This study assessed the efficacy of chitosan (CHI) and Mentha piperita L. essential oil (MPEO) alone or in combination to control the mycelial growth of five different Colletotrichum species, C. asianum, C. dianesei, C. fructicola, C. tropicale and C. karstii, identified as potential anthracnose-causing agents in mango (Mangifera indica L.). The efficacy of coatings of CHI and MPEO mixtures in controlling the development of anthracnose in mango cultivar Tommy Atkins was evaluated. CHI (2.5, 5, 7.5 and 10 mg/mL) and MPEO (0.3, 0.6, 1.25, 2.5 and 5 μL/mL) alone effectively inhibited mycelial growth of all tested Colletotrichum strains in synthetic media. Mixtures of CHI (5 or 7.5 mg/mL) and MPEO (0.3, 0.6 or 1.25 μL/mL) strongly inhibited mycelial growth and showed additive or synergistic inhibitory effects on the tested Colletotrichum strains based on the Abbott index. The application of coatings of CHI (5 or 7.5 mg/mL) and MPEO (0.6 or 1.25 μL/mL) mixtures that presented synergistic interactions decreased anthracnose lesion severity in mango artificially contaminated with either of the tested Colletotrichum strains over 15 days of storage at 25 °C. The anthracnose lesion severity in mango coated with the mixtures of CHI and MPEO was similar or lower than those observed in mango treated with the synthetic fungicides thiophanate-methyl (10 μg a.i./mL) and difenoconazole (0.5 μg a.i./mL). The application of coatings containing low doses of CHI and MPEO may be an effective alternative for controlling the postharvest development of anthracnose in mango cultivar Tommy Atkins.

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This study investigated the effects of carvacrol (CAR) and 1,8-cineole (CIN) alone (at the MIC) or in combination at subinhibitory amounts (both at 1/8 MIC) on the cell viability, membrane permeability, and morphology of Aeromonas hydrophila INCQS 7966 (A. hydrophila) cultivated in a vegetable-based broth. CAR and CIN alone or in combination severely affected the viability of the bacteria and caused dramatic changes in the cell membrane permeability, leading to cell death, as observed by confocal laser microscopy. Scanning and transmission electron microscopy images of bacterial cells exposed to CAR or CIN or the mixture of both compounds revealed severe changes in cell wall structure, rupture of the plasma membrane, shrinking of cells, condensation of cytoplasmic content, leakage of intracellular material, and cell collapse. These findings suggest that CAR and CIN alone or in combination at subinhibitory amounts could be applied to inhibit the growth of A. hydrophila in foods, particularly as sanitizing agents in vegetables.

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This study evaluated corn steep liquor (CSL) and papaya peel juice (PPJ) in mixture as substrates for the cultivation (96h, 28°C, pH 5.6, 150rpm) of Mucorales fungi for chitosan production, and determined the growth-inhibitory effect of the fungal chitosan (FuCS) obtained under optimized conditions against phytopathogenic Colletotrichum species. All Mucorales fungi tested were capable of growing in CSL-PPJ medium, showing FuCS production in the range of 5.02 (Fennelomyces heterothalicus SIS 28) - 15.63mg/g (Cunninghamella elegans SIS 41). Highest FuCS production (37.25mg/g) was achieved when C. elegans was cultivated in medium containing 9.43% CSL and 42.5% PPJ. FuCS obtained under these conditions showed a deacetylation degree of 86%, viscosity of 120cP and molecular weight of 4.08×10g/mol. FuCS at 5000, 7500 and 10,000ppm inhibited the growth of all Colletotrichum species tested. FuCS also induced alterations in the morphology of C. fructicola hyphae. CSL-PPJ mixtures are suitable substrates for the cultivation of Mucorales fungi for FuCS production. Chitosan from C. elegans cultivated in CSL-PPJ medium is effective in inhibiting phytopathogenic Colletotrichum species.

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