DEVELOPMENT OF BIOFUNGICIDAL COATINGS BASED ON BIOPOLYMERS AND YEAST METSCHNIKOWIA PULCHERRIMA

The development of biofungicides as an alternative method for commercial fungicides use in postharvest disease control is a premise for achieving sustainable development. The objective of this study was to develop a biofungicidal coating based on alginate (ALG), carboxymethyl cellulose (CMC) and Metschnikowia pulcherrima (DSM 70336) yeast and evaluate its antifungal potential controlling green mold. Initially, the yeast antagonistic activity was tested in vitro against Penicillium digitatum, the causal agent of green mold in citrus. M. pulcherrima was grown in PDA medium for 48 h, after 200 µL of suspensions of these cells (10², 10⁴, 10⁶, and 10⁸ cells/mL) were spread on PDA plates. A sterilized paper disc was placed in the center of each plate and inoculated with 10 µL of P. digitatum suspension (10⁵ CFU/mL). The plates were incubated in BOD at 25°C. The growth of the fungal colonies was measured after 10 days of incubation to calculate the mycelial growth inhibition (ICM). Subsequently, filmogenic solutions were prepared using crosslinked ALG (1% w/v and 0.75% mCaCl₂/mALG) and CMC (0.5% w/v), mixed in a 1:1 ratio, and glycerol (20% w/v). Suspensions of 10⁶ and 10⁸ cells/mL of M. pulcherrima were added to the polymer solution, as they presented the best results in the previous test, and then applied to previously wounded orange fruits. After the coatings dried on the fruits, they were inoculated with a suspension of P. digitatum spores (10⁶ CFU/mL) and stored at 25°C for 7 days. Data were analysed by ANOVA and Tukey’s test. The responses of the inhibition test showed that the highest concentrations of M. pulcherrima (10⁶ and 10⁸ cells/mL) were able to inhibit 100% of mycelial growth, presenting significant differences in means when compared to the control (without yeast) and to concentrations of 10² and 10⁴ cells/mL (0 and 95.1±2.24%, respectively). Coating solutions with 10⁶ or 10⁸ cells/mL were applied to the orange fruits. After 7 days of storage, 55.55% of the uncoated fruits (control) showed disease symptoms, and both treatments coated with M.pulcherrima cells coating showed 33.33% of the fruits with symptoms, with no significant difference between the treatments. These results demonstrate that higher is the concentration of M. pulcherrima, greater and more efficient is the in vitro control. This results justifies the study of coating optimization for better in vivo results.