Controlled self-release of ClO2 as an encapsulated antimicrobial agent for smart packaging

Chlorine Dioxide (ClO2)-Releasing Sachet for Preservation of Cherry Tomatoes

Chlorine dioxide (ClO2) is a powerful sterilizing agent that is widely used to prevent the spoilage of fresh foods during delivery and storage. However, its practical applications are hindered by a short sterilization duration, complex deployment processes, and high treatment costs. To address these challenges, an innovative ClO2 self-releasing sachet was developed, which was specifically designed for use in retail and wholesale markets. The sachet utilizes polyether block amide (PEBAX®) as a hydrophilic polymer to facilitate the dissociation of sodium chlorite (NaClO2) and citric acid (CA), which generates ClO2. A PEBAX/CA composite film was coated onto kraft paper to construct the sachet. This design extended the ClO2 release period to over 3 d, with a controllable release rate being achieved by adjusting the concentrations of NaClO2 and CA. In practical tests, the sachets inhibited fungal growth by >50% over 14 d at 20 °C within a corrugated box. Furthermore, they preserved the quality of the cherry tomatoes for 16 d during storage. These results demonstrate that the newly developed sachet offers an economical and user-friendly solution for fresh-food packaging, effectively preserving product quality.

Large-scale dual-responsive ClO2 controlled-release film for strawberry preservation

Chlorine dioxide (ClO2) exhibits promising potential for the application in food preservation. However, the large-scale production of controlled-release ClO2 films faces challenges. The sodium chlorite microcapsules (Micro-SC) were successfully prepared in this study using polyvinyl alcohol (PVA) as the wall material through the spray drying method. Furthermore, A large-scale preparation of temperature and humidity dual-responsive ClO2 controlled-release films (Micro-SC@EVA) was achieved using melt extrusion. The film could release ClO2 triggered by water vapor for 36 days. The antibacterial effects were significantly enhanced with the increase of microcapsule ratio from 4 % to 8 %. The Micro-SC@EVA film reduced the total viable count and wight loss of strawberries, inhibits ethylene production, and extended the shelf life of by 150 % compared with the control group at 25 °C. The application evaluation results show that the novel approach for the large-scale preparation of ClO2 controlled-release film holds significant implications for food packaging.

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.

Polylactic acid-based microcapsules for moisture-triggered release of chlorine dioxide and its application in cherry tomatoes preservation

Polylactic acid (PLA)-based microcapsules, capable of releasing chlorine dioxide (ClO2) upon exposure to moisture, have been developed for fruits and vegetables preservation. The microcapsules were prepared by emulsion solvent evaporation, utilizing PLA as the wall material, and NaClO2 as the core material. After optimization, NaClO2 microcapsules exhibited an encapsulation efficiency of 55.75% and an average particle size of 498.08 μm. Citric acid microcapsules were prepared using the same process, but with citric acid as the core material. When the two kinds of microcapsules were mixed, gaseous ClO2 was released in a highly humid environment. The release rate could be adjusted by temperature and the ratio between the two microcapsules, and the release period could be as long as 17 days at 20 °C. With a certain amount of microcapsules placed in the package of cherry tomatoes, the decay rate and weight loss rate of the fruits were reduced by 63 % and 34 %, respectively, compared to the control group. The microcapsules also helped to maintain the good appearance, hardness, and the content of total soluble solid content and titratable acid content of cherry tomatoes. Therefore, the PLA-based microcapsules have satisfied convenience and effectiveness for application in fruit and vegetables preservation.

Preparation and evaluation of a novel chlorine dioxide preservative based on citric acid grafted carboxymethyl chitosan

Instrument-free chlorine dioxide (ClO₂) preservative for fruit and vegetable has gained great attention due to its convenience and safety. In this study, a series of carboxymethyl chitosan (CMC) with citric acid (CA) substituents were synthesized, characterized, and further used to prepare a novel ClO₂ slow-releasing preservative for longan. UV-Vis and FT-IR spectra revealed that CMC-CA#1-3 were successfully prepared. Further potentiometric titration showed that the mass ratios of CA grafted in CMC-CA#1-3 were 0.18:1, 0.42:1, and 0.42:1, respectively. The composition and concentration of ClO₂ slow-releasing preservative were optimized, and the best formulation was as follows: NaClO₂:CMC-CA#2:Na₂SO₄:starch = 3:2:1:1. The maximum ClO₂ release time of this preservative reached >240 h at 5-25 °C, and the maximum release rate always occurred at 12-36 h. Longan treated with 0.15-1.2 g ClO₂ preservative had significantly (p < 0.05) higher L* and a* values but lower respiration rate and total microbial colony counts than the CK group (0 g ClO₂ preservative). After 17 days of storage, longan treated with 0.3 g ClO₂ preservative had the highest L* value of 47.47 and lowest respiration rate of 34.42 mg·kg^-1·h^-1, showing the best pericarp color and pulp quality. This study provided a safe, effective, and simple solution for longan preservation.

Reflections on food security and smart packaging

Estimating the number of COVID-19 cases in 2020 exacerbated the food contamination and food supply issues. These problems make consumers more concerned about food and the need to access accurate information on food quality. One of the main methods for preserving the quality of food commodities for export, storage, and finished products is food packaging itself. In the food industry, food packaging has a significant role in the food supply which acts as a barrier against unwanted substances and preserves the quality of the food. Meanwhile, packaging waste can also harm the environment; namely, it can become waste in waterways or become garbage that accumulates because it is nonrenewable and nonbiodegradable. The problem of contaminated food caused by product packaging is also severe. Therefore, to overcome these challenges of safety, environmental impact, and sustainability, the role of food packaging becomes very important and urgent. In this review, the authors will discuss in more detail about new technologies applied in the food industry related to packaging issues to advance the utilization of Smart Packaging and Active Packaging.

Antimicrobial Nanomaterials Based on Halloysite Clay Mineral: Research Advances and Outlook

Bacterial infections represent one of the major causes of mortality worldwide. Therefore, over the years, several nanomaterials with antibacterial properties have been developed. In this context, clay minerals, because of their intrinsic properties, have been efficiently used as antimicrobial agents since ancient times. Halloysite nanotubes are one of the emerging nanomaterials that have found application as antimicrobial agents in several fields. In this review, we summarize some examples of the use of pristine and modified halloysite nanotubes as antimicrobial agents, scaffolds for wound healing and orthopedic implants, fillers for active food packaging, and carriers for pesticides in food pest control.

Direct and Activated Chlorine Dioxide Oxidation for Micropollutant Abatement: A Review on Kinetics, Reactive Sites, and Degradation Pathway

Recently, ClO2-based oxidation has attracted increasing attention to micropollutant abatement, due to high oxidation potential, low disinfection byproduct (DBPs) formation, and easy technical implementation. However, the kinetics, reactive sites, activation methods, and degradation pathways involved are not fully understood. Therefore, we reviewed current literature on ClO2-based oxidation in micropollutant abatement. In direct ClO2 oxidation, the reactions of micropollutants with ClO2 followed second-order reaction kinetics (kapp = 10−3–106 M−1 s−1 at neutral pH). The kapp depends significantly on the molecular structures of the micropollutant and solution pH. The reactive sites of micropollutants start with certain functional groups with the highest electron densities including piperazine, sulfonyl amido, amino, aniline, pyrazolone, phenol groups, urea group, etc. The one-electron transfer was the dominant micropollutant degradation pathway, followed by indirect oxidation by superoxide anion radical (O2•−) or hydroxyl radical (•OH). In UV-activated ClO2 oxidation, the reactions of micropollutants followed the pseudo-first-order reaction kinetics with the rates of 1.3 × 10−4–12.9 s−1 at pH 7.0. Their degradation pathways include direct ClO2 oxidation, direct UV photolysis, ozonation, •OH-involved reaction, and reactive chlorine species (RCS)-involved reaction. Finally, we identified the research gaps and provided recommendations for further research. Therefore, this review gives a critical evaluation of ClO2-based oxidation in micropollutant abatement, and provides recommendations for further research.