Effect of Thymol and Carvacrol Encapsulated in Hp-Β-Cyclodextrin by Two Inclusion Methods against Geotrichum citri-aurantii

Polymeric films of corn starch enhance the lethal effects of thymol and carvacrol terpenes upon Rhipicephalus microplus ticks

The tick Rhipicephalus microplus is a parasite of great importance in cattle breeding. It is responsible for huge economic losses. The application of synthetic acaricides is used as a form of control. However, resistant strains have been selected over the years, making it necessary to search for new alternative formulations. The present study aimed to formulate biodegradable films impregnated with the terpenes carvacrol and thymol and evaluate their efficacy on larvae and adults of R. microplus through in vitro tests. The following formulations were prepared: Film 1 (starch based); Film 2 (based on starch and glycerol); Film 1 + Carvarcol or Thymol; Film 2 + Carvarcol or Thymol. Terpenes had a final concentration of 5.0 mg/mL. To evaluate the formulations on larvae, the immersion test was performed by dividing into six groups according to the concentration of terpenes: 5.0, 2.5, 1.25, 0.625, 0.313, 0.156 mg/mL and the control groups: 1% ethanol solution; 10% ethanol solution; Film 1; and Film 2. For the evaluations on adult ticks, ten experimental groups (n = 10) were used: 1) Carvacrol; 2) Film 1 + Carvacrol; 3) Film 2 + Carvacrol; 4) Thymol; 5) Film 1 + Thymol; 6) Film 2 + Thymol; 7) Distilled water; 8) 10% ethanol solution; 9) Film 1; and 10) Film 2. In experimental groups 1-6, carvacrol and thymol (free or incorporated in two different biodegradable film formulations) were evaluated at the same concentration (5.0 mg/mL). Each group of ticks was immersed in their respective solutions for five minutes. The results of the tests on larvae showed that the Film 1 + thymol and Film 2 + carvacrol formulations had the lowest lethal concentrations (0.076 and 0.255 mg/mL, respectively), values up to 9.0-fold lower than the monoterpenes tested outside the formulation. Carvacrol and thymol at the concentrations tested were effective in controlling engorged females with a percentage of 32.2% and 63.8%, respectively. When incorporated into biodegradable film formulations, these monoterpenes showed much greater efficacy. Film 1 + carvacrol and Film 2 + carvacrol with control percentages of 71.6% and 97.2%, respectively, while the formulations Film 1 + thymol and Film 2 + thymol showed values of 96.9% and 100.0%. The tick control activity of the biopolymer formulations with thymol and carvacrol was demonstrated through the high mortality rates of larvae and engorged females of the tick R. microplus. Therefore, the results obtained indicate that these formulations have great potential for tick control mainly because of the percentage of control up to 100% in engorged females in in vitro tests.

Exploring the efficacy of carvacrol as a biocontrol agent against pear Valsa canker

Valsa canker, a fungal disease caused by Valsa pyri, poses a significant threat to the pear industry. Currently, chemical control serves as the primary method to control valsa canker. However, the emergence of resistance can pose a challenge to its effectiveness. Biopesticides are a relatively new option for disease control, but there is limited research on their effects on pear Valsa canker. To determine the effectiveness of different biopesticides, we selected 10 common biopesticides to test their inhibition efficacy and impacts on mycelial growth rate and conidial germination. Results showed that carvacrol had very good antifungal activity; therefore its inhibition mechanisms were further investigated. Electron microscopy and transcriptome data analysis were utilized to examine how carvacrol impeded V. pyri by inducing mycelium deformation, wrinkling, and rupture. Carvacrol also affected plant hormones, thus improving plant resistance to the disease. This study lays the groundwork for the utilization of 10 distinct biopesticides to control V. pyri while elucidating how carvacrol harms the pathogen and prompts the plant defense control mechanism.

The GRAS Salts of Na2SiO3 and EDTA-Na2 Control Citrus Postharvest Pathogens by Disrupting the Cell Membrane

Sodium silicate (Na₂SiO₃) and ethylenediaminetetraacetic acid disodium salt (EDTA-Na₂) are inorganic salts classified as 'Generally Recognized as Safe' (GRAS) compounds with great advantages in controlling various pathogens of postharvest fruits and vegetables. Here, we determined the median effective concentration (EC₅₀) of Na₂SiO₃ (0.06%, 0.05%, 0.07% and 0.08%) and EDTA-Na₂ (0.11%, 0.08%, 0.5%, and 0.07%) against common pathogens affecting postharvest citrus fruit, including Penicillium digitatum, Penicillium italicum, Geotrichum citri-aurantii, and Colletotrichum gloeosporioides. Na₂SiO₃ and EDTA-Na₂ treatments at the EC₅₀ decreased the spore germination rate, visibly disrupted the spore cell membrane integrity, and significantly increased the lipid droplets (LDs) of the four postharvest pathogens. Moreover, both treatments at EC₅₀ significantly reduced the disease incidence of P. italicum (by 60% and 93.335, respectively) and G. citri-aurantii (by 50% and 76.67%, respectively) relative to the control. Furthermore, Na₂SiO₃ and EDTA-Na₂ treatment resulted in dramatically lower disease severity of the four pathogens, while also demonstrating no significant change in citrus fruit quality compared with the control. Therefore, Na₂SiO₃ and EDTA-Na₂ present a promising approach to control the postharvest diseases of citrus fruit.

Inhibitory effect of carvacrol against Alternaria alternata causing goji fruit rot by disrupting the integrity and composition of cell wall

Goji (Lycium barbarum L.) is a widely planted crop in China that is easily infected by the pathogenic fungus Alternaria alternata, which causes rot after harvest. Previous studies showed that carvacrol (CVR) significantly inhibited the mycelial growth of A. alternata in vitro and reduced Alternaria rot in goji fruits in vivo. The present study aimed to explore the antifungal mechanism of CVR against A. alternata. Optical microscopy and calcofluor white (CFW) fluorescence observations showed that CVR affected the cell wall of A. alternata. CVR treatment affected the integrity of the cell wall and the content of substances in the cell wall as measured by alkaline phosphatase (AKP) activity, Fourier transform-infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Chitin and β-1,3-glucan contents in cells decreased after CVR treatment, and the activities of β-glucan synthase and chitin synthase decreased. Transcriptome analysis revealed that CVR treatment affected cell wall-related genes in A. alternata, thereby affecting cell wall growth. Cell wall resistance also decreased with CVR treatment. Collectively, these results suggest that CVR may exert antifungal activity by interfering with cell wall construction, leading to impairment of cell wall permeability and integrity.

Screening of Oxygenated Aromatic Compounds for Potential Antifungal Activity against Geotrichum citri-aurantii through Structure-Activity Relationship Analysis

Sour rot caused by Geotrichum citri-aurantii (G. citri-aurantii) is responsible for huge economic losses during citrus fruit storage. However, the availability of chemical fungicides for controlling this disease is rather limited. In the present study, the antifungal activities of 25 oxygenated aromatic compounds against the mycelial growth of G. citri-aurantii were determined, and their corresponding structure-activity relationships were illustrated. Salicylaldehyde (pMIC = 2.689) possessed the strongest inhibitory effect on G. citri-aurantii growth, followed by thymol (pMIC = 2.478) and o-phthalaldehyde (pMIC = 2.429). Molecular electrostatic potential and molecular orbital analysis showed that the antifungal efficiency of test compounds was determined by the number and location of hydroxyl and aldehyde groups and the length of the ester chain. All compounds were selected for quantitative structure-antifungal activity relationship (QSAR) analysis. A three-dimensional-QSAR model of G. citri-aurantii inhibitors was established and demonstrated good predictive capability [comparative molecular field analysis, q² = 0.532, optimum number of components (ONC) =10, R² = 0.996, F = 560.325, standard error of estimation (SEE) = 0.034, and two descriptors; comparative similarity index analysis, q² = 0.675, ONC = 6, R² = 0.989, F = 263.354, SEE = 0.054, and five descriptors]. QSAR analysis showed that substitution at position 1 with hydrophilic and electron-withdrawing groups produced a hydrogen donor and thus improved the antifungal activity. In contrast, substitution at positions 4 or 5 with hydrophilic and electron-donating groups decreased its antifungal activity. These findings can provide theoretical guidance for preparing effective antifungal drugs for controlling sour rot in citrus.

Thymol Disrupts Cell Homeostasis and Inhibits the Growth of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a typical kind of symbiotic bacteria, which can cause human pneumonia, food poisoning, and other health problems. Nowadays, the corresponding prevention and treatment have been a hot issue of general concern in related research areas. However, the mechanism of action against S. aureus is not well understood. In order to tackle such problem, we used broth microdilution to discuss the antibacterial effect of 5-methyl-2-isopropylphenol and determine inhibitory concentration. In addition, membrane potential and lipid peroxidation levels were also measured under experimental conditions. The experimental results suggested that 300 μg/mL thymol might cause cell membrane damage and decrease of NADPH concentration and increase of NADP⁺ and lipid peroxidation level. In such condition, thymol has the potential to result in membrane rupture and disruption of cellular homeostasis. Furthermore, we also found that NOX₂ is involved in maintaining the balance of NADPH/NADP⁺ in cells. Finally, our work confirms that NOX₂ is a potential downstream target for thymol in the cell. Such target can provide specific guidance and recommendations for its application in antifungal activity. Meanwhile, our study also provides a new inspiration for the molecular mechanism of thymol's bacteriostatic action.

Fabrication and characterization of ethyl acetate-hydroxypropyl-β-cyclodextrin inclusion complex

Flavors play crucial role in food industry. Ethyl acetate, as probably one of the most used of all flavor chemicals by volume, is used widely in many industries. However, ethyl acetate is not too stable and can be slowly decomposed by moisture. Furthermore, ethyl acetate is a volatile liquid insoluble in water and it does not last long enough. In order to solve these problems, hydroxypropyl-β-cyclodextrin was used as wall material to encapsulate ethyl acetate in this work. The product was characterized by Fourier transform infrared (FTIR) spectroscopy and thermalgravimetric analysis (TGA). The results showed that the peaks at 1,744 and 1,056 cm^-1 in the FTIR spectrum of ethyl acetate disappeared in the FTIR spectrum of ethyl acetate-hydroxypropyl-β-cyclodextrin inclusion complex. After the encapsulation of ethyl acetate, the O-H and C-H stretching absorption of hydroxypropyl-β-cyclodextrin changed. The TGA results showed that from 77°C to 292°C ethyl acetate is released from the ethyl acetate-hydroxypropyl-β-cyclodextrin inclusion complex in temperatures far beyond ethyl acetate 77°C boiling point. This phenomenon confirmed that the lastingness and thermal stability of ethyl acetate can be improved by the formation of an inclusion complex. The loading capacity of ethyl acetate was 4.86 ± 0.08% and ethyl acetate:hydroxypropyl-β-cyclodextrin stoichiometry is close to 1:1. The interaction of ethyl acetate and hydroxypropyl-β-cyclodextrin was investigated using molecular mechanics calculation. The binding energy was calculated and the possible conformation of ethyl acetate-hydroxypropyl-β-cyclodextrin inclusion complex was optimized to the minimum energy. The binding energy minimum is at the 0.44 × 10^-10  m point and its value is -103.9 kJ/mol. PRACTICAL APPLICATION: Encapsulation of ethyl acetate in hydroxypropyl-β-cyclodextrin is a possible way to protect ethyl acetate, improve its stability, water solubility, and may also enhance its lastingness.

Effect of PLA Active Packaging Containing Monoterpene-Cyclodextrin Complexes on Berries Preservation

Blackberries and raspberries are highly perishable and fragile products, which limits their shelf life. The effect of biodegradable active packaging of blackberries and raspberries containing 2.5% and 5.0% weight (wt%) of thymol or carvacrol complexed in β-cyclodextrins (β-CDs), successively added to poly (lactic acid) (PLA), and melt-processed by injection molding was evaluated under stored conditions at 4 °C for 21 days, using as reference commercial clamshell and PLA package control samples. Thus, physicochemical, headspace, microbiological, and sensory quality studies were carried out in order to compare the efficacy of the different packages. Concerning weight loss, color, and total phenolic and soluble solids content, significant differences were detected when compared with commercial clamshell packaging. The results show that the PLA packages containing thymol and carvacrol complexes maintained the color, weight, and phenolic content of berries until day 21, with a score up to 45% better compared to commercial clamshell. The headspace analysis detected 101 mg L⁻¹ (ppm) of thymol and 35 ppm of carvacrol on the first day of refrigeration; these concentrations decreased with time. This release mechanism of carvacrol and thymol into the PLA package modified the initial atmosphere composition. After 21 days of storage, the berries had 4.25 degrees of acceptance, without adverse perception of aroma or flavor for both carvacrol and thymol compounds. A general microbial inhibition was observed for yeast and molds, which increased with the concentration of monoterpene in PLA packages, and showed an inhibition of 3.5 log units for PLA packages containing thymol, and of 3 log units for those containing carvacrol. Overall results show that PLA/β-CD-thymol 5.0% packages prolonged raspberries’ and blackberries’ shelf life by one more week at 4 °C, compared with commercial clamshell packaging.

Thymol Encapsulated into HP-β-Cyclodextrin as an Alternative to Synthetic Fungicides to Induce Lemon Resistance against Sour Rot Decay

Consumers demand the use of eco-friendly fungicides to treat fruit and vegetables and governmental authorities have unauthorized the application of chemical antifungals for the efficient control of sour rot. In the present research, the microwave irradiation (MW) method was used to encapsulate thymol into 2-hydroxylpropyl-beta-cyclodextrin (HP-β-CD) and the effect of these HP-β-CD on controlling sour rot in citrus fruit, caused by Geotrichum citri-aurantii, was evaluated. Amounts of 25 and 50 mM of HP-β-CD-thymol were used, and compared with propiconazole, to control the decay of inoculated lemon fruit. The treatments were performed in curative and preventive experiments. The incidence and severity of Geotrichum citri-aurantii in 25 and 50 mM HP-β-CD-thymol-treated fruit were reduced in both experiments. The preventive 50 mM HP-β-CD-thymol treatment showed the best effect, reducing the sour rot, respiration rate and fruit weight loss during storage at 20 °C. HP-β-CD-thymol increased polyphenol concentration and the activity of antioxidant enzymes, such as catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD) in lemon peel, and the highest effects were found with the 50-mM dose. In conclusion, the results show that the use of thymol encapsulated by MW into HP-β-CD could be an effective and sustainable tool, a substitute to the synthetic fungicides, for G. citri-auriantii control in citrus fruit.

Development and Characterization of a Biodegradable PLA Food Packaging Hold Monoterpene-Cyclodextrin Complexes against Alternaria alternata

The fungi of the genus Alternaria are among the main pathogens causing post-harvest diseases and significant economic losses. The consumption of Alternaria contaminated foods may be a major risk to human health, as many Alternaria species produce several toxic mycotoxins and secondary metabolites. To protect consumer health and extend the shelf life of food products, the development of new ways of packaging is of outmost importance. The aim of this work was to investigate the antifungal capacity of a biodegradable poly(lactic acid) (PLA) package filled with thymol or carvacrol complexed in β-cyclodextrins (β-CDs) by the solubility method. Once solid complexes were obtained by spray drying, varying proportions (0.0%, 1.5%, 2.5%, and 5.0 wt%) of β-CD-thymol or β-CD-carvacrol were mixed with PLA for packaging development by injection process. The formation of stable complexes between β-CDs and carvacrol or thymol molecules was assessed by Fourier-transform infrared spectroscopy (FTIR). Mechanical, structural, and thermal characterization of the developed packaging was also carried out. The polymer surface showed a decrease in the number of cuts and folds as the amount of encapsulation increased, thereby reducing the stiffness of the packaging. In addition, thermogravimetric analysis (TGA) revealed a slight decrease in the temperature of degradation of PLA package as the concentration of the complexes increased, with β-CD-carvacrol or β-CDs-thymol complexes acting as plasticisers that lowered the intermolecular forces of the polymer chains, thereby improving the breaking point. Packages containing 2.5% and 5% β-CD-carvacrol, or 5% β-CD-thymol showed Alternaria alternata inhibition after 10 days of incubation revealing their potential uses in agrofood industry.