Abstract
Cherry tomato (Lycopersicon esculentum Mill) fruits are susceptible to contamination by Aspergillus flavus, which may cause the development of fruit rot and significant postharvest losses. Currently there are significant drawbacks for the use of synthetic fungicides to control pathogenic fungi in tomato fruits, and it has increased the interest in exploring new alternatives to control the occurrence of fungal infections in these fruits. This study evaluated the efficacy of chitosan (CHI) from Mucor circinelloides in combination with carvacrol (CAR) in inhibiting A. flavus in laboratory media and as a coating on cherry tomato fruits (25°C, 12 days and 12°C, 24 days). During a period of storage, the effect of coatings composed of CHI and CAR on autochthonous microflora, as well as on some quality characteristics of the fruits such as weight loss, color, firmness, soluble solids, and titratable acidity was evaluated. CHI and CAR displayed MIC valuesof 7.5 mg/mL and 10 μL/mL, respectively, against A. flavus. The combined application of CHI (7.5 or 3.75 mg/mL) and CAR (5 or 2.5 μL/mL) strongly inhibited the mycelial growth and spore germination of A. flavus. The coating composed of CHI (3.75 mg/mL) and CAR (2.5 or 1.25 μL/mL) inhibited the growth of A. flavus in artificially contaminated fruits, as well as the native fungal microflora of the fruits stored at room or low temperature. The application of the tested coatings preserved the quality of cherry tomato fruits as measured by some physicochemical attributes. From this, composite coatings containing CHI and CAR offer a promising alternative to control postharvest infection caused by A. flavus or native fungal microflora in fresh cherry tomato fruits without negatively affecting their quality over storage.
Highlights
In recent years, the population has shown more interest in acquiring a good quality of life including a balanced diet, which requires a regular consumption of fresh fruits and vegetables
CHI at 7.5 or 3.75 mg/mL and CAR at 5 and 2.5 μL/mL were tested in different combinations (CHI 7.5 mg/mL + CAR 5 μL/mL, CHI 7.5 mg/mL + CAR 2.5 μL/mL, CHI 3.75 mg/mL + CAR 5 μL/mL and CHI 3.75 mg/mL + CAR 2.5 μL/mL) in assays that measured the effects on mycelial growth and spore germination of A. flavus
The combined application of CHI and CAR at different concentrations (MIC values and/or subinhibitory concentrations) induced the inhibition of the mycelial growth and spore germination of A. flavus in laboratory media. These findings are interesting because fungi are commonly less tolerant to antimicrobial compounds during the mycelial growth stages than during the spore germination stage, most likely because the stronger antimicrobial resistance of fungal spore structures
Summary
The population has shown more interest in acquiring a good quality of life including a balanced diet, which requires a regular consumption of fresh fruits and vegetables. The global consumption of tomato products is near 31,000 tons/year, with an average annual per capita consumption of ∼6 kg/inhabitant and fresh fruits represent near 75% of this consumption (World Processing Tomato Council [WPTC], 2010). These fruits are susceptible to various forms of contamination by phytopathogen agents during production, handling, distribution and storage. This contamination can limit their shelf life of tomato fruits and cause postharvest losses as high as 40% in less industrialized countries (Liu et al, 2007; Ramos-García et al, 2012)
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