RESUMEN
Introduction: Lactic acid bacteria (LAB) produce various metabolites (i.e. metabiotics) with inhibitory capacity towards harmful foodborne pathogens. Methods: This study aimed to design several antimicrobial formulations based on metabiotics obtained from different native LAB species (Lactobacillus pentosus UTNGt5, Lactococcus lactis UTNGt28, and Weissella cibaria UTNGt21O) and to detect the possible mode of action towards two multidrug resistant Staphylococcus spp. strains isolated from avocado (Persea nubigena var. guatemalensis) fruits. Additionally, the formulation with the highest inhibitory activity was tested ex vitro on avocados at the immature (firm) ripeness stage to evaluate their effect on microorganisms' growth and fruit quality attributes post-harvest. Results and discussion: Out of the top five formulations showing the highest bactericidal effect in vitro at their minimum inhibitory concentration (1 x MIC) on both Staphylococcus spp. targets one candidate annotated P11 (consisting of UTNGt21O and UTNGt28; 1:3, v/v) was selected. Co-cultivation of Staphylococcus strains with P11 formulation results in cell viability reduction by 98%, by impairing the integrity of the cell membrane inducing cytoplasm molecule content leakage, protein profile changes, and finally bacterial death. Even though the total coliforms, Staphylococcus spp., Enterobacter spp., molds, and yeasts counts were not fully eliminated by day 13 of storage, a statistically significant reduction (p < 0.05) in viable cell counts were observed by day 8 upon the P11 treatment compared with non-treated control (C) and treated with a commercial disinfectant (T1) samples, suggesting that P11 formulation inhibited microbial colonization during storage. Likewise, no visible dark spots were observed on the mesocarp (pulp) upon the treatment with P11, whereas T1 and C fruits showed greater dark spots on the pulp as indicative of damage. The quality attributes, such as pH, total soluble solids, total titratable acidity, antioxidant capacity, and total polyphenol content, were not affected by the treatment. Principal Component Analysis (PCA) conducted on these five variables showed a clear separation of samples according to the maturity stage regardless of the treatment. Conclusion: These results suggest that the active metabolites from LAB strains might create a barrier between the exocarp and mesocarp, inhibiting the microorganisms colonization, reducing fruit damage, and lengthening the fruit quality and safety after harvest.
RESUMEN
Papaya (Carica papaya) is one of the most cultivated and consumed tropical fruit worldwide. Its production might be limited by preharvest and postharvest diseases. The fruit rot caused by Phytophthora palmivora is one of the most important postharvest diseases of papaya in Brazil. The control of these diseases is usually made with fungicide applications. Therefore, studies concerning biocontrol of postharvest diseases might generate data that may reduce the environmental impacts caused by pesticides. Thus, the biological control by Trichoderma in postharvest diseases is an alternative to the use of fungicides for the postharvest control of P. palmivora in the papaya fruit. Four antagonists [T. asperellum (SF04), T. virens (255C1), T. harzianum (THP) and T. longibrachiatum (4088)] were tested, as follow: 1) Trichoderma spp. applied 1 hour after inoculation of P. palmivora and; 2) Trichoderma spp. applied 24 hours after inoculation of P. palmivora; 3) Trichoderma spp. applied 1 hour before inoculation of P. palmivora, and 4) Trichoderma spp. applied 24 hours before inoculation of P. palmivora. All Trichoderma significantly (P£0,05) reduced the incidence and severity of disease. The 4088 (T. longibrachiatum) isolate was the best controller agent of P. palmivora in postharvest.
O mamão é uma fruta muito cultivada e consumida nas regiões tropicais e subtropicais do mundo e apresenta diversos problemas fitossanitários. Sendo assim, estudos de doenças pós-colheita com biocontroladores viabilizam a diminuição de impactos causados pelo uso de fungicidas. A podridão-dos-frutos (Phytophthora palmivora) é uma importante doença pós-colheita em mamão no Brasil. Neste contexto, o controle biológico desta doença na póscolheita com Trichoderma é uma alternativa viável ao uso de fungicidas e foi aplicado neste estudo para avaliar a eficácia de Trichoderma spp. para o biocontrole de P. palmivora em mamão na pós-colheita. Foram utilizados quatro potenciais antagonistas: T. asperellum (SF04), T. virens (255C1), T. harzianum (THP) e T. longibrachiatum (4088). E as frutas foram submetidas aos seguintes tratamentos: Inoculação de P. palmivora e 1 hora depois inoculação do Trichoderma spp.; Inoculação de P. palmivora e 24 horas depois inoculação do Trichoderma spp.; Inoculação de Trichoderma spp. e 1 hora depois inoculação do P. palmivora e; Inoculação de Trichoderma spp. e 24 horas depois inoculação do P. palmivora. Todos os isolados de Trichoderma reduziram significativamente tanto na incidência como na severidade da doença. O isolado 4088 (T. longibrachiatum) foi o melhor no controle da podridão.