| Sumario: | Almond processing industries generate significant amounts of by-products than can pose environmental problems. Almond skin (AMS) is known for its antioxidant properties due to the presence of polyphenols, which may also exert some antifungal activity. The exploitation of value-added compounds contributes to circular economy as well as to the EU Green Deal. AMS extracts were obtained using ultrasound (UAE) and microwave-assisted (MAE) green extractions and their total phenolic content (TPC) and total antioxidant capacity (TAC) were determined. Extracts efficacy in inhibiting Botrytis cinerea (BC) and Monilinia fructicola (MF), the causal agents of gray mold and brown rot, respectively, was assessed using an in vitro microtiter assay. Selected extracts were further tested in in vivo primary screenings with 'Carmina 22' nectarines wound inoculated with the pathogens and treated 2 h later by depositing a drop of the extract in the rind inoculation point. Disease incidence (% of infected wounds) and severity (lesion diameter) were measured after 7 days of incubation at 20 °C. TPC levels were 3.9 and 2.7 GAE/g dry weight for AMS-UAE and AMS-MAE, respectively, while TAC levels were the same for both extracts (16.7 g AAE/L). In terms of their antifungal properties, both extracts showed significant in vitro inhibitory effects, with 90.3 and 67.0% inhibition of BC and 98.9 and 98.4% inhibition of MF by AMS-MAE and AMS-UAE, respectively. When tested in vivo, AMS-MAE was not effective in reducing the incidence and severity of brown rot on nectarines, but it did reduce the incidence and severity of gray mold by 42 and 62%, respectively, compared to control fruit treated with water. These findings suggest that AMS-MAE extract is a promising environmentally friendly option for reducing nectarine gray mold, offering a sustainable alternative to the chemical fungicides currently used for the control of postharvest fungal diseases of stone fruits.
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