Convenient, nondestructive monitoring and sustained-release of ethephon/chitosan film for on-demand of fruit ripening

Self-triggered carboxymethyl chitosan hydrogel for the convenient sustained release of ClO2 gas with environmental stability and long-term antimicrobial effect

Challenges associated with the storage and uncontrolled release of ClO2 gas present significant hurdles to its practical application. Herein, a clever strategy for self-triggering the sustained release of chlorine dioxide (ClO2) gas is proposed by crosslinking carboxymethyl chitosan (CMCS) with Zn2+ to construct a novel CMCS-Zn@NaClO2 gel with eco-friendly, environmental stability, and convenient, long term, and efficient antibacterial activity. The precursor (NaClO2) in the CMCS solution was alkaline and triggered by the acidic Zn(NO3)2·6H2O solution to achieve sustained self-triggering ClO2 release. The ClO2 gas self-release could be sustained on demand at different temperatures for at least 20 days due to the environmental structure stability of the gel. The hydrogels showed an increase in pore size after sustained release. Molecular dynamics simulations showed the spontaneous release of ClO2 gas at room temperature and the contraction of the CMCS agglomeration, which were consistent with the macroscopic behaviour. The gel displayed a long-acting and high antibacterial efficacy, resulting in a bacteria-killing rate of over 99.9% (inhibitory concentrations of 2.5 mg mL-1 against E. coli and 0.16 mg mL-1 against S. aureus). The hydrogels could effectively extend the shelf life of fruits and demonstrated an excellent wide range of antibacterial properties. This work provides a new approach to solving the storage difficulty of ClO2 gas and offers a fresh perspective on the design of materials with convenient self-triggering release by a precursor, as well as the relationship between the material microstructure and sustained-release behaviour.

Carboxymethyl chitosan/sodium alginate hydrogel films with good biocompatibility and reproducibility by in situ ultra-fast crosslinking for efficient preservation of strawberry

Strawberry is a seasonal and regional fruit. Thus, strawberry waste caused by spoilage and decay is an urgent problem that must be solved. Developing hydrogel films (HGF) for multifunctional food packaging can effectively slow down strawberry. Based on the carboxymethyl chitosan/sodium alginate/citric acid with excellent biocompatibility, preservation effect, and ultrafast (10 s) coating on the strawberry surface, HGF specimens were designed and prepared through the electrostatic interaction of opposite charges between polysaccharides. The prepared HGF specimen exhibited excellent low moisture permeability and antibacterial properties. Its lethality rates against both Escherichia coli and Staphylococcus aureus were more than >99 %. The HGF could keep strawberries fresh for up to 8, 19, and 48 days at 25.0, 5.0, and 0 °C, respectively, by delaying the fruits' ripening, dehydration, microbial invasion, and respiration rate. The HGF dissolved and regenerated five times still exhibited good performance. The water vapor transmission rate of the regenerative HGF could reach 98 % of that of the original HGF. The regenerative HGF could maintain the freshness of strawberries for up to 8 days at 25.0 °C. This study provides new insight into an alternative film design for convenient, green, and renewable alternative films to delay perishable fruit spoilage.

Flexible SERS strip based on HKUST-1(cu)/biomimetic antibodies composite multilayer for trace determination of ethephon

A surface-enhanced Raman scattering (SERS) sensor based on the folding and assembly characteristics of the three-dimensional structure of paper fibers, the skeleton controllability of metal-organic framework materials (MOFs), and the morphology designability of plasmonic noble metal materials has been established for rapid on-site determination of ethephon in food. HKUST-1(Cu) was assembled onto a carbon-treated chromatographic paper matrix by electrodeposition, and its skeleton respiration and sponge effect were used to overcome the bottleneck problem of poor affinity of SERS substrate for target molecules. Further coupled with the targeted recognition specificity of biomimetic antibodies, a paper-based interface with high specificity of molecular sensitivity was constructed. A sandwich multi-stage progressive enhancement structure was designed to couple plasma pine branch-shaped silver material in situ at the interface to realize superposition and collaborative amplification of SERS signals. When the paper-based strip sensor was used to monitor ethephon, it demonstrated a linear range of 10^-3 to 10 mg kg^-1 and a detection limit of around 1.39 × 10^-4 mg kg^-1. The construction and application of the paper-based HKUST-1(Cu)/biomimetic antibodies/pine branch-shaped silver material sensor will provide technical means and theoretical support for the rapid and efficient identification of biological ripening agent residues in food with multi-level signal enhancement.

Flexible, sensitive and rapid humidity-responsive sensor based on rubber/aldehyde-modified sodium carboxymethyl starch for human respiratory detection

Natural polymers with abundant hydrophilic groups are potential candidates for humidity sensor designing. Unfortunately, most of natural polymers lack essential stretchability and high conductivity, which hinder their development in the field of flexible humidity sensor. Cooperation with rubbers and conductive nanometer materials is an effective method to make the best use of natural polymers in flexible humidity sensor. In this paper, a flexible and sensitive sensor with rapid response to humidity change is fabricated based on aldehyde-modified sodium carboxymethyl starch (ACMS), carboxylated styrene-butadiene rubber (XSBR) and Ag nanoflakes through film-forming method. The pre-prepared ACMS owns a better dispersibility in the aqueous phase and serves as reducing agent for formation of Ag nanoflakes. After the film-forming process, the composite film shows a strength of 5.66 MPa and a high stretchability with strain of 367 %. Besides, our sensor shows a rapider response to humidity change than the commercial electronic hygrometer that it takes only 1 s to respond to the humidity change from 25 % RH to 27 % RH. Therefore, the XSBR/ACMS/Ag sensor possesses an impressive sensitive response to slight sweat on human skin and breath, which could find applications in monitoring people's health and distinguish their physical condition.

A comprehensive review of intelligent packaging for fruits and vegetables: Target responders, classification, applications, and future challenges

Post-harvest fruits and vegetables are extremely susceptible to dramatic and accelerated quality deterioration deriving from their metabolism and adverse environmental influences. Given their vigorous physiological metabolism, monitoring means are lacking due to the extent that unnecessary waste and damage are caused. Numerous intelligent packaging studies have been hitherto carried out to investigate their potential for fruit and vegetable quality monitoring. This state-of-the-art overview begins with recent advances in target metabolites for intelligent packaging of fruits and vegetables. Subsequently, the mechanisms of action between metabolites and packaging materials are presented. In particular, the exact categorization and function of intelligent packaging of fruits and vegetables, are all extensively and comprehensively described. In addition, for the sake of further research in this field, the obstacles that impede the scaling up and commercialization of intelligent packaging for fruits and vegetables are also explored, to present valuable references.

Enhanced antibacterial effect and biodegradation of coating via dual-in-situ growth based on carboxymethyl cellulose

The lack of antimicrobial effect of commercial paper coating for food packaging makes it difficult to prevent food spoilage and harms the environment by non-biodegradation. Herein, carboxymethyl cellulose (CMC) provides negatively charged sites for anchoring Ag⁺ and Zn²⁺ to grow AgNPs and ZIF-8 in situ on its molecular chains. The ZIF-8/AgNPs@CMC paper coating has excellent synergistic antibacterial activity to prolong the shelf-life of food. It not only has good thermal stability but binds closely to the paper and its adhesion force reaches 628.9 nN. Besides, the ZIF-8/AgNPs@CMC coated paper has better mechanical properties, water vapor barrier, and resists water solubility. Interestingly, due to the confinement effect of ZIF-8, the cumulative release of AgNPs after 168 h is only 2.66 % to avoid possible food safety risks. Especially, the coating can be almost biodegraded in the soil after 30 days, which provides the possibility to replace the non-biodegradable coatings in food packaging.