Polymethoxylated flavonoids (PMFs)-loaded citral nanoemulsion controls green mold in citrus by damaging the cell membrane of Penicillium digitatum

Starch-octenyl succinic anhydride nanoemulsions with clove and white thyme essential oils: In vitro antifungal activity and application on orange (Citrus sinensis cv. Salustiana) preservation

Starch modified by octenyl succinic anhydride (OSA) is a polysaccharide that can be used as a stabilizer in the development of emulsions added with essential oils (EOs). The objective of this study was to develop nanoemulsions based on starch-OSA containing clove essential oil (CEO) and white thyme essential oil (WTEO) and a proportional mixture of the two EOs (CWTEO) using high-pressure homogenization. The emulsions were characterized by particle size, zeta potential, polydispersity index, stability during 150 days, and antifungal activity, with inhibition of mycelial growth, against the fungus Penicillium digitatum. The addition of WTEO and CWTEO in concentrations of 1.5 and 2 % allowed the formation of stable nanoemulsions, with particle sizes ranging from 72 to 293 nm. These nanoemulsions presented the potential to reduce the mycelial growth of P. digitatum (100 % for nanoemulsion with 2 % WTEO and 80.5 % to 2 % CWTEO) up to 150 days of storage. A nanoemulsion containing 2 % WTEO was applied to orange fruits, and its antifungal potential was evaluated in vivo. This nanoemulsion was able to reduce the incidence of rot caused by P. digitatum in oranges, demonstrating their potential for application as an alternative to synthetic fungicides to reduce postharvest losses in citrus fruits.

Inhibitory activity and antioomycete mechanism of citral against Phytophthora capsici

The natural terpenoid citral has antifungal activity against multiple fungi, but its bioactivity against oomycetes is unclear. Therefore, this study investigated the antioomycete activity and mechanism of citral against Phytophthora capsici, a highly destructive invasive oomycete. Results showed that citral not only had a great inhibition on the mycelial growth of P. capsici (EC50 = 94.15 mg/L), but also had a significant inhibition on multiple spores, such as sporangia formation, zoospore discharge and zoospore germination. Citral at 4000 mg/L exhibited favorable protective (73.33%) and curative efficacy (55.11%) against pepper Phytophthora blight. Citral significantly damaged the hyphal morphology, disrupted the cell membrane integrity, increased the permeability of cell membrane, and increased the glycerol content in P. capsici. A total of 250 upregulated and 288 downregulated proteins were identified in iTRAQ-based quantitative proteomic analysis. Downregulated proteins were mostly enriched in pathways of ABC transporters, cyanoamino acid metabolism and starch and sucrose metabolism, suggesting an inhibition of citral on transmembrane transporter (e.g., ABC transporters) and pathogenicity (e.g., β-glucosidases) proteins. Upregulated proteins were enriched in biosynthesis of unsaturated fatty acids, pyruvate metabolism and glycolysis/gluconeogenesis, suggesting an activation of citral on energy generation proteins, including acyl-CoA oxidase, D-lactate dehydrogenase, pyruvate kinase, acetyl-CoA synthetase and phosphoenolpyruvate carboxykinase. Biochemical and iTRAQ analysis suggested that cell membrane may be the target of citral in P. capsici.

A Novel Preservative Film with a Pleated Surface Structure and Dual Bioactivity Properties for Application in Strawberry Preservation due to Its Efficient Apoptosis of Pathogenic Fungal Cells

Botrytis cinerea (B. cinerea) and Colletotrichum gloeosporioides (C. gloeosporioides) were isolated from the decaying strawberry tissue. The antifungal properties of Monarda didyma essential oil (MEO) and its nanoemulsion were confirmed, demonstrating complete inhibition of the pathogens at concentrations of 0.45 μL/mL (0.37 mg/mL) and 10 μL/mL, respectively. Thymol, a primary component of MEO, was determined as an antimicrobial agent with IC50 values of 34.51 (B. cinerea) and 53.40 (C. gloeosporioides) μg/mL. Hippophae rhamnoides oil (HEO) was confirmed as a potent antioxidant, leading to the development of a thymol-HEO-chitosan film designed to act as an antistaling agent. The disease index and weight loss rate can be reduced by 90 and 60%, respectively, with nutrients also being well-preserved, offering an innovative approach to preservative development. Studies on the antifungal mechanism revealed that thymol could bind to FKS1 to disrupt the cell wall, causing the collapse of mitochondrial membrane potential and a burst of reactive oxygen species.

Nobiletin enhances the antifungal activity of eugenol nanoemulsion against Penicillium italicum in both in vitro and in vivo settings

The study prepared and used eugenol nanoemulsion loaded with nobiletin as fungistat to study its antifungal activity and potential mechanism of Penicillium italicum (P. italicum). The results showed that the minimum inhibitory concentration (MIC) of eugenol nanoemulsion loaded with nobiletin (EGN) was lower than that of pure eugenol nanoemulsion (EG), which were 160 μg/mL and 320 μg/mL, respectively. At the same time, the mycelial growth inhibition rate of EGN nanoemulsion (54.68 %) was also higher than that of EG nanoemulsion (9.92 %). This indicates that EGN nanoemulsion is more effective than EG nanoemulsion. Compared with EG nanoemulsion, the treatment of EGN nanoemulsion caused more serious damage to the cell structure of P. italicum. At the same time, in vitro inoculation experiments found that EGN nanoemulsion has better control and delay the growth and reproduction of P. italicum in citrus fruits. And the results reflected that EGN nanoemulsion may be considered as potential resouces of natural antiseptic to inhibit blue mold disease of citrus fruits, because it has good antifungal activity.

Effect of polyethoxylated flavonoids (PMFs)-loaded citral and chitosan composite coatings on citrus preservation: From the perspective of fruit resistance

Previous studies have shown that polymethoxylated flavonoids-loaded citral emulsion (PCT) can inhibit the growth and reproduction of Penicillium in citrus; however, PCT is difficult to apply to fruit preservation due to its high fluidity and volatility. Therefore, in this study, we combined PCT with chitosan (CS) to investigate the effect of a composite coating on citrus preservation. The results showed that compared to the control group, the CS-PCT group could effectively reduce the decay rate and maintain moisture availability, color difference, and hardness. Moreover, the contents of nonenzymatic antioxidants and volatile substances with antimicrobial activity were better preserved. In addition, the activities of related antioxidant enzymes were greater in the treatment group, and the expression of the corresponding enzyme-encoding genes was upregulated. Consequently, CS-PCT treatment could effectively maintain fruit quality and improve the resistance of citrus fruits during storage; moreover, it can be considered a nontoxic and efficient citrus preservative.

Citrus essential oils - Based nano-emulsions: Functional properties and potential applications

Citrus essential oils are natural products with various bioactive properties (e.g., antimicrobial, antioxidant, and antimutagenic activities), that are generally recognized as safe (GRAS) by Food and Drug Administration (FDA) to be used as flavorings and food additives. Nonetheless, due to their high volatility, low solubility in water, low thermal stability, susceptibility to oxidation, and strong flavor, their applications in the food industry are limited. Nanotechnology allows the incorporation of citrus essential oils into nano-emulsion systems, thus protecting them from the deterioration caused by external factors and maintaining or even improving their functional properties. This study aims to summarize the antioxidant, antimicrobial, and antimutagenic effects of the nano-emulsions based on essential oils from citrus peels with emphasis on their mechanisms of action and potential applications in, e.g., foods, pharmaceuticals, and cosmetics.