Micro/nanomotor technology: the new era for food safety control.

Food poisoning caused by eating contaminated food remains a threat to global public health. Making the situation even worse is the aggravated global environmental pollution, which poses a major threat to the safety of agricultural resources. Food adulteration has been rampant owing to negligent national food safety regulations. The speed at which contaminated food is detected and disposed of determines the extent to which consumers' lives are safeguarded and agricultural economic losses are prevented. Micro/nanomotors offer a high-speed mobile loading platform that substantially increases the chemical reaction rates and, accordingly, exhibit great potential as alternatives to conventional detection and degradation techniques. This review summarizes the propulsion modes applicable to micro/nanomotors in food systems and the advantages of using micro/nanomotors, highlighting examples of their potential use in recent years for the detection and removal of food contaminants. Micro/nanomotors are an emerging technology for food applications that is moving toward mass production, simple preparation, and important functions.

Functional characterization of T3SS C-ring component VscQ and evaluation of its mutant as a live attenuated vaccine in zebrafish (Danio rerio) model.

Vibrio alginolyticus, a Gram-negative bacterium, has been recognized as an opportunistic pathogen in marine animals as well as humans. Type III secretion system (T3SS) is critical for pathogen virulence and disease development. However, no more information is known about the C-ring component VscQ and its physiological role. In this study, gene vscQ was cloned from V. alginolyticus wild-type strain HY9901 and the mutant strain HY9901ΔvscQ was constructed by the in-frame deletion method. The HY9901ΔvscQ mutant showed an attenuated swarming phenotype and a closely 4.6-fold decrease in the virulence to Danio rerio. However, the HY9901ΔvscQ mutant showed no difference in growth, biofilm formation and ECPase activity. HY9901ΔvscQ reduces the release of LDH, NO and caspase-3 activity of infected FHM cell, which are involved in fish cell apoptosis. Deletion of gene vscQ downregulates the expression level of T3SS-related genes including vscL, vopB, hop, vscO, vscK, vopD, vcrV and vopS and flagellum-related genes (flaA and fliG). And Danio rerio vaccinated via i.m injection with HY9901ΔvscQ induced a relative percent survival (RPS) value of 71% after challenging with the wild-type HY9901. Real-time PCR assays showed that vaccination with HY9901ΔvscQ enhanced the expression of immune-related genes, including TNF-α, TLR5, IL-6R, IgM and c/ebpß in liver and spleen after vaccination, indicating that it is able to induce humoral and cell-mediated immune response in zebrafish. These results demonstrate that the HY9901ΔvscQ mutant could be used as an effective live vaccine to combat V. alginolyticus infection.

Clinically Approved Ferric Maltol: A Potent Nanozyme with Added Effect for High-Efficient Catalytic Disinfection.

Nanozyme has been proven to be an attractive and promising candidate to alleviate the current pressing medical problems. However, the unknown clinical safety and limited function beyond the catalysis of the most reported nanozymes cannot promise an ideal therapeutic outcome in further clinical application. Herein, we find that ferric maltol (FM), a clinically approved iron supplement synthesized through a facile scalable method, exhibits excellent peroxidase-like activity than natural horseradish peroxidase-like (HRP) and commonly reported Fe-based nanozymes, and also shows high antibacterial performance for methicillin-resistant Staphylococcus aureus (MRSA) elimination (100%) and wound disinfection. In addition, with added effects inherited from contained maltol, FM can accelerate skin barrier recovery. Therefore, the exploration of FM as a safe and desired nanozyme provides a timely alternative to current antibiotic therapy against drug-resistant bacteria.

Phytochemicals-based edible coating for photodynamic preservation of fresh-cut apples.

Nature-derived chemicals have recently gained increased attention to settle down the challenges in the food industry. Quercetin has long been used as a natural medicine but its photoactivity has been neglected. In this work, by combining photodynamic bacteria inactivation (PDI) with an edible coating (Pectin/Quercetin) derived from FDA-approved chemicals, extend shelf-life and protected commercial quality of fresh-cut apples were achieved. Firstly, the potential photoactivated antibacterial performance of Quercetin (a natural plant flavonoid) was clarified with the treatment of a simulated sunlight lamp, realizing antibacterial efficacy of 100 % towards S. aureus (50 min) and L. monocytogenes (80 min) with light treatment. To develop safe and effective preservation of fresh-cut apples, Pectin/Quercetin edible coatings with 100 µmol/L quercetin were adopted. The results showed that the prepared edible coatings form a protective barrier over the surface of apples, effectively resisting bacterial infection and extending shelf life to 10 days while maintaining good commercial quality (including preferable color, keeping 100 % hardness, 80 % sugar content and 17.3 % weightlessness rate). Therefore, the prepared light-driven Pectin/Quercetin in this work has the potential to develop as fresh-cut fruit preservation technology.

Tannic acid-derived selective capture of bacteria from apple juice.

Given the enormous burden pathogens pose on human health, rapid capture and removal of bacteria for sterilization or further bacterial detection is essential. Herein, tannic acid-functionalized virus-like Fe3O4 (vFe3O4-TA) was established for bacterial enrichment. We investigated the ability of vFe3O4-TA to capture Gram-negative bacteria (E. coli, S. flex and S. typhi) and Gram-positive bacteria (S. aureus, MRSA and LM), respectively. Compared to the capture efficiency of <15 % for Gram-negative bacteria, vFe3O4-TA showed excellent selectivity and efficiency in isolating Gram-positive bacteria with >87 % removal efficiency. GFN-xTB semiempirical quantum chemical calculations revealed that the selective recognition originates from the high affinity between TA and peptidoglycan. Without impacting ingredients, the TA-mediated trapper also shows excellent ability to distinguish Gram-positive bacteria in juice samples. These results are expected to reveal the interaction of TA with bacteria, and inaugurate a potential natural safe tool for food safety control, medical treatment and environmental remediation.

Natural melanin nanoparticle-based photothermal film for edible antibacterial food packaging.

Although nanocomposite films had shown excellent potential in antibacterial food packaging, their potential harmful impact limits their further application in reality. Therefore, exploring a Generally Recognized As Safe (GRAS) nanomaterial that has antibacterial ability is the pioneer for the fabrication of a real edible nanocomposite-based antibacterial packaging film. Herein, for the first time by using the natural nanostructure extracted from cuttlefish ink, an edible antibacterial food packaging with high safety were constructed. The natural melanin nanoparticles (NMPs) in cuttlefish ink have good photothermal conversion ability. As such, by incorporating with natural pectin (PC) film and with near infrared (NIR) irradiation triggering, the results show that PC/NMPs films perform high-efficiency and short-term bactericidal activity against foodborne pathogenic bacteria, including thermotolerant Listeria monocytogenes. The sterilization rate could reach more than 90 % within only 5 min. Also, this nanocomposite film showed better mechanical properties, thermal stability and barrier properties than the neat pectin film. Antibacterial test on food sample also proved the good antibacterial ability of the PC/NMPs films. Therefore, exploring GRAS natural functional nanocomposite film is expected to be the effective way to promote edible nano-antibacterial packaging.

Glucose Oxidase-Integrated Metal-Polyphenolic Network as a Microenvironment-Activated Cascade Nanozyme for Hyperglycemic Wound Disinfection.

The high systemic blood glucose concentration of hyperglycemic wound microenvironment (WME) severely impedes the disinfection and healing of infected skin wounds. Herein, a WME-activated smart natural product, integrated GOx-GA-Fe nanozyme (GGFzyme), is engineered, which combines a nanozyme and natural enzyme to promote reactive oxygen species (ROS) generation in situ for hyperglycemic wound disinfection. GGFzyme can consume a high concentration of glucose in hyperglycemia wounds and generate H2O2. The conversion of glucose into gluconic acid not avails starvation treatment but reduces the pH of WME to elevate the catalytic activities of both the nanozyme (GA-Fe) and natural enzyme (GOx). And H2O2 is then high efficiently catalyzed into •OH and O2•- in situ to combat pathogenic bacteria and promote wound disinfection. The high catalytic antibacterial capacity and superior biosafety, combined with beneficial WME modulation, demonstrate that GGFzyme is a promising therapeutic agent for hyperglycemic wounds.

Dimensionality reduction boosts the peroxidase-like activity of bimetallic MOFs for enhanced multidrug-resistant bacteria eradication.

The antibacterial strategy using cutting-edge metal-organic framework (MOF)-based nanozymes can effectively solve the problem caused by antibiotic resistance to protect human health and the environment; however it has been significantly limited by the complicated modification method and non-ideal catalytic activity. Herein, we report a facile dimensionality-reduction strategy to improve the catalytic activity of MOF-based nanozymes. By reducing the dimensionality of two-dimensional Co-TCPP(Fe) (Co-Fe NSs) to zero-dimensional Co-TCPP(Fe) (Co-Fe NDs), the peroxidase-like activity of the prepared bimetallic Co-Fe NDs was almost tripled. Consequently, the bimetallic Co-Fe NDs can highly efficiently catalyze the lower-concentration H2O2 into reactive oxygen species (ROS), resulting in a favorable antibacterial effect against methicillin-resistant Staphylococcus aureus (MRSA). Meanwhile, Co-Fe NDs can effectively promote wound healing and water environment disinfection with good biocompatibility. This work reveals the potential of a zero-dimensional bimetallic MOF-based nanozyme in resisting drug-resistant bacteria and holds great promise for future clinical and environmental applications.

Magnetic Nanoseparation Technology for Efficient Control of Microorganisms and Toxins in Foods: A Review.

Outbreaks of foodborne diseases mediated by food microorganisms and toxins remain one of the leading causes of disease and death worldwide. It not only poses a serious threat to human health and safety but also imposes a huge burden on health care and socioeconomics. Traditional methods for the removal and detection of pathogenic bacteria and toxins in various samples such as food and drinking water have certain limitations, requiring a rapid and sensitive strategy for the enrichment and separation of target analytes. Magnetic nanoparticles (MNPs) exhibit excellent performance in this field due to their fascinating properties. The strategy of combining biorecognition elements with MNPs can be used for fast and efficient enrichment and isolation of pathogens. In this review, we describe new trends and practical applications of magnetic nanoseparation technology in the detection of foodborne microorganisms and toxins. We mainly summarize the biochemical modification and functionalization methods of commonly used magnetic nanomaterial carriers and discuss the application of magnetic separation combined with other instrumental analysis techniques. Combined with various detection techniques, it will increase the efficiency of detection and identification of microorganisms and toxins in rapid assays.

Lycium Barbarum Polysaccharide-Iron (III) Chelate as Peroxidase Mimics for Total Antioxidant Capacity Assay of Fruit and Vegetable Food.

Quantitative evaluation of the antioxidant capacity of foods is of great significance for estimating food's nutritional value and preventing oxidative changes in food. Herein, we demonstrated an easy and selective colorimetric method for the total antioxidant capacity (TAC) assay based on 3,3',5,5'-tetramethyl-benzidine (TMB), hydrogen peroxide (H2O2) and synthetic Lycium barbarum polysaccharide-iron (III) chelate (LBPIC) with high peroxidase (POD)-like activity. The results of steady-state kinetics study showed that the Km values of LBPIC toward H2O2 and TMB were 5.54 mM and 0.16 mM, respectively. The detection parameters were optimized, and the linear interval and limit of detection (LOD) were determined to be 2-100 µM and 1.51 µM, respectively. Additionally, a subsequent study of the determination of TAC in six commercial fruit and vegetable beverages using the established method was successfully carried out. The results implied an expanded application of polysaccharide-iron (III) chelates with enzymatic activity in food antioxidant analysis and other biosensing fields.

Natural Products Self-Assembled Nanozyme for Cascade Detection of Glucose and Bacterial Viability in Food.

Sugar content and bacterial contamination levels are important indicators for the health and safety of food, respectively. Therefore, it is important to construct a method that can detect both glucose and bacterial activity. Herein, natural compounds (gallic acid and glucose oxidase) were assembled into nanozyme (GOx@GA-Fe (ii)) for mild cascade detection. The nanozyme catalyzes glucose to produce hydrogen peroxide, which is then converted to ·OH and oxidized colorless TMB from blue oxidized TMB. Under the optimal conditions, the method has a good linear relationship in the glucose concentration range of 1-500 µM (R2 = 0.993) with minimum detection concentration of 0.43 µM. Based on the glucose consumption of bacteria metabolism, the cascade reaction was then applied to detect the viability of 5 common bacteria. As such, a cascade method based on a natural self-assembled nanozyme was fabricated to monitor the quality of food.