Aplicação de revestimento formulado com alginato de sódio e cultura mista de bactérias láticas para controle de antracnose e preservação da qualidade pós-colheita em goiaba e manga

Abstract

Guava and mango are widely marketed tropical fruits; however, as climacteric fruits, they undergo physiological changes that make them more susceptible to pathogens. Anthracnose, caused by fungi of the genus Colletotrichum, is one of the main post-harvest diseases of these fruits. Although conventional disease control involves the use of chemical fungicides, the deleterious impacts associated with the continuous use of these compounds have driven the search for sustainable alternatives. In this context, the use of lactic acid bacteria (LAB) as biocontrol agents, combined with edible coatings such as sodium alginate (SA), stands out as an innovative and effective strategy for inhibiting phytopathogens and biopreserving fruits. This thesis aimed to develop, characterize, and apply a new SA-based coating and LAB mixed culture to control anthracnose and preserve the post-harvest quality of guava (cv.) Paluma and mango (cv.) Palmer. The effect of a mixed culture composed of three strains of different LAB species (Levilactobacillus brevis 59, Lactiplantibacillus pentosus 129, and Limosilactobacillus fermentum 263) was evaluated in vitro against ten Colletotrichum isolates. Subsequently, a formulation containing AS and a mixed culture of lyophilized LAB (AS+LAB) was developed, which was characterized in terms of thermal, morphological, physicochemical, and biodegradability properties. The survival, as well as the physiological and metabolic responses of the LAB incorporated into the coating and film, were also evaluated under different storage conditions (15 days at 25 °C and 4 °C). The effect of coatings on controlling the development of anthracnose lesions in guava and mango, as well as on maintaining post -harvest quality indicator parameters, was evaluated during 15 days of storage at 25 °C. The mixed culture inhibited mycelial growth of all isolates tested, achieving up to 100% effectiveness in the well diffusion method. Film characterization demonstrated that the incorporation of LAB promoted modifications in the polymeric matrix, resulting in greater thermal stability, a more homogeneous surface, and no pores. The AS+LAB film showed lower roughness, thickness, moisture content, water solubility, hygroscopicity, and water activity, without alteration in color parameters, when compared to the film without LAB. Furthermore, the ABTS•+, DPPH•, and FRAP assays indicated an increase in antioxidant capacity after the incorporation of LAB into the films. Both films demonstrated high biodegradability in soil, freshwater, and seawater, with almost complete degradation in 20 days. Samples stored under refrigeration showed viable cell counts >7.5 log CFU/g, and 31.73% and 55.85% of cell subpopulations with non-permeabilized membranes and enzymatic activities (viable cells), respectively, at the end of storage. The application of the AS+BAL coating to guava and mango delayed the development and reduced the diameter of anthracnose lesions by up to 78.94% in guava and 83.44% in mango after 15 days of storage (15 days; 25 ± 0.5 °C). In the coated fruits, preservation of post -harvest quality was observed, evidenced by less weight loss and greater maintenance of color, as well as ascorbic acid and carotenoid content at the end of storage. Additionally, fruits treated with AS+BAL showed better preservation of sensory characteristics, especially color, aroma, and texture, as well as less perceived ripening throughout the storage period. The results highlight that the AS+BAL coating can be effective for post-harvest biocontrol of anthracnose in guava and mango. Furthermore, this coating may be a sustainable alternative for preserving fruit quality during the post-harvest period.