Aplicação de revestimentos formulados com alginato de sódio e extratos hidroalcoólicos de subprodutos de frutas fermentados com bactérias láticas para o controle de antracnose em mangas e goiabas

Abstract

Anthracnose is a fungal disease that affects the quality of fruits such as mangoes and guavas. The use of fungicides, the main strategy applied to control anthracnose, presents health and environmental risks, which requests for studies into sustainable and safe strategies applied to the management of phytopathogens. Preparing plant extracts from fruit by-products is a viable alternative for formulating natural antifungals. In addition, the fermentation of these by-products with lactic acid bacteria (LAB) can enhance the production of bioactive compounds. Coatings with natural products have also been used as innovative strategies to control post-harvest diseases, and can be used as carriers of active substances for application to fruit. The aim of this study was to evaluate the potential of a coating formulated with sodium alginate and extracts of fruit by-products fermented by LAB to control anthracnose on Palmer mango and Paluma guava. For this purpose, by-products of acerola, cashew, mango and grape were collected from fruit pulp processing industries, sterilized (121 °C, 1 atm, 15 minutes), freeze-dried and stored (-18 ± 0.5 °C). To the fermentation process, the by-products were diluted 1:5 in sterilized distilled water, autoclaved and then inoculated with a mixed LAB culture (Levilactobacillus brevis 59, Lactiplantibacillus pentosus 129 and Limosilactobacillus fermentum 263) at a concentration of approximately 9 log CFU/mL. The fermentation process took place at 37ºC for 24 hours on an orbital shaker (200 rpm) under aerobic conditions. The fermented fruit by-products were mixed with ethanol (70% or 80%; 1:10 v/v), and homogenized at 37 °C, 200 rpm for 2 hours. These solutions were centrifuged, the liquid part was recovered and the solvent was removed using a rotary evaporator. Viable LAB cell counts on the fermented product and physicochemical analyses of the extracts obtained were performed. The extracts obtained were used to assess antifungal activity using the agar well diffusion method and minimum inhibitory concentration, with results expressed as % mycelial growth inhibition (%MGI). The extracts with the best in vitro results were incorporated into a coating formulated with sodium alginate (1.5%) and applied to mangoes and guavas to assess their potential to reduce anthracnose lesion diameter (%ALDR). The fermented hydroalcoholic extracts of acerola (75 and 100 mg/mL) and mango by-products (75 and 100 mg/mL) showed the highest rate of mycelial growth inhibition (%MGI 35.00-82.75) in all the isolates of Colletotrichum tested in vitro. With regard to the physicochemical characteristics, the extracts showed variations in acidity, pH, total soluble solids and ascorbic acid, with a higher acidification in the fermented hydroalcoholic extracts (pH 3.28-3.47). Color analysis indicated significant differences associated with fruit pigmentation. Variations in the content of total phenolic compounds, flavonoids and antioxidant activities were also observed. The application of sodium alginate coatings added to the fermented hydroalcoholic extracts of acerola and mango (100 mg/mL) delayed the development of anthracnose in mangoes and guavas during storage (%ALDR xx-75.80). These results indicate that coatings formulated with fermented fruit by-products extracts could be innovative and sustainable strategies for managing post-harvest anthracnose caused by Colletotrichum in fruits.