Microencapsulation of Peumus boldus oil by complex coacervation to provide peanut seed protection against fungal pathogens

GIRARDI, N; GARCÍA, D; PASSONE, A; NESCI, A.; ETCHEVERRY, M

Barcelona

Congreso; IV International Conference on Environmental, Industrial and Applied Microbiology; 2015

Boldo essential oil (EO) (Peumus boldus Mol.) has proven to be effective in controlling peanut storage fungi [1]. However, fast decreases of boldo residues were observed after the oil was applied on the grain surfaces [2]. In this study, boldo EO microcapsules were prepared using the complex coacervation technique with gelatin/gum arabic, in order to enhance the dwell period of this preservative in the storage system. The effect of gelatin bloom (220 and 240) and the crosslinking conditions: type of crosslinking agent (without crosslinking agent (WCA), formaldehyde (F) and glutaraldehyde (G)) and crosslinking time (0, 10, 60 and 120 min), on the size and encapsulation efficiency (EE%) of the microcapsules were studied. The release of boldo EO from the microcapsules that showed the higher EE% was evaluated at different temperatures (4 and 25 °C) and on peanut grains conditioned at three water activities (0.65, 0.85 and 0.95 aW). Boldo EO formulation, was applied in a dose of 3000 ppm on peanut kernels intended for seeds -medium and low PG, with and without seed treatment methyl thiophanate 10% + metalaxyl 1.33% + micronutrients [Co and Mo]-), which were stored at room temperature (20-25 °C) for 114 days. Boldo EO microcapsules showed a mean diameter of 7.61 μm and the EE% ranged between 67 and 97%. Moreover, microencapsulated EO showed very low release rates (between 4 x 10-3 and 4 x 10-5 %) after 10 days of storage. When boldo EO formulation was applied on peanut kernels, significant fungal count reductions were observed, especially when the application was made after seed treatment (69.5%). Microencapsulated boldo EO also exerted an adverse effect on the ability of seed germination, with reductions of PG estimated between 88 and 95%.In conclusion, the complex coacervation technique allowed encapsulating boldo EO with high efficiency percentages, without affect the antifungal capacity. The treatment with boldo EO microcapsules after the application of seed fungicide treatments could increase the seed protection against fungal pathogens during a storage period of 114 days. To avoid the effect on seed PG, the application of boldo EO formulation on unshelled stored peanut before fungicide treatment will be evaluated in future studies.