Visible detection of chilled beef freshness using a paper-based colourimetric sensor array combining with deep learning algorithms

This study developed an innovative approach that combines a colourimetric sensor array (CSA) composed of twelve pH-response dyes with advanced algorithms, aiming to detect amine gases and assess the freshness of chilled beef. With the assistance of multivariate statistical analysis, the sensor array can effectively distinguish five amine gases and enable rapid quantification of trimethylamine vapour with a limit of detection (LOD) of 8.02 ppb and visually monitor the fresh levels of chilled beef. Moreover, the utilization of deep learning models (ResNet34, VGG16, and GoogleNet) for chilled beef freshness evaluation achieved an overall accuracy of 98.0 %. Furthermore, t-distributed stochastic neighbour embedding (t-SNE) visualized the feature extraction process and provided explanations to understand the classification process of deep learning. The results demonstrated that applying deep learning techniques in the process of pattern recognition of CSA can help in realizing the rapid, robust, and accurate assessment of chilled beef freshness.

Bridging biological and food monitoring: A colorimetric and fluorescent dual-mode sensor based on N-doped carbon dots for detection of pH and histamine

Rapid and sensitive monitoring of pH and histamine is crucial for bridging biological and food systems and identifying corresponding abnormal situations. Herein, N-doped carbon dots (CDs) are fabricated by a hydrothermal method employing dipicolinic acid and o-phenylenediamine as precursors. The CDs exhibit colorimetric and fluorescent dual-mode responses to track pH and histamine variations in living cells and food freshness, respectively. The aggregation-induced emission enhancement and intramolecular charge transfer result in a decrease in absorbance and an increase in fluorescence, which become readily apparent as the pH changes from acidic to neutral. This property enables precise differentiation between normal and cancerous cells. Furthermore, given the intrinsic basicity of histamine, pH-responsive CDs are advantageous for additional colorimetric and fluorescent monitoring of histamine in food freshness, achieving linearities of 25-1000 µM and 30-1000 µM, respectively, which are broader than those of alternative nanoprobes. Interestingly, the smartphone-integrated sensing platform can portably and visually evaluate pH and histamine changes due to sensitive color changes. Therefore, the sensor not only establishes a dynamic connection between pH and histamine for the purposes of biological and food monitoring, but also presents a novel approach for developing a multifunctional biosensor that can accomplish environmental monitoring and biosensing simultaneously.

Continuous monitoring of temperature and freshness in cold chain transport based on the dual-responsive fluorescent hydrogel

Comprehensive attention should be paid to the potential food spoilage in food transport. However, there is a problem of freshness destruction by repeated freezing and thawing during the cold chain transport. Herein, a fluorescent hydrogel with N-doped green-emitting carbon dots (N-GCDs), bovine serum albumin-gold nanoclusters (BSA-AuNCs) as fluorescent probes and polyvinyl alcohol-sodium alginate hydrogel as carrier matrix was developed to continuously detect temperature and freshness. Due to the solvatochromic effect of N-GCDs, when the temperature surpassed the threshold, the mixture of water and dimethyl sulfoxide underwent a phase transition and melted into the gel, changing the fluorescence color to realize the temperature monitoring. Then, due to the pH effect of BSA-AuNCs, the gel could respond to pH changes in food deterioration to monitor the food freshness. Thus, the changes of both fluorescence color and intensity of the hydrogel provides a new method for visual and portable authenticity of food freshness.

A ratiometric fluorescence amine sensor based on carbon quantum dot-loaded electrospun polyvinylidene fluoride film for visual monitoring of food freshness

A ratiometric fluorescence sensor based on dual-emission carbon quantum dots (CQD) was developed to real time monitor food spoilage. Two hydrophobic electrospun fluorescent films were developed using polyvinylidene fluoride (PVDF) as the film-forming polymer in combination with CQD as the fluorescent probe. The CQD/PVDF film and CQD@PVDF film enabled the analysis of TMA with limits of detection (LODs) of 1.04 μM and 2.1 μM, respectively, and they exhibited excellent stability at 4 °C. By these virtues, the CQD@PVDF film exhibited visible fluorescence color changes from yellow green to blue by real time and nondestructively sensing volatile amines generated from beef, pork and shrimp in a packaging system with high humidity. This strategy provided a simple but useful, non-destructive, robust, and platform to real time monitor food spoilage for intelligent food packaging.

Terbium doping and energy level modification of zirconium organic frameworks as probes for the improved determination of histamine and visual inspection of food freshness

Food safety is a common concern among people, and the development of high-performance food freshness detection technology is crucial, but is still highly challenging. Fluorescent sensing based on metal organic frameworks is a promising technology to tackle this issue. In this work, three UiO-66 type Zirconium organic frameworks (ZrOFs) which are functionalized with varying numbers of hydroxyl groups to alter the energy levels, and partial replacement of Zirconium(IV) by Terbium(III) ions to introduce additional emitting centers, were explored as probes for the sensing of Histamine (His). With one hydroxyl group introduced, UiO-66-OH@Tb can be developed as ratiometric fluorescent probe with improved sensing performance, showing a wide detection range of 0 to 120 mg/L, and a low detection limit of 0.13 mg/L. UiO-66-OH@Tb can also be fabricated into composite film to function as visual sensing material of His. This work can provide instructions for the development of other fluorescent sensors.

Fabrication of ammonia and acetic acid-responsive intelligent films based on grape skin anthocyanin via adjusting the pH of film-forming solution

pH-responsive intelligent films for food freshness monitoring have attracted great attentions recently. In this study, several intelligent films based on chitosan (CS), polyvinyl alcohol (PVA), and grape skin anthocyanin (GSA) were prepared, and the effect of film-forming solution pH on the properties of intelligent films was investigated. The results of SEM, FTIR, XRD and TGA displayed that the hydrogen bond between CS and GSA was strong at strong acidic conditions (2.0-2.5), and it weakened at weak acidic conditions (3.0-4.5). Meanwhile, the hydrogen bond between PVA and GSA was negligible under strong acidic conditions, and it appeared under weak acidic conditions. Consequently, the films fabricated under weak acidic conditions displayed lower water solubility, lower water vapor permeability, and higher elongation at break. The tensile strength of films increased firstly and subsequently decreased with pH increasing, reaching a maximum value of 31.44 MPa at pH 3.5. Additionally, the films prepared at pH 2.5 and 4.0 showed the best color responsiveness to ammonia and acetic acid, respectively. Overall, the intelligent films prepared under variant pH have the potential to realize the goal of monitoring the freshness of different types of food, thereby expanding the application subject of anthocyanins-based intelligent films.

Fluorescence turn-on mode of Eu3+ complex nanocomposite to detect histamine for seafood freshness

Biogenic amines (BAs), which naturally occur as chemicals in seafood, are indicators of food freshness and quality. High concentrations of BAs can cause an undesirable inflammatory response. However, traditional detection methods cannot meet the needs of rapid analysis nowadays. It is essential to explore a simple and valid method to monitor the food quality. Herein, we design and prepare a nanoclay-based turn on fluorescent material with BAs response, which could be used for the real-time and visual detection of raw fish freshness. As the concentration of BAs increase, the sensor of the fluorescence signal is significantly enhanced. The sensor demonstrated wonderful response and sensitivity which showed a detection limit of 0.935 mg/L for typical BAs histamine within a linear range of 2-14 mg/L in an aqueous solution. More importantly, we developed a responsive BAs device by doping the sensor into polyvinyl alcohol (PVA), which is well applied as a rapid-responsive fluorescent marker for visual monitoring the freshness of raw fish.

Dual-signal fluorescent test strips for spoilage sensing of packaged seafood: Visual monitoring of volatile basic nitrogens

With the food safety issues abounding, exploring reliable and efficient methods for evaluating food safety is crucial. Herein, a ratiometric test strip was proposed by using green-yellow fluorescent d-penicillamine capped silver nanocluster (DPA-AgNCs) as indicator and red-emitting bimetallic gold/silver nanoclusters (AuAgNCs) as an internal reference, providing a real-time and visual monitoring system for food freshness. Results showed that the as-prepared DPA-AgNCs displayed an excellent response and good sensitivity for volatile basic nitrogens (VBNs), with a limit of detection (LOD) of 0.51 μM and 0.08 ppm for spermidine and ammonia hydroxide, respectively. Subsequently, a ratiometric test strip was developed to visually monitor ammonia vapour, displaying an obvious fluorescence colour variation from mustard to deep-red. Moreover, the presented ratiometric test strip was successfully applied for non-contact and visual evaluating and monitoring VBNs in the shrimp sample, showing high potential for in-situ monitoring.

An antibacterial and intelligent cellulose-based label self-assembled via electrovalent bonds for a multi-range sensing of food freshness

Intelligent labels provide customers with food freshness information. However, the existing label response is limited and can only detect a single kind of food. Here, an intelligent cellulose-based label with highly antibacterial activity for a multi-range sensing freshness was developed to overcome the limitation. Cellulose fibers were modified using oxalic acid to graft -COO^- followed by binding chitosan quaternary ammonium salt (CQAS), the remaining charges of which attached methylene red and bromothymol blue to form response fibers and to further self-assemble into the intelligent label. CQAS electrostatically gathered the dispersed fibers, resulting in an increase in TS and EB of 282 % and 16.2 %, respectively. After that, the rest positive charges fixed the anionic dyes to broaden pH response range of 3-9 effectively. More significantly, the intelligent label exhibited highly antimicrobial activity, killing 100 % of staphylococcus aureus. The rapid acid-base response revealed the potential for practical application in which the label color from green to orange represented the milk or spinach from fresh to close to spoiled, and from green to yellow, and to light green indicated the pork fresh, acceptable, and close to spoiled. This study paves a way for the preparation of intelligent labels in large-scale and promote the commercial application to improve food safety.

pH-Responsive strips integrated with resazurin and carbon dots for monitoring shrimp freshness

Carbon dots (CDs) were synthesized via a one-step hydrothermal approach using tangerine peel (Tan) and resazurin (Res) to fabricate biocompatible indicators for food freshness. The CDs' pH-responsive mechanism, morphology, zeta potential, XPS, and optical and fluorescence analysis were investigated. The as-prepared tangerine peel/resazurin carbon dots (Tan/Res CDs) exhibited pH-responsive emission that changed from yellow to orange as the pH value increased. The Tan/Res CDs showed the sensing ability of ammonia with a detection limit of 0.84 μM by proportionally losing fluorescence intensity as the concentration increased from 1 to 100 μM. The CDs were coated onto paper strips to impart biogenic amine (BAs) detection for pH-responsive intelligent monitoring of packaged foods. The Tan/Res CDs paper-based indicator exhibited an impressive color change from yellow to brown during the detection of ammonia vapor. The indicator also showed the ability to detect BAs through a color change, demonstrating the ability to monitor the freshness of shrimp in situ. Additionally, the efficacy of the Tan/Res CDs indicator is validated by total volatile basic nitrogen (TVB-N), providing customers and suppliers with a simple, inexpensive, and portable tool to monitor the freshness of seafood in real-time.

Hydrogen-bond activated ESIPT in naphthalimide-based fluorescent probe for sensing volatile amines

Amines levels present important indicative value in food safety and human health. Although they are involved in some normal physiological responses of the organism, their overproduction or intake may cause pathological responses. Herein, we report a recyclable visual packaging bag for volatile amines detections based on the naphthylamide derivative N-S and its positive PL characteristics. Specifically, handmade test strips based on compound N-S have been applied to fish freshness labeling, and the cyclic fumigation experiment shows its restorable PL effect and efficiency. The possible PL transfer mechanism of naphthylamide derivative N-S is uncovered by the density functional theory (DFT) calculation and titration mass spectrometer and ¹H NMR. This work expands a conjugation in a molecule by hydrogen-bond activated ESIPT (H-ESIPT) and provides a portable detection method for volatile amines detection.

Reversible AIE-active fluorescent probe with a large emission peak shift for ratiometric detection of food freshness indicator H2S

It is crucial to on-site monitor H₂S for addressing the concerns associated with food safety. We rationally prepared an AIE-active fluorescent probe (CLBZ) with the aggregated state conversion for sensing H₂S in a ratiometric response manner. CLBZ displayed ratiometric response, fast response time (5 s), well-resolved emission peak shift (147 nm) and high selectivity towards H₂S, and it can be used as a reversible and reusable probe. The probe-based test strip was also developed to conveniently detect H₂S generated during food spoilage in the absence of laboratory instruments. It achieved the consistent results and sensitivity with that determined by the colony forming unit (CFU) assay. These results paved a successful way to develop an effective analytical method for food quality and safety.

Orange emissive carbon dots for fluorescent determination of hypoxanthine in fish

Sensitive determination of hypoxanthine (HX), an indicator reflecting the degradation of meat and fish, is significantly important in monitoring food freshness. Herein, we design a novel sensor consisting of orange emissive carbon dots (O-CDs), nitrotetrazolium blue chloride (NTBC), and xanthine oxidase (XOD) for fluorescence turn-off detection of HX. O-CDs, possessing a high fluorescence quantum yield of 37%, are synthesized by hydrothermal treatment of 2,3-diaminopyridine in sulfuric acid. NTBC can react with HX/XOD-generated H₂O₂ and O₂^- to yield a violet-colored formazan, which remarkably quenches the orange fluorescence of O-CDs through inner filter effect. There is a linearity between the quenching efficiency and HX concentration in the range of 2-250 μM, and the limit of detection is 0.61 μM, lower than those of most reported HX sensors. In addition, the proposed method exhibits excellent selectivity, and can be applied to quantify HX in fish samples with satisfactory results.

Schiff base complex/TiO2 chemosensor for visual detection of food freshness level

Histamine is one of the important biomarkers for food spoilage in the food sectors. In the present study, a rapid and simple analytical tool has been developed to detect histamine as an indirect strategy to monitor food freshness level. Optical histamine sensor with carboxyl-substituted Schiff base zinc(II) complex with hydroxypropoxy side chain deposited onto titanium dioxide nanoparticles was fabricated and was found to respond successfully to histamine. The Schiff base zinc(II) complex-histamine binding generated an enhancement of the fluorescent signal. Under the optimal reaction condition, the developed sensor can detect down to 2.53 × 10^-10 M in the range of between 1.0 × 10^-9 and 1.0 × 10^-5 M (R² = 0.9868). Selectivity performance of the sensor towards histamine over other amines was confirmed. The sensor also displayed good reproducibility performances with low relative standard deviation values (1.45%-4.95%). Shelf-life studies suggested that the developed sensor remains stable after 60 days in histamine detection. More importantly, the proposed sensor has been successfully applied to determine histamine in salmon fillet with good recoveries. This strategy has a promising potential in the food quality assurance sectors, especially in controlling the food safety for healthy consumption among consumers.

Monitoring aging of hen egg by integrated quantitative peptidomic procedures

Environmental conditions and timing of egg storage highly affect raw material quality. Aging and endogenous processing of constituent proteins can determine important changes in specific functions and technological properties of inner egg compartments. We here used integrated peptidomic procedures to identify peptide markers of egg freshness. At first, peptides extracted from egg white and yolk plasma taken from eggs stored for different times were subjected to a label-free untargeted quantitation procedure based on nanoLC-ESI-Q-Orbitrap-MS/MS, which identified 836 and 1974 unique variable molecules, respectively. By applying stringent criteria for filtering data, 30 and 66 putative egg aging markers were selected for egg white and yolk plasma, respectively. Proposed molecules were then validated through a targeted label-free parallel reaction monitoring procedure based on nanoLC-ESI-Q-Orbitrap-MS/MS, confirming quantitative trends for 19 and 25 peptides in egg white and yolk plasma, respectively, and generating a robust panel of egg storage markers. Quantitative results reflected physico-chemical phenomena occurring in egg compartments during storage and offered essential information for the development of novel control procedures to assess quality features of fresh/stored raw material.

Solid-state potentiometric sensor for the rapid assay of the biologically active biogenic amine (tyramine) as a marker of food spoilage

Tyramine (TYR) is a vasoactive biogenic amine found in food products due to improper storage and poor hygiene. High TYR intake results in a wide range of life-threatening physiological reactions. The work optimizes a solid-state potentiometric sensor in the absence of a reported potentiometric method for rapid and direct TYR assay. The optimization study included thirteen membrane cocktails of different compositions. The optimized sensor proved a near-Nernstian slope of 57.30 mV/decade, a quantification limit of 10.6 ppm, and a detection limit of 7.9 ppm. Validation results confirmed the sensor ability for the direct assay of TYR in blue cheese, aged cheese, Egyptian pickled cottage cheese, and pickled herring. A comparison with the reported chromatographic method expresses the merits and potentials of the developed sensor for the rapid testing of food edibility, quality, and safety based on its TYR content. Chemical compounds studied in this article: Tyramine (PubChem CID: 5610); Tyramine hydrochloride (PubChem CID: 66449); Poly(vinyl chloride) (PubChem SID: 24864273); Tricresyl phosphate (PubChem CID: 6529); sodium phosphotungstate tribasic hydrate (PubChem SID: 329753864).

Influence of external ear occlusion on food perception

PURPOSE

The present study aimed to explore if food perception can be influenced by sound mastication level when the external ear canal was occluded.

METHODS

Fifty-nine adults (38 women) with normal hearing, smell, and taste participated in the study. They tasted five crispy and five soft food items over two sessions: one with and one without an earplug inserted in the external ear canal. Participants were asked to rate freshness and taste of the food as well as their willingness to eat more of it and how much they usually like this kind of food. The sound pressure level related to the food mastication was recorded with a probe microphone placed in the external ear canal.

RESULTS

Compared to the open ear canal condition, levels of the mastication sounds were higher when the participants had their ears occluded, as well as for crispy than for soft food. Regarding food freshness, food appreciation, and willingness to eat more of the same food, there was no significant difference concerning food type, ear condition, and sex. For soft foods, men rated their usual liking of this food higher when they were wearing ear plugs compared to the opened condition.

CONCLUSION

Plugging the ear canals led to increased mastication sound levels. Participants did not seem to consider these additional acoustic cues when they rated food freshness, food appreciation, and willingness of eating the specific food. Only men seemed to take these cues into account when they rated their habit consumption of soft food.