review provides an up-to-date overview of the occurrence of mycotoxins and recent advancements in detection methods. It examines the crucial role of mycotoxin standards as reference materials for ensuring reliable results in mycotoxins analysis in agriculture commodities. The review addresses emerging challenges, knowledge gaps, and future research directions in mycotoxin detection and reference material development. By synthesizing existing literature, this review aims to provide valuable resources for researchers, policymakers, and other stakeholders in food safety, highlighting the importance of integrated approaches to mitigate mycotoxin contamination and ensuring food safety.

Recent advances in the analytical methods for quantitative determination of antioxidants in food matrices

Antioxidants are crucial in reducing oxidative stress and enhancing health, necessitating precise quantification in food matrices. Advanced techniques such as biosensors and nanosensors offer high sensitivity and specificity, enabling real-time monitoring and accurate antioxidant quantification in complex food systems. These technologies herald a new era in food analysis, improving food quality and safety through sophisticated detection methods. Their application facilitates comprehensive antioxidant profiling, driving innovation in food technology to meet the rising demand for nutritional optimization and food integrity. These are complemented by electrochemical techniques, spectroscopy, and chromatography. Electrochemical methods provide rapid response times, spectroscopy offers versatile chemical composition analysis, and chromatography excels in precise separation and quantification. Collectively, these methodologies establish a comprehensive framework for food analysis, essential for improving food quality, safety, and nutritional value. Future research should aim to refine these analytical methods, promising significant advancements in food and nutritional science.

New semisynthetic α-glucosidase inhibitor from a doubly-chemically engineered extract

Chemically engineered extracts represent a promising source of new bioactive semi-synthetic molecules. Prepared through direct derivatization of natural extracts, they can include constituents enriched with elements and sub-structures that are less common in natural products compared to drugs. Fourteen such extracts were prepared through sequential reactions with hydrazine and a fluorinating reagent, and their α-glucosidase inhibition properties were compared. For the most bioactive mixture, a chemically modified propolis extract, enzyme inhibition increased 22 times due to the reaction sequence. Bio-guided fractionation led to the isolation of a new fluorinated pyrazole produced within the extract by chemical transformation of the flavonoid chrysin. The inhibitor results from the action of the two reagents used on four common functional groups present in natural products (carbonyl, phenol, aromatic carbon, and a double bond). The reactions led to the opening of a 6-member oxygenated heterocycle to produce a 5-member nitrogenated one, as well as the dehydroxylation and fluorination in two different positions of one of the aromatic rings of the natural starting material, all within a complex mixture of natural products. Overall, these transformations led to an approximately 20-fold increase in the α-glucosidase inhibition by the isolated inhibitor compared to its natural precursor.

A Cu/β-cyclodextrin/reduced graphene oxide nanocomposite for efficient and multi-aflatoxin detection in rice, ginger and bean samples

Aflatoxins (AFs) are some of the most important mycotoxins or fungal toxins that cause contamination of food products and are considered a threat to human and animal health. An efficient Cu/β-cyclodextrin/reduced graphene oxide nanocomposite (Cu/β-CD/rGO) has been prepared and applied as a new solid-phase extraction adsorbent for the separation and preconcentration of four AFs (B1, B2, G1, and G2) using high-performance liquid chromatography with fluorescence detection (HPLC-FLD). The successful synthesis of the prepared nanocomposite was confirmed using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The impacts of pH, amount of adsorbent, sample volume, desorption solvent volume, and salt concentration on the recovery of AFs were precisely investigated and optimized by central composite design (CCD). Under the optimal conditions, the introduced method demonstrated good linearity in the range of 0.4-5.4, 0.08-1.08, 0.4-5.4, and 0.08-1.08 ng g-1 for AFs B1, B2, G1 and G2, respectively. The limits of detection and quantification for the four AFs were obtained in the range of 0.06-0.53 and 0.20-1.62 ng g-1, respectively. The accuracy of the method was evaluated using recovery measurements in spiked real samples such as rice, bean, and ginger samples, and satisfactory recoveries were obtained in the range of 83.5-109.0% with good precision (RSDs between 2.4 and 8.6%). The results of this research revealed that our developed method is sensitive, highly effective, and convenient to perform for the trace analysis of AFs in different real samples.

Biosynthesis of Feruloyl Glycerol from Ferulic Acid and Glycerol Through a Two-Enzyme Cascade Reaction

Feruloyl glycerol (FG) has a variety of biological activities, but the green synthesis methods of FG remain rare. In this study, FG was prepared by a cascade reaction catalyzed by 4-coumarate coenzyme A ligase (4CL) and hydroxycinnamoyl acyltransferase 4 (HCT4). The cascade reaction carried out at solvent water and room temperature is more convenient and greener. Firstly, the product derived from the cascade reaction was characterized by TLC, HPLC, FTIR, and ESI-MS. The results showed that the product was FG. Secondly, the effects of temperature, pH, enzyme ratio, Mg2+ concentration, and CoA concentration on the cascade reaction were investigated. Consequently, the highest reaction rate was obtained at 30 °C, pH 6, an enzyme ratio of 1:3, and Mg2+ concentration of 5 mM. Finally, semi-preparative scale synthesis for FG was conducted. The production of FG reached 35.1 mM at 24 h with the FG conversion of 70.18%. In a word, a novel idea for the efficient and green synthesis of FG was proposed, which had great potential for industrial application.

Green Recovery and Identification of Antioxidant and Enzyme Inhibitor Molecules from Pisco Grape Pomace by Targeted Effects Analysis Using Thin-Layer Chromatography, Bioassay, and Mass Spectrometry

The search and identification of inhibitory molecules from novel natural sources, such as pisco grape pomace extract obtained by green techniques, may help to develop agents with therapeutic potential that are beneficial to health with fewer adverse effects than drugs. Many drugs act as enzyme inhibitors, decreasing their activity and thus correcting a metabolic imbalance. This study aims to identify bioactive molecules with antioxidant and inhibitory activity over acetylcholinesterase and cyclooxygenase enzymes present in pisco grape pomace green extracts. Bioactive molecules were detected and identified applying directed effect analysis on planar chromatography coupled to mass spectrometry. For the first time, the presence of antioxidant molecules (quercetin-3-O-glucuronide, quercetin-3-O-glucoside, and gallic acid) and inhibitors of acetylcholinesterase (kaempferol-3-O-glucoside) and cyclooxygenase (gallic acid) enzymes are reported in pisco grape pomace. According to the results, grape pomace could be an alternative to develop novel functional foods and nutraceuticals that provide health benefits and, at the same time, generate a circular economy in the industry.

A simple thin-layer chromatography autography for the detection of peroxidase inhibitors

Thin layer chromatography bioautographic assays facilitate the acquisition of activity-profile chromatograms and assist in pinpointing active constituents within complex mixtures by observing the inhibition halos they produce. Peroxidase is an enzyme implicated in the browning of different fresh cut vegetables and in several diseases. A peroxidase bioautographic assay was developed, based on enzyme agarose immobilization and the 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt/radical cation (ABTS/ABTS·+) reporter system. Peroxidase was purified from potatoes with the aim to detect specific inhibitors. To reduce false positives, a non-enzymatic assay was also employed. The best results are obtained when a solution containing agarose, ABTS, hydrogen peroxide, and peroxidase in phosphate buffer is poured over the TLC plate (final concentrations: 0.031 mmoles/cm2, 0.239 µmoles/cm2, and 84.04 U/cm2) and incubated for 70 min. Limit of detection and quantification for quercetin is 0.16 µg and 0.54 µg, respectively. The developed system is able to detect quercetin in a Solidago chilensis Meyen extract and a peroxidase inhibitor in a Cichorium intybus L. extract. Therefore, the assay can detect inhibitory constituents in complex mixtures and differentiate between peroxidase inhibitors and ABTS·+ radical scavengers before any preparative fractionation, helping to take early operational decisions that can save time and resources.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-024-05946-w.

Chemically engineered essential oils prepared through thiocyanation under solvent-free conditions: chemical and bioactivity alteration

The generation of chemically engineered essential oils (CEEOs) prepared from bi-heteroatomic reactions using ammonium thiocyanate as a source of bioactive compounds is described. The impact of the reaction on the chemical composition of the mixtures was qualitatively demonstrated through GC-MS, utilizing univariate and multivariate analysis. The reaction transformed most of the components in the natural mixtures, thereby expanding the chemical diversity of the mixtures. Changes in inhibition properties between natural and CEEOs were demonstrated through acetylcholinesterase TLC autography, resulting in a threefold increase in the number of positive events due to the modification process. The chemically engineered Origanum vulgare L. essential oil was subjected to bioguided fractionation, leading to the discovery of four new active compounds with similar or higher potency than eserine against the enzyme. The results suggest that the directed chemical transformation of essential oils can be a valuable strategy for discovering new acetylcholinesterase (AChE) inhibitors.

Expanding Chemical Frontiers: Approaches for Generating Diverse and Bioactive Natural Product-Like Compounds Libraries from Extracts

The realms of natural products and synthetic compounds exhibit distinct chemical spaces that not only differ but also complement each other. While the convergence of these two domains has been explored through semisynthesis and conventional pharmacomodulation endeavours applied to natural frameworks, a recent and innovative approach has emerged that involves the combinatorial generation of libraries of 'natural product-like compounds' (NPLCs) through the direct synthetic derivatization of natural extracts. This has led to the production of numerous NPLCs that incorporate structural elements from both their natural (multiple saturated rings, oxygen content, chiral centres) and synthetic (aromatic rings, nitrogen and halogen content, drug-like properties) precursors. Through careful selection of extracts and reagents, specific bioactivities have been achieved, and this strategy has been deployed in various ways, showing great promise without reaching its full potential to date. This review seeks to provide an overview of reported examples involving the chemical engineering of extracts, showcasing a spectrum of natural product alterations spanning from simple substitutions to complete scaffold remodelling. It also includes an analysis of the accomplishments, perspectives and technical challenges within this field.

Reversible polarity-switch of thin-layer chromatography by photo-induction with multi-regulation in spatial dimension

Generally, thin-layer chromatography always undertakes the indispensable role in rapid screening and identification of specific compounds. Stationary phase is the core part of thin-layer chromatography with fixed property, which leading to the limitations of separation mode of only regulating the composition of mobile phase. This work was an attempt to fabricate the unique photosensitive thin-layer chromatography to make up the above major drawback. 4-[3-(Triethoxysilyl)propoxy]azobenzene (azo-PTES) was synthesized as photosensitive modifier to fabricate the photosensitive stationary phase, and the transformation of cis-trans structure of azo-PTES proceeds along with polarity difference under 365 nm and 473 nm irradiation. Based on this, the proposed photosensitive thin-layer chromatography shows the reversible switch of polarity of stationary phase by photoinduction, followed by the deserved reversible separation behavior. Furthermore, multi-regulation in spatial dimension was achieved based on the high freedom of spatial regulation of photoinduction, which brings about the integration of stationary phase with different polarity, just by photoinduction. The concept of photosensitive thin-layer chromatography provides new idea for improving separation efficiency and developing multi-dimensional thin-layer chromatography on the one plate.

Application of effect-directed analysis using TLC-bioautography for rapid isolation and identification of antidiabetic compounds from the leaves of Annona cherimola Mill

INTRODUCTION

Type 2 diabetes mellitus is a globally prevalent chronic disease characterised by hyperglycaemia and oxidative stress. The search for new natural bioactive compounds that contribute to controlling this condition and the application of analytical methodologies that facilitate rapid detection and identification are important challenges for science. Annona cherimola Mill. is an important source of aporphine alkaloids with many bioactivities.

OBJECTIVE

The aim of this study is to isolate and identify antidiabetic compounds from alkaloid extracts with α-glucosidase and α-amylase inhibitory activity from A. cherimola Mill. leaves using an effect-directed analysis by thin-layer chromatography (TLC)-bioautography.

METHODOLOGY

Guided fractionation for α-glucosidase and α-amylase inhibitors in leaf extracts was done using TLC-bioassays. The micro-preparative TLC was used to isolate the active compounds, and the identification was performed by mass spectrometry associated with web-based molecular networks. Additionally, in vitro estimation of the inhibitory activity and antioxidant capacity was performed in the isolated compounds.

RESULTS

Five alkaloids (liriodenine, dicentrinone, N-methylnuciferine, anonaine, and moupinamide) and two non-alkaloid compounds (3-methoxybenzenepropanoic acid and methylferulate) with inhibitory activity were isolated and identified using a combination of simple methodologies. Anonaine, moupinamide, and methylferulate showed promising results with an outstanding inhibitory activity against both enzymes and antioxidant capacity that could contribute to controlling redox imbalance.

CONCLUSIONS

These high-throughput methodologies enabled a rapid isolation and identification of seven compounds with potential antidiabetic activity. To our knowledge, the estimated inhibitory activity of dicentrinone, N-methylnuciferine, and anonaine against α-glucosidase and α-amylase is reported here for the first time.

An electrochemical immunosensor based on a carboxylated multiwalled carbon nanotube-silver nanoparticle-chitosan functional layer for the detection of fipronil

Fipronil (FP) is a very effective phenylpyrazole insecticide and is now widely used in agriculture. At the same time, the water and soil in the environment are polluted by FP. For the rapid detection of FP toxicants in food and the environment, we have designed an entirely novel electrochemical immunosensor that employs the combined functionalities of a cMWCNTs-AgNPs-CS-FAb-BSA layer to modify an SPCE by the freeze-drying technique. The high porosity of chitosan (CS) coupled with an excellent electron transfer enabled by the cMWCNTs and AgNPs increased the surface area for anti-fipronil (FAb) antibody immobilization and enhanced the current signal of the immunosensor. Cyclic voltammetry (CV) was applied for the quantitative determination of FP under optimized conditions (0.1 M PBS, pH 7.5, 35 °C incubation temperature, and 40 min incubation duration). The modified electrochemical immunosensor displayed excellent analytical performance, including a wide linear concentration range from 0.1 to 1000 ng mL-1 with a very low limit of detection of 0.021 ng mL-1 and good reproducibility (RSD = 2.58%, n = 6), stability (80.4% sensitivity after 5 days), and selectivity. Not only could the modified electrochemical immunosensor be applied in the FP residue analysis of agricultural products, but the present immobilization strategy can also potentially be applied to different biomolecules.

Sample preparation for planar chromatography

High-performance thin-layer chromatography has favorable properties for high-throughput separations with a high matrix tolerance. Sample preparation, however, is sometimes required to control specific matrix interferences and to enhance the detectability of target compounds. Trends in contemporary applications have shifted from absorbance and fluorescence detection to methods employing bioassays and mass spectrometry. Traditional methods (shake-flask, heat at reflux, Soxhlet, and hydrodistillation) are being challenged by automated instrumental approaches (ultrasound-assisted and microwave-assisted solvent extraction, pressurized liquid extraction, and supercritical fluid extraction) and the quick, easy cheap, efficient, rugged, and safe extraction method for faster and streamlined sample processing. Liquid-liquid extraction remains the most widely used approach for sample clean-up with increasing competition from solid-phase extraction. On-layer sample, clean-up by planar solid-phase extraction is increasingly used for complex samples and in combination with heart-cut multimodal systems. The automated spray-on sample applicator, the elution head interface, biological detection of target and non-target compounds, and straightforward mass spectrometric detection are highlighted as the main factors directing current interest toward faster and simpler sample workflows, analysis of more complex samples, and the determination of minor contaminants requiring high concentration factors.

Planar chromatography - Current practice and future prospects

Planar chromatography, in the form of thin-layer or high-performance thin-layer chromatography (TLC, HPTLC), continues to provide a robust and widely used separation technique. It is unrivaled as a simple and rapid qualitative method for mixture analysis, or for finding bioactive components in mixtures. The format of TLC/HPTLC also provides a unique method for preserving the separation, enabling further investigation of components of interest (including quantification/structure determination) separated in both time and space from the original analysis. The current practice of planar chromatography and areas of development of the technology are reviewed and promising future directions in the use of TLC/HPTLC are outlined.

In Silico Analysis of PTP1B Inhibitors and TLC-MS Bioautography-Based Identification of Free Radical Scavenging and α-Amylase Inhibitory Compounds from Heartwood Extract of Pterocarpus marsupium

Type 2 diabetes mellitus leads to metabolic impairment caused by insulin resistance and hyperglycemia, giving rise to chronic diabetic complications and poor disease prognosis. The heartwood of Pterocarpus marsupium has been used in Ayurveda for a long time, and we sought to find the actual mechanism(s) driving its antidiabetic potential. Methanol was used to prepare the extract using a Soxhlet extraction, and the identification of metabolites was performed by thin-layer chromatography (TLC) and ultraperformance-liquid chromatography and mass spectroscopy (UP-LCMS). The antioxidant potential of methanolic heartwood extract of Pterocarpus marsupium MHPM was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and a reducing power assay. The α-amylase and α-glucosidase enzyme inhibitory potential of MHPM were investigated for their antidiabetic activity against acarbose. TLC-MS-bioautography was performed to identify the compounds responsible for possible antioxidant and antidiabetic activities. Moreover, targeting protein tyrosine phosphatase 1B (PTP1B), a key regulator of insulin resistance, by identified metabolites from MHPM through molecular docking and all-atom molecular dynamics (MD) simulations was also undertaken, suggesting its potential as an antidiabetic herb. The IC₅₀ of free-radical scavenging activity of MHPM against DPPH was 156.342 ± 10.70 μg/mL. Further, the IC₅₀ values of MHPM in α-amylase and α-glucosidase enzymatic inhibitions were 158.663 ± 10.986 μg/mL and 180.21 ± 11.35 μg/mL, respectively. TLC-MS-bioautography identified four free radical scavenging metabolites, and vanillic acid identified by MS analysis showed both free radical scavenging activity and α-amylase inhibitory activity. Among the identified metabolites from MHPM, epicatechin showed significant PTP1B docking interactions, and its MD simulations revealed that PTP1B forms a stable protein-ligand complex with epicatechin throughout the progression, which indicates that epicatechin may be used as a promising scaffold in the development of the antidiabetic drug after isolation from Pterocarpus marsupium. Overall, these findings imply that Pterocarpus marsupium is a source of valuable metabolites that are accountable for its antioxidant and antidiabetic properties.

Recent Progress on Techniques in the Detection of Aflatoxin B1 in Edible Oil: A Mini Review

Contamination of agricultural products and foods by aflatoxin B1 (AFB1) is becoming a serious global problem, and the presence of AFB1 in edible oil is frequent and has become inevitable, especially in underdeveloped countries and regions. As AFB1 results from a possible degradation of aflatoxins and the interaction of the resulting toxic compound with food components, it could cause chronic disease or severe cancers, increasing morbidity and mortality. Therefore, rapid and reliable detection methods are essential for checking AFB1 occurrence in foodstuffs to ensure food safety. Recently, new biosensor technologies have become a research hotspot due to their characteristics of speed and accuracy. This review describes various technologies such as chromatographic and spectroscopic techniques, ELISA techniques, and biosensing techniques, along with their advantages and weaknesses, for AFB1 control in edible oil and provides new insight into AFB1 detection for future work. Although compared with other technologies, biosensor technology involves the cross integration of multiple technologies, such as spectral technology and new nano materials, and has great potential, some challenges regarding their stability, cost, etc., need further studies.

Effect-Directed Synthesis of PhoP/PhoQ Inhibitors to Regulate Salmonella Virulence

Salmonella spp. are among the leading bacterial causes of foodborne infections. The PhoP/PhoQ two-component regulatory system serves as a master virulence regulator in Salmonella. Although PhoP/PhoQ represents an ideal target for disarming Salmonella virulence, it has very few inhibitors reported so far. We describe a novel platform by which an inhibitor was selected out of around 185 compounds directly from reaction media containing thiosemicarbazones and mono-, di-, and trihydrazones. To achieve this, tandem library preparation, thin-layer chromatography (TLC) bioautography, and effect-directed deconvolution were applied. We illustrate the potential of this effect-directed synthesis for the identification of new useful bioactive compounds for the food field.

A DNA tetrahedral nanomaterial-based dual-signal ratiometric electrochemical aptasensor for the detection of ochratoxin A in corn kernel samples

Ochratoxin A (OTA) is a highly toxic food contaminant and is harmful to human beings.