Natural antimicrobials in spray-dried microparticles based on cellulose derivatives as potential eco-compatible agrochemicals

Abstract

It has been demonstrated that some aromatic substances synthesized by plants serve as plant defense mechanisms. However, natural extracts are difficult to use due to their poor physicochemical characteristics and low concentration. Biocompatible microparticles for the delivery of the model antimicrobial compound Gallic acid (GA) were prepared by spray drying technique using hydroxyl-propyl-methylcellulose-phtalate (HPMCP) and ethyl cellulose. The selection of appropriate experimental parameters allowed the obtaining of the following instrumental settings: (a) feed rate of the polymer solution 0.6 ml/min, (b) air flow rate of the nebulization device 600 l/h, (c) flow of drying air 28 m3/h and (d) air drying temperature 90 °C. Optical and electron microscopies showed microparticles characterized by acceptable morphology and narrow dimensional distribution. In vivo tests carried out in greenhouse tomato plants, cv. Pullrex Bio, contaminated with a bacterial suspension of Pseudomonas syringae pv. tomato (106 CFU/ml), demonstrated that HPMCP-GA microparticles were able to significantly reduce the Pst epiphytic population showing an activity comparable to that obtained by copper salts. Biocompatible spray-dried microparticles with good activity were obtained and allowed the formulation of innovative products useful to reduce phytotoxicity and risk of copper resistance in plant pathogens associated with the frequent agricultural use of cupric compounds.