Application of atomic force microscopy in the characterization of fruits and vegetables and associated substances toward improvement in quality, preservation, and processing: nanoscale structure and mechanics perspectives.

Fruits and vegetables are essential horticultural crops for humans. The quality of fruits and vegetables is critical in determining their nutritional value and edibility, which are decisive to their commercial value. Besides, it is also important to understand the changes in key substances involved in the preservation and processing of fruits and vegetables. Atomic force microscopy (AFM), a powerful technique for investigating biological surfaces, has been widely used to characterize the quality of fruits and vegetables and the substances involved in their preservation and processing from the perspective of nanoscale structure and mechanics. This review summarizes the applications of AFM to investigate the texture, appearance, and nutrients of fruits and vegetables based on structural imaging and force measurements. Additionally, the review highlights the application of AFM in characterizing the morphological and mechanical properties of nanomaterials involved in preserving and processing fruits and vegetables, including films and coatings for preservation, bioactive compounds for processing purposes, nanofiltration membrane for concentration, and nanoencapsulation for delivery of bioactive compounds. Furthermore, the strengths and weaknesses of AFM for characterizing the quality of fruits and vegetables and the substances involved in their preservation and processing are examined, followed by a discussion on the prospects of AFM in this field.

Development of a microfluidic device to enrich and detect zearalenone in food using quantum dot-embedded molecularly imprinted polymers.

Mycotoxins are secondary metabolites of certain moulds, prevalent in 60-80% of food crops and many processed products but challenging to eliminate. Consuming mycotoxin-contaminated food and feed can lead to various adverse effects on humans and livestock. Therefore, testing mycotoxin residue levels is critical to ensure food safety. Gold standard analytical methods rely on liquid chromatography coupled with optical detectors or mass spectrometers, which are high-cost with limited capacity. This study reported the successful development of a microfluidic "lab-on-a-chip" device to enrich and detect zearalenone in food samples based on the fluorescence quenching effect of quantum dots and selective affinity of molecularly imprinted polymers (MIPs). The dummy template and functional polymer were synthesized and characterized, and the detailed microfluidic chip design and optimization of the flow conditions in the enrichment module were discussed. The device achieved an enrichment factor of 9.6 (±0.5) in 10 min to quantify zearalenone spiked in food with high recoveries (91-105%) at 1-10 mg kg-1, covering the concerned residue levels in the regulations. Each sample-to-answer test took only 20 min, involving 3 min of manual operation and no advanced equipment. This microfluidic device was mostly reusable, with a replaceable detection module compatible with fluorescence measurement using a handheld fluorometer. To our best knowledge, the reported device was the first application of an MIP-based microfluidic sensor for detecting mycotoxin in real food samples, providing a novel, rapid, portable, and cost-effective tool for monitoring mycotoxin contamination for food safety and security.

Survival of Salmonella in Tea Under Different Storage Conditions and Brewing Methods.

Salmonella is one of the leading causes of bacterial gastroenteritis. High prevalence of Salmonella in environment is partially due to its ability to enter the "viable but non-culturable" (VBNC) state when they encounter unfavorable conditions. Dried teas are traditionally believed to have a low risk of causing salmonellosis. This study investigated the survival of Salmonella in four types of dried teas under different storage conditions and brewing methods. A method that coupled propidium monoazide (PMA) and quantitative PCR was optimized to quantify VBNC Salmonella cells to assess the risk of Salmonella contamination in teas after brewing. Each tea sample was inoculated with Salmonella at an 8 log CFU/ml concentration and stored at 4, 10, and 25°C. Under three storage conditions, the number of survived Salmonella was highest in teas stored at 4°C and lowest in teas stored at 25°C. After storage of 120 days, culturable Salmonella was detected from all samples ranging from 6-7 log CFU/g (4°C storage) to 3-4 log CFU/g (25°C storage). The effectiveness of brewing methods in inactivating Salmonella was assessed by brewing inoculated teas at room temperature, 55, 75, and 100°C for 10 min. Brewing teas at 75 and 100°C significantly (P < 0.05) reduced the number of viable Salmonella, but VBNC Salmonella formed when brewed at 75°C. Altogether, Salmonella can persist in dried teas for over 3 months at a temperature ranging from 4 to 25°C, and thermal treatment delivered during home brewing may not eradicate Salmonella in teas.

Inhibition of AI-2 Quorum Sensing and Biofilm Formation in Campylobacter jejuni by Decanoic and Lauric Acids.

Campylobacter jejuni is a major bacterial cause of human diarrheal diseases worldwide. Despite its sensitivity to environmental stresses, C. jejuni ubiquitously distributes throughout poultry production chains. Biofilm formation mediated by quorum sensing is suggested to be critical to the survival of C. jejuni in agroecosystem. C. jejuni possesses LuxS, the enzyme involved in the production of autoinducer-2 (AI-2) signaling molecules. In this study, two fatty acids, namely decanoic acid and lauric acid, were identified to be effective in inhibiting AI-2 activity of C. jejuni. Both decanoic acid and lauric acid at 100 ppm inhibited ∼90% AI-2 activity (P < 0.05) of C. jejuni without bacterial inactivation. The biofilm biomass of two C. jejuni strains was reduced by 10-50% (P < 0.05) after treatment by both fatty acids, while increased biofilm formation was observed for one C. jejuni strain. In addition, both fatty acids effectively reduced the motility of all tested C. jejuni strains. These findings can aid in developing alternative C. jejuni control strategies in agri-food and clinical settings.

Identification of donkey meat in foods using species-specific PCR combined with lateral flow immunoassay.

Food authenticity is a global issue and has raised increasing concerns in the past decades. DNA-based methods are more favourable than the conventional protein-based techniques and have been applied to species identification and meat fraud detection. To effectively identify donkey meat for meat product authentication, a highly specific and robust method that coupled polymerase chain reaction (PCR) with lateral flow immunoassay (LFI) was developed. Donkey-specific PCR primers were designed by targeting at the mitochondrial D-loop gene and the specificity was verified in silico and in vitro against 22 species involved in meat authentication. A limit of detection of 0.0013 ng µL-1 DNA extract was achieved and as low as 0.001% w/w (raw) and 0.01% w/w (cooked) donkey meat in beef were successfully detected using the developed PCR-LFI. LFI strip-based visualization of PCR products allowed for a 10-fold higher sensitivity than conventional gel electrophoresis and significantly reduced the analysis time for the post-PCR analysis. This PCR-LFI is highly suitable for rapid identification of donkey or incorporating into multiplex screening protocol for other meat authentication in the laboratories of both regulatory agencies and commercial services.

Detecting Chemical Hazards in Foods Using Microfluidic Paper-Based Analytical Devices (µPADs): The Real-World Application.

Food safety remains one of the most important issues in most countries and the detection of food hazards plays a key role in the systematic approach to ensuring food safety. Rapid, easy-to-use and low-cost analytical tools are required to detect chemical hazards in foods. As a promising candidate, microfluidic paper-based analytical devices (µPADs) have been rarely applied to real food samples for testing chemical hazards, although numerous papers have been published in this field in the last decade. This review discusses the current status and concerns of the µPAD applications in the detection of chemical hazards in foods from the perspective of food scientists, mainly for an audience with a background in mechanical and chemical engineering who may have interests in exploring the potential of µPAD to address real-world food safety issues.

Detection and Characterization of Antibiotic-Resistant Bacteria Using Surface-Enhanced Raman Spectroscopy.

This mini-review summarizes the most recent progress concerning the use of surface-enhanced Raman spectroscopy (SERS) for the detection and characterization of antibiotic-resistant bacteria. We first discussed the design and synthesis of various types of nanomaterials that can be used as the SERS-active substrates for biosensing trace levels of antibiotic-resistant bacteria. We then reviewed the tandem-SERS strategy of integrating a separation element/platform with SERS sensing to achieve the detection of antibiotic-resistant bacteria in the environmental, agri-food, and clinical samples. Finally, we demonstrated the application of using SERS to investigate bacterial antibiotic resistance and susceptibility as well as the working mechanism of antibiotics based on spectral fingerprinting of the whole cells.

Analysis of Biomolecules Based on the Surface Enhanced Raman Spectroscopy.

Analyzing biomolecules is essential for disease diagnostics, food safety inspection, environmental monitoring and pharmaceutical development. Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for detecting biomolecules due to its high sensitivity, rapidness and specificity in identifying molecular structures. This review focuses on the SERS analysis of biomolecules originated from humans, animals, plants and microorganisms, combined with nanomaterials as SERS substrates and nanotags. Recent advances in SERS detection of target molecules were summarized with different detection strategies including label-free and label-mediated types. This comprehensive and critical summary of SERS analysis of biomolecules might help researchers from different scientific backgrounds spark new ideas and proposals.