Microwave assisted extraction of polyphenols of Artocarpus heterophyllus Lam. with antifungal activity against Alternaria sp. (e-Latin Food 2020)
Introduction. Jackfruit (Artocarpus heterophyllus L.) constitutes a strategic crop not only for its fruit, but also because it is a source of protein and different phytochemicals with antimicrobial activity and other properties. Taking into account the incidence of Alternaria spp., as a phytopathogenic and foodborne microorganism, it is interesting to investigate the possibilities of using A. heterophyllus leaf extracts in postharvest processes of fruit, damaged by this fungus. The objective of the present work was to determine the optimal conditions for the recovery of leaf jackfruit polyphenols with antimicrobial activity against an Alternaria sp. strain isolated from tomato, using microwave assisted extraction (MAE). Methodology. The extracts were obtained in ethanol: water solution (4:1, v/v), 1:10 leaf powder: solvent ratio. The simultaneous effect of power (600-1080 W) and extraction time (1-3 min) on the concentration of total soluble phenols (TSP) and total flavonoids (TF), and the antimicrobial activity (inhibition of mycelial growth) was optimized, using a factorial design 32. Temperature was registered in all cases. The polyphenolic profile of MAE extracts obtained at optimal conditions was characterized using HPLC-MS analysis. Besides that, 3 cycles MAE procedure was studied. Results. The increase of power and time until 840W and 2 min favored the increment of FST (148.8 mg GAE / g dry weight) and TF (13.3 mg RE / g dry weight) contents. At these conditions, 39.9% mycelial growth inhibition with 1 mg. mL-1 TSP was exhibited. Predicted TSP, TF and AA by the model values were satisfactory compared with the experimental values. Furthermore, the MAE in three cycles allowed to obtain extract with 277.3 mg GAE/ mg DW and 23 mg RE/ mg DW of TSP and TF respectively. Different flavonoids and some phenolic, and organic acids reported in jackfruit and other Ficus species extracts were tentatively identified. Implications. The compounds responsible by antifungal activity must be isolated and encapsulated to improve their effectiveness for future agrofood applications. Originality. The antifungal activity of A. heterophyllus leaf extracts against Alternaria sp. is being reported for the first time. Conclusions. The optimal MAE conditions for the polyphenolic jackfruit leaf extraction with significant antimicrobial activity against Alternaria sp were determined (840 W and 2 min). The results suggest the potentialities of this residue as a source of natural antimicrobial agents for postharvest processes of tomato and other crops.
Keywords: microwave assisted extraction; polyphenols; Artocarpus heterophyllus; antifungal activity; Alternaria sp.