Essential oils based formulations as safe preservatives for stored plant masticatories against fungal and mycotoxin contamination: A review

Non-phytotoxic compounds of Baccharis from the Atlantic Forest as a sustainable alternative for controlling stored-wheat fungi

Among the plants present in the Atlantic Forest, Baccharis species have potential fungicidal activity against different fungi of agricultural interest. In this context, this study evaluated the fungicidal activity of essential oils (EOs) and hydrolates (HDs) of Baccharis articulata, Baccharis calvescens, and Baccharis milleflora (Asteraceae) against Aspergillus flavus, Aspergillus niger, Aspergillus nomius, Fusarium culmorum, and Fusarium graminearum, in addition to its effect on the germination of wheat seeds (Triticum aestivum). The EOs and HDs were extracted by steam distillation method, and the compounds present were identified by gas chromatography-mass spectrometry. The fungicidal activity was carried out by the contact method and volatilization. The yield content varied between species, with B. articulata presenting the highest value (0.77%). A total of 7, 16, and 27 chemical compounds were identified, corresponding to 92.62, 91.04, and 83.09% of the total chemical composition of EOs from B. articulata, B. calvescens, and B. milleflora, respectively. Using the contact method, Baccharis EOs and HDs were more effective in controlling Aspergillus and Fusarium isolates. Aspergillus flavus isolate had greater sensitivity to the EO from B. articulata (67.22% inhibition), while the HD from B. milleflora inhibited the growth of A. nomius by 71.66%. HDs caused inhibition between 25.84 and 44.22% of F. culmorum isolates. Using the volatilization method, isolates of A. flavus and F. culmorum (NRRL25475) had greater sensitivity to Baccharis EOs, with inhibition ranging from 4.25 to 20.20%. Wheat seed germination rate was greater than 90% for all treatments. The products obtained from the secondary metabolism of Baccharis species demonstrated fungicidal activity against storage pathogens and therefore may be promising substitutes for synthetic fungicides to control these microorganisms.

The Impact of Microorganisms on the Performance of Linseed Oil and Tung Tree Oil Impregnated Composites Made of Hemp Shives and Corn Starch

In this study, the performance characteristics of hemp shives impregnated with linseed oil and tung tree oil (HS)- and corn starch (CS)-based biocomposites containing flame retardants were evaluated before and after treatment with the mixture of bacterium Pseudomonas putida and fungus Rhizopus oryzae. Enzymatic activities and physical-mechanical properties such as water absorption, thickness swelling, compressive strength, and thermal conductivity were tested to evaluate the suitability of selected composites for thermal insulation purposes. In addition, electron microscopy was used to investigate the impact of microorganisms on the microstructure of the material. It was determined that the type of oil used for impregnation significantly affects the properties of biocomposites after 6 months of incubation with mixture of bacterium P. putida and fungus Rh. oryzae. Biocomposites impregnated with linseed oil and after treatment with a mixture of microorganisms had cellulase activity of 25 U/mL, endo β-1-4-glucanase activity of 26 U/mL, lipase activity of 101 U/mL, only a 10% decrease in compressive strength, 50% higher short-term water absorption, unchanged swelling in thickness, and slightly decreased thermal conductivity compared to control biocomposites. At the same time, biocomposites with tung tree oil had a much more pronounced deterioration of the properties tested, cellulase activity of 28 U/mL, endo β-1-4-glucanase activity of 37 U/mL, lipase activity of 91 U/mL, two times lower compressive strength and two times higher short-term water absorption, 2.5 times greater thickness swelling, and a slightly increased thermal conductivity. We conclude that linseed oil provides better protection against the action of microorganisms compared to impregnation with tung tree oil.

Antifungal Activity of Essential Oil and Plant-Derived Natural Compounds against Aspergillus flavus

Aspergillus flavus is a facultative parasite that contaminates several important food crops at both the pre- and post-harvest stages. Moreover, it is an opportunistic animal and human pathogen that causes aspergillosis diseases. A. flavus also produces the polyketide-derived carcinogenic and mutagenic secondary metabolite aflatoxin, which negatively impacts global food security and threatens human and livestock health. Recently, plant-derived natural compounds and essential oils (EOs) have shown great potential in combatting A. flavus spoilage and aflatoxin contamination. In this review, the in situ antifungal and antiaflatoxigenic properties of EOs are discussed. The mechanisms through which EOs affect A. flavus growth and aflatoxin biosynthesis are then reviewed. Indeed, several involve physical, chemical, or biochemical changes to the cell wall, cell membrane, mitochondria, and related metabolic enzymes and genes. Finally, the future perspectives towards the application of plant-derived natural compounds and EOs in food protection and novel antifungal agent development are discussed. The present review highlights the great potential of plant-derived natural compounds and EOs to protect agricultural commodities and food items from A. flavus spoilage and aflatoxin contamination, along with reducing the threat of aspergillosis diseases.

Essential oils and plant extracts for tropical fruits protection: From farm to table

The tropical fruit industry in Malaysia makes up a large proportion of the agriculture sector, contributing to the local economy. Due to their high sugar and water content, tropical fruits are prone to pathogenic infections, providing optimal microorganism growth conditions. As one of the largest exporters of these fruits globally, following other Southeast Asian countries such as Thailand, Indonesia and the Philippines, the quality control of exported goods is of great interest to farmers and entrepreneurs. Traditional methods of managing diseases in fruits depend on chemical pesticides, which have attracted much negative perception due to their questionable safety. Therefore, the use of natural products as organic pesticides has been considered a generally safer alternative. The extracts of aromatic plants, known as essential oils or plant extracts, have garnered much interest, especially in Asian regions, due to their historical use in traditional medicine. In addition, the presence of antimicrobial compounds further advocates the assessment of these extracts for use in crop disease prevention and control. Herein, we reviewed the current developments and understanding of the use of essential oils and plant extracts in crop disease management, mainly focusing on tropical fruits. Studies reviewed suggest that essential oils and plant extracts can be effective at preventing fungal and bacterial infections, as well as controlling crop disease progression at the pre and postharvest stages of the tropical fruit supply chain. Positive results from edible coatings and as juice preservatives formulated with essential oils and plant extracts also point towards the potential for commercial use in the industry as more chemically safe and environmentally friendly biopesticides.

Sequence-Selected C13-Dipeptide Self-Assembled Hydrogels for Encapsulation of Lemon Essential Oil with Antibacterial Activity

Supramolecular self-assembling peptide hydrogels are attracting attention. The switching of even one amino acid may lead to differences in structure and functions of peptide hydrogels. Herein, we investigate the effect of substitution of a single amino acid residue on the gelation properties of C₁₃-dipeptide hydrogels. We show that four C₁₃-R₁Y (C₁₃-VY, C₁₃-FY, C₁₃-WY, and C₁₃-YY) can form hydrogels with drastically tunable rigidity (the G' values were 5.74, 0.16, 27.74, and 67.90 KPa, respectively). Moreover, C₁₃-WY and C₁₃-YY hydrogels with high stability and excellent mechanical properties formed β-sheet nanofiber cross-linked networks. Furthermore, we applied four hydrogels into encapsulation of lemon essential oil (LEO). The peptide hydrogels had a high encapsulation rate and slowly released the LEO. Importantly, the LEO-loaded hydrogels showed enhanced antibacterial activity than free LEO. Our results clearly demonstrate the significance of side-chain interactions in determining hydrogel properties and their potential application in encapsulation for nutrition agents and hydrophobic drugs.

Assessment of preservative potential of Bunium persicum (Boiss) essential oil against fungal and aflatoxin contamination of stored masticatories and improvement in efficacy through encapsulation into chitosan nanomatrix

The study reports the preservative efficacy of Bunium persicum (Boiss) essential oil (BPEO) against fungal and aflatoxin B₁ (AFB₁) contamination of stored masticatories and boosting of its efficacy through encapsulation into chitosan. BPEO was chemically characterized through GC-MS analysis, which revealed γ-terpinene as the major compound. The BPEO at 1.2 μL/mL concentration completely inhibited the growth of toxigenic strain of Aspergillus flavus (AF-LHP-PE-4) along with 15 common food borne moulds and AFB₁ secretion. The BPEO exerts its antifungal action on plasma membrane, as confirmed through ergosterol inhibition, alteration of membrane fluidity and enhancement of cellular ions and 260 and 280 nm absorbing material leakage. The antiaflatoxigenic mechanism of action of BPEO was confirmed through methylglyoxal reduction. Further, BPEO showed strong antioxidant activity (IC₅₀ = 7.36 μL/mL) as measured by DPPH^· assay. During in situ investigation, BPEO completely inhibited AFB₁ production in model food (Phyllanthus emblica) system without altering the sensory properties and also exhibited high LD₅₀ value (14,584.54 μL/kg) on mice. In addition, BPEO was encapsulated into chitosan, characterized and tested for their potential to inhibit growth and AFB₁ production. The mean particle size, PDI and zeta potential of formed BPEO-loaded chitosan nanoparticle (CS-Np-BPEO) were performed to confirm successful encapsulation. The result revealed nanoencapsulated BPEO showed enhanced activity and completely inhibited the growth and AFB₁ production by AF-LHP-PE-4 at 0.8 μL/mL. Based on findings, it could be concluded that the BPEO and its encapsulated formulation can be recommended as a potential plant-based preservative against fungal and aflatoxin contamination of stored masticatories.

The antimycotic effect of ellagitannins from raspberry (Rubus idaeus L.) on Alternaria alternata ŁOCK 0409

Alternaria spp. fungi, characterized by a high tolerance to unfavorable environmental conditions, are one of the threats for foods of plant origin. The increasing incidence of diseases caused by a demanding lifestyle, and a higher social awareness of the role of a diet in maintaining health and good condition, results in the dynamically growing demand for natural protective measures that would be safe for consumers. Ellagitannins, i.e. a group of bio-active polyphenols, may constitute an alternative for chemical preservatives. Studies demonstrated that the raspberry (Rubus idaeus L.) ellagitannin formula limited the growth of Alternaria alternata 0409. The minimal inhibitory concentration (MIC) was determined (0.156 mg/ml), along with the minimal fungicidal concentration (MFC) (0.312 mg/ml). The fungistatic (FA) activity and the ratio of linear growth (T) were also determined for the ellagitannin formula. A strong antimycotic activity of ellagitannins was demonstrated at the formula level of 0.1 mg/ml. Unfortunately, the activity was not maintained over time and after 9 days it was only 16.0%. For the ellagitannin formula, concentrations of 0.312 mg/ml (MFC) and 0.5 mg/ml (below the MFC value), a complete arrest of growth of Alternaria alternata 0409 was observed, and it was maintained for 9 days. The antimycotic activity of the ellagitannin formula was also confirmed in food environment, with cottage cheese and cherry tomatoes used as the matrix. Results confirmed that ellagitannins from raspberry (Rubus idaeus L.) could be successfully used as a natural food preservative.

Efficacy of binary combinations between methyl salicylate and carvacrol against thrips Anaphothrips obscurus: laboratory and field trials

BACKGROUND

Thrips Anaphothrips obscurus are one of the cosmopolitan major pests feeding on cereals and other grasses. In order to develop alternatives of chemical insecticides for thrips control, based on fumigant activity screening and evaluation of 22 essential oil (EO) compounds against the thrips, the binary interactions of methyl salicylate and carvacrol (MS-C) with high fumigant toxicity were studied systematically by bioassay and field trials.

RESULTS

The bioassay results showed that six in 22 EO compounds had high fumigant toxicity against both the second-instar nymphs and adults of A. obscurus, including methyl salicylate, carvacrol, thymol, trans-cinnamaldehyde, diallyl trisulfide, and L-perillaldehyde. Furthermore, the combination of methyl salicylate mixed with carvacrol at a volume ratio of 5:5 exhibited the most significant synergism against A. obscurus, with a poison ratio value of 1.32 and a co-toxicity coefficient of 151.15. The optimal formulation of microemulsion (ME) was composed of 5% methyl salicylate, 5% carvacrol, 46% adjuvant and 44% deionized water. The result of dynamic light scattering and stability showed that MS-C 10% ME was a transparent, single-phase and homogeneous liquid system. Field trials indicated that the ME displayed a significant control efficacy of about 89.17% on thrips in peppers, and 82.59% in broad bean on the seventh day post application with a dosage of 600.0 g A.I hm^-2 , respectively.

CONCLUSION

The binary combination of MS-C possesses strikingly synergistic action against thrips A. obscurus, and the MS-C 10% ME has the potential to be developed as a botanical pesticide product for thrips control. © 2019 Society of Chemical Industry.