Microencapsulação do óleo de linhaça (Linum usitatissimum L.) em matriz de alginato para controle de patógenos em sementes de soja (Glycine max L.)

Abstract

The soybean crop (Glycine max L.) is the main commodity in the Brazilian economy, but productivity is severely compromised by the incidence of pathogens, especially fungi transmitted via seeds and soil, which results in considerable economic losses. Despite the effectiveness of chemical seed treatment, it raises environmental and human/animal health toxicity concerns, driving the search for more sustainable alternatives, such as bio-inputs. In this context, flaxseed oil emerges as a promising option due to its intrinsic antimicrobial properties, attributed to active compounds like fatty acids and flavonoids. However, its direct application is limited by rapid oxidation, loss of active compounds, and high viscosity, which complicate handling. The objective of this study was to develop and characterize flaxseed oil microcapsules within an alginate matrix, using lecithin as a surfactant, and to evaluate their potential as a biofungicide for the control of Fusarium sp. in soybean seeds, in addition to other fungi. The microencapsulation methodology via ionic gelation resulted in stable formulations, with the 1.0gOL/ALG/LEC formulation exhibiting the best physicochemical characteristics, including an average diameter of 202 μm, a polydispersity index of 0.252, and a homogeneous structure. In in vitro assays, flaxseed oil demonstrated excellent activity, with a minimum inhibitory concentration (MIC) of 16,000 ppm (equivalent to 1.6% oil) inhibiting the mycelial growth of Fusarium sp. by approximately 89% over 216 hours. However, the seed treatment with the equivalent maximum dose (96 mg oil/100 g seeds) did not achieve the expected inhibition against Fusarium sp. in inoculated seeds, with high incidence persisting, though it did show a lower incidence in non-inoculated seeds. It was observed that the microcapsules did not inhibit seed germination, with the 1.5gOL/ALG/LEC treatment surpassing the control by 2.04%. It is concluded that, despite the physicochemical stability and promising in vitro potential against Fusarium sp., the low efficacy in direct seed treatment may be related to the lack of homogeneity in the contact between the microcapsules and the seeds and the need to calibrate the dose for other pathogens, such as Aspergillus. The microencapsulation of flaxseed oil is a viable strategy, but it requires adjustments in dose calibration and better homogenization of the immersion medium for its potential as a biofungicide to be fully realized.