Chlorine Dioxide Controls Green Mold Caused by Penicillium digitatum in Citrus Fruits and the Mechanism Involved

A carboxymethyl cellulose-based pH-responsive chlorine dioxide release film for strawberry preservation

Fruit spoilage caused by microorganisms results in huge economic losses and health risks worldwide every year. To develop an intelligent antimicrobial material capable of responding to the physiological activity of postharvest fruits and releasing antibacterial agents on demand, we fabricated a pH-responsive film for the release of chlorine dioxide (ClO2) using carboxymethyl cellulose (CMC) and sodium chlorite (NaClO2) via the solution casting method, with a CMC:NaClO2 ratio of 1:2 w/w. An acid environment simulated by 4 % acetic acid activated 43 % of ClO2 released by the film within 7 days. A 1 × 2 cm2 film in acid environment effectively inhibited the growth of Staphylococcus aureus (106 CFU/mL), Escherichia coli (105 CFU/mL), and Aspergillus niger on agar media (with colony diameters reduced from 60.00 mm to 19.07 mm). A 3 × 3 cm2 film reduced the decay incidence caused by A. niger in strawberry from 100 % (control) to only 20 % on day 6. Compared with the control group, no significant differences in color, total soluble solids (TSSs) or triable acidity (TA) were observed in the film-treated groups. The development of pH-responsive NaClO2-CMC films offers a practical and effective solution for extending the shelf-life and maintaining the quality of fruit.

Biochemical mechanism of chlorine dioxide fumigation in inhibiting Ceratocystis fimbriata and black rot in postharvest sweetpotato

The inhibitory properties and underlying mechanism of chlorine dioxide (ClO2) fumigation on the pathogen Ceratocystis fimbriata (C. fimbriata) and resultant sweetpotato black rot were investigated in vitro and in vivo. Results revealed that the ClO2 fumigation effectively inhibited fungal growth and induced obvious morphological variation of C. fimbriata mycelia. Furthermore, the mycelial membrane suffered damage, as evidenced by a significant increase in malondialdehyde content and the leakage of protein and nucleic acid from mycelia cells, accompanied by a marked decrease in ergosterol content. Additionally, ClO2 fumigation caused spores cell membrane damage, a notable decrease in spore viability, and induced cell apoptosis as indicated by reductions in spore germination rate, two fluorescence staining observations, and flow cytometry analysis. Moreover, the decay diameter of sweetpotato black rot lesions decreased significantly after ClO2 fumigation, and the growth of C. fimbriata was also inhibited. These findings present a novel and effective technology for inhibiting the progression of sweetpotato black rot.

γ-Cyclodextrin encapsulated thymol for citrus preservation and its possible mechanism against Penicillium digitatum

The volatility of essential oils greatly limits their industrial applications. Here, we successfully prepared γ-cyclodextrin (γ-CD) inclusion compounds (γ-CDTL) containing thymol (TL) for the control of green mold caused by Penicillium digitatum (P. digitatum) in citrus fruit. In vitro experiment showed that the minimum fungicidal concentration (MFC) of γ-CDTL against the hyphae growth of P. digitatum was 2.0 g/L, and 8 × MFC treatment significantly reduced the occurrence of green mold in citrus fruit and had no adverse effect on fruit quality in vivo test compared to prochloraz. Scanning electron microscopy (SEM), x-ray diffraction (XRD), fourier transform-infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), physical properties and sustained release properties were also performed, results indicated that the hydrogen bonds between TL and γ-CD were the basis for the formation of γ-CDTL. We further investigated the inhibition mechanism of γ-CDTL. SEM and TEM experiments showed that γ-CDTL treatment caused severe damage to the hyphal morphology and cells in 30 min and disrupted the permeability of P. digitatum mycelial cell walls by increasing the chitinase activity, thus accelerating the leakage of intracellular lysates. However, the integrity of the cell membrane was obviously damaged only after 60 min of treatment. In conclusion, we prepared a novel inclusion complex γ-CDTL with obvious antifungal effects and preliminarily elucidated its inclusion mechanism and antifungal mechanism. γ-CDTL might be a potent alternative to chemical fungicides for controlling the postharvest decay of citrus.

Generation, mechanisms, kinetics, and effects of gaseous chlorine dioxide in food preservation

Food preservation is a critical issue in ensuring food safety and quality. Growing concern around industrial pollution of food and demand for environmentally sustainable food has led to increased interest in developing effective and eco-friendly preservation techniques. Gaseous ClO2 has gained attention for its strong oxidizing properties, high efficacy in microorganism inactivation, and potential for preserving the attributes and nutritional quality of fresh food while avoiding the formation of toxic byproducts or unacceptable levels of residues. However, the widespread use of gaseous ClO2 in the food industry is limited by several challenges. These include large-scale generation, high cost and environmental considerations, a lack of understanding of its mechanism of action, and the need for mathematical models to predict inactivation kinetics. This review aims to provide an overview of the up-to-date research and application of gaseous ClO2 . It covers preparation methods, preservation mechanisms, and kinetic models that predict the sterilizing efficacy of gaseous ClO2 under different conditions. The impacts of gaseous ClO2 on the quality attributes of fresh produce and low-moisture foods, such as seeds, sprouts, and spices, are also summarized. Overall, gaseous ClO2 is a promising preservation approach, and future studies are needed to address the challenges in large-scale generation and environmental considerations and to develop standardized protocols and databases for safe and effective use in the food industry.

Biocontrol Microneedle Patch: A Promising Agent for Protecting Citrus Fruits from Postharvest Infection

With increasing human awareness of food safety, the replacement of highly toxic pesticides with biocompatible antimicrobials has become a trend. This study proposes a biocontrol microneedle (BMN) to expand the application of the food-grade preservative epsilon-poly-L-lysine (ε-PL) in fruit preservatives by utilizing a dissolving microneedle system. The macromolecular polymer ε-PL not only possesses broad-spectrum antimicrobial activity but also exhibits good mechanical properties. With the addition of a small amount of polyvinyl alcohol, the mechanical strength of the ε-PL-based microneedle patch could be further improved to achieve an enhanced failure force of needles at 1.6 N/needle and induce an approximately 96% insertion rate in citrus fruit pericarps. An ex vivo insertion test revealed that the microneedle tips could be effectively inserted into the citrus fruit pericarp, rapidly dissolve within 3 min, and produce inconspicuous needle holes. Moreover, the high drug loading capacity of BMN was observed to reach approximately 1890 μg/patch, which is essential for enhancing the concentration-dependent antifungal activity of ε-PL. The drug distribution study has confirmed the feasibility of mediating the local diffusion of EPL in the pericarp through BMN. Therefore, BMN has great potential to reduce the incidence of invasive fungal infections in local areas of citrus fruit pericarp.

Chlorine Dioxide Reprograms Rhizosphere Microbial Communities to Enrich Interactions with Tobacco (Nicotiana tabacum)

For decades chlorine dioxide has been used in water disinfection with excellent results. As the scope of application expands, chlorine dioxide has the potential for soil disinfection. We used amplicon sequencing and gas chromatography-mass spectrometry to compare the changes of four mixed rhizosphere microbial community samples and 12 tobacco leaf volatile samples four months after the flood irrigation with chlorine dioxide in different concentrations (0, 2, 4, 8 mg/l). Phenotypic data of 60 tobacco plants were also collected. The effects of chlorine dioxide on rhizosphere microorganisms were positively correlated with dose gradients. Bacteria responded more strongly in both community structure and metabolic pathways than fungi. Five new bacterial phyla (Firmicutes, Bacteroidota, Myxococcota, Patescibacteria, Verrucomicroboata) appeared in chlorine dioxide treatment groups, while the fungal community only appeared as one new fungal phylum (Basidomycota). Alterations in 271 predicted metabolic bacterial pathways were found. However, in the fungal community were only 10 alternations. The correlations between leaf volatile compounds and rhizosphere microorganisms under the influence of chlorine dioxide treatment could be observed based on network results. However, natural connectivity had already been declining rapidly when less than 20% of the network's nodes were removed. Therefore, the microbe-metabolite network is not stable. It might be why chlorine dioxide treatments did not significantly affect tobacco quality (p = 0.754) and phenotype (p = 0.867). As a comprehensive investigation of chlorine dioxide in agriculture, this study proves the effectiveness and safety of chlorine dioxide soil disinfection and widens the application range of chlorine dioxide.

Development of chlorine dioxide sustained-release device using carboxymethyl cellulose-polyvinyl alcohol-β-cyclodextrin ternary hydrogel and a new sustained-release kinetic model

Owing to unique physiochemical and biological properties as well as the ability to be combined with a wide variety of materials for both biocompatibility and hydrophilia, carboxymethyl cellulose (CMC) is an excellent choice as a carrier. Loading Chlorine dioxide (ClO₂) into biodegradable carrier for its good disinfection performance and high safety factors has attracted significantattention. Therefore, in this study, we used ClO₂ as a model drug, and a sustained-ClO₂-gas-release gel was developed from degradable materials, such as carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and β-cyclodextrin (βCD), through a simple and benign crosslinking strategy. Notably, the gel had sustained-release property in a wide temperature range of 4-35 ℃ and released ClO₂ gas effectively for more than 30 days. Furthermore, a loss factor was proposed based on the incomplete release of the drug in the sustained release process to a chieve a good fit with the gas diffusion process. A new diffusion model was designed based on the Korsmeyer-Peppas model, and an excellent fit was obtained. This sustained-ClO₂-gas-release gel provides theoretical and technical guidance for the development of sustained-disinfectant-release agents for use in space and offers new insights into the sustained release model of skeleton-soluble hydrogels.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10570-023-05070-6.

Occurrence of fungal spores in drinking water: A review of pathogenicity, odor, chlorine resistance and control strategies

Fungi in drinking water have been long neglected due to the lack of convenient analysis methods, widely accepted regulations and efficient control strategies. However, in the last few decades, fungi in drinking water have been widely recognized as opportunity pathogens that cause serious damage to the health of immune-compromised individuals. In drinking water treatment plants, fungal spores are more resistant to chlorine disinfection than bacteria and viruses, which can regrow in drinking water distribution systems and subsequently pose health threats to water consumers. In addition, fungi in drinking water may represent an ignored source of taste and odor (T&O). This review identified 74 genera of fungi isolated from drinking water and presented their detailed taxonomy, sources and biomass levels in drinking water systems. The typical pathways of exposure of water-borne fungi and the main effects on human health are clarified. The fungi producing T&O compounds and their products are summarized. Data on free chlorine or monochloramine inactivation of fungal spores and other pathogens are compared. At the first time, we suggested four chlorine-resistant mechanisms including aggregation to tolerate chlorine, strong cell walls, cellular responses to oxidative stress and antioxidation of melanin, which are instructive for the future fungi control attempts. Finally, the inactivation performance of fungal spores by various technologies are comprehensively analyzed. The purpose of this study is to provide an overview of fungi distribution and risks in drinking water, provide insight into the chlorine resistance mechanisms of fungal spores and propose approaches for the control of fungi in drinking water.

Chlorine Dioxide Treatment Modulates Ripening-Related Genes and Antioxidant System to Improve the Storability of Tomato

Chlorine dioxide (ClO2) is used to maintain quality and safety of fresh produce. However, ClO2 action mechanism in fresh produce is unknown. In this study, firstly, we evaluated the efficacy of ClO2 treatment on the quality, chilling injury, and calyx molding of tomatoes stored at two different temperatures. Then, ClO2 effect on the expression of cell wall- and ripening-related genes and on the activity of antioxidant enzymes was investigated. Tomatoes were treated with gaseous ClO2 for 15 min before transferring them to 13°C for 12 days and/or 4°C for 14 days, followed by 5 days at 20°C (shelf-life conditions). ClO2 treatment marginally reduced the rate of respiration but did not affect ethylene production at 13°C and 4°C storage or at shelf-life conditions. When stored at 13°C, treatment with ClO2 reduced the loss of firmness, with concomitant repression of pectin esterase 1, a cell wall-related gene. Additionally, at 13°C storage conditions, ClO2 treatment maintained tomato quality in terms of soluble solid content, titratable acidity, and color and was associated with the downregulation of the ripening-relatedethylene response factors B3/C1/E1 and the induction of antioxidant genes encoding catalase and ascorbate peroxidase. At 4°C storage conditions, ClO2 at a concentration of 15 ppm not only maintained the firmness and quality of tomatoes but also inhibited pitting during shelf-life with a concomitant increase of catalase activity. Moreover, treatment with 15 ppm ClO2 significantly reduced the calyx molding that is generally observed in fruits stored at 13°C and under shelf-life conditions. Hence, our results indicate that ClO2 treatment effectively maintained tomato quality and inhibited calyx molding by partially regulating ripening-related genes and antioxidant systems, thereby improving the storability of postharvest tomatoes.

The Effects of Storage Temperature, Light Illumination, and Low-Temperature Plasma on Fruit Rot and Change in Quality of Postharvest Gannan Navel Oranges

Gannan navel orange (Citrus sinensis Osbeck cv. Newhall) is an economically important fruit, but postharvest loss occurs easily during storage. In this study, the effects of different temperatures, light illuminations, and low-temperature plasma treatments on the water loss and quality of the Gannan navel orange were investigated. The fruit began to rot after 90 d of storage at 5 °C and 20-45 d at 26 °C. Navel oranges stored at 26 °C had 7.2-fold and 3.1-fold higher rates of water loss at the early and late storage stages, respectively, as compared with those stored at 5 °C. Storage at 5 °C decreased the contents of total soluble solids at the early storage stage and the contents of titratable acids at the late storage stage, whereas storage at 26 °C decreased the contents of total soluble solids at the late storage stage and the contents of titratable acids at the early storage stage, respectively. Application of low-temperature plasma produced by air ionization for 6 min, or continuous blue or red light illumination significantly inhibited water loss within 7 and 21 d of storage at 22 °C, respectively, but exhibited no significant effect on fruit quality. Furthermore, the low-temperature plasma treatment protected against fruit rot. Thus, treatment with low-temperature plasma followed by storage at a low temperature under continuous red or blue light illumination was of potential value as a green technology for preserving Gannan navel orange during storage.

Lignin Biosynthesis Pathway and Redox Balance Act Synergistically in Conferring Resistance against Penicillium italicum Infection in 7-Demethoxytylophorine-Treated Navel Orange

7-Demethoxytylophorine (DEM), a natural water-soluble phenanthroindolizidine alkaloid, has a great potential for in vitro suppression of Penicillium italicum growth. In the present study, we investigated the ability of DEM to confer resistance against P. italicum in harvested "Newhall" navel orange and the underlying mechanism. Results from the in vivo experiment showed that DEM treatment delayed blue mold development. The water-soaked lesion diameter in 40 mg L^-1 DEM-treated fruit was 35.2% lower than that in the control after 96 h. Moreover, the decrease in peel firmness loss and increase in electrolyte leakage, superoxide anion (O₂^•-) production, and malondialdehyde (MDA) content were significantly inhibited by DEM treatment. Hydrogen peroxide (H₂O₂) burst in DEM-treated fruit at the early stage of P. italicum infection contributed to the conferred resistance by increasing the activities of lignin biosynthesis-related enzymes, along with the expressions of their encoding genes, resulting in lignin accumulation. The DEM-treated fruit maintained an elevated antioxidant capacity, as evidenced by high levels of ascorbic acid and glutathione content, and enhanced or upregulated the activities and gene expression levels of APX, GR, MDHAR, DHAR, GPX, and GST, thereby maintaining ROS homeostasis and reducing postharvest blue mold. Collectively, the results in the present study revealed a control mechanism in which DEM treatment conferred the resistance against P. italicum infection in harvested "Newhall" navel orange fruit by activating lignin biosynthesis and maintaining the redox balance.

An injectable and biodegradable hydrogel incorporated with photoregulated NO generators to heal MRSA-infected wounds

The development of degradable hydrogel fillers with high antibacterial activity and wound-healing property is urgently needed for the treatment of infected wounds. Herein, an injectable, degradable, photoactivated antibacterial hydrogel (MPDA-BNN6@Gel) was developed by incorporating BNN6-loaded mesoporous polydopamine nanoparticles (MPDA-BNN6 NPs) into a fibrin-based hydrogel. After administration, MPDA-BNN6@Gel created local hyperthermia and released large quantities of NO gas to treat methicillin-resistant Staphylococcus aureus infection under the stimulation of an 808 nm laser. Experiments confirmed that the bacteria were eradicated through irreversible damage to the cell membrane, genetic metabolism, and material energy. Furthermore, in the absence of laser irradition, the fibrin and small amount of NO that originated from MPDA-BNN6@Gel promoted wound healing in vivo. This work indicates that MPDA-BNN6@Gel is a promising alternative for the treatment of infected wounds and provides a facile tactic to design a photoregulated bactericidal hydrogel for accelerating infected wound healing. STATEMENT OF SIGNIFICANCE: The development of a degradable hydrogel with high antibacterial activity and wound-healing property is an urgent need for the treatment of infected wounds. Herein, an injectable, degradable, and photo-activated antibacterial hydrogel (MPDA-BNN6@Gel) has been developed by incorporating BNN6-loaded mesoporous polydopamine nanoparticles (MPDA-BNN6 NPs) into a fibrin-based hydrogel. After administration of MPDA-BNN6@Gel, the MPDA-BNN6@Gel could generate local hyperthermia and release large quantities of NO gas to treat the methicillin-resistant Staphylococcus aureus infection under the irradiation of 808 nm laser. Furthermore, in the absence of a laser, the fibrin and a small amount of NO originating from MPDA-BNN6@Gel could promote wound healing in vivo.

Involvement of Organic Acid in the Control Mechanism of ε-Poly-L-lysine (ε-PL) on Blue Mold Caused by Penicillium expansum in Apple Fruits

Blue mold is one of the most serious postharvest diseases in apples caused by Penicillium expansum. The purpose of this study is to determine the effect of ε-poly-L-lysine (ε-PL) on the pathogenicity of P. expansum and explore the potential mechanism from the perspective of organic acid. The study investigates the effect of ε-PL treatment on the growth and acid production of P. expansum in vitro and in vivo. When the concentration of ε-PL was 50 mg/L, the growth of P. expansum was inhibited and the decrease in pH value was delayed in the medium. For example, on the third day of culture, P. expansum reduced the pH of the medium from 6.1 to 4.15, and ε-PL inhibited the decrease in the pH value at most 34.4%. When the concentration reached 1000 or 2000 mg/L, the infection of P. expansum in fruits was effectively inhibited. During the growth and infection of P. expansum, gluconic acid is one of the main factors leading to the pH value falling in the local environment. After ε-PL treatment, the accumulation of gluconic acid decreased, the activity of glucose oxidase was suppressed, and then the decline in the local environmental pH slowed down. In addition, after ε-PL treatment, the activities of cell-wall-degrading enzymes, such as cellulase (CL) and polygalacturonase (PG), in the different areas of the P. expansum–apple interaction were also affected by pH change. The results show that ε-PL inhibited the pathogenicity of P. expansum by affecting the accumulation of gluconic acid and slowing the decline in pH in fruit tissues, so as to affect the pathogenicity of P. expansum. This is the first time that the mechanism of ε-PL interfering with the pathogenicity of P. expansum from the perspective of organic acids is clarified.

LC-ESI-QTOF/MS characterization of antimicrobial compounds with their action mode extracted from vine tea (Ampelopsis grossedentata) leaves

Vine tea (Ampelopsis grossedentata) is a tea plant cultivated south of the Chinese Yangtze River. It has anti-inflammatory properties and is used to normalize blood circulation and detoxification. The leaves of vine tea are the most abundant source of flavonoids, such as dihydromyricetin and myricetin. However, as the main bioactive flavonoid in vine tea, dihydromyricetin was the main focus of previous research. This study aimed to explore the antibacterial activities of vine tea against selected foodborne pathogens. The antimicrobial activity of vine tea extract was evaluated by the agar well diffusion method. Cell membrane integrity and bactericidal kinetics, along with physical damage to the cell membrane, were also observed. The extract was analyzed using a high-performance liquid chromatography-diode array detector (HPLC-DAD), and the results were confirmed using a modified version of a previously published method that combined liquid chromatography and electrospray-ionized quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF/MS). Cell membrane integrity and bactericidal kinetics were determined by releasing intracellular material in suspension and monitoring it at 260 nm using an ultraviolet (UV) spectrophotometer. A scanning electron microscope (SEM) was used to detect morphological alterations and physical damage to the cell membrane. Six compounds were isolated successfully: (1) myricetin (C15H10O8), (2) myricetin 3-O-rhamnoside (C21H20O12), (3) 5,7,8,3,4-pentahydroxyisoflavone (C15H10O7), (4) dihydroquercetin (C15H12O7), (5) 6,8-dihydroxykaempferol (C15H10O8), and (6) ellagic acid glucoside (C20H16O13). Among these bioactive compounds, C15H10O7 was found to have vigorous antimicrobial activity against Bacillus cereus (AS11846) and Staphylococcus aureus (CMCCB26003). A dose-dependent bactericidal kinetics with a higher degree of absorbance at optical density 260 (OD260) was observed when the bacterial suspension was incubated with C15H10O7 for 8 h. Furthermore, a scanning electron microscope study revealed physical damage to the cell membrane. In addition, the action mode of C15H10O7 was on the cell wall of the target microorganism. Together, these results suggest that C15H10O7 has vigorous antimicrobial activity and can be used as a potent antimicrobial agent in the food processing industry.

Organic acid, a virulence factor for pathogenic fungi, causing postharvest decay in fruits

Decay due to fungal infection is a major cause of postharvest losses in fruits. Acidic fungi may enhance their virulence by locally reducing the pH of the host. Several devastating postharvest fungi, such as Penicillium spp., Botrytis cinerea, and Sclerotinia sclerotiorum, can secrete gluconic acid, oxalic acid, or citric acid. Emerging evidence suggests that organic acids secreted by acidic fungi are important virulence factors. In this review, we summarized the research progress on the biosynthesis of organic acids, the role of the pH signalling transcription factor PacC in regulating organic acid, and the action mechanism of the main organic acid secreted via postharvest pathogenic fungi during infection of host tissues. This paper systematically demonstrates the relationships between tissue acidification and postharvest fungal pathogenicity, which will motivate the study of host-pathogen interactions and provide a better understanding of virulence mechanisms of the pathogens so as to design new technical strategies to prevent postharvest diseases.

Fresh Produce Safety and Quality: Chlorine Dioxide's Role

Maintaining microbial safety and quality of fresh fruits and vegetables are a global concern. Harmful microbes can contaminate fresh produce at any stage from farm to fork. Microbial contamination can affect the quality and shelf-life of fresh produce, and the consumption of contaminated food can cause foodborne illnesses. Additionally, there has been an increased emphasis on the freshness and appearance of fresh produce by modern consumers. Hence, disinfection methods that not only reduce microbial load but also preserve the quality of fresh produce are required. Chlorine dioxide (ClO₂) has emerged as a better alternative to chlorine-based disinfectants. In this review, we discuss the efficacy of gaseous and aqueous ClO₂ in inhibiting microbial growth immediately after treatment (short-term effect) versus regulating microbial growth during storage of fresh produce (long-term effect). We further elaborate upon the effects of ClO₂ application on retaining or enhancing the quality of fresh produce and discuss the current understanding of the mode of action of ClO₂ against microbes affecting fresh produce.